Avoiding Vne [Archive] - AviationBanter

K.P. Termaat

March 26th 04, 07:32 AM

Hi guys,

Thanks for the discussion. Once one has exceeded Vne a choice must be made
by the pilot of either pulling the airbrakes or put some backpressure on the
stick or do both. We know the dramatic outcome of the Nimbus 4DM at Minden a
couple of years ago when doing the latter. Probably I would go for only
putting some backpressure on the stick and have the max g-load number for
the wing available. Hopefully the wing will survive flutter that may occur
and will not destroy the whole wing. Some years ago I saw and heard a tail
of a Cirrus move about heavily in a too fast fly by, but the glider survived
with minimum damage.
However the above is not my concern. I am worried about a possible means to
avoid Vne to be exceeded after recovery when the glider is still in its
spinning (rotation) mode. The idea is to pull the airbrakes even before the
rotation has stopped.

Karel, NL

"K.P. Termaat" > schreef in bericht
...
> Hello Erik,
>
> Yes that's what my handbook says for my Ventus-2cxT also.
> I guess however that when recovering from a spin using the standard method
> (or the more advanced one including a bit of aileron) that then Vne will
be
> exceeded after rotation has stopped and pitch angle is something like 60°.
> To avoid this the idea is to pull the brakes even before the rotation has
> stopped. But I am worried about that.
>
> Karel, NL
>
> "Erik Braun" > schreef in bericht
> ...
> > K.P. Termaat wrote:
> > > Yesterday evening I talked with a friend about avoiding excessive
speed
> when
> > > recovering from a spin in a modern low drag glider with the somewhat
> larger
> > > span.
> > > He came up with the idea of pulling the airbrakes when still
recovering
> from
> > > the rotating mode. I am not sure this can be done without disturbing
the
> > > recovering action or without hurting the glider.
> > > Any comment will appreciated.
> > >
> > > Karel, NL
> > >
> > >
> >
> > Pulling the airbrakes is what most handbooks say on this subject. But if
> > you're already very fast I'd do this carefully.
> >
>
>

Erik Braun

March 26th 04, 09:03 AM

Pete Zeugma wrote:

> must have slipped my notice that airbrakes on 'modern
> low drag gliders' were speed limiting. my speed stays
> pretty much constant at full travel.

Of course, if the glider is already running at Vne I wouldn't pull the
airbrakes but try to recover really carefully. But up to ~220kmh, I'd do
this, because they DO produce a big drag an make the glider slower (in
my experience at least, which doesn't include a Nimbus or the other big
ones).

Erik

Erik Braun

March 26th 04, 09:06 AM

Exceeding VNE may induce aerodynamic flutter, this
>> can and almost certainly will cause catastrophic failure
>> of the airframe. Put simply try and avoid both but
>> if the choice is exceed the placarded G loading or
>> VNE the G loading is the only choice. The potential
>> for catastophic failure is much much greater if VNE
>> is exceeded,
>
>
> Why?
>
> exceeding VNE is therefore not an option.
>
> Isn't there a built in safety margin for both G's and VNE?

A modern sailplane is built to withstand a sudden updraft of 10 m/s at
Vne. If you pull at the same time, it is more than likely that the wing
won't make it.

Stefan

March 26th 04, 09:15 AM

K.P. Termaat wrote:

> Thanks for the discussion. Once one has exceeded Vne ...

This whole discussion is somewhat bizarre. I've been doing spins on a
regular basis and exceeding Vne has never been an issue. Certainly not
when still spinning (no acceleration in spinning mode), but not during
pull out either. I can't help assuming that no one contributing to this
thread has ever done a spin himself.

Stefan

Bert Willing

March 26th 04, 09:46 AM

Nonsense. Exceed the structural g-load limit and you fly without wings.

--
Bert Willing

ASW20 "TW"

"Don Johnstone" > a écrit dans le
message de ...
> OK the answer to this one is very simple, VNE stands
> for 'Velocity never exceed' the never is not optional.
> Pulling the airbrakes or pulling back hard on the stick
> may cause structural damage to the glider, however
> this structural damage is not likely to be catastrophic.
> Exceeding VNE may induce aerodynamic flutter, this
> can and almost certainly will cause catastrophic failure
> of the airframe. Put simply try and avoid both but
> if the choice is exceed the placarded G loading or
> VNE the G loading is the only choice. The potential
> for catastophic failure is much much greater if VNE
> is exceeded, exceeding VNE is therefore not an option.
>
> I have no doubt there will now be lots of postings
> from people who say they have exceeded VNE and got
> away with it. Even idiots can be lucky sometimes.
>
> At 11:30 25 March 2004, Bert Willing wrote:
> >If you are already very fast and pull the airbrakes,
> >you have to be very
> >careful during the pull up because the wing won't stand
> >the same g-load as
> >without airbrakes.
> >
> >--
> >Bert Willing
> >
> >ASW20 'TW'
> >
> >
> >'Erik Braun' a écrit dans le message de
> ...
> >> K.P. Termaat wrote:
> >> > Yesterday evening I talked with a friend about avoiding
> >>>excessive speed
> >when
> >> > recovering from a spin in a modern low drag glider
> >>>with the somewhat
> >larger
> >> > span.
> >> > He came up with the idea of pulling the airbrakes
> >>>when still recovering
> >from
> >> > the rotating mode. I am not sure this can be done
> >>>without disturbing the
> >> > recovering action or without hurting the glider.
> >> > Any comment will appreciated.
> >> >
> >> > Karel, NL
> >> >
> >> >
> >>
> >> Pulling the airbrakes is what most handbooks say on
> >>this subject. But if
> >> you're already very fast I'd do this carefully.
> >>
> >
> >
> >
>
>
>

Bert Willing

March 26th 04, 11:36 AM

Well, your contribution does make me assume than you never did a spin in a
large span glider. I once had to choose between exceeding Vne and pulling
the airbrakes, and I didn't pull them. As someone said earlier, I was one of
the lucky idiots who got away with it.

--
Bert Willing

ASW20 "TW"

"Stefan" > a écrit dans le message de
...
> K.P. Termaat wrote:
>
> > Thanks for the discussion. Once one has exceeded Vne ...
>
> This whole discussion is somewhat bizarre. I've been doing spins on a
> regular basis and exceeding Vne has never been an issue. Certainly not
> when still spinning (no acceleration in spinning mode), but not during
> pull out either. I can't help assuming that no one contributing to this
> thread has ever done a spin himself.
>
> Stefan
>

Don Johnstone

March 26th 04, 01:13 PM

To put the record straight
1. When I referred to idiots and exceeding VNE I meant
those who had done so deliberately, not those who had
done so inadvertantly.
2. Pulling excess G can damage the airframe, however
the damage is likely to be far less than the damage
caused by flutter. I am not sure that enough G could
be pulled at speeds below VNE to cause serious catastrophic
failure as there is a margin between the placarded
limit and the design limit of most gliders. (We are
talking about avoiding exceeding VNE) For example from
memory the Grob 103 Acro is placarded +3G -1G in the
UK. (This might be the LBA limit). If I remember correctly
Grob place a limit of +8G -3.5G for the airframe. I
stand to be corrected but I suspect it is unlikely
that 8G could be attained at an airspeed less than
VNE. Other design limits may of course be closer to
the placarded limit but again I suspect it may be difficult
to exceed the design limit at speeds below VNE.
3. Airframe flutter can occur at less than VNE. The
likelyhood of flutter increases dramatically above
VNE and the severity increases with the speed. The
flutter may mean that there is no control of the aircraft
and therefore no way to recover. Aerodynamic flutter
breaks airplanes (and bridges) and the failure is almost
always catastrophic. The N really does stand for never.

Excess G is the lesser of 2 evils, I know which i would
choose.

However whatever floats your boat but if you intend
to exceed VNE I would be grateful if you did not do
it over my head, all thos falling bits can really spoil
your day.

Yes Bert, you were indeed lucky if you exceeded VNE
but read my first paragraph as to the rest. I have
spun a large span glider (ASW17) and I have to say
I have never got anywhere near VNE or the placarded
G limit in the recovery. Will airbrakes effect the
recovery from a spin, I don't know yet, I will let
you know.

At 11:48 26 March 2004, Bert Willing wrote:
>Well, your contribution does make me assume than you
>never did a spin in a
>large span glider. I once had to choose between exceeding
>Vne and pulling
>the airbrakes, and I didn't pull them. As someone said
>earlier, I was one of
>the lucky idiots who got away with it.
>
>--
>Bert Willing
>
>ASW20 'TW'
>
>
>'Stefan' a écrit dans le message de
...
>> K.P. Termaat wrote:
>>
>> > Thanks for the discussion. Once one has exceeded
>>>Vne ...
>>
>> This whole discussion is somewhat bizarre. I've been
>>doing spins on a
>> regular basis and exceeding Vne has never been an
>>issue. Certainly not
>> when still spinning (no acceleration in spinning mode),
>>but not during
>> pull out either. I can't help assuming that no one
>>contributing to this
>> thread has ever done a spin himself.
>>
>> Stefan
>>
>
>
>

Stefan

March 26th 04, 01:35 PM

Bert Willing wrote:

> Well, your contribution does make me assume than you never did a spin in a
> large span glider.

I did spins up and including a Duo. I've never flown an ASH 25 or a
Nimbus 4, so I can't comment these from my own experience. However, JAR
requires that they can be safely spun up to 5 full rotations. To my
undertanding, "safely" means that they can be recovered without dirty
tricks and without exceeding their operation limits.

Stefan

Jean

March 26th 04, 01:35 PM

Why don't you check your glider's flight manual ?
Jean
"K.P. Termaat" > a écrit dans le message de
...
> Yesterday evening I talked with a friend about avoiding excessive speed
when
> recovering from a spin in a modern low drag glider with the somewhat
larger
> span.
> He came up with the idea of pulling the airbrakes when still recovering
from
> the rotating mode. I am not sure this can be done without disturbing the
> recovering action or without hurting the glider.
> Any comment will appreciated.
>
> Karel, NL
>
>

Stefan

March 26th 04, 01:36 PM

Don Johnstone wrote:

> I am not sure that enough G could
> be pulled at speeds below VNE to cause serious catastrophic
> failure as there is a margin between the placarded
> limit and the design limit of most gliders.

IIRC, JAR requires a safety margin of 1.5

Stefan

Bert Willing

March 26th 04, 01:42 PM

Once I was in that situation I didn't behave as an idiot. But to get there,
I did all to qualify as an idiot.

What speed you build up during recovery largely depends on how long the ship
continues to turn after the counter measures. In my case the ship (26m)
passed from spin through a form of spiral dive, and that makes builing up of
speed very fast. Vne in this case was 200 km/h.

What happens if you step outside the flight enveloppe - your guess is as
good as mine. Flutter test on modern gliders is done up to Vne + 10%, but
10% is not very much in such a situation. If flutter starts, your day is
spoiled.
If you exceed g-loads during pull-up, you have a 1.5 design factor for a
clean wing (that's more than 10%...), but pulling the airbrakes will shift
the load distribution on the wing dramatically.

So, you have to make a choice between two sub-optimal solutions. But, in a
certified glider there is basically no reason to get there.

--
Bert Willing

ASW20 "TW"

"Don Johnstone" > a écrit dans le
message de ...
> To put the record straight
> 1. When I referred to idiots and exceeding VNE I meant
> those who had done so deliberately, not those who had
> done so inadvertantly.
> 2. Pulling excess G can damage the airframe, however
> the damage is likely to be far less than the damage
> caused by flutter. I am not sure that enough G could
> be pulled at speeds below VNE to cause serious catastrophic
> failure as there is a margin between the placarded
> limit and the design limit of most gliders. (We are
> talking about avoiding exceeding VNE) For example from
> memory the Grob 103 Acro is placarded +3G -1G in the
> UK. (This might be the LBA limit). If I remember correctly
> Grob place a limit of +8G -3.5G for the airframe. I
> stand to be corrected but I suspect it is unlikely
> that 8G could be attained at an airspeed less than
> VNE. Other design limits may of course be closer to
> the placarded limit but again I suspect it may be difficult
> to exceed the design limit at speeds below VNE.
> 3. Airframe flutter can occur at less than VNE. The
> likelyhood of flutter increases dramatically above
> VNE and the severity increases with the speed. The
> flutter may mean that there is no control of the aircraft
> and therefore no way to recover. Aerodynamic flutter
> breaks airplanes (and bridges) and the failure is almost
> always catastrophic. The N really does stand for never.
>
> Excess G is the lesser of 2 evils, I know which i would
> choose.
>
> However whatever floats your boat but if you intend
> to exceed VNE I would be grateful if you did not do
> it over my head, all thos falling bits can really spoil
> your day.
>
> Yes Bert, you were indeed lucky if you exceeded VNE
> but read my first paragraph as to the rest. I have
> spun a large span glider (ASW17) and I have to say
> I have never got anywhere near VNE or the placarded
> G limit in the recovery. Will airbrakes effect the
> recovery from a spin, I don't know yet, I will let
> you know.
>
>
>
> At 11:48 26 March 2004, Bert Willing wrote:
> >Well, your contribution does make me assume than you
> >never did a spin in a
> >large span glider. I once had to choose between exceeding
> >Vne and pulling
> >the airbrakes, and I didn't pull them. As someone said
> >earlier, I was one of
> >the lucky idiots who got away with it.
> >
> >--
> >Bert Willing
> >
> >ASW20 'TW'
> >
> >
> >'Stefan' a écrit dans le message de
> ...
> >> K.P. Termaat wrote:
> >>
> >> > Thanks for the discussion. Once one has exceeded
> >>>Vne ...
> >>
> >> This whole discussion is somewhat bizarre. I've been
> >>doing spins on a
> >> regular basis and exceeding Vne has never been an
> >>issue. Certainly not
> >> when still spinning (no acceleration in spinning mode),
> >>but not during
> >> pull out either. I can't help assuming that no one
> >>contributing to this
> >> thread has ever done a spin himself.
> >>
> >> Stefan
> >>
> >
> >
> >
>
>
>

W.J. $Bill$ Dean $U.K.$.

March 26th 04, 02:00 PM

Unless you are the designer, you don't know what was the limiting factor
which sets the limit speed.

I once saw the wreck of an ASW20C just after it crashed at about 200 knots.
It turns out that the stability and control characteristics of that type are
such that above a certain speed it is impossible to recover from a dive even
with the stick on the back stop; this is because the wing twists.

I also saw the wreckage of a Vega where the trailing edge brakes had been
deployed at too high a speed.

If you exceed VNE you are taking a risk, if you pull too hard above
manoeuvring speed you are taking a risk, and if you pull hard and roll at
the same time you are taking a risk. If you pull the brakes you are
increasing the bending load on the wings.

If you get it wrong and have to take one of the risks, I am told that you
should centralise the ailerons, then pull however hard is necessary not to
exceed VNE, and make sure the brakes stay shut.

It is clear that some types are marginal in recovering from an inadvertent
spin entry without exceeding limits, especially if the entry is from an
accelerated stall. An ETA broke up recovering from a deliberate stall/spin
entered for certification purposes.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

>
> "Bert Willing" > wrote in
> message ...
>
> Well, your contribution does make me assume than you never did a spin in a
> large span glider. I once had to choose between exceeding Vne and
> pulling the airbrakes, and I didn't pull them. As someone said earlier,
> I was one of the lucky idiots who got away with it.
>
> Bert Willing
>
> ASW20 "TW"
>

Stefan

March 26th 04, 02:55 PM

W.J. (Bill) Dean (U.K.). wrote:

> It is clear that some types are marginal in recovering from an inadvertent
> spin entry without exceeding limits, especially if the entry is from an
> accelerated stall. An ETA broke up recovering from a deliberate stall/spin
> entered for certification purposes.

This is exactly the point: Certificated gliders can always be recovered
from a spin without exceeding the limits, otherwise they wouldn't have
been certificated. The ETA wasn't certificated and broke up during a
test flight. It won't get certificated before this issue is fixed.

Stefan

Tony Verhulst

March 26th 04, 03:23 PM

Bert Willing wrote:
> Nonsense. Exceed the structural g-load limit and you fly without wings.

Not so much fly as.... plummet.

Tony V. :-)

Andreas Maurer

March 26th 04, 04:26 PM

On Fri, 26 Mar 2004 14:00:08 -0000, "W.J. $Bill$ Dean $U.K.$."
> wrote:

>I once saw the wreck of an ASW20C just after it crashed at about 200 knots.
>It turns out that the stability and control characteristics of that type are
>such that above a certain speed it is impossible to recover from a dive even
>with the stick on the back stop; this is because the wing twists.

pretty interesting case - I had expected that the 20 (and 20C) would
loose its wings due to aileron/flap flutter at this speed.

>It is clear that some types are marginal in recovering from an inadvertent
>spin entry without exceeding limits, especially if the entry is from an
>accelerated stall. An ETA broke up recovering from a deliberate stall/spin
>entered for certification purposes.

The eta case is particularly interesting:

Afaik it did not break up because it exceeded Vne (in fact it lost its
tail at "only" about 200 kp/h), but because it exceeded the yellow
line with fully deflected rudder (from the spin recovery) and the
resulting torque broke the tail boom that was not designed for this
case of load (fully deflected rudder at this speed).

Bye
Andreas

Denis

March 26th 04, 06:31 PM

W.J. (Bill) Dean (U.K.). wrote:

> Unless you are the designer, you don't know what was the limiting factor
> which sets the limit speed.
>
> I once saw the wreck of an ASW20C just after it crashed at about 200 knots.
> It turns out that the stability and control characteristics of that type are
> such that above a certain speed it is impossible to recover from a dive even
> with the stick on the back stop; this is because the wing twists.

are YOU the designer of the ASW20C ???

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 26th 04, 06:44 PM

W.J. (Bill) Dean (U.K.). wrote:

> If you get it wrong and have to take one of the risks, I am told that you
> should centralise the ailerons, then pull however hard is necessary not to
> exceed VNE, and make sure the brakes stay shut.

No.

You should "pull however is necessary but not exceeding the maximum g
permitted near VNE (usually it is reduced to 4 g's at that speed, even
without airbrakes). And certainly not "pull hard" because a even very
small force backwards on the stick is likely to cause higher than
expected g's !

If your speed is going to exceed VNE within this manoeuvre, you should
stop or reduce pulling and apply full airbrakes. At any dive angle up to
45° this prevents the glider to exceeding VNE, and you have time to
recover pulling gently (under 2 g's). This of course supposes that there
is sufficient ground clearance...

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Eric Greenwell

March 26th 04, 06:59 PM

Stefan wrote:
> Don Johnstone wrote:
>
>> I am not sure that enough G could
>> be pulled at speeds below VNE to cause serious catastrophic
>> failure as there is a margin between the placarded
>> limit and the design limit of most gliders.
>
>
> IIRC, JAR requires a safety margin of 1.5

Va (maneuvering speed) is generally accepted as the highest speed you
can make full control deflections without exceeding the flight limits.
If there is a 1.5 safety margin, a speed only 22% higher would allow you
to exceed the design limits. On my ASH 26 Va is 99 knots, so this speed
would be 121 knots, 25 knots _below_ Vne. I am sure enough G can be
pulled at speeds below Vne to cause serious catastrophic failure.

Further, At Vne (47% higher than Va), you could pull 2.2 times the
flight limits!

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Edward Downham

March 26th 04, 07:00 PM

I would tend to side with Don here.

Given a choice between exceeding Vne or the placard 'g' loading, I would go for
pulling hard every time.

From what I can remember, the glider manufacturer comes up with a 'Design Dive
Speed', Vd, which is then reduced (c.10%) to give a 'Never Exceed Speed', Vne.

It is important to note that this margin is there to cope with things such as
ASI position and calibration errors. When you fly a glider at an _indicated_
speed of Vne, you might actually be nearer Vd and the realm of the test pilot.

Flutter is a big problem and I am told that it is usually the determining
factor in the calculations used to produce Vd. Remember this is for a new
glider, with factory mass-balancing and pristine seals on the flying surfaces.

On the other hand, the airframe 'g' limits have: (a) a regulatory margin of
1.5, often much greater by the time the glider is made (it musn't be below 1.5.
so ends up being 1.6+) and (b) been promulgated for max. flight-mass (leading
to an even bigger margin if you are below this).

To use an example, the K-21 has a Vne of 280Kph/151Kts and declared flight
manual 'g' limits of +5.3/-4.0. That makes Vd around 166Kts. The design 'g'
limits work out as 8/-6 and it is unlikely to fail at that point.

As Bill Dean has mentioned, some gliders lose a lot of their control authority
over Vd. You may find yourself flying faster and faster and unable to do much
about it. Also, the faster you get, the more likely you are to overstress the
airframe with control inputs (and I don't just mean the elevator).

I agree with other posters about the use of airbrakes; either pull the brakes
OR pull hard but NOT BOTH. The Nimbus-4 which broke up near Minden was handled
in this way.

In most modern gliders you should be able to pull 6g+ without breaking any bits
off them. The rise is drag is high, and will pretty certainly arrest any
further speed build-up and bring the nose up quite smartly. Also you won't get
so close to the ground, if this is a factor.

Denis

March 26th 04, 07:04 PM

Don Johnstone wrote:

> 2. Pulling excess G can damage the airframe, however
> the damage is likely to be far less than the damage
> caused by flutter.

Both may cause the same damage : loosing the wings (and both have)

> I am not sure that enough G could
> be pulled at speeds below VNE to cause serious catastrophic
> failure

Below manouevreing speed, no. Above it (and below VNE) yes !

> I stand to be corrected but I suspect it is unlikely
> that 8G could be attained at an airspeed less than
> VNE.

If 8 g is the extreme limit this includes a safety margin and the real
limit is what is placarded (in most gliders it's about 5 or 5.5 g). And
this limit is only valid at manouevering speed, at VNE it is much lower.

yes 8 g may be attained well below VNE (if stalling speed is 70 km/h,
you may exceed 8 g at 198 km/h, as lift depends on square of speed.) At
270 km/h you'd reach 14.9 g !!!

> 3. Airframe flutter can occur at less than VNE. The
> likelyhood of flutter increases dramatically above
> VNE and the severity increases with the speed.

Nonsense. Flutter cannot appear under Vc, a design speed that is just
above VNE.

Not all modes of flutter are catastrophic (it depends of the damping)
but most are explosive. At any speed above flutter speed.

> The N really does stand for never.

Yes, but the G limits are *never* to be exceeded too, even if nobody has
thought to call it GNE. It is exactly the same.

> Will airbrakes effect the
> recovery from a spin, I don't know yet,

That was the question. Thus if you don't know, please don't reply !

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

K.P. Termaat

March 26th 04, 07:05 PM

That is not the issue Jean. I am talking about pulling the airbrakes before
the rotation of the glider has stopped. This not in the manual of course.
The idea is to avoid a high speed with the glider at a pitch angle of
something like 60° directly after it has stopped rotation.
Testing what happens when I do the whole thing with my new rather heavy low
drag Ventus-2cxT is an invitation to others to call me an "idiot". Probably
I will do that myself too.
For me it is more like an "if then" case. While instructing I have done tens
of spins with students with a ASK-13, but that's easy of course and does
hardly apply to what can happen to modern gliders.

Thanks

Karel, NL

"Jean" > schreef in bericht
...
> Why don't you check your glider's flight manual ?
> Jean
> "K.P. Termaat" > a écrit dans le message de
> ...
> > Yesterday evening I talked with a friend about avoiding excessive speed
> when
> > recovering from a spin in a modern low drag glider with the somewhat
> larger
> > span.
> > He came up with the idea of pulling the airbrakes when still recovering
> from
> > the rotating mode. I am not sure this can be done without disturbing the
> > recovering action or without hurting the glider.
> > Any comment will appreciated.
> >
> > Karel, NL
> >
> >
>
>

Eric Greenwell

March 26th 04, 07:17 PM

Edward Downham wrote:

> I would tend to side with Don here.
>
> Given a choice between exceeding Vne or the placard 'g' loading, I would go for
> pulling hard every time.

Does "pulling hard" mean: a) pulling hard on the stick, or b) pulling
"high Gs"? There is a big difference!

> To use an example, the K-21 has a Vne of 280Kph/151Kts and declared flight
> manual 'g' limits of +5.3/-4.0.

My manual, as do many, show a _reduced_ allowable G load at increasing
speeds, going from 5.3 G (Va) to only 4 G at Vne.

> That makes Vd around 166Kts. The design 'g'
> limits work out as 8/-6 and it is unlikely to fail at that point.

"Unlikely"? How about gusts or simultaneous control deflections (say, a
bit of rudder or aileron)? Have you talked to a Schleicher designer (or
any designer) about this, or are you speculating?

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Marc Ramsey

March 26th 04, 07:17 PM

Edward Downham wrote:
> Given a choice between exceeding Vne or the placard 'g' loading, I would go for
> pulling hard every time.

As Eric has indicated, it is a given that once you exceed Va by a
significant margin, whether or not you exceed Vne, you can pull hard
enough to cause a structural failure.

I think there is a point here that some are missing, and I'd like to
hear some discussion around this. With long wing gliders, it is easier
to unstall the wing, than it is to stop the rotation. If you are
unstalled and rotating, you are in a spiral. If you pull in a spiral,
your speed will increase, not decrease. The most important thing to
remember, as far as I'm concerned, is never pull before the rotation has
stopped...

Marc

Andy Blackburn

March 26th 04, 08:44 PM

I'm sure everyone agrees the best advice is not to
get into a situation where you have to choose between
Vne and the G-limit. Thinking ahead with respect to
attitude and configuration as you initiate recovery
is your best bet.

I don't see anything obviously bad about deploying
speed brakes early in the recovery, particularly if
they are terminal velocity brakes and the flight manual
allows for their use. It ups the pilot workload a bit,
so I'd be wary of getting overloaded - fly the airplane
first.

I'm not as keen on the idea of pulling out the breaks
in situations where the G-loading in pullout is likely
to be near the limit. As has been observed, with the
breaks deployed the G-limit is significantly lower
because with no lift on the inner portion of the wing,
the bending moments on the wing are a lot higher for
any given G-loading.

I disagree strongly with the statement that you can
over-G a composite sailplane and encounter non-catastrophic
structural damage. This may be somewhat true for aluminum,
but the characteristics of composites are such than
they flex elastically until the break in spectacular
fashion - there is no intermediate 'plastic deformation'
mode. If you reach the ultimate limit there will be
essentially no warning before you turn into a high-speed
lawn dart. I know of several cases where this has happened.

If you find yourself steeply nose down and accelerating,
I would consider pulling the breaks only if I have
enough altitude for a relatively low-G pullout and
I am not too fast already. Under all other circumstances
I would pull smoothly back on the stick until I reach
the G-limit (question, if you don't have a G-meter,
how well calibrated is your backside?). I'd only pull
harder: a) to avoid hitting the ground, or b) if the
speed was still building at an alarming rate - of course
if you get to this point you are in a world of hurt
anyway so the amount of over-G versus over-Vne is subject
to your personal risk profile.

9B

At 19:12 26 March 2004, K.P. Termaat wrote:
>That is not the issue Jean. I am talking about pulling
>the airbrakes before
>the rotation of the glider has stopped. This not in
>the manual of course.
>The idea is to avoid a high speed with the glider at
>a pitch angle of
>something like 60° directly after it has stopped rotation.
>Testing what happens when I do the whole thing with
>my new rather heavy low
>drag Ventus-2cxT is an invitation to others to call
>me an 'idiot'. Probably
>I will do that myself too.
>For me it is more like an 'if then' case. While instructing
>I have done tens
>of spins with students with a ASK-13, but that's easy
>of course and does
>hardly apply to what can happen to modern gliders.
>
>Thanks
>
>Karel, NL
>
>'Jean' schreef in bericht
...
>> Why don't you check your glider's flight manual ?
>> Jean
>> 'K.P. Termaat' a écrit dans le message de
>> ...
>> > Yesterday evening I talked with a friend about avoiding
>>>excessive speed
>> when
>> > recovering from a spin in a modern low drag glider
>>>with the somewhat
>> larger
>> > span.
>> > He came up with the idea of pulling the airbrakes
>>>when still recovering
>> from
>> > the rotating mode. I am not sure this can be done
>>>without disturbing the
>> > recovering action or without hurting the glider.
>> > Any comment will appreciated.
>> >
>> > Karel, NL
>> >
>> >
>>
>>
>
>
>

Mark James Boyd

March 26th 04, 08:57 PM

K.P. Termaat > wrote:
>Yesterday evening I talked with a friend about avoiding excessive speed when
>recovering from a spin in a modern low drag glider with the somewhat larger
>span.

A lot has been written here about G loads. I recall that the
T-34 (an aerobatic power plane I have a little time in
which is sortof a tandem Beech 33) had some issues with wings
coming off during aerobatics. The recorded G loads and mauevers
indicated the aircraft wasn't flown outside of G limits.

How did the wings separate? Some smarty folks said it was
because the twisting G load that the wing could endure was
much less than the static tested load. If the ailerons were
deflected and the thing was in a steep spiral (as opposed
to straight dive) there were twisting loads.

Now I ain't no aerodinymakist. I took a plastic spoon and
tried to bend it in half. No luck. Took the same
spoon and twisted it and bent it in half. Bingo. What
does this mean? Don't make wings out of plastic spoons... ;)

Anyway, I also recall the Sprint Ultralight had some airframe
separations, and before I flew it the first time, the
owner (who was also an A&P) told me he'd installed additional
bracing wires to reduce wing twisting.

Come to find out, there are more than a few aerodyne designs
which use drag and anti-drag wires (maybe the wrong technical
name but yo get the idea) inside and outside the wing to help
prevent twisting.

I tell ya, I'm personally a big fan of wings-level
dives vs. spirals. I'd go 1.2 x Vne in a dive before I'd go
1.0 x Vne in a steep spiral. Dunno if this is right,
but that's what my instinct tells me...
--

------------+
Mark Boyd
Avenal, California, USA

mat Redsell

March 27th 04, 12:12 AM

Now if you used carbon rods for the spars one could pull about 15 G's and
not suffer a failure . In our designs we only design to the deflection
desired.... and the resulting G loading is always well beyond the required
specs.

Just a thought! -mat

Andreas Maurer

March 27th 04, 12:31 AM

On Fri, 26 Mar 2004 10:59:41 -0800, Eric Greenwell
> wrote:

>Va (maneuvering speed) is generally accepted as the highest speed you
>can make full control deflections without exceeding the flight limits.
>If there is a 1.5 safety margin, a speed only 22% higher would allow you
>to exceed the design limits. On my ASH 26 Va is 99 knots, so this speed
>would be 121 knots, 25 knots _below_ Vne.
>I am sure enough G can be
>pulled at speeds below Vne to cause serious catastrophic failure.

Indeed.
Va is directly linked to the aerodynamic forces that your wing can
create and does not contain any safety factor.

Bye
Andreas

Andreas Maurer

March 27th 04, 12:51 AM

On Thu, 25 Mar 2004 08:53:00 GMT, "K.P. Termaat" > wrote:

>Yesterday evening I talked with a friend about avoiding excessive speed when
>recovering from a spin in a modern low drag glider with the somewhat larger
>span.
>He came up with the idea of pulling the airbrakes when still recovering from
>the rotating mode. I am not sure this can be done without disturbing the
>recovering action or without hurting the glider.
>Any comment will appreciated.

What has not been discussed so far in this thread is the acceleration
of the glider in a steep dive:

If you extend the airbrakes (far) below Vne, you have a lot more time
to pull out of the dive until your airspeed reaches Vne because the
acceleration of the glider is a lot slower.

Typical case: You extend your airbrakes once you exceed a certain
speed (for example Va or slightly higher).

Glider airbrakes are typically designed to keep the glider under Vne
at a dive angle of more or less 30 degrees, so if your nose-down
attitude is less than 30 degrees, the glider will decelerate while you
are still pulling out of the dive - this means that once you have
reached 30 degrees nose-down attitude, you are already safe and can
take all the time in the world to pull out the last 30 degrees till
level flight (...if you have enough height, of course) without
worrying about exceeding Vne.

You are probably going to loose more height during the recovery
(because of the "soft" pullout) this way, but the g-load will be kept
realtively low.

With retracted airbrakes the glider will accelerate quickly, therefore
you are going to need to pull higher g-load to get out of the dive
before you exceed Vne - and the glider will accelerate all the time
until it is nearly in level flight. And as others have already pointed
out in this thread, extending the airbrakes close to (or over) Vne at
high g-load is probably going to ruin your day...

Bye
Andreas

Jack

March 27th 04, 01:40 AM

On 3/26/04 1:04 PM, in article ,
"Denis" > wrote:

>> Will airbrakes effect the
>> recovery from a spin, I don't know yet,
>
> That was the question. Thus if you don't know, please don't reply !

You write like a guy who got all his experience from a book, or a seminar.
But that could just be a language problem, I suppose. How much test pilot
work have you done?

Jack

F.L. Whiteley

March 27th 04, 07:46 PM

"Mark James Boyd" > wrote in message
news:4064994c$1@darkstar...
> K.P. Termaat > wrote:
> >Yesterday evening I talked with a friend about avoiding excessive speed
when
> >recovering from a spin in a modern low drag glider with the somewhat
larger
> >span.
>
> A lot has been written here about G loads. I recall that the
> T-34 (an aerobatic power plane I have a little time in
> which is sortof a tandem Beech 33) had some issues with wings
> coming off during aerobatics. The recorded G loads and mauevers
> indicated the aircraft wasn't flown outside of G limits.
>
> How did the wings separate? Some smarty folks said it was
> because the twisting G load that the wing could endure was
> much less than the static tested load. If the ailerons were
> deflected and the thing was in a steep spiral (as opposed
> to straight dive) there were twisting loads.
>
Thought I heard that inspections showed T-34 wings were suffering from
fatigue cracks. Kind of shot down some of the 'fighter dude' thrill rides
(we have/had one in Colorado). We have a disassembled T-34 wrapped in
plastic in our hangar. I recall a conversation about the value dropping by
about 50% when the crack problem was discovered.

Frank Whiteley

Denis

March 28th 04, 05:43 PM

Jack wrote:

> You write like a guy who got all his experience from a book, or a seminar.
> But that could just be a language problem, I suppose. How much test pilot
> work have you done?

None (and I never pretended to have, did I ?). Although I worked for
years as a flight test engineer and a few thousand flight hours as a
pilot. Also some hours reading books, but I did not log them ;-)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 28th 04, 06:33 PM

Andy Blackburn wrote:

> I'm sure everyone agrees the best advice is not to
> get into a situation where you have to choose between
> Vne and the G-limit. Thinking ahead with respect to
> attitude and configuration as you initiate recovery
> is your best bet.

(...)

> if you get to this point you are in a world of hurt
> anyway so the amount of over-G versus over-Vne is subject
> to your personal risk profile.

I agree with all Andy said. I would add that "pulling as hard as
required to avoid VNE" is easier to say that to do, because :

- it is impossible, if you are not an experimented glider aerobatics
pilot, to know how many g's you need to avoid exceeding VNE,

- depending on dive angle and speed, it may be just impossible to avoid
VNE without airbrakes, even if pulling 15 g's (supposing the wings have
not briken before)

- it is impossible without a g-meter to know if you pull 5 g (or just a
little more, comprised in the "safety margin"), or 10 g's or more.
Especially at high speeds, because a very small stick input may result
in high g's, or pilot induced oscillation, etc.

And, last but not least, if you have been above VNE and lucky enough not
to have encountered flutter, you are lucky andy the glider is still safe.

If you have pulled too many g's and the wings have not broken, you are
lucky but the *glider structure may have been damaged* and you, or
another pilot, may encounter a catastrophic failure in a subsequent
flight within the certificated flight enveloppe !

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 28th 04, 07:30 PM

Edward Downham wrote:

> It is important to note that this margin is there to cope with things such as
> ASI position and calibration errors. When you fly a glider at an _indicated_
> speed of Vne, you might actually be nearer Vd and the realm of the test pilot.

No. VNE is an indicated airspeed limit (IAS). If there is a airspeed
calibration error, VNE has been reduced to correct it. The margin is
there for instrumental errors, and *pilot* errors.

> As Bill Dean has mentioned, some gliders lose a lot of their control authority
> over Vd. You may find yourself flying faster and faster and unable to do much
> about it. Also, the faster you get, the more likely you are to overstress the
> airframe with control inputs (and I don't just mean the elevator).

Have you any reference for this affirmation ? THis is a know issue on
earlier delta wings, also in earlier near-transsonic aircraft, but I
don't know any glider with such a problem.

> In most modern gliders you should be able to pull 6g+ without breaking any bits
> off them.

Not at VNE !!!

> The rise is drag is high, and will pretty certainly arrest any
> further speed build-up and bring the nose up quite smartly. Also you won't get
> so close to the ground, if this is a factor.

The drag rise is not enough to avoid overspeeds. The rise in drag
provided by *airbrakes* (not pulling too hard) is the *only* way to
avoid either flutter (above VNE) or breaking the wings (by overloading).

Except when too close to the ground this is always the only thing to do.

And to come back to the original question, I think there is nothing to
fear pulling the airbrakes before getting out of the spin, since it will
help stopping the rotation (the outer airbrake will have a greater drag
due to greater airspeed)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

W.J. $Bill$ Dean $U.K.$.

March 28th 04, 07:50 PM

No, it is only one point.

There have been several cases of certificated gliders overstressed in
stall/spin recoveries, some of them broke up.

I saw a Ka6E being repaired after such an incident (in this case a
deliberate stall/spin for self-training, the pilot was a current
instructor), you can read about it in "Gliding Safety" by Derek Piggott, on
page 53 in my copy (second edition), under "Stall and spin-related
accidents", "Light stick forces".

You can also read about the Nimbus 4DM at Minden; 99.07.13 - LAX99MA251 -
http://www.ntsb.gov/NTSB/brief.asp?ev_id=20031009X01702&key=1 Nimbus 4DM -
Minden - Two killed.

With some gliders it is both important and difficult to get the recovery
exactly right. I suspect the modern generation of gliders, Standard, 15M
and Open come into this category especially when fully ballasted and flown
in really strong conditions. The critical manoeuvre is likely to be an
inadvertent departure from a steep thermal turn in rough strong lift.
Don't let anyone tell you that it won't depart when flown like this, it may,
even if you can't get it to do it deliberately.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

>
> "Stefan" > wrote in message
> ...
>
> >
> > W.J. (Bill) Dean (U.K.). wrote:
> >
> > It is clear that some types are marginal in recovering from an
> > inadvertent spin entry without exceeding limits, especially if the entry
> > is from an accelerated stall. An ETA broke up recovering from a
> > deliberate stall/spin entered for certification purposes.
> >
>
> This is exactly the point: certificated gliders can always be recovered
> from a spin without exceeding the limits, otherwise they wouldn't have
> been certificated. The ETA wasn't certificated and broke up during a
> test flight. It won't get certificated before this issue is fixed.
>
> Stefan.
>

W.J. $Bill$ Dean $U.K.$.

March 28th 04, 08:44 PM

My comments on the ASW20C accident are based on my memories of what I saw at
the time, and on my memories of the subsequent investigation and report. I
never saw the actual report, but comments were published at the time.

The investigators estimated the speed when the glider hit the ground, it was
certainly of the order of 200 knots. I gather that the investigators
contacted Schleichers about the accident, and the information that the
glider would be unrecoverable at some speed below 200 knots, because the
pitch down force from wing twist would overcome the pitch up force from full
up elevator, came from Schleichers probably from Waible.

This accident is a perfect illustration of how the pilot is unlikely to know
what is critical if limits are exceeded. The ASW20C did not flutter, and
did not break up in flight; the first failure was loss of control.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

>
> "Andreas Maurer" > wrote in message
> ...
>
> >
> > On Fri, 26 Mar 2004 14:00:08 -0000, "W.J. $Bill$ Dean $U.K.$."
> > > wrote:
> >
> > I once saw the wreck of an ASW20C just after it crashed at about 200
> > knots. It turns out that the stability and control characteristics of
> > that type are such that above a certain speed it is impossible to
> > recover from a dive even with the stick on the back stop; this is
> > because the wing twists.
> >
>
> pretty interesting case - I had expected that the 20 (and 20C) would
> lose its wings due to aileron/flap flutter at this speed.
>
> <snip>
>
> Bye
> Andreas
>

Jon Meyer

March 28th 04, 08:52 PM

I agree with Ed in most respects, and I think you need
to get a few facts right Denis.

>Have you any reference for this affirmation ? THis
>is a know >issue on earlier delta wings, also in earlier
>near-transsonic >aircraft, but I don't know any glider
>with such a problem.

Yes, as has already been mentioned the ASW20 has a
problem, where exceeding Vd can result in wing twist
that results in a terminal dive even with the stick
fully back. Not to mention what flutter can do anyway.

>> In most modern gliders you should be able to pull
>>6g+ without breaking any bits
>> off them.
>
>Not at VNE !!!

Yes, I think Ed is probably right. Although the glider
will probably be a write-off after you land, because
the material will yield in highly stressed areas. Glider
wings are bloody strong, and are unlikely to snap,
but the reason you dont want to exceed the G-limits
every day is because bits will start to creep, and
your glider's structure will gradually deteriorate
and eventually fail, but as a One-off it is unlikely
to result in failure, particularly as the stalling
angle of the wing will limit the maximum g you can
pull below VNE. It will be pretty high, but is unlikely
to be more than 10g, and you shouldnt need to pull
this hard anyway. To be honest if it was a choice between
flutter, where bits like ailerons and elevator might
come off, and exceeding the G-limits where the wing
might be a write off but the plane will remain flyable
and be safe to land (or at least bail out of), I know
which I would choose.

>The drag rise is not enough to avoid overspeeds. The
>rise in <drag
>provided by *airbrakes* (not pulling too hard) is the
>*only* <way to
>avoid either flutter (above VNE) or breaking the wings
>(by >overloading).

I believe that with the airbrakes open your safe positive
G-limit reduces to +2.5G. This is because you are forcing
most of the lift to be produced near the tip and thereby
increasing the wing bending moment at the root, and
there is also a hell of a shear force produced. God
knows what happens if you open them suddenly above
Va while pulling 3.5g but i suspect it would not be
pretty. (I also suspect that it may be this that caused
several big gliders to have wings come off in spin
recovery)

Ask an aerobatic pilot if you don't want to take my
word for it, but I believe their rule of thumb is that
it is always better to exceed the g-limits than to
exceed VNE, and that you should NEVER open the airbrakes
in an attempt to limit speed, because it has such a
small effect on drag and such a huge effect on the
g-limits.

Hope this in some way helps, though I think I am just
re-iterating what a lot of other people have already
said.

J.

Marc Ramsey

March 28th 04, 09:06 PM

Jon Meyer wrote:
> Ask an aerobatic pilot if you don't want to take my
> word for it, but I believe their rule of thumb is that
> it is always better to exceed the g-limits than to
> exceed VNE, and that you should NEVER open the airbrakes
> in an attempt to limit speed, because it has such a
> small effect on drag and such a huge effect on the
> g-limits.

Didn't you mean to say "it is always better to exceed VNE
than to exceed the g-limits"?

Marc

Eric Greenwell

March 28th 04, 10:00 PM

Jon Meyer wrote:

> Yes, as has already been mentioned the ASW20 has a
> problem, where exceeding Vd can result in wing twist
> that results in a terminal dive even with the stick
> fully back. Not to mention what flutter can do anyway.

According to Bill Dean "I gather that the investigators
contacted Schleichers about the accident, and the information that the
glider would be unrecoverable at some speed below 200 knots,"

NO mention of Vd (about 160 knots), so it is speculation to say
exceeding Vd can result wing twist. It might be 170, 180, 190,... we
don't know.

>>>In most modern gliders you should be able to pull
>>>6g+ without breaking any bits
>>>off them.
>>
>>Not at VNE !!!
>
>
> Yes, I think Ed is probably right. Although the glider
> will probably be a write-off after you land, because
> the material will yield in highly stressed areas. Glider
> wings are bloody strong, and are unlikely to snap,
> but the reason you dont want to exceed the G-limits
> every day is because bits will start to creep, and
> your glider's structure will gradually deteriorate
> and eventually fail, but as a One-off it is unlikely
> to result in failure, particularly as the stalling
> angle of the wing will limit the maximum g you can
> pull below VNE. It will be pretty high, but is unlikely
> to be more than 10g, and you shouldnt need to pull
> this hard anyway.

At Vne, my ASH 26 can pull 2.2 times the flight limits of 5.3 G. And if
you hit a gust at the same time, or have some aileron or rudder input...

To be honest if it was a choice between
> flutter, where bits like ailerons and elevator might
> come off, and exceeding the G-limits where the wing
> might be a write off but the plane will remain flyable
> and be safe to land (or at least bail out of), I know
> which I would choose.

Who wouldn't choose a plane that was safe to land instead of one where
bits have fallen off? What we are discussing is if the choice is "and
exceeding the G-limits where the wings might break off".

>>The drag rise is not enough to avoid overspeeds. The
>>rise in <drag
>>provided by *airbrakes* (not pulling too hard) is the
>>*only* <way to
>>avoid either flutter (above VNE) or breaking the wings
>>(by >overloading).
>
>
> I believe that with the airbrakes open your safe positive
> G-limit reduces to +2.5G.

For my ASH 26 E at Vne: 4 G load factor (down from 5.3 at Va); 3.5 G
load factor airbrakes extended. It looks like the G limits at Vne are
fairly close together. I am curious about why they decrease.

snip

> Ask an aerobatic pilot if you don't want to take my
> word for it, but I believe their rule of thumb is that
> it is always better to exceed the g-limits than to
> exceed VNE, and that you should NEVER open the airbrakes
> in an attempt to limit speed, because it has such a
> small effect on drag and such a huge effect on the
> g-limits.

Are they talking specifically about gliders designed for aerobatic use?
Quite a different bird than what most of us fly, with very high G and
Vne ratings. Perhaps their rule of thumb applies just to them? And, I am
very skeptical of the "small effect on drag" remark, since at Vne, the
air brake drag will be greatest drag of all the sources. Or maybe not,
if you mean gliders designed for aerobatic use.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Denis

March 28th 04, 10:17 PM

W.J. (Bill) Dean (U.K.). wrote:

> There have been several cases of certificated gliders overstressed in
> stall/spin recoveries, some of them broke up.

(...)

> You can also read about the Nimbus 4DM at Minden; 99.07.13 - LAX99MA251 -
> http://www.ntsb.gov/NTSB/brief.asp?ev_id=20031009X01702&key=1 Nimbus 4DM -
> Minden - Two killed.

the link is actually
http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19310&key=1

the conclusion is "The pilot's excessive use of the elevator control
during recovery (...) resulted in the overload failure of the wings at
loadings beyond the structure's ultimate design loads."

[the possibility of speed being over VNE or Vd is neither confirmed nor
being one of the causes of the wing failure according to the report]

This supposes that unfortunately the pilots did what Bill told : "pull
however hard is necessary" with the result that "At the ultimate load
limit, the deflection was 46.5-degrees, similar to the witness
observations of the wing deflection just prior to the break up."

Do you imagine you may safely "pull however hard you need" with your
wings bent at 45° up ??? I don't.

The report quotes also that the G limit for the Nimbus 4 at VNE is 3.5 g
*only* (compared to 5.3 g at Va) and the design "safety margin" is
between 1.55 to 1.75. Thus even on a plane in perfect condition, and if
the manufacturer made no mistake, it *will* break between 5.4 and 6.1 g
at VNE (even without airbrakes)

Remember that at that speed (285 km/h) you could pull about 16 g ! and
at Vd (324 km/h) more than 20 g...

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

>>"Stefan" > wrote in message
...

>>This is exactly the point: certificated gliders can always be recovered
>>from a spin without exceeding the limits, otherwise they wouldn't have
>>been certificated. The ETA wasn't certificated and broke up during a
>>test flight. It won't get certificated before this issue is fixed.

Denis Flament

March 28th 04, 10:22 PM

W.J. (Bill) Dean (U.K.). wrote:

> There have been several cases of certificated gliders overstressed in
> stall/spin recoveries, some of them broke up.

(...)

> You can also read about the Nimbus 4DM at Minden; 99.07.13 - LAX99MA251 -
> http://www.ntsb.gov/NTSB/brief.asp?ev_id=20031009X01702&key=1 Nimbus 4DM -
> Minden - Two killed.

the link is actually
http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19310&key=1

the conclusion is "The pilot's excessive use of the elevator control
during recovery (...) resulted in the overload failure of the wings at
loadings beyond the structure's ultimate design loads."

[the possibility of speed being over VNE or Vd is neither confirmed nor
being one of the causes of the wing failure according to the report]

This supposes that unfortunately the pilots did what Bill told : "pull
however hard is necessary" with the result that "At the ultimate load
limit, the deflection was 46.5-degrees, similar to the witness
observations of the wing deflection just prior to the break up."

Do you imagine you may safely "pull however hard you need" with your
wings bent at 45° up ??? I don't.

The report quotes also that the G limit for the Nimbus 4 at VNE is 3.5 g
*only* (compared to 5.3 g at Va) and the design "safety margin" is
between 1.55 to 1.75. Thus even on a plane in perfect condition, and if
the manufacturer made no mistake, it *will* break between 5.4 and 6.1 g
at VNE (even without airbrakes)

Remember that at that speed (285 km/h) you could pull about 16 g ! and
at Vd (324 km/h) more than 20 g...

Yes it was certificated, but certification does *not* guarantee you that
the glider will not break if you pull 20 g... !

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

>>"Stefan" > wrote in message
...

>>This is exactly the point: certificated gliders can always be recovered
>>from a spin without exceeding the limits, otherwise they wouldn't have
>>been certificated. The ETA wasn't certificated and broke up during a
>>test flight. It won't get certificated before this issue is fixed.

Denis

March 28th 04, 10:24 PM

W.J. (Bill) Dean (U.K.). wrote:

> There have been several cases of certificated gliders overstressed in
> stall/spin recoveries, some of them broke up.

(...)

> You can also read about the Nimbus 4DM at Minden; 99.07.13 - LAX99MA251 -
> http://www.ntsb.gov/NTSB/brief.asp?ev_id=20031009X01702&key=1 Nimbus 4DM -
> Minden - Two killed.

the link is actually
http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19310&key=1

the conclusion is "The pilot's excessive use of the elevator control
during recovery (...) resulted in the overload failure of the wings at
loadings beyond the structure's ultimate design loads."

[the possibility of speed being over VNE or Vd is neither confirmed nor
being one of the causes of the wing failure according to the report]

This supposes that unfortunately the pilots did what Bill told : "pull
however hard is necessary" with the result that "At the ultimate load
limit, the deflection was 46.5-degrees, similar to the witness
observations of the wing deflection just prior to the break up."

Do you imagine you may safely "pull however hard you need" with your
wings bent at 45° up ??? I don't.

The report quotes also that the G limit for the Nimbus 4 at VNE is 3.5 g
*only* (compared to 5.3 g at Va) and the design "safety margin" is
between 1.55 to 1.75. Thus even on a plane in perfect condition, and if
the manufacturer made no mistake, it *will* break between 5.4 and 6.1 g
at VNE (even without airbrakes)

Remember that at that speed (285 km/h) you could pull about 16 g ! and
at Vd (324 km/h) more than 20 g...

Yes it was certificated, but certification does *not* guarantee you that
the glider will not break if you pull 20 g... !

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

>> "Stefan" > wrote in message
>> ...

>> This is exactly the point: certificated gliders can always be recovered
>> from a spin without exceeding the limits, otherwise they wouldn't have
>> been certificated. The ETA wasn't certificated and broke up during a
>> test flight. It won't get certificated before this issue is fixed.

Denis

March 28th 04, 10:54 PM

Jon Meyer wrote:

> Yes, as has already been mentioned the ASW20 has a
> problem, where exceeding Vd can result in wing twist
> that results in a terminal dive even with the stick
> fully back.

It was not at Vd but at 200 kts ! (if I remember well VNE is 145 kts in
an ASW 20)

> Not to mention what flutter can do anyway.

Flutter is the likeliest cause of failure at 200 kt (40% above VNE !!!).

Don't seek any other cause even if someone reported you that he
remembered someone has told him that ;-)

>>>In most modern gliders you should be able to pull
>>>6g+ without breaking any bits
>>>off them.
>>
>>Not at VNE !!!
>
>
> Yes, I think Ed is probably right.

See my previous post about the NSTB report that demonstrate that the
Nimbus 4 will break between 5 and 6 g (like I suppose any other
non-aerobatic glider)

> angle of the wing will limit the maximum g you can
> pull below VNE. It will be pretty high, but is unlikely
> to be more than 10g,

again, 15 g at VNE, 20 g at design speed (three time more than the wing
can support without breaking !).

> To be honest if it was a choice between
> flutter, where bits like ailerons and elevator might
> come off, and exceeding the G-limits where the wing
> might be a write off but the plane will remain flyable
> and be safe to land (or at least bail out of), I know
> which I would choose.

Neither choice is good. Your choice belongs to you. But don't let other
pilots think that exceeding G-limits "is not good, but I can do it from
time to time". Please don't play with /their/ lives.

> Ask an aerobatic pilot if you don't want to take my
> word for it,

Aerobatic gliders have a much higher allowed G-loads (the physiological
limits of most pilots are below those of the glider).

And the question was about open-class gliders. Did you see many
open-class aerobatic gliders ?

> Hope this in some way helps, though I think I am just
> re-iterating what a lot of other people have already
> said.

Unfortunately yes, many people think like you (that the gliders are much
stronger that what is written in the manual, don't worry until 10 G,
etc.). That was perhaps true with older, low-span gliders (because the
design was less accurate than today and the margins greater). But it's
definitely *not* true.

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 28th 04, 11:07 PM

Eric Greenwell wrote:

>> I believe that with the airbrakes open your safe positive
>> G-limit reduces to +2.5G.
>
> For my ASH 26 E at Vne: 4 G load factor (down from 5.3 at Va); 3.5 G
> load factor airbrakes extended. It looks like the G limits at Vne are
> fairly close together.

Airbrakes out at Va it's 3.5 g instead of 5.3, thus the difference is
significant. I don't know why there is almost no difference at VNE, butI
suspect that in that case the margin is higher without airbrakes than with.

> I am curious about why they decrease.

There is a loss of lift at the airbrakes, thus for the same G the outer
wing is more loaded, and the bending momentat wing root increases.

Perhaps the loss of lift is lesser at high speeds (lower angle of attack) ?

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Andy Blackburn

March 28th 04, 11:08 PM

I may not be exactly right about this, but I believe
that most certified aircraft (including gliders) are
tested to, and must be able to hold together at, a
static G-load of roughly 150% of maximum. To meet this
requirement the wings are generally tested to destruction
(check out the DG website for a video of this procedure
for the DG 1000).

With respect to the flutter speed, I believe that the
manufacturer must demonstrate dives with some margin
above Vne. Question: does anyone know how much faster
over Vne a sailplane must demonstrate flight and under
what combinations of G-loading and control inputs?
Needless to say, certified sailplanes are not generally
tested to destruction by flutter - for obvious reasons.

Conclusion: There is a relatively certain G-load beyond
which you will pull the wings off your glider - just
multiply the certified G-limit by the certification
margin. With respect to flutter at speeds beyond Vne,
it's more of a roll of the dice, since flutter is a
dynamic interaction between aerodynamic forces and
structural ones. Flutter can be affected by control
inputs, control balance, and G-loading, among other
factors. The speed at which wing or tail flutter starts
is not usually an empirical number (Grob 102/103 not
withstanding - customers established these speeds after
the fact), since flight tests don't confirm absolutely
when flutter begins. All we know is the speed below
which flutter doesn't start (Vne x certifcation margin).
That's all that's demonstrated. You may in fact be
able to get away with a bit faster - of course, you
are taking your chances. In summary, it seems like
a choice between certain catastrophe versus possible
catastrophe.

Also, I find it a bit strange that some here feel that
it is possible to over-G a sailplane to damage, but
not destruction. It seems like a fine point to me and
there are several examples of unlucky souls who have
misjudged the point.

One additional thought - I suspect that for older gliders,
wearing of bearings/bushings may degrade the flutter
margin faster than normal material aging degrades the
G-limit, so you might need to think differently if
you have a high-time glider.

Thoughts?

At 21:30 28 March 2004, Denis wrote:
>W.J. (Bill) Dean (U.K.). wrote:
>
>> There have been several cases of certificated gliders
>>overstressed in
>> stall/spin recoveries, some of them broke up.
>
> (...)
>
>> You can also read about the Nimbus 4DM at Minden;
>>99.07.13 - LAX99MA251 -
>> http://www.ntsb.gov/NTSB/brief.asp?ev_id=20031009X01702&key=1
>>Nimbus 4DM -
>> Minden - Two killed.
>
>the link is actually
>http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19310&key=1
>
>the conclusion is 'The pilot's excessive use of the
>elevator control
>during recovery (...) resulted in the overload failure
>of the wings at
>loadings beyond the structure's ultimate design loads.'
>
>[the possibility of speed being over VNE or Vd is neither
>confirmed nor
>being one of the causes of the wing failure according
>to the report]
>
>This supposes that unfortunately the pilots did what
>Bill told : 'pull
>however hard is necessary' with the result that 'At
>the ultimate load
>limit, the deflection was 46.5-degrees, similar to
>the witness
>observations of the wing deflection just prior to the
>break up.'
>
>Do you imagine you may safely 'pull however hard you
>need' with your
>wings bent at 45° up ??? I don't.
>
>The report quotes also that the G limit for the Nimbus
>4 at VNE is 3.5 g
>*only* (compared to 5.3 g at Va) and the design 'safety
>margin' is
>between 1.55 to 1.75. Thus even on a plane in perfect
>condition, and if
>the manufacturer made no mistake, it *will* break between
>5.4 and 6.1 g
> at VNE (even without airbrakes)
>
>Remember that at that speed (285 km/h) you could pull
>about 16 g ! and
>at Vd (324 km/h) more than 20 g...
>
>Yes it was certificated, but certification does *not*
>guarantee you that
>the glider will not break if you pull 20 g... !
>
>--
>Denis
>
>R. Parce que ça rompt le cours normal de la conversation
>!!!
>Q. Pourquoi ne faut-il pas répondre au-dessus de la
>question ?
>
>
>
> >> 'Stefan' wrote in message
> >> ...
>
>
> >> This is exactly the point: certificated gliders can
>>>always be recovered
> >> from a spin without exceeding the limits, otherwise
>>>they wouldn't have
> >> been certificated. The ETA wasn't certificated
>>>and broke up during a
> >> test flight. It won't get certificated before this
>>>issue is fixed.
>

March 28th 04, 11:26 PM

W.J. (Bill) Dean (U.K.). wrote:
> glider would be unrecoverable at some speed below 200 knots, because the
> pitch down force from wing twist would overcome the pitch up force from full
> up elevator, came from Schleichers probably from Waible.
>
> This accident is a perfect illustration of how the pilot is unlikely to know
> what is critical if limits are exceeded. The ASW20C did not flutter, and
> did not break up in flight; the first failure was loss of control.

Was there any discussion at all about the possibility to attempt
controlling it with the flaps ?

Not that it is likely to help, possibly just the opposite, since
you'd be even more in exess of the (lower) Vne for flap positions
other than fully negative.

But if it is really out of control one would imagine trying anything,
if only as a last-ditch attempt to stabilise things a little and be
able to bail out.

Bailing out at 200 kts can't be exactly easy either.
CV

Stefan

March 28th 04, 11:26 PM

W.J. (Bill) Dean (U.K.). wrote:

> With some gliders it is both important and difficult to get the recovery
> exactly right.

Wasn't there a thread in r.a.s not long ago in which most American
pilots considered spin training superfluous and dangerous? Hmmm...

Stefan

(Yes, I've realilzed you're British.)

Michael McNulty

March 29th 04, 12:44 AM

"Stefan" > wrote in message
...
> W.J. (Bill) Dean (U.K.). wrote:
>
> > With some gliders it is both important and difficult to get the recovery
> > exactly right.
>
> Wasn't there a thread in r.a.s not long ago in which most American
> pilots considered spin training superfluous and dangerous? Hmmm...
>
> Stefan
>
> (Yes, I've realilzed you're British.)
>

I don't think that "most American pilots" have ever bothered to express
their opinions with respect to spin training, or any other subject for that
matter, in r.a.s. Perhaps you should have said that some pilots, some of
whom were American, expressed a concern that spin training in designs with
questionable spin related accident records should be reconsidered.
Hmmmm......

Eric Greenwell

March 29th 04, 01:17 AM

Stefan wrote:
> W.J. (Bill) Dean (U.K.). wrote:
>
>> With some gliders it is both important and difficult to get the recovery
>> exactly right.
>
>
> Wasn't there a thread in r.a.s not long ago in which most American
> pilots considered spin training superfluous and dangerous? Hmmm...

No. Pehaps you are thinking of some other newsgroup.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Eric Greenwell

March 29th 04, 01:24 AM

Denis wrote:

>> For my ASH 26 E at Vne: 4 G load factor (down from 5.3 at Va); 3.5 G
>> load factor airbrakes extended. It looks like the G limits at Vne are
>> fairly close together.
>
>
> Airbrakes out at Va it's 3.5 g instead of 5.3, thus the difference is
> significant. I don't know why there is almost no difference at VNE, butI
> suspect that in that case the margin is higher without airbrakes than with.
>
> > I am curious about why they decrease.
>
> There is a loss of lift at the airbrakes, thus for the same G the outer
> wing is more loaded, and the bending momentat wing root increases.

I should have said "I'm curious about why the G loading (airbrakes
closed) is lower at Vne than at Va". Perhaps it is to absorb gusts, or
to allow greater control deflections.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Pete Zeugma

March 29th 04, 07:03 AM

At 17:42 28 March 2004, Denis wrote:
>Andy Blackburn wrote:
>
>> I'm sure everyone agrees the best advice is not to
>> get into a situation where you have to choose between
>> Vne and the G-limit. Thinking ahead with respect
>>to
>> attitude and configuration as you initiate recovery
>> is your best bet.
>
>(...)
>
>> if you get to this point you are in a world of hurt
>> anyway so the amount of over-G versus over-Vne is
>>subject
>> to your personal risk profile.

cant remember ever having to pull more that 5g in the
odd incipient spin in the ls6, but then you have also
the additional problem in your spin recovery of having
to dump the flaps into full reflex.

>I agree with all Andy said. I would add that 'pulling
>as hard as
>required to avoid VNE' is easier to say that to do,
>because :
>
>- it is impossible, if you are not an experimented
>glider aerobatics
>pilot, to know how many g's you need to avoid exceeding
>VNE,

you pull as hard as you need, and its not impossible
to know either, thats why you should practice spin
recovery.

>- depending on dive angle and speed, it may be just
>impossible to avoid
>VNE without airbrakes,
even if pulling 15 g's (supposing the wings have
>not briken before)

and presuming you have not blacked out by then also,
i start to grey out at about 7g from more than 5 secs
exposure at that level.

>
>- it is impossible without a g-meter to know if you
>pull 5 g (or just a
>little more, comprised in the 'safety margin'), or
>10 g's or more.

you would probably have blacked out about 9g

as seems to be typical here, not much mention of prevention,
or the possible reason for why you got yourself into
a position where you are approaching Vne. When it says
'ease the stick forward until the glider unstalls'
that does not mean push it to the forward stop and
dive out of the spin............

Andreas Maurer

March 29th 04, 02:11 PM

On Mon, 29 Mar 2004 00:26:29 +0200, CV > wrote:

>Was there any discussion at all about the possibility to attempt
>controlling it with the flaps ?
>
>Not that it is likely to help, possibly just the opposite, since
>you'd be even more in exess of the (lower) Vne for flap positions
>other than fully negative.

>Bailing out at 200 kts can't be exactly easy either.

Could anyone please tell me how one can get an ASW-20 to 200 kts
without noticing it? I've got a couple of hours in the 20, but I have
not found any situation where this could have been possible.

Bye
Andreas

Jon Meyer

March 29th 04, 02:54 PM

Sorry,

when I made my comments earlier I was assuming that
people were discussing exceeding the placarded g-limits,
not the certified ultimate limits. I believe 6-7g would
result in damage but perhaps not failure (depending
on the margins), but 10g, 15g!!!, how the hell do you
get yourself in a situation where you have to pull
that hard?
Personally I think it should be unnecessary to exceed
5g in even the worst spin recovery......unless you
enter a spiral dive and do not stop the rotation, in
which case all the arguments are irrelevant. If you
are in a spiral dive and do not stop the rotation then
you will exceed both the ultimate g-limits AND vne.
Assuming you are a reasonable pilot who can recognise
a spiral dive and recover promptly, then opening the
airbrakes while pulling the 5g or so which may be necessary
to recover below vne will simply result in damage to
the wings, where not opening them would not.
I think most of the structural failures resulting from
poor spin recovery must have been spiral dives.
Again, proper pilot training should ensure that this
never happens.

W.J. $Bill$ Dean $U.K.$.

March 29th 04, 03:04 PM

Andreas,

You are obviously referring to my posts earlier.

If you read them again, you will see that when you get close to 200 knots
diving an ASW20C it does not matter whether you notice it or not, it is too
late (this is not my opinion or experience, it came from Schleicher).

The pilot was fairly inexperienced, and new to the type. This was true for
me in the past, how about you?

It is not unheard of for pilots recovering from a stall/spin to be too
enthusiastic about the recovery, and to finish diving too steeply for too
long. If you have ever had any experience as an instructor, you have
surely had a pupil do this to you, I certainly have (which is one reason
why we practice recoveries dual). I gather this is what happened with the
accident I commented about, I believe the whole thing started below about
2,000 ft. above the crash site.

If you have read the report of the Minden accident on 13th July 1999 you
will find much the same thing. There were other factors at Minden of
course, so were there with the ASW20C.

I think the date of the accident was 11th January, 1987.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

>
> "Andreas Maurer" > wrote in message
> ...
>
> Could anyone please tell me how one can get an ASW-20 to 200 kts
> without noticing it? I've got a couple of hours in the 20, but I have
> not found any situation where this could have been possible.
>
> Bye
> Andreas
>

W.J. $Bill$ Dean $U.K.$.

March 29th 04, 03:13 PM

Sorry about the wrong link to the Minden Nimbus 4DM accident on 99.07.13.

With regard to this accident:

The report makes it clear that the airbrakes were extended when the glider
broke up.

The brief report states:
"Detailed examination of witness marks and other evidence in the wreckage
established that the pilot extended the airbrakes at some point in an
attempt to slow the glider during the descent prior to the break-up.
Concerning limitations on use of the airbrakes, the AFM notes that while
airbrakes may be extended up to Vne they should only be used at such high
speeds in emergency or if the maximum permitted speeds are being exceeded
inadvertently. The manufacturer noted that the airbrakes function like
spoilers and have the effect of shifting the aerodynamic loads outboard on
the wings. The control linkages for the airbrakes and flaps are
interconnected so that when full airbrake deployment is achieved, the flaps
are extended to their full down limit."

The report does not give an estimate of the speed or 'G' loading at the
point when the brakes were extended, or comment on whether this was a
wise thing to do; it assumes that the deployment was deliberate.

There were postings to Rec. Aviation Soaring when the report was published,
from pilots with experience of the Nimbus 4 and similar models who had
experience of inadvertent deployment of the airbrakes. If the brakes
deployed inadvertently while the pilots were recovering from the dive, this
surely may have been the reason for the amount of bending seen; and for the
overload which led to failure. Presumably those investigating the accident
were not aware of these incidents when writing the report.

The probable cause of the accident is given as:
"The National Transportation Safety Board determines that the probable cause
of this accident was the pilot’s excessive use of the elevator control
during recovery from an inadvertently entered spin and/or spiral dive during
which the glider exceeded the maximum permissible speed, which resulted in
the overload failure of the wings at loadings beyond the structure’s
ultimate design loads."

Note that the authors of the report are unclear as to whether the machine
was spinning or in a spiral dive. If the departure started with a spin
entry, they do not give an opinion as to when the machine became unstalled.

The report does not say why they think the machine exceeded Vne, though this
seems a reasonable deduction from the witness reports. With the brakes out
and flaps down the machine could surely have broken up at a speed close to
but below Vne.

The recovery was described by a witness:
"A glider pilot who witnessed the in-flight break-up stated that his glider
was soaring about 1,000 feet below the accident glider when he observed the
accident glider in a high-speed spiral with a 45-degree nose-down attitude.
After two full rotations, the rotation stopped, the flight stabilized on a
northeasterly heading, and the nose pitched further down to a near-vertical
attitude."
Other witness reports were consistent with this.

Note that water ballast was not carried, the accident started at about 9,000
to 11,000 ft. msl., and the conditions were rough strong thermals, a "strong
day".

For authoritative figures and information, in particular limitations, you
have to go to the manufacturer's handbook etc. (Aircraft Flight Manual), and
to JAR-22 to which all modern European gliders are designed.

See:
Joint Aviation Authorities, Europe. http://www.jaa.nl/ ,
JARs – Section 1 – JAR-22 http://www.jaa.nl/section1/jars/445499.pdf .

Denis, you are very scathing. What do you think went wrong?

What would you have done?

Do you have any experience in the Nimbus 3 & 4 series? I don't.

Are you more experienced or better than the pilots who did not make it?

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

>
> "Denis" > wrote in message
> ...
>
> >
> > W.J. (Bill) Dean (U.K.). wrote:
> >
> > There have been several cases of certificated gliders overstressed in
> > stall/spin recoveries, some of them broke up.
> >
> > (...)
> >
> > You can also read about the Nimbus 4DM at Minden; 99.07.13 -
> > LAX99MA251 -
> > http://www.ntsb.gov/NTSB/brief.asp?ev_id=20031009X01702&key=1 Nimbus
> > 4DM - Minden - Two killed.
> >
>
> the link is actually
> http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19310&key=1
>
> the conclusion is "The pilot's excessive use of the elevator control
> during recovery (...) resulted in the overload failure of the wings at
> loadings beyond the structure's ultimate design loads."
>
> [the possibility of speed being over VNE or Vd is neither confirmed nor
> being one of the causes of the wing failure according to the report]
>
> This supposes that unfortunately the pilots did what Bill told : "pull
> however hard is necessary" with the result that "At the ultimate load
> limit, the deflection was 46.5-degrees, similar to the witness
> observations of the wing deflection just prior to the break up."
>
> Do you imagine you may safely "pull however hard you need" with your
> wings bent at 45° up ??? I don't.
>
> The report quotes also that the G limit for the Nimbus 4 at VNE is 3.5 g
> *only* (compared to 5.3 g at Va) and the design "safety margin" is
> between 1.55 to 1.75. Thus even on a plane in perfect condition, and if
> the manufacturer made no mistake, it *will* break between 5.4 and 6.1 g
> at VNE (even without airbrakes)
>
> Remember that at that speed (285 km/h) you could pull about 16 g ! and
> at Vd (324 km/h) more than 20 g...
>
> Yes it was certificated, but certification does *not* guarantee you that
> the glider will not break if you pull 20 g... !
>
> Denis
>

Denis

March 29th 04, 07:01 PM

Eric Greenwell wrote:

> I should have said "I'm curious about why the G loading (airbrakes
> closed) is lower at Vne than at Va". Perhaps it is to absorb gusts, or
> to allow greater control deflections.

The only physical reason I see is that there is a torsional stress on
the wing, increasing with the square of the speed, and which might add
somewhere to the bending stress due to G loading.

Another reason is that the certification standards don't require the
same limitation in G-loads at VNE that at Va, and the flight manual
reflects that...

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 29th 04, 07:34 PM

W.J. (Bill) Dean (U.K.). wrote:

> There were postings to Rec. Aviation Soaring when the report was published,
> from pilots with experience of the Nimbus 4 and similar models who had
> experience of inadvertent deployment of the airbrakes. If the brakes
> deployed inadvertently while the pilots were recovering from the dive, this
> surely may have been the reason for the amount of bending seen; and for the
> overload which led to failure. Presumably those investigating the accident
> were not aware of these incidents when writing the report.

If airbrakes deploy inadvertently, the first effect (along with the very
high drag) will be a *decrease* in G-loading *and* bending moment), both
due to the loss of lift near the airbrakes. The increase of bending
would happen only after the angle of attack has been further increased
(voluntarily or not) to restore the initial G-loading with more lift on
the outer panels (instead of the airbrakes section), hence the higher
bending.

> Denis, you are very scathing.

That is not my intention... all I want is to give my opinion when I
think something is said here that may lead to dangerous flying - such as
sentences like "don't exceed VNE, but no problem if you exceed permitted
G-loading".

> What do you think went wrong?
>
> What would you have done?
>
> Do you have any experience in the Nimbus 3 & 4 series? I don't.
>
> Are you more experienced or better than the pilots who did not make it?

I don't know them and I would not pretend to be better (there are no
good pilots, only old pilots...). And although I have some experience in
Nimbus 4D (more on ASH 25) I never experienced a spin recovery and I
hope I never will have to. Therefore I don't know what I would do in
such a situation. All I can say is what I think (sitting comfortably in
my chair) is the better thing to do, as I said in a previous post :

"If your speed is going to exceed VNE within this manoeuvre [pulling
up], you should stop or reduce pulling and apply full airbrakes. At any
dive angle up to 45° this prevents the glider to exceeding VNE, and you
have time to recover pulling gently (under 2 g's). This of course
supposes that there is sufficient ground clearance... "

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 29th 04, 07:48 PM

Pete Zeugma wrote:

> you pull as hard as you need, and its not impossible
> to know either, thats why you should practice spin
> recovery.

AFAIK spin training is prohibited in most, if not all, open class ships...

> and presuming you have not blacked out by then also,
> i start to grey out at about 7g from more than 5 secs
> exposure at that level.

> you would probably have blacked out about 9g

Yes, except grey out or black out happens only after a few seconds (the
time needed for the blood to fall into your lower boby). And it is very
dependant of the condition and trainig of the pilot.

But a glider wing breaks within milliseconds of overstressing !

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Jack

March 29th 04, 08:00 PM

On 3/29/04 12:34 PM, in article ,
"Denis" > wrote:

> ...there are no good pilots, only old pilots....

You must always fly by yourself.

> I never experienced a spin recovery and...[t]herefore I don't know what I
would do in such a situation.

With your (claimed) thousands of hours of flight experience?

Jack

Edward Downham

March 29th 04, 08:41 PM

>Eric Greenwell wrote:
>
>> I should have said "I'm curious about why the G loading (airbrakes
>> closed) is lower at Vne than at Va". Perhaps it is to absorb gusts, or
>> to allow greater control deflections.
>
>The only physical reason I see is that there is a torsional stress on
>the wing, increasing with the square of the speed, and which might add
>somewhere to the bending stress due to G loading.
>
>Another reason is that the certification standards don't require the
>same limitation in G-loads at VNE that at Va, and the flight manual
>reflects that...
>
>--
>Denis
>
>R. Parce que ça rompt le cours normal de la conversation !!!
>Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?
>
>
>
>
>
>

I think (and my memory is hazy on this, so I stand to be corrected) it might
possibly have something to do with the gust case. Va I understand to be the
speed at which any one control can be fully deflected and not exceed the design
specifications; at Vne this is reduced to 1/3 of any one control.

'Rough air speed', normally the same as Va (but not always) is the highest
speed at which the glider can encounter an 'OSTIV Strong Gust' (10m/s
instantaneous shear) and stay within the flight envelope. At Vne the airframe
should be able to withstand a 'OSTIV Weak Gust' (2m/s anybody?) without
reverting to kit form. (As an aside, just think about that next time you
redline it across the airfield during the soaring day...)

I'm still chewing over why 'g' limits reduce between Va & Vne. I can picture a
typical flight envelope and this does indeed happen: whether this is a real
(structural/aerodynamic) limitation or just something the manufacturers put in
there to stop us going mad I don't know (probably the former).

Any budding aerodynamicists care to comment?

Cliff Hilty

March 29th 04, 10:01 PM

At 22:18 28 March 2004, Andy Blackburn wrote:
>I may not be exactly right about this, but I believe
>that most certified aircraft (including gliders) are
>tested to, and must be able to hold together at, a
>static G-load of roughly 150% of maximum. To meet this
>requirement the wings are generally tested to destruction
>(check out the DG website for a video of this procedure
>for the DG 1000).
>

I think your definetly right Andy. My Ventus is in
the shop now replacing worn bushings in the aileron
circuits. Last year when getting very close to VNE
on final glide (you know me always coming in high:)
I had to hold a little right aileron into it so the
aileron would not 'start vibrating' which I interept
as incipent to flutter. Side note is I thought it was
only the bushings at the connect point on the aileron,
turns out I had wear on both ends and the 'slide' that
the tube rides on had worn half way through the tube'
Glad I had Bill check them out.

Cliff

Cliff Hilty

March 29th 04, 10:05 PM

At 22:18 28 March 2004, Andy Blackburn wrote:
>One additional thought - I suspect that for older gliders,
>wearing of bearings/bushings may degrade the flutter
>margin faster than normal material aging degrades the
>G-limit, so you might need to think differently if
>you have a high-time glider.
>
>Thoughts?

I think your definetly right Andy. My Ventus is in
the shop now replacing worn bushings in the aileron
circuits. Last year when getting very close to VNE
on final glide (you know me always coming in high:)
I had to hold a little right aileron into it so the
aileron would not 'start vibrating' which I interept
as incipent to flutter. Side note is I thought it was
only the bushings at the connect point on the aileron,
turns out I had wear on both ends and the 'slide' that
the tube rides on had worn half way through the tube'
Glad I had Bill check them out.

Cliff

Andreas Maurer

March 29th 04, 11:22 PM

On Mon, 29 Mar 2004 15:04:46 +0100, "W.J. $Bill$ Dean $U.K.$."
> wrote:

>You are obviously referring to my posts earlier.
Yes. :)

>If you read them again, you will see that when you get close to 200 knots
>diving an ASW20C it does not matter whether you notice it or not, it is too
>late (this is not my opinion or experience, it came from Schleicher).

No doubt about that (I'm still of the opinion that most 20 and 20C's
will break up due to flutter before they come close to 200 kts) - but
honestly: Flying far over Vne and not noticing it?

>The pilot was fairly inexperienced, and new to the type. This was true for
>me in the past, how about you?
We all were inexperienced once - but this is not the point.
How often did you fly 55 kts faster than Vne when you were
inexperienced with a new glider? Or screwed up a spin recovery so
badly that you ended up far over Vne (and this in a 20 that can be
kept under 100 kts in a properly executed spin recovery)?

Pilot error is pilot error - and in this case the pilot error was
huge. And huge pilot errors unfortunately kill a pilot most of the
time - even the smartest designs cannot prevent that.

Bye
Andreas

W.J. $Bill$ Dean $U.K.$.

March 29th 04, 11:25 PM

You are just plain wrong. The immediate effect of opening Schempp-Hirth
type airbrakes, if nothing else is done, is to make the wings bend more.

Have you ever tried opening the airbrakes with a bendy wing and watched what
actually happens?

When I flew an ASW20L I always used some landing flap when approaching to
land. Sometimes I would keep the brakes closed until near the ground. I
always opened them as I rounded out, because as soon as I did this the wings
bent up, to give me better ground clearance!

I remember flying a Skylark 3 at about 75 knots (fast for the type), at this
speed the tips bent down a bit, because of the washout. If I then opened
the airbrakes, the wings bent up.

Your theory is wrong, it does not work! Don't try to argue that I did not
see what I know I did see, get in something with bendy wings such as a
Pegasus, and try it.

I also remember seeing an article in "Technical Soaring" with a photo of a
Jantar 1 at Vne, and at 1 g., with the brakes fully out. The wing bend, at
1 g. remember, was horrendous. Don't try and give us some theoretical
reason why this cannot happen, it does!

You also say:
"all I want is to give my opinion when I think something is said here that
may lead to dangerous flying - such as sentences like "don't exceed VNE, but
no problem if you exceed permitted G-loading" ".
Who said that, which posting?

This whole discussion has been around the point, if you look as if you are
going to exceed Vne, what should you do?

Exceeding Vne is outside limits and dangerous, so are any of the
alternatives - the discussion is about which of the alternatives is the
least worst.

With the Minden accident on 13th July 1999, it is clear from the report that
the glider was pitched down to well beyond a 45 degree dive, so the
airbrakes would not have been speed limiting.

You say "I never experienced a spin recovery", presumably you mean in a
large span glider. I hope you have done plenty in training and short span
machines. An essential part of stall/spin recovery training is to be able
to distinguish at once the difference between a spin and a spiral dive. If
you treat a spiral dive as if it is still a spin, this is very likely to
lead to excessive speed, as well as using more height for the recovery.

I still think that the advice I gave in my first posting to this thread is
correct:
"If you exceed Vne you are taking a risk, if you pull too hard above
manoeuvring speed you are taking a risk, and if you pull hard and roll at
the same time you are taking a risk. If you pull the brakes you are
increasing the bending load on the wings.

"If you get it wrong and have to take one of the risks, I am told that you
should centralise the ailerons, then pull however hard is necessary not to
exceed Vne, and make sure the brakes stay shut."

Denis (Denis who and from where?), if you still feel like answering, please
answer what I have actually written.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

>
> "Denis" > wrote in message
> ...
>
> >
> > W.J. (Bill) Dean (U.K.). wrote:
> >
> > There were postings to Rec. Aviation Soaring when the report was
> > published, from pilots with experience of the Nimbus 4 and similar
> > models who had experience of inadvertent deployment of the airbrakes.
> > If the brakes deployed inadvertently while the pilots were recovering
> > from the dive, this surely may have been the reason for the amount of
> > bending seen; and for the overload which led to failure. Presumably
> > those investigating the accident were not aware of these incidents when
> > writing the report.
> >
>
> If airbrakes deploy inadvertently, the first effect (along with the very
> high drag) will be a *decrease* in G-loading *and* bending moment), both
> due to the loss of lift near the airbrakes. The increase of bending
> would happen only after the angle of attack has been further increased
> (voluntarily or not) to restore the initial G-loading with more lift on
> the outer panels (instead of the airbrakes section), hence the higher
> bending.
>
> >
> > Denis, you are very scathing.
> >
>
> That is not my intention... all I want is to give my opinion when I
> think something is said here that may lead to dangerous flying - such as
> sentences like "don't exceed VNE, but no problem if you exceed permitted
> G-loading".
>
> >
> > What do you think went wrong?
> >
> > What would you have done?
> >
> > Do you have any experience in the Nimbus 3 & 4 series? I don't.
> >
> > Are you more experienced or better than the pilots who did not make it?
> >
>
> I don't know them and I would not pretend to be better (there are no
> good pilots, only old pilots...). And although I have some experience in
> Nimbus 4D (more on ASH 25) I never experienced a spin recovery and I
> hope I never will have to. Therefore I don't know what I would do in
> such a situation. All I can say is what I think (sitting comfortably in
> my chair) is the better thing to do, as I said in a previous post :
>
> "If your speed is going to exceed VNE within this manoeuvre [pulling
> up], you should stop or reduce pulling and apply full airbrakes. At any
> dive angle up to 45° this prevents the glider to exceeding VNE, and you
> have time to recover pulling gently (under 2 g's). This of course
> supposes that there is sufficient ground clearance... "
>
> Denis
>

Pete Zeugma

March 30th 04, 07:19 AM

At 18:54 29 March 2004, Denis wrote:
>Pete Zeugma wrote:
>
>> you pull as hard as you need, and its not impossible
>> to know either, thats why you should practice spin
>> recovery.
>
>AFAIK spin training is prohibited in most, if not all,
>open class ships...

probably why we use k13's and puch's then and if you
are going to examine spin characteristics of big floppy
wings, you do it for spin entry and not any further.
but then again, you shouldnt be flying at a speed where
you are going to end up in a spin in the first place,
let alone suddenly realising that you've let your speed
build up to Vne! which is the whole point of spin training........

>
>> and presuming you have not blacked out by then also,
>> i start to grey out at about 7g from more than 5 secs
>> exposure at that level.
>
>> you would probably have blacked out about 9g
>
>Yes, except grey out or black out happens only after
>a few seconds (the
>time needed for the blood to fall into your lower boby).
>

er.. didnt i say that? 5 secs....

>And it is very
>dependant of the condition and trainig of the pilot.

and seating position, and how much height exposure
he's had during the days flying........... (oxy saturation)

but then a well trained pilot wouldnt have got himself
into the position of entering a spin, let alone contemplating
what to do because hes suddenly at all the airframe
limits!

>
>But a glider wing breaks within milliseconds of overstressing
>!

no they dont, they have to fail progressivly. no glider
would be alowed in the air by any regulating body if
a wing could break in a 1000th of a second. i dont
think you really understand the force that would be
needed to do that. the instantanious g-load to do that
would kill you out right.

>
>
>--
>Denis
>
>R. Parce que ça rompt le cours normal de la conversation
>!!!
>Q. Pourquoi ne faut-il pas répondre au-dessus de la
>question ?
>

iPilot

March 30th 04, 07:46 AM

You may be correct. However, I have heard of some cases where there have been structural failures
resulting from excessive g-forces, but the glider has remained landable after that. Aerobatics books
also recommend to "pull as hard as necessary", but to keep an eye on your g-meter and ASI. High AoA
eats energy rather fast. Flutter from overspeeding will definately disintegrate your wing.
Excessive-g may not. The trick is to stay within the limits as long as possible. Therefore it's
necessary to know the limits and their use. In abovementioned Nimbus 4 incident it seems that pilot
exchausted g-limits before the Vne arrived. But no-one knows what really happened.

BTW, there is one energy-burning device on every glider that may save you the very necessary second
or two - the wheel. Lower it as soon as you feel the threat of overspeeding. You may lose the wheel
doors because of the speed and g-forces, but this is not nearly as catastrophical as losing wing
because of pulling the airbrakes at Vne and high-g.

>

Bert Willing

March 30th 04, 08:46 AM

You're both partially right. The moment you deploy the airbrakes and
maintain a constant angle of attack, you loose lift which means the glider
accelerates it's sink rate. G load decreases, bending decreases. Once the
sink rate is stabilized, the initial lift must have been restored but it's
different distribution along the wing span increases the bending.

BTW, Denis is fairly well know in France (an Morocco...)

--
Bert Willing

ASW20 "TW"

"W.J. (Bill) Dean (U.K.)." > a écrit dans le message
de ...
> You are just plain wrong. The immediate effect of opening Schempp-Hirth
> type airbrakes, if nothing else is done, is to make the wings bend more.
>
> Have you ever tried opening the airbrakes with a bendy wing and watched
what
> actually happens?
>
> When I flew an ASW20L I always used some landing flap when approaching to
> land. Sometimes I would keep the brakes closed until near the ground.
I
> always opened them as I rounded out, because as soon as I did this the
wings
> bent up, to give me better ground clearance!
>
> I remember flying a Skylark 3 at about 75 knots (fast for the type), at
this
> speed the tips bent down a bit, because of the washout. If I then opened
> the airbrakes, the wings bent up.
>
> Your theory is wrong, it does not work! Don't try to argue that I did
not
> see what I know I did see, get in something with bendy wings such as a
> Pegasus, and try it.
>
> I also remember seeing an article in "Technical Soaring" with a photo of a
> Jantar 1 at Vne, and at 1 g., with the brakes fully out. The wing bend,
at
> 1 g. remember, was horrendous. Don't try and give us some theoretical
> reason why this cannot happen, it does!
>
> You also say:
> "all I want is to give my opinion when I think something is said here
that
> may lead to dangerous flying - such as sentences like "don't exceed VNE,
but
> no problem if you exceed permitted G-loading" ".
> Who said that, which posting?
>
> This whole discussion has been around the point, if you look as if you are
> going to exceed Vne, what should you do?
>
> Exceeding Vne is outside limits and dangerous, so are any of the
> alternatives - the discussion is about which of the alternatives is the
> least worst.
>
> With the Minden accident on 13th July 1999, it is clear from the report
that
> the glider was pitched down to well beyond a 45 degree dive, so the
> airbrakes would not have been speed limiting.
>
> You say "I never experienced a spin recovery", presumably you mean in a
> large span glider. I hope you have done plenty in training and short
span
> machines. An essential part of stall/spin recovery training is to be
able
> to distinguish at once the difference between a spin and a spiral dive.
If
> you treat a spiral dive as if it is still a spin, this is very likely to
> lead to excessive speed, as well as using more height for the recovery.
>
> I still think that the advice I gave in my first posting to this thread is
> correct:
> "If you exceed Vne you are taking a risk, if you pull too hard above
> manoeuvring speed you are taking a risk, and if you pull hard and roll at
> the same time you are taking a risk. If you pull the brakes you are
> increasing the bending load on the wings.
>
> "If you get it wrong and have to take one of the risks, I am told that you
> should centralise the ailerons, then pull however hard is necessary not to
> exceed Vne, and make sure the brakes stay shut."
>
> Denis (Denis who and from where?), if you still feel like answering,
please
> answer what I have actually written.
>
> W.J. (Bill) Dean (U.K.).
> Remove "ic" to reply.
>
> >
> > "Denis" > wrote in message
> > ...
> >
> > >
> > > W.J. (Bill) Dean (U.K.). wrote:
> > >
> > > There were postings to Rec. Aviation Soaring when the report was
> > > published, from pilots with experience of the Nimbus 4 and similar
> > > models who had experience of inadvertent deployment of the airbrakes.
> > > If the brakes deployed inadvertently while the pilots were recovering
> > > from the dive, this surely may have been the reason for the amount of
> > > bending seen; and for the overload which led to failure. Presumably
> > > those investigating the accident were not aware of these incidents
when
> > > writing the report.
> > >
> >
> > If airbrakes deploy inadvertently, the first effect (along with the very
> > high drag) will be a *decrease* in G-loading *and* bending moment), both
> > due to the loss of lift near the airbrakes. The increase of bending
> > would happen only after the angle of attack has been further increased
> > (voluntarily or not) to restore the initial G-loading with more lift on
> > the outer panels (instead of the airbrakes section), hence the higher
> > bending.
> >
> > >
> > > Denis, you are very scathing.
> > >
> >
> > That is not my intention... all I want is to give my opinion when I
> > think something is said here that may lead to dangerous flying - such as
> > sentences like "don't exceed VNE, but no problem if you exceed permitted
> > G-loading".
> >
> > >
> > > What do you think went wrong?
> > >
> > > What would you have done?
> > >
> > > Do you have any experience in the Nimbus 3 & 4 series? I don't.
> > >
> > > Are you more experienced or better than the pilots who did not make
it?
> > >
> >
> > I don't know them and I would not pretend to be better (there are no
> > good pilots, only old pilots...). And although I have some experience in
> > Nimbus 4D (more on ASH 25) I never experienced a spin recovery and I
> > hope I never will have to. Therefore I don't know what I would do in
> > such a situation. All I can say is what I think (sitting comfortably in
> > my chair) is the better thing to do, as I said in a previous post :
> >
> > "If your speed is going to exceed VNE within this manoeuvre [pulling
> > up], you should stop or reduce pulling and apply full airbrakes. At any
> > dive angle up to 45° this prevents the glider to exceeding VNE, and you
> > have time to recover pulling gently (under 2 g's). This of course
> > supposes that there is sufficient ground clearance... "
> >
> > Denis
> >
>
>
>

Andy Blackburn

March 30th 04, 09:52 AM

That's correct. If you kill the lift over part of the
wing by opening the spoilers, the rest of the wing
needs to produce a higher coefficient of lift to keep
the glider from accelerating downward. This can only
happen through an increase in angle of attack. This
will cause the wing to flex more because the center
of lift has moved outboard (imagine lifting your glider
on the ground by the wingtips versus the wing roots
to appreciate the point).

If you don't increase the angle of attack to compensate
then lift<weight and the glider will accelerate downward
(accelerating sink rate). In this case the outer panels
are producing no more lift (same aoa, same airspeed)
and the inner portion of the wing is spoiled so net-net
there is less lift, less bending moment and less flex
in the wings. However, this is a transient state since
we all naturally compensate for the loss of lifting
surface by pulling back ever so slightly on the stick
and loading up the tips - hence the extra flex.

It's hard to notice the aoa shift in flight because
you need a lower pitch attitude to maintain airspeed
(due to higher drag) at the same time that aoa goes
up to produce enough lift to hold the glider up. Remember
pitch attitude and aoa are not the same.

Try going from dive brakes closed and locked to fully
open on landing rollout - AFTER you're sure you have
the tailwheel down. In this case aoa should be held
pretty constant. See what the wings do then.

9B

At 07:54 30 March 2004, Bert Willing wrote:
>You're both partially right. The moment you deploy
>the airbrakes and
>maintain a constant angle of attack, you loose lift
>which means the glider
>accelerates it's sink rate. G load decreases, bending
>decreases. Once the
>sink rate is stabilized, the initial lift must have
>been restored but it's
>different distribution along the wing span increases
>the bending.
>
>BTW, Denis is fairly well know in France (an Morocco...)
>
>--
>Bert Willing
>
>ASW20 'TW'
>
>
>'W.J. (Bill) Dean (U.K.).' a écrit dans le message
>de ...
>> You are just plain wrong. The immediate effect of
>>opening Schempp-Hirth
>> type airbrakes, if nothing else is done, is to make
>>the wings bend more.
>>
>> Have you ever tried opening the airbrakes with a bendy
>>wing and watched
>what
>> actually happens?
>>
>> When I flew an ASW20L I always used some landing flap
>>when approaching to
>> land. Sometimes I would keep the brakes closed until
>>near the ground.
>I
>> always opened them as I rounded out, because as soon
>>as I did this the
>wings
>> bent up, to give me better ground clearance!
>>
>> I remember flying a Skylark 3 at about 75 knots (fast
>>for the type), at
>this
>> speed the tips bent down a bit, because of the washout.
>> If I then opened
>> the airbrakes, the wings bent up.
>>
>> Your theory is wrong, it does not work! Don't try
>>to argue that I did
>not
>> see what I know I did see, get in something with bendy
>>wings such as a
>> Pegasus, and try it.
>>
>> I also remember seeing an article in 'Technical Soaring'
>>with a photo of a
>> Jantar 1 at Vne, and at 1 g., with the brakes fully
>>out. The wing bend,
>at
>> 1 g. remember, was horrendous. Don't try and give
>>us some theoretical
>> reason why this cannot happen, it does!
>>
>> You also say:
>> 'all I want is to give my opinion when I think something
>>is said here
>that
>> may lead to dangerous flying - such as sentences like
>>'don't exceed VNE,
>but
>> no problem if you exceed permitted G-loading' '.
>> Who said that, which posting?
>>
>> This whole discussion has been around the point, if
>>you look as if you are
>> going to exceed Vne, what should you do?
>>
>> Exceeding Vne is outside limits and dangerous, so
>>are any of the
>> alternatives - the discussion is about which of the
>>alternatives is the
>> least worst.
>>
>> With the Minden accident on 13th July 1999, it is
>>clear from the report
>that
>> the glider was pitched down to well beyond a 45 degree
>>dive, so the
>> airbrakes would not have been speed limiting.
>>
>> You say 'I never experienced a spin recovery', presumably
>>you mean in a
>> large span glider. I hope you have done plenty in
>>training and short
>span
>> machines. An essential part of stall/spin recovery
>>training is to be
>able
>> to distinguish at once the difference between a spin
>>and a spiral dive.
>If
>> you treat a spiral dive as if it is still a spin,
>>this is very likely to
>> lead to excessive speed, as well as using more height
>>for the recovery.
>>
>> I still think that the advice I gave in my first posting
>>to this thread is
>> correct:
>> 'If you exceed Vne you are taking a risk, if you pull
>>too hard above
>> manoeuvring speed you are taking a risk, and if you
>>pull hard and roll at
>> the same time you are taking a risk. If you pull
>>the brakes you are
>> increasing the bending load on the wings.
>>
>> 'If you get it wrong and have to take one of the risks,
>>I am told that you
>> should centralise the ailerons, then pull however
>>hard is necessary not to
>> exceed Vne, and make sure the brakes stay shut.'
>>
>> Denis (Denis who and from where?), if you still feel
>>like answering,
>please
>> answer what I have actually written.
>>
>> W.J. (Bill) Dean (U.K.).
>> Remove 'ic' to reply.
>>
>> >
>> > 'Denis' wrote in message
>> > ...
>> >
>> > >
>> > > W.J. (Bill) Dean (U.K.). wrote:
>> > >
>> > > There were postings to Rec. Aviation Soaring when
>>>>the report was
>> > > published, from pilots with experience of the Nimbus
>>>>4 and similar
>> > > models who had experience of inadvertent deployment
>>>>of the airbrakes.
>> > > If the brakes deployed inadvertently while the pilots
>>>>were recovering
>> > > from the dive, this surely may have been the reason
>>>>for the amount of
>> > > bending seen; and for the overload which led to
>>>>failure. Presumably
>> > > those investigating the accident were not aware
>>>>of these incidents
>when
>> > > writing the report.
>> > >
>> >
>> > If airbrakes deploy inadvertently, the first effect
>>>(along with the very
>> > high drag) will be a *decrease* in G-loading *and*
>>>bending moment), both
>> > due to the loss of lift near the airbrakes. The increase
>>>of bending
>> > would happen only after the angle of attack has been
>>>further increased
>> > (voluntarily or not) to restore the initial G-loading
>>>with more lift on
>> > the outer panels (instead of the airbrakes section),
>>>hence the higher
>> > bending.
>> >
>> > >
>> > > Denis, you are very scathing.
>> > >
>> >
>> > That is not my intention... all I want is to give
>>>my opinion when I
>> > think something is said here that may lead to dangerous
>>>flying - such as
>> > sentences like 'don't exceed VNE, but no problem
>>>if you exceed permitted
>> > G-loading'.
>> >
>> > >
>> > > What do you think went wrong?
>> > >
>> > > What would you have done?
>> > >
>> > > Do you have any experience in the Nimbus 3 & 4 series?
>>>> I don't.
>> > >
>> > > Are you more experienced or better than the pilots
>>>>who did not make
>it?
>> > >
>> >
>> > I don't know them and I would not pretend to be better
>>>(there are no
>> > good pilots, only old pilots...). And although I
>>>have some experience in
>> > Nimbus 4D (more on ASH 25) I never experienced a
>>>spin recovery and I
>> > hope I never will have to. Therefore I don't know
>>>what I would do in
>> > such a situation. All I can say is what I think (sitting
>>>comfortably in
>> > my chair) is the better thing to do, as I said in
>>>a previous post :
>> >
>> > 'If your speed is going to exceed VNE within this
>>>manoeuvre [pulling
>> > up], you should stop or reduce pulling and apply
>>>full airbrakes. At any
>> > dive angle up to 45° this prevents the glider to
>>>exceeding VNE, and you
>> > have time to recover pulling gently (under 2 g's).
>>>This of course
>> > supposes that there is sufficient ground clearance...
>>>'
>> >
>> > Denis
>> >
>>
>>
>>
>
>
>

Don Johnstone

March 30th 04, 12:50 PM

When I made my original post on this subject my contention
was quite simple, if faced with the choice of exceeding
VNE or pulling to avoid exceeding VNE and overstressing
the glider I would choose the latter. I would hope
that I would never get to the situation where I had
to do either and if I keep my wits about me I never
will. I stand by what I said but this was not an original
thought, it was the advice of someone who knows a great
deal more than me.

An earlier posting said 'Also, I find it a bit strange
that some here feel that it is possible to over-G a
sailplane to damage, but
not destruction. It seems like a fine point to me and
there are several examples of unlucky souls who have
misjudged the point'. Of course it is possible but
I accept it is purely a matter of luck. I never made
the above statement, I did say that overstress may
cause serious damage, but flutter is much more likely
to be catastrophic.

With some gliders there is such a large margin between
placarded limits and the forces the airframe will withstand
that overstressing is definitely the lesser of 2 evils.
The Grob Acro is a perfect example of this. One of
the Acros delivered to the RAF in the UK in the 80's
was given to Slingsbys to test on a rig. After the
'normal' testing (The wing spigot problem was discovered
in this test and I was told that had this failed in
flight the airframe would probably have stayed in one
piece). Following this attempts were then made to break
the glider but despite every effort the only thing
that broke was the test rig, the glider never did.
There is no such margin for the onset of flutter. Not
all gliders have the strength of the Grob I would agreed
but there is still a margin of some sort.

The way the whole thing was explained to me was that
pulling excess G may break the glider, in particular
it may cause damage to the wing/fuselage fixing but
this damage is not necessarily total (See above re
wing spigot problem). The damage caused by flutter
is much more likely to cause total failure not only
of the wing but other aerodynamic surfaces as well
(the tailplane and fin) and a glider without a tailplane/fin
is not where I would want to be. I am told that the
weakest point on any glider is the fuselage just in
front of the fin. Again I am told that when an aircraft
breaks up in flight the cause is almost invariably
flutter, the result of overspeed, whether this is preceeded
by overstress causing loss of control or not.

There has been a lot of use of words such as rubbish
and other derogatory terms. You do not have to agree
with me but I would suggest that perhaps you might
be better researching and then posting a cogent argument
why I am wrong instead of just gainsaying. (Remember
the Python :-) UK joke)

I stand by my original post, faced with the choice
of exceeding VNE or pulling too much G I would chose
the latter as the lesser of two very great evils.

W.J. $Bill$ Dean $U.K.$.

March 30th 04, 02:01 PM

Don, I agree with you completely. You have made the points which I have
been trying to put.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

>
> "Don Johnstone" > wrote in
> message ...
>
> When I made my original post on this subject my contention
> was quite simple, if faced with the choice of exceeding
> VNE or pulling to avoid exceeding VNE and overstressing
> the glider I would choose the latter. I would hope
> that I would never get to the situation where I had
> to do either and if I keep my wits about me I never
> will. I stand by what I said but this was not an original
> thought, it was the advice of someone who knows a great
> deal more than me.
>
> An earlier posting said 'Also, I find it a bit strange
> that some here feel that it is possible to over-G a
> sailplane to damage, but not destruction. It seems like a fine point to
> me and there are several examples of unlucky souls who have
> misjudged the point'. Of course it is possible but
> I accept it is purely a matter of luck. I never made
> the above statement, I did say that overstress may
> cause serious damage, but flutter is much more likely
> to be catastrophic.
>
> With some gliders there is such a large margin between
> placarded limits and the forces the airframe will withstand
> that overstressing is definitely the lesser of 2 evils.
> The Grob Acro is a perfect example of this. One of
> the Acros delivered to the RAF in the UK in the 80's
> was given to Slingsbys to test on a rig. After the
> 'normal' testing (The wing spigot problem was discovered
> in this test and I was told that had this failed in
> flight the airframe would probably have stayed in one
> piece). Following this attempts were then made to break
> the glider but despite every effort the only thing
> that broke was the test rig, the glider never did.
> There is no such margin for the onset of flutter. Not
> all gliders have the strength of the Grob I would agreed
> but there is still a margin of some sort.
>
> The way the whole thing was explained to me was that
> pulling excess G may break the glider, in particular
> it may cause damage to the wing/fuselage fixing but
> this damage is not necessarily total (See above re
> wing spigot problem). The damage caused by flutter
> is much more likely to cause total failure not only
> of the wing but other aerodynamic surfaces as well
> (the tailplane and fin) and a glider without a tailplane/fin
> is not where I would want to be. I am told that the
> weakest point on any glider is the fuselage just in
> front of the fin. Again I am told that when an aircraft
> breaks up in flight the cause is almost invariably
> flutter, the result of overspeed, whether this is preceded
> by overstress causing loss of control or not.
>
> There has been a lot of use of words such as rubbish
> and other derogatory terms. You do not have to agree
> with me but I would suggest that perhaps you might
> be better researching and then posting a cogent argument
> why I am wrong instead of just gainsaying. (Remember
> the Python :-) UK joke).
>
> I stand by my original post, faced with the choice
> of exceeding VNE or pulling too much G I would chose
> the latter as the lesser of two very great evils.
>

Bert Willing

March 30th 04, 04:34 PM

Non-catastrophic may happen if you have a structure which has a plastic
behavious prior to rupture.
Ironically, you don't have that with "plastic" gliders. You might well
enconter that you can pull more g's because the designer has put lots of
margins, and nothing will happen
But if *something* happens, you're wings are simply gone on a GRP/CRP ship.
The idea that you'll get away with some sort of damage and land the ship is,
hm, fairly naive.

But to the initial question: If you are going to exceed Vne in a dive, you
can chose between putting your joker on a good spacing between Vne and
flutter speed, or put your joker on a pessimistic design margin and a well
crafted serial number. There is actually no way to tell the answer
beforehand.

But pulling the airbrakes would be fairly suicidal.

--
Bert Willing

ASW20 "TW"

"W.J. (Bill) Dean (U.K.)." > a écrit dans le message
de ...
> Don, I agree with you completely. You have made the points which I have
> been trying to put.
>
> W.J. (Bill) Dean (U.K.).
> Remove "ic" to reply.
>
> >
> > "Don Johnstone" > wrote in
> > message ...
> >
snip
> > The way the whole thing was explained to me was that
> > pulling excess G may break the glider, in particular
> > it may cause damage to the wing/fuselage fixing but
> > this damage is not necessarily total

Eric Greenwell

March 30th 04, 06:11 PM

iPilot wrote:
> You may be correct. However, I have heard of some cases where there
> have been structural failures resulting from excessive g-forces, but
> the glider has remained landable after that. Aerobatics books also
> recommend to "pull as hard as necessary", but to keep an eye on your
> g-meter and ASI.

Aerobatic aircraft are built to much higher G and Vne limits, and the
pilots flying them are also accustomed to using high Gs. How many
sailplane pilots have a G meter and will be looking at it in a spin
recovery gone wrong?

> High AoA eats energy rather fast. Flutter from
> overspeeding will definately disintegrate your wing.

It is this claim that we are discussing. I know of many people that have
experienced flutter and not lost a wing. I also know flutter can have
many different modes, including those that involve the rudder, elevator,
ailerons, wing, and tail boom. It seems most dogmatic to claim "Flutter
from overspeeding will definitely disintegrate your wing". Since you are
so certain, perhaps you could tell us the reasons for your certainty?

> Excessive-g may
> not.

Has flutter caused any of the in-flight breakups discussed here? Perhaps
I missed them. I thought all were due to exceeding G limits, some likely
due to the reduced G loadings with the spoilers extended.

> The trick is to stay within the limits as long as possible.
> Therefore it's necessary to know the limits and their use. In
> abovementioned Nimbus 4 incident it seems that pilot exchausted
> g-limits before the Vne arrived. But no-one knows what really
> happened.
>
> BTW, there is one energy-burning device on every glider that may save
> you the very necessary second or two - the wheel. Lower it as soon as
> you feel the threat of overspeeding. You may lose the wheel doors
> because of the speed and g-forces, but this is not nearly as
> catastrophical as losing wing because of pulling the airbrakes at Vne
> and high-g.

Does anyone have an idea of how much effect this would have? If it is
small, perhaps a pilot should not even think of attempting it as he
struggles with a recovery near Vne. In many gliders, it requires the
pilot to switch hands on the stick to lower the gear, and would be a
distraction at critical time in all of them.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Eric Greenwell

March 30th 04, 07:10 PM

Bert Willing wrote:

> Non-catastrophic may happen if you have a structure which has a plastic
> behavious prior to rupture.
> Ironically, you don't have that with "plastic" gliders. You might well
> enconter that you can pull more g's because the designer has put lots of
> margins, and nothing will happen
> But if *something* happens, you're wings are simply gone on a GRP/CRP ship.
> The idea that you'll get away with some sort of damage and land the ship is,
> hm, fairly naive.
>
> But to the initial question: If you are going to exceed Vne in a dive, you
> can chose between putting your joker on a good spacing between Vne and
> flutter speed, or put your joker on a pessimistic design margin and a well
> crafted serial number. There is actually no way to tell the answer
> beforehand.

I agree with Bert. To imagine Don's advice to be suitable for all
gliders is too ignore the huge differences in design and materials. For
example, the flexible, fiberglass wing of ASW 20 probably means it has a
greater strength reserve because of the extra material needed to control
flutter, while the stiffer carbon wing in the ASW 27 might give it the
reverse margins. Consider the Standard Cirrus with it's relatively thick
fiberglass wing: where are it's margins the greatest? And, it appears
the 25 m gliders may have special problems.

Until you have discussed the design of your _particular_ glider with
it's designer, you are simply speculating about the dangers of
overspeeding versus overloading. Even the designer may not know, if the
glider hasn't been tested to flutter! And if you damage the structure
during a high G pull-up, what do you suppose will happen to the speed at
which flutter occurs? You may now have damaged glider experiencing flutter!

Fortunately, this situation seems to rare. Personally, I have never
encountered it in 4500 hours of soaring, not even an incipient spin.
Here is more speculation: I think the reality is most pilots that have
the problem will use Don's method out of reflex, not training or
conscious choice.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Bruce Greeff

March 30th 04, 08:00 PM

Don

First - I agree entirely that you are contemplating which of two evils you
should perpetrate having got yourself into an untenable situation. But having
got there you need to at least have considered what you should do in the event.
I doubt there would be much time for deliberation.

I suggest that the correct action depends on the aircraft to some degree, but
that flutter is much more damaging to the structure than moderate overstress in
most cases since it introduces large cyclical and localised loads on the
structure in addition to whatever G load the aircraft is exposed to.

First generation glass, before the finite element analysis programs allowed the
designers to design to the limit is probably much safer to over stress than
overspeed. Similarly the latest carbon designs seem to have G limits imposed by
the JAR22 deflection limits rather than ultimate strength. Presumably these
aircraft have huge strength reserves. For interest look at the wing test on the
DG1000.

When I asked Schempp-hirth about the possibility of flutter damage in an
incident where a Std Cirrus had made a loud chattering noise on a high speed
pass, they replied that it would be unlikely to have been flutter. This because
they did not think it likely that the aircraft would remain controllable due to
control system damage in the event of flutter.

In inspection we found that the noise came from an airbrake cap that had lost
some tension in the retention springs. It was sucking slightly open and banging
against the sides of the slot as the pilot pulled up. Over one G, close to Vne
and soft springs combined to allow a millimeter or so of play. The noise was
disconcertingly loud from the ground, we thought there might be a glass-fibre
confetti shower.

I'd take a gamble on the Cirrus's wings handling more Gs than the manual said if
my life depended on it. Conversely I take great pains not to get even near that
point in a 32 year old glider.

Don Johnstone

March 30th 04, 10:53 PM

At 19:18 30 March 2004, Bruce Greeff wrote:

>
>When I asked Schempp-hirth about the possibility of
>flutter damage in an
>incident where a Std Cirrus had made a loud chattering
>noise on a high speed
>pass, they replied that it would be unlikely to have
>been flutter. This because
>they did not think it likely that the aircraft would
>remain controllable due to
>control system damage in the event of flutter.

and this is really the crux of the whole thing. Once
flutter starts there may be a complete loss of control;
end ex.
Probably one of the best demonstrations of flutter
I have ever seen was the video of a suspension bridge
breaking up in high wind. Once started complete destruction
is guaranteed unless the cause can be removed (speed
reduced), In the case of the bridge the wind speed
did not reduce, it not being controlled. If loss of
control of the glider occurs, same result, lots of
little bits.

The other point I neglected to mention earlier was
that any margin on the VNE is established on an airframe
where the control hinges are a good fit and all the
control rods have no slack.

Having looked at and lifted the bits of my ASW17 I
think I am happy that there is a reasonable margin
on the loading placard.

Jim

March 30th 04, 10:56 PM

On Sun, 28 Mar 2004 20:30:57 +0200, Denis
> wrote:

>Edward Downham wrote:
>
>> It is important to note that this margin is there to cope with things such as
>> ASI position and calibration errors. When you fly a glider at an _indicated_
>> speed of Vne, you might actually be nearer Vd and the realm of the test pilot.
>
>No. VNE is an indicated airspeed limit (IAS). If there is a airspeed
>calibration error, VNE has been reduced to correct it. The margin is
>there for instrumental errors, and *pilot* errors.

Well, this one is just a little scary. For more than one glider of my
acquaintance Vne is given as a TAS in the manual. This can be
converted to IAS of course, but the IAS would, of course, decrease
with altitude.

Vstall, on the other hand, seems just about always to be given as an
IAS, and as an IAS the stall speed will remain about the same as
altitude increases. This is all pretty basic stuff I know, so I
probably misinterpreted your statement about Vne.

One way to look at the "coffin corner" situation where some very
high-flying aircraft, such as the U-2, I suppose, can end up at an
altitude where the stall speed, in TAS, has come very close to the
Vne, as a TAS.

Andy Blackburn

March 31st 04, 04:44 AM

I agree with Eric and Bert - and the guys who taught
materials, structures and aerodynamics in school 20+years
ago.

Couple of points to clarify:

Some have been talking about the G-load in the manual,
others (like me) have talked about the ultimate loading
to which the airframe is tested (a bigger number).
In a panic I'd probably pull past the first, but wouldn't
get near the second. I don't think Don was recommending
anything much different - Don?

References to what aerobatic pilots do ('pull as much
as necessary') are not applicable to gliders for one
simple reason: aerobatic aircraft are generally good
for Gs past G-LOC (G-induced loss of consciousness)
- not so for gliders. For GRP or CRP structures pull
to the ultimate load at your peril. You'll probably
get away with going over the placarded limit. The main
point for me remains that I can't tell how many Gs
I'm pulling from my butt alone - at least not with
a whole lot of accuracy.

Flutter is a dynamic effect and can happen to the wing,
or any of the control surfaces - I think the horizontal
and vertical stabs are generally too stiff to go first.
Each flutter mode has a different natural frequency,
damping (positive or negative) and corresponding airspeeds
at which they can start.

I've heard of several cases of control surface flutter
in sailplanes (often older ones with looser control
circuits - and Grobs with poor mass balancing). I've
not heard of sailplanes fluttered apart in flight (though
this isn't to say it has never happened). Maybe it's
because everyone who has been forced to make a choice
pulls the wings off first.

Something to think about...

At 18:18 30 March 2004, Eric Greenwell wrote:
>Bert Willing wrote:
>
>> Non-catastrophic may happen if you have a structure
>>which has a plastic
>> behavious prior to rupture.
>> Ironically, you don't have that with 'plastic' gliders.
>>You might well
>> enconter that you can pull more g's because the designer
>>has put lots of
>> margins, and nothing will happen
>> But if *something* happens, you're wings are simply
>>gone on a GRP/CRP ship.
>> The idea that you'll get away with some sort of damage
>>and land the ship is,
>> hm, fairly naive.
>>
>> But to the initial question: If you are going to exceed
>>Vne in a dive, you
>> can chose between putting your joker on a good spacing
>>between Vne and
>> flutter speed, or put your joker on a pessimistic
>>design margin and a well
>> crafted serial number. There is actually no way to
>>tell the answer
>> beforehand.
>
>I agree with Bert. To imagine Don's advice to be suitable
>for all
>gliders is too ignore the huge differences in design
>and materials. For
>example, the flexible, fiberglass wing of ASW 20 probably
>means it has a
>greater strength reserve because of the extra material
>needed to control
>flutter, while the stiffer carbon wing in the ASW 27
>might give it the
>reverse margins. Consider the Standard Cirrus with
>it's relatively thick
>fiberglass wing: where are it's margins the greatest?
>And, it appears
>the 25 m gliders may have special problems.
>
>Until you have discussed the design of your _particular_
>glider with
>it's designer, you are simply speculating about the
>dangers of
>overspeeding versus overloading. Even the designer
>may not know, if the
>glider hasn't been tested to flutter! And if you damage
>the structure
>during a high G pull-up, what do you suppose will happen
>to the speed at
>which flutter occurs? You may now have damaged glider
>experiencing flutter!
>
>Fortunately, this situation seems to rare. Personally,
>I have never
>encountered it in 4500 hours of soaring, not even an
>incipient spin.
>Here is more speculation: I think the reality is most
>pilots that have
>the problem will use Don's method out of reflex, not
>training or
>conscious choice.
>
>--
>-----
>change 'netto' to 'net' to email me directly
>
>Eric Greenwell
>Washington State
>USA
>
>

Kirk Stant

March 31st 04, 06:51 AM

Jim > wrote in message >

> One way to look at the "coffin corner" situation where some very
> high-flying aircraft, such as the U-2, I suppose, can end up at an
> altitude where the stall speed, in TAS, has come very close to the
> Vne, as a TAS.

More precisely, I think it's when the stall speed (IAS in the cockpit)
but really a TAS issue) approaches the limiting Mach number. Since
Mach vs TAS decreases with altitude, and TAS vs IAS increases with
altitude, the problem is inevitable for the right (or wrong, depending
on your point of view!) kind of plane.

Kirk

iPilot

March 31st 04, 12:38 PM

Well. I have no experience fortunately from such situations. Statements that I have made are almost
directly taken from the book "Glider aerobatics".

About lowering the wheel: I don't know how much does it help, but if you try to fly around with the
wheel out, the performance loss is there and one can feel it. Afaik in fitting the fixed wheel
glider with retractable-one gives some 1-2 L/D points better performance.
I agree with you regarding the problem of switching hands. However, I think that in most gliders at
high g, just disarresting the wheel will lower it. One don't have to fix it.

"Eric Greenwell" > wrote in message
...
> iPilot wrote:
> > You may be correct. However, I have heard of some cases where there
> > have been structural failures resulting from excessive g-forces, but
> > the glider has remained landable after that. Aerobatics books also
> > recommend to "pull as hard as necessary", but to keep an eye on your
> > g-meter and ASI.
>
> Aerobatic aircraft are built to much higher G and Vne limits, and the
> pilots flying them are also accustomed to using high Gs. How many
> sailplane pilots have a G meter and will be looking at it in a spin
> recovery gone wrong?
>
> > High AoA eats energy rather fast. Flutter from
> > overspeeding will definately disintegrate your wing.
>
> It is this claim that we are discussing. I know of many people that have
> experienced flutter and not lost a wing. I also know flutter can have
> many different modes, including those that involve the rudder, elevator,
> ailerons, wing, and tail boom. It seems most dogmatic to claim "Flutter
> from overspeeding will definitely disintegrate your wing". Since you are
> so certain, perhaps you could tell us the reasons for your certainty?
>
> > Excessive-g may
> > not.
>
> Has flutter caused any of the in-flight breakups discussed here? Perhaps
> I missed them. I thought all were due to exceeding G limits, some likely
> due to the reduced G loadings with the spoilers extended.
>
> > The trick is to stay within the limits as long as possible.
> > Therefore it's necessary to know the limits and their use. In
> > abovementioned Nimbus 4 incident it seems that pilot exchausted
> > g-limits before the Vne arrived. But no-one knows what really
> > happened.
> >
> > BTW, there is one energy-burning device on every glider that may save
> > you the very necessary second or two - the wheel. Lower it as soon as
> > you feel the threat of overspeeding. You may lose the wheel doors
> > because of the speed and g-forces, but this is not nearly as
> > catastrophical as losing wing because of pulling the airbrakes at Vne
> > and high-g.
>
> Does anyone have an idea of how much effect this would have? If it is
> small, perhaps a pilot should not even think of attempting it as he
> struggles with a recovery near Vne. In many gliders, it requires the
> pilot to switch hands on the stick to lower the gear, and would be a
> distraction at critical time in all of them.
>
>
> --
> -----
> change "netto" to "net" to email me directly
>
> Eric Greenwell
> Washington State
> USA
>

Denis

March 31st 04, 06:53 PM

Jim wrote:

>>No. VNE is an indicated airspeed limit (IAS). If there is a airspeed
>>calibration error, VNE has been reduced to correct it. The margin is
>>there for instrumental errors, and *pilot* errors.
>
>
> Well, this one is just a little scary. For more than one glider of my
> acquaintance Vne is given as a TAS in the manual. This can be
> converted to IAS of course, but the IAS would, of course, decrease
> with altitude.

I did not want to raise the question of VNE at altitude (a more
difficult subject ;-) and the relation between IAS and TAS.

I replied to someone who mentioned the errors of static ports : The
calibrated airspeed (CAS) may be higher than the indicated airspeed
(IAS) depending og static ports location ; in that case, it is measured
during the tests and all limits are corrected to be given in *indicated*
airspeed.

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 31st 04, 06:55 PM

Jack wrote:

>>I never experienced a spin recovery and...[t]herefore I don't know what I
>
> would do in such a situation.
>
> With your (claimed) thousands of hours of flight experience?

Please quote correctly. I never experienced a spin recovery *in a Nimbus 4*

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 31st 04, 07:16 PM

W.J. (Bill) Dean (U.K.). wrote:

> You are just plain wrong.

Who are you answering to ? What are you speaking about ?

Please reply after what you quote and not before.

> You also say:
> "all I want is to give my opinion when I think something is said here that
> may lead to dangerous flying - such as sentences like "don't exceed VNE, but
> no problem if you exceed permitted G-loading" ".
> Who said that, which posting?

You in > :

" pull however hard is necessary not to exceed VNE,"

> Exceeding Vne is outside limits and dangerous, so are any of the
> alternatives - the discussion is about which of the alternatives is the
> least worst.

No. Pulling airbrakes at or below VNE is safe and permitted, if you
respect the G limits. The other two (exceeding VNE or exceeding
g-limits) are unsafe and prohibited. I really don't understand why you
(and not you alone, unfortunately) cannot understand that.

> With the Minden accident on 13th July 1999, it is clear from the report that
> the glider was pitched down to well beyond a 45 degree dive, so the
> airbrakes would not have been speed limiting.

Of course not. But it would have considerably limited the speed increase
in the few seconds needed to get at or below 45° dive.

> You say "I never experienced a spin recovery", presumably you mean in a
> large span glider. I hope you have done plenty in training and short span
> machines.

Yes. Including some with a VNE at 550 kt...

> Denis (Denis who and from where?),

Does it really import my family name or where I am from ? You'd better
try to find more convincing arguments.

Anyway the answer to your questions is in my headers or any search engine.

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Mark James Boyd

March 31st 04, 07:22 PM

I'd recommend reading about the asymmetric loading arguments
presented at:

http://www.avweb.com/news/columns/182086-1.html

The meat of the matter starts about halfway down
the page. Essentially it says full aileron and full elevator
when applied simultaneously create a much greater chance of wing
failure at a lower airspeed than just applying either one independently.

I'm not aware of how this may or may not apply to
gliders. Perhaps some expert in wing construction
can give most welcome educated opinion... :)

F.L. Whiteley > wrote:
>
>"Mark James Boyd" > wrote in message
>news:4064994c$1@darkstar...
>> K.P. Termaat > wrote:
>> >Yesterday evening I talked with a friend about avoiding excessive speed
>when
>> >recovering from a spin in a modern low drag glider with the somewhat
>larger
>> >span.
>>
>> A lot has been written here about G loads. I recall that the
>> T-34 (an aerobatic power plane I have a little time in
>> which is sortof a tandem Beech 33) had some issues with wings
>> coming off during aerobatics. The recorded G loads and mauevers
>> indicated the aircraft wasn't flown outside of G limits.
>>
>> How did the wings separate? Some smarty folks said it was
>> because the twisting G load that the wing could endure was
>> much less than the static tested load. If the ailerons were
>> deflected and the thing was in a steep spiral (as opposed
>> to straight dive) there were twisting loads.
>>
>Thought I heard that inspections showed T-34 wings were suffering from
>fatigue cracks. Kind of shot down some of the 'fighter dude' thrill rides
>(we have/had one in Colorado). We have a disassembled T-34 wrapped in
>plastic in our hangar. I recall a conversation about the value dropping by
>about 50% when the crack problem was discovered.
--

------------+
Mark Boyd
Avenal, California, USA

Denis

March 31st 04, 07:34 PM

Bert Willing wrote:

> But to the initial question: If you are going to exceed Vne in a dive, you
> can chose between putting your joker on a good spacing between Vne and
> flutter speed, or put your joker on a pessimistic design margin and a well
> crafted serial number. There is actually no way to tell the answer
> beforehand.
>
> But pulling the airbrakes would be fairly suicidal.

I suppose you meant "pulling the airbrakes while pulling too hard" ???

As Eric noticed it, the allowed G-loading at VNE in ASH26 (for example)
is 4 G without airbrakes, and a very close 3.5 G with airbrakes.

Thus in most cases it will be *safer* to pull airbrakes (including close
to the ground, if the dive angle is high).

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 31st 04, 07:48 PM

Bruce Greeff wrote:

> First generation glass, before the finite element analysis programs
> allowed the designers to design to the limit is probably much safer to
> over stress than overspeed. Similarly the latest carbon designs seem to
> have G limits imposed by the JAR22 deflection limits rather than
> ultimate strength. Presumably these aircraft have huge strength
> reserves. For interest look at the wing test on the DG1000.

I agree that *some* earlier, 15m designs may have a good safety margin
in overstress, mostly those in glassfiber (more flexible).

But not *all*, and certainly not modern open-class gliders.

I recall what I posted before, because there are facts from NTSB and
manufacturer data, which I think are more reliable than some honorable
but ill-based opinions expressed in this thread, and which nobody here
have contested yet:

> the link (on Minden Nimbus 4 accident) :
> http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19310&key=1
(...)
> The report quotes that the G limit for the Nimbus 4 at VNE is 3.5 g
> *only* (compared to 5.3 g at Va) and the design "safety margin" is
> between 1.55 to 1.75. Thus even on a plane in perfect condition, and if
> the manufacturer made no mistake, it *will* break between 5.4 and 6.1 g
> at VNE (even without airbrakes)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

March 31st 04, 08:02 PM

Todd Pattist wrote:

> With flutter, you don't know when it will start, and you
> don't know what will happen if it does. In my experience,
> fatal flutter-caused accidents are relatively rare.
> G-caused breakage seems to be both more common and more
> predictable. I'll leave my brakes closed, pull to somewhat
> over my max positive G-limit (but nowhere near as hard as I
> can) and let the speed do what it has to do as I bring the
> nose up.

I agree, except for "I'll leave my brakes closed"...

I think opening the airbrakes would allow you to do the same without
exceeding placarded airbrakes-out G-limit and with a lower speed at the
bottom of the recovery...

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Andy Blackburn

March 31st 04, 08:56 PM

This has yielded some good food for thought and further
investigation as the season gets going:

1) Look through your flight manual with an eye towards
operating limits, particularly with respect to G-limits
and recommended/allowed use of airbrakes in spins/dives.
I have to admit I've forgotten mine.

2) If you don't have a G-meter in your sailplane get
some stick time in a plane with one pulling 2, 3, 4
Gs to get a good sense for what it feels like by the
seat of your pants.

3) At a safe altitude, pull the spoilers and try some
steep nose down attitudes to get a sense for speed
buildup under different attitudes/configurations (don't
overdo it!). If allowed by the flight manual (and within
your comfort zone/experience), try some spin recoveries
with and without speed brakes deployed. I for one would
love to hear an actual pilot report on maximum speed
achieved, maximum Gs pulled and altitude lost under
each scenario (yes I know there are multiple possible
combinations).

4) Be aware of the likely chain of events that lead
to being sharply nose-down at high speed. A couple
of scenarios come to mind: Open-class ships where it's
just hard to stop the rotation and you end up in a
spiral dive, or late recognition of stall recovery,
resulting in rapid speed buildup. Not much to do about
the first one beyond precise flying technique. The
second one it seems can be prevented with practice
and an eye on the airspeed indicator.

Lastly, I would love to hear factory advice on potential
implications of popping speed brakes near and above
Vne. Assuming you don't exceed the G-limit are there
other issues? It stikes me as a potentially violent
change in configuration, but maybe pilot and plane
can handle the sudden deceleration onset. It seems
like a relatively important decision in a pinch, but
there has been no real resolution of the matter here.

Safe flying,

9B

At 19:12 31 March 2004, Denis wrote:
>Todd Pattist wrote:
>
>> With flutter, you don't know when it will start, and
>>you
>> don't know what will happen if it does. In my experience,
>> fatal flutter-caused accidents are relatively rare.
>> G-caused breakage seems to be both more common and
>>more
>> predictable. I'll leave my brakes closed, pull to
>>somewhat
>> over my max positive G-limit (but nowhere near as
>>hard as I
>> can) and let the speed do what it has to do as I bring
>>the
>> nose up.
>
>I agree, except for 'I'll leave my brakes closed'...
>
>I think opening the airbrakes would allow you to do
>the same without
>exceeding placarded airbrakes-out G-limit and with
>a lower speed at the
>bottom of the recovery...
>
>--
>Denis
>
>R. Parce que ça rompt le cours normal de la conversation
>!!!
>Q. Pourquoi ne faut-il pas répondre au-dessus de la
>question ?
>

Bob Kuykendall

March 31st 04, 09:18 PM

Earlier, Bruce Greeff > wrote:

> ...Similarly the latest carbon designs
> seem to have G limits imposed by
> the JAR22 deflection limits rather
> than ultimate strength...

I'll certainly agree that composite sailplane structure is bounded
more by stiffness than by strength. However, I've spent my lunch hour
searching JAR22 and I can't find anything that codifies deflection
limits. The closest thing I found seems to be:

: JAR 22.305 Strength and deformation
: (a) The structure must be able to support
: limit loads without permanent deformation. At
: any load up to limit loads, the deformation may
: not interfere with safe operation. This applies in
: particular to the control system.
: with respect to the sailplane.

Do you know of other relevant JARs that specify maximum structure
deflection in quantifiable terms? I'm not trying to nitpick or
anything, I just want to make sure I'm not missing something
important.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com

Denis

March 31st 04, 09:19 PM

Todd Pattist wrote:

> You seem to be of the opinion that opening the brakes
> guarantees not exceeding Vne. It's not true. If it was,
> you'd be right to open the brakes, provided you have enough
> altitude AND provided that FUD (fear uncertainty and doubt)
> did not inadvertently make you pull above the max permitted
> reduced G-load and break the wing tips off.

You're right that it does not guarantee not exceeding VNE, but it helps
a lot...

> This accident
> is one of the most common, so anyone advising opening the
> brakes in a highly nose down high speed scenario had better
> be sure that the net result is less fatal accidents, not
> more regardless of their theoretical justification. I have
> my doubts.

I'm sure that *I* would do that. And I'm sure that most flight manuals
advise that too, therefore I'm confident that it may be true.

> I've seen this accident several times. I have
> not seen the fatal flutter accident. I don't say they don't
> happen, but it's not as common

If a glider breaks in a high speed (above Vd) recovery, I think you
cannot determine if it broke because of G-loading or flutter, except if
you have a close look to it when it breaks.

> It's you that misses the fact that you can get a modern
> glider into an altitude/attitude/speed where at least one
> limit must be exceeded.

Yes I understand that. But I prefer recommend not to get trapped into
that situation...

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Eric Greenwell

March 31st 04, 10:59 PM

Bob Kuykendall wrote:
> Earlier, Bruce Greeff > wrote:
>
>
>>...Similarly the latest carbon designs
>>seem to have G limits imposed by
>>the JAR22 deflection limits rather
>>than ultimate strength...
>
>
> I'll certainly agree that composite sailplane structure is bounded
> more by stiffness than by strength.

I've been told that is more likely true for fiberglass construction, but
not so likely to be true for carbon fiber construction, because of the
great differences in material characteristics, such as stiffness. So, it
might correct to argue that a glass fiber sailplane has a "substantial"
G loading margin, but not correct for the carbon fiber sailplane.

And the bounds might be quite different for a 15 meter glider and a 25
meter glider, or a thick wing trainer and a thin wing racer.

--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Denis

March 31st 04, 11:37 PM

Todd Pattist wrote:

> OK, if you are going to open the brakes, you're going to
> have to be sure you can stay below the reduced G-load.

Right. I admit that it is difficult to "be sure" of how many G's you
pull without an accelerometre, but it is the same with or without
airbrakes. And for my ship (ASH 26) it's not very different (0.5 G less
with airbrakes, only). How much is it in your Ventus ?

> personally think we've had some accidents brakes out where
> that was a contributing factor, but let's assume you're
> better than I suspect I am, so you're willing to risk the
> reduced G-load. Now we have to do some calculation, because
> as long as your nose is below 30 degrees down, your brakes
> out aren't going to keep you below Vne.

Right. But even in a 90° dive they give you almost twice more time
before reaching to VNE ; thus you may pull much less for the same speed
at the end (and the additional drag due to pulling will be by far
greater with airbrakes than without - and will stop the acceleration
*before* 30° which is the limit angle in 1 G flight)

> You're also going
> to lose more altitude than me,

Wrong ! I will loose more total energy, of course, but not more altitude.

If I pull the same G's, I will loose *less* altitude.

If I pull lower G's, I will loose *more or less* altitude depending of
the glider (the differences in G w and w/o airbrakes), the speed, the
initial dive angle...

Anyway the difference will be very small (either way) high enough to
avoid the ground in one case and not the other is very low (although
when somewhat low the usual reflex will be to pull harder than necessary)

> I've got my brakes in, so I can develop more lift and higher
> G. My higher lift and higher G turns me vertically faster

Don't forget that your turn radius increase with the square of the
speed, thus this is not true - even if your rate of turn is faster!

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Pete Zeugma

April 1st 04, 07:57 AM

I have a much better idea, practice your spin recovery
so that you dont end up going through Vne, or having
to pull excessive G to prevent it! It's quite easy
really. There really is no excuse for allowing a spin
to develop beyond the wing drop stage in any other
situation other than forced spinning exercises.

I dont particularly want to read an accident report
for a pilot practicing what has been 'recommended'
as the correct way to recover from a spin in these
cercumstances.......... Do it right from the start
is the only solution!

At 20:06 31 March 2004, Andy Blackburn wrote:
>This has yielded some good food for thought and further
>investigation as the season gets going:
>
>1) Look through your flight manual with an eye towards
>operating limits, particularly with respect to G-limits
>and recommended/allowed use of airbrakes in spins/dives.
>I have to admit I've forgotten mine.
>
>2) If you don't have a G-meter in your sailplane get
>some stick time in a plane with one pulling 2, 3, 4
>Gs to get a good sense for what it feels like by the
>seat of your pants.
>
>3) At a safe altitude, pull the spoilers and try some
>steep nose down attitudes to get a sense for speed
>buildup under different attitudes/configurations (don't
>overdo it!). If allowed by the flight manual (and within
>your comfort zone/experience), try some spin recoveries
>with and without speed brakes deployed. I for one would
>love to hear an actual pilot report on maximum speed
>achieved, maximum Gs pulled and altitude lost under
>each scenario (yes I know there are multiple possible
>combinations).
>
>4) Be aware of the likely chain of events that lead
>to being sharply nose-down at high speed. A couple
>of scenarios come to mind: Open-class ships where it's
>just hard to stop the rotation and you end up in a
>spiral dive, or late recognition of stall recovery,
>resulting in rapid speed buildup. Not much to do about
>the first one beyond precise flying technique. The
>second one it seems can be prevented with practice
>and an eye on the airspeed indicator.
>
>Lastly, I would love to hear factory advice on potential
>implications of popping speed brakes near and above
>Vne. Assuming you don't exceed the G-limit are there
>other issues? It stikes me as a potentially violent
>change in configuration, but maybe pilot and plane
>can handle the sudden deceleration onset. It seems
>like a relatively important decision in a pinch, but
>there has been no real resolution of the matter here.
>
>Safe flying,
>
>9B
>
>
>At 19:12 31 March 2004, Denis wrote:
>>Todd Pattist wrote:
>>
>>> With flutter, you don't know when it will start, and
>>>you
>>> don't know what will happen if it does. In my experience,
>>> fatal flutter-caused accidents are relatively rare.
>>> G-caused breakage seems to be both more common and
>>>more
>>> predictable. I'll leave my brakes closed, pull to
>>>somewhat
>>> over my max positive G-limit (but nowhere near as
>>>hard as I
>>> can) and let the speed do what it has to do as I bring
>>>the
>>> nose up.
>>
>>I agree, except for 'I'll leave my brakes closed'...
>>
>>I think opening the airbrakes would allow you to do
>>the same without
>>exceeding placarded airbrakes-out G-limit and with
>>a lower speed at the
>>bottom of the recovery...
>>
>>--
>>Denis
>>
>>R. Parce que ça rompt le cours normal de la conversation
>>!!!
>>Q. Pourquoi ne faut-il pas répondre au-dessus de la
>>question ?
>>
>
>
>
>

Jack

April 1st 04, 08:25 AM

Denis wrote:

> Please quote correctly. I never experienced a spin recovery *in a Nimbus 4*

I'll take your word for it, but that is not quite what you said.
However, it was close enough to give you the benefit of the doubt.

You did say:

"And although I have some experience in Nimbus 4D
(more on ASH 25) I never experienced a spin recovery
and I hope I never will have to."

It would not be unreasonable to ASSUME you meant to say that you had
never experienced a spin recovery, "in Nimbus 4D", but your statement is
too vague for a reader to be certain.

Thanks for the clarification.

Jack

Bert Willing

April 1st 04, 08:25 AM

Yes. However, judging g-loads with the seating position in modern gliders is
difficult - especially if you run on 100% adrenaline.

--
Bert Willing

ASW20 "TW"

"Denis" > a écrit dans le message de
...
> Bert Willing wrote:
>

> > But pulling the airbrakes would be fairly suicidal.
>
> I suppose you meant "pulling the airbrakes while pulling too hard" ???
>
> As Eric noticed it, the allowed G-loading at VNE in ASH26 (for example)
> is 4 G without airbrakes, and a very close 3.5 G with airbrakes.
>
> Thus in most cases it will be *safer* to pull airbrakes (including close
> to the ground, if the dive angle is high).
>
>
> --
> Denis
>
> R. Parce que ça rompt le cours normal de la conversation !!!
> Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

April 1st 04, 04:55 PM

Pete Zeugma wrote:

>>But a glider wing breaks within milliseconds of overstressing
>>!
>
> no they dont, they have to fail progressivly. no glider
> would be alowed in the air by any regulating body if
> a wing could break in a 1000th of a second. i dont
> think you really understand the force that would be
> needed to do that. the instantanious g-load to do that
> would kill you out right.

Another dangerous misconception :-(((

If the actual extreme load is 6 g, the glider will loose wings as soon
as G-loading is greater than 6 g. Not 5 seconds later, not 0.5 second
later, but immediately. And not "progressively" (can you loose wings
progressively ???)

And in a modern ship near VNE, a small stick input may bring you from 1
to 6 G in less than 1 second.

Hence there is no chance at all that black-out or grey-out warn the
pilot of a too high G-load in an emergency situation.

You may have plenty of spin training on an ASK 13, it's better than
none, it will not prevent you to getting in a dangerous situation with
an open class glider. Spin training in these is prohibited, but high
speed flying is not : everybody should train to fly at higher and higher
speeds up to VNE in order to get used to the very high sensitivity of
most modern gliders at high speeds and to master the technique to use
only very small control inputs (including putting their hand firmly on
their leg to prevent unwanted or G-induced stick movements)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Tony Verhulst

April 1st 04, 05:10 PM

> If the actual extreme load is 6 g, the glider will loose wings as soon
> as G-loading is greater than 6 g. Not 5 seconds later, not 0.5 second
> later, but immediately. And not "progressively" (can you loose wings
> progressively ???)

Yes - on some gliders anyway. The Schweizer 1-34 is designed so that the
*first* failure occurs about 2/3 out from the root at about 8 Gs.

Tony V
http://home.comcast.net/~verhulst/SOARING

Bruce Greeff

April 4th 04, 02:06 PM

HI Bob

That is what I was referring to.

The deformation limit for carbon designs with thin wings appears to be the point
at which it becomes impossible to maintain control movement.

As an example, there are various apocryphal tales of uncommanded airbrake
openings on open class aircraft with thin flexible wings. The Nimbus 4 appears
to be the most common suspect here.

So the deflection limit is not a "x degrees from rest", or a plastic deformation
(although there is a requirement for this in the regulations) but a deflection
beyond which the control actuators do not work correctly or have unacceptably
high resistance.

My point came from published discussions on the construction of the Eta, and the
DG1000 where both constructors commented that the ultimate strength of the
structure was well in excess of the limit load, and that the limit load was
imposed by the deflection of the wing.

There is an interesting test story at:

http://www.dg-flugzeugbau.de/bruchversuch-e.html

The destructive test requirement is that the wing must withstand 1.725* the
limit load for three seconds at a temperature of 54Celsius. The DG1000 wing
withstood this - and eventually failed at 1.95 times the design load limit. This
is one reason why I believe you would probably be able to get away with a brief
overstress load. I am not sure of the limits on older designs, but would expect
there to be less margin of strength.

As I understand it the modern thin section wings are flexible enough that the
load limit is imposed by control freedom limitation, and the wing must withstand
1.725 times this load in test. Flutter is the subject of speed limitation which
give speeds and margins that the designer/manufacturer must demonstrate flying
to. The regulations imply that the glider must be demonstrated safe at a minimum
of 23% margin above the placarded Vne. So your margins for flutter, versus
ultimate strength are 1.23 vs 1.725 in JAR22 (unless I got the math wrong)

Andy Blackburn

April 4th 04, 05:10 PM

Finally, someone bothered to get the regs out.

I still believe that the G-limit is better understood
in most designs than the Vne limit, just due to the
difference in testing approach. G-loads are tested
to destruction, Vne is not.

In either case it's good to know the demonstrated margins
in excess of certified limits - just in case.

At 13:12 04 April 2004, Bruce Greeff wrote:
>HI Bob
>
>That is what I was referring to.
>
>The deformation limit for carbon designs with thin
>wings appears to be the point
>at which it becomes impossible to maintain control
>movement.
>
>As an example, there are various apocryphal tales of
>uncommanded airbrake
>openings on open class aircraft with thin flexible
>wings. The Nimbus 4 appears
>to be the most common suspect here.
>
>So the deflection limit is not a 'x degrees from rest',
>or a plastic deformation
>(although there is a requirement for this in the regulations)
>but a deflection
>beyond which the control actuators do not work correctly
>or have unacceptably
>high resistance.
>
>My point came from published discussions on the construction
>of the Eta, and the
>DG1000 where both constructors commented that the ultimate
>strength of the
>structure was well in excess of the limit load, and
>that the limit load was
>imposed by the deflection of the wing.
>
>There is an interesting test story at:
>
> http://www.dg-flugzeugbau.de/bruchversuch-e.html
>
>The destructive test requirement is that the wing must
>withstand 1.725* the
>limit load for three seconds at a temperature of 54Celsius.
>The DG1000 wing
>withstood this - and eventually failed at 1.95 times
>the design load limit. This
>is one reason why I believe you would probably be able
>to get away with a brief
>overstress load. I am not sure of the limits on older
>designs, but would expect
>there to be less margin of strength.
>
>As I understand it the modern thin section wings are
>flexible enough that the
>load limit is imposed by control freedom limitation,
>and the wing must withstand
>1.725 times this load in test. Flutter is the subject
>of speed limitation which
>give speeds and margins that the designer/manufacturer
>must demonstrate flying
>to. The regulations imply that the glider must be demonstrated
>safe at a minimum
>of 23% margin above the placarded Vne. So your margins
>for flutter, versus
>ultimate strength are 1.23 vs 1.725 in JAR22 (unless
>I got the math wrong)
>

Denis

April 5th 04, 06:40 PM

Bruce Greeff wrote:

> As I understand it the modern thin section wings are flexible enough
> that the load limit is imposed by control freedom limitation, and the
> wing must withstand 1.725 times this load in test. Flutter is the
> subject of speed limitation which give speeds and margins that the
> designer/manufacturer must demonstrate flying to. The regulations imply
> that the glider must be demonstrated safe at a minimum of 23% margin
> above the placarded Vne. So your margins for flutter, versus ultimate
> strength are 1.23 vs 1.725 in JAR22 (unless I got the math wrong)

It's perhaps mathematically true but your argument is wrong (if your
conclusion is to say that there is more risk of flutter than
overloading). You cannot compare pourcentages of load and speed !

It takes less tenth of second at any moment to take the 2 or 3 g's that
will exceed your (supposed) 72.5% load margin, whereas it will take
several seconds to take the 60 or 65 km/h of margin in speed (supposing
23% margin), or depending of the dive angle you might never get over the
speed margin...

And although it may be true that some parts of the wing (e.w. center
section) has more stress margin due to deflection limit, it does *not*
guarantee you that all the parts of the wing has the same extra margin:
in the Nimbus 4 accident the central wing did not break, but the outer
wing did, with fatal consequences :-(

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

April 5th 04, 06:46 PM

Andy Blackburn wrote:

> Finally, someone bothered to get the regs out.
>
> I still believe that the G-limit is better understood
> in most designs than the Vne limit, just due to the
> difference in testing approach. G-loads are tested
> to destruction, Vne is not.

Another difference: if *you* survived to overspeed (i.e. flutter did not
occur), your glider is still safe for you or *other pilots*

If you survived overloading (i.e. over limit G-load but the wings did
not break) your glider may be *unsafe* and next time might break well
under extreme G-load limit...

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

K.P. Termaat

April 5th 04, 10:17 PM

Started this thread (Avoiding Vne) some weeks ago with a kind invitation to
respond to the idea of pulling the airbrakes while still in the rotating
mode of a spin. The idea behind it is when rotation has been stopped with
the glider at a pitch angle of say 60° or more this will be at a lower speed
then when the airbrakes stay closed all the time. Possibly a build up of
speed to over Vne can then be avoided after that. Of course airbrakes should
be closed again in the following pull up manouvre.
Any comments?

"Denis" > schreef in bericht
...
> Bruce Greeff wrote:
>
> > As I understand it the modern thin section wings are flexible enough
> > that the load limit is imposed by control freedom limitation, and the
> > wing must withstand 1.725 times this load in test. Flutter is the
> > subject of speed limitation which give speeds and margins that the
> > designer/manufacturer must demonstrate flying to. The regulations imply
> > that the glider must be demonstrated safe at a minimum of 23% margin
> > above the placarded Vne. So your margins for flutter, versus ultimate
> > strength are 1.23 vs 1.725 in JAR22 (unless I got the math wrong)
>
> It's perhaps mathematically true but your argument is wrong (if your
> conclusion is to say that there is more risk of flutter than
> overloading). You cannot compare pourcentages of load and speed !
>
> It takes less tenth of second at any moment to take the 2 or 3 g's that
> will exceed your (supposed) 72.5% load margin, whereas it will take
> several seconds to take the 60 or 65 km/h of margin in speed (supposing
> 23% margin), or depending of the dive angle you might never get over the
> speed margin...
>
> And although it may be true that some parts of the wing (e.w. center
> section) has more stress margin due to deflection limit, it does *not*
> guarantee you that all the parts of the wing has the same extra margin:
> in the Nimbus 4 accident the central wing did not break, but the outer
> wing did, with fatal consequences :-(
>
>
> --
> Denis
>
> R. Parce que ça rompt le cours normal de la conversation !!!
> Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Don Johnstone

April 5th 04, 10:45 PM

OK taking your point about the Nimbus 4. Exactly why
did the wing break, because of pilot induced overstress
or because of overstress caused by flutter? What did
the crew say in evidence?

At 17:48 05 April 2004, Denis wrote:
>Bruce Greeff wrote:
>
>> As I understand it the modern thin section wings are
>>flexible enough
>> that the load limit is imposed by control freedom
>>limitation, and the
>> wing must withstand 1.725 times this load in test.
>>Flutter is the
>> subject of speed limitation which give speeds and
>>margins that the
>> designer/manufacturer must demonstrate flying to.
>>The regulations imply
>> that the glider must be demonstrated safe at a minimum
>>of 23% margin
>> above the placarded Vne. So your margins for flutter,
>>versus ultimate
>> strength are 1.23 vs 1.725 in JAR22 (unless I got
>>the math wrong)
>
>It's perhaps mathematically true but your argument
>is wrong (if your
>conclusion is to say that there is more risk of flutter
>than
>overloading). You cannot compare pourcentages of load
>and speed !
>
>It takes less tenth of second at any moment to take
>the 2 or 3 g's that
>will exceed your (supposed) 72.5% load margin, whereas
>it will take
>several seconds to take the 60 or 65 km/h of margin
>in speed (supposing
>23% margin), or depending of the dive angle you might
>never get over the
>speed margin...
>
>And although it may be true that some parts of the
>wing (e.w. center
>section) has more stress margin due to deflection limit,
>it does *not*
>guarantee you that all the parts of the wing has the
>same extra margin:
>in the Nimbus 4 accident the central wing did not break,
>but the outer
>wing did, with fatal consequences :-(
>
>
>--
>Denis
>
>R. Parce que ça rompt le cours normal de la conversation
>!!!
>Q. Pourquoi ne faut-il pas répondre au-dessus de la
>question ?
>

Denis

April 6th 04, 08:02 AM

Don Johnstone wrote:
> OK taking your point about the Nimbus 4. Exactly why
> did the wing break, because of pilot induced overstress
> or because of overstress caused by flutter? What did
> the crew say in evidence?

I have no information except the link that have been provided by Bill
earlier in this thread :
http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19310&key=1

The likliest cause of the outer wings failure seems to be pulling out of
the dive beyond extreme load, since the observed wing bending (45°)
correspond to that expected by the manufacturer for ultimate load limit

> NTSB Identification: LAX99MA251. The docket is stored on NTSB microfiche number DMS.
> 14 CFR Part 91: General Aviation
> Accident occurred Tuesday, July 13, 1999 in MINDEN, NV
> Probable Cause Approval Date: 9/30/02
> Aircraft: Schempp-Hirth NIMBUS 4DM, registration: N807BB
> Injuries: 2 Fatal.
>
> The glider broke up in flight during the recovery phase after a departure from controlled flight while maneuvering in thermal lift conditions. Airborne witnesses in other gliders who saw the beginning of the sequence said the glider was in a tight turn, as if climbing in a thermal, when it entered a spiral or a spin. With a 45-degree nose down attitude, the speed quickly built up as the glider completed two full rotations. The rotation then stopped, the flight stabilized on a northeasterly heading, and the nose pitched further down to a near vertical attitude (this is consistent with the spin recovery technique specified in the Flight Manual). The glider was observed to be pulling out of the dive, with the wings bending upward and the wing tips coning higher, when the outboard wing tip panels departed from the glider, the wings disintegrated, and the fuselage dove into the ground. Several witnesses estimated the wing deflection reached 45-degrees or more before the wings f
ailed. Examination of the wreckage disclosed that the left and right outboard wing sections failed symmetrically at 2 locations.
>
> The glider is a high performance sailplane with an 87-foot wingspan and is constructed from fiber reinforced plastic (FRP) composites. The manufacturing process uses a hand lay-up of carbon and glass materials with applied epoxy resins. The glider is certificated in the normal category in Germany under the provisions of the European Joint Airworthiness Regulations.
>
> Pilots with experience in the Nimbus 4 series gliders stated that the glider was particularly sensitive to over input of the rudder control during turns due to the 87-foot wingspan, with a resulting tendency for unwanted rolling moments. The manufacturer reported that to avoid undesired rolling moments once the bank is established the ailerons must be deflected against the bank.
>
> Maneuvering speed (Va) is 180 km/h (97 kts) and the AFM notes that full control surface deflections may only be applied at this speed and below. Never exceed speed (Vne) is 285 km/h (154 kts) and control deflections are limited to one third of the full range at this speed and a bold print cautionary note reads, "Avoid especially sudden elevator control movements." The manufacturer reported that design dive speed (Vd) is 324 km/h (175 kts). The manufacturer also said that, assuming a 45-degree nose down attitude with airbrakes closed, the glider would accelerate from stall speed to Vne in 8.6 seconds, with an additional 1.8 seconds to accelerate from Vne to Vd. While no specific information on stick force per 'g' was available, certification flight test data showed that the elevator control stick forces were relatively light, with only 11.9 pounds of force (nose down) required to hold a fixed attitude at Vne versus the neutral stick force trim speed of 135 km/h (72.89 kts).

>
> Detailed examination of witness marks and other evidence in the wreckage established that the pilot extended the airbrakes at some point in an attempt to slow the glider during the descent prior to the break-up. Concerning limitations on use of the airbrakes, the AFM notes that while airbrakes may be extended up to Vne they should only be used at such high speeds in emergency or if the maximum permitted speeds are being exceeded inadvertently. The manufacturer noted that the airbrakes function like spoilers and have the effect of shifting the aerodynamic loads outboard on the wings. The control linkages for the airbrakes and flaps are interconnected so that when full airbrake deployment is achieved, the flaps are extended to their full down limit.
>
> The maximum maneuvering load factor limits (in units of gravity or g's) change with variations in glider speed and flap/airbrake configuration. From a "flaps up" configuration at Va to the condition of airbrakes and flaps extended at Vne, the maximum maneuvering load factor limits decrease from positive 5.3 to a positive 3.5.
>
> The pertinent certification regulations require a minimum safety margin of 1.5 above the design limit load, which is defined as ultimate load. Review of the manufacturers data on safety margins in the wing spar disclosed that in the area of the primary wing failures, the structural design safety margin ranged between 1.55 and 1.75.
>
> The manufacturer supplied data of the wing deflections under various load and aerodynamic conditions. At the design load limit (3.5g's) with airbrakes extended and at Vd, the wings were deflected to a 31-degree angle. At the ultimate load limit, the deflection was 46.5-degrees, similar to the witness observations of the wing deflection just prior to the break up.
>
> An extensive series of scientific investigations were undertaken to establish: 1) if the structure as built conformed with the approved production drawings; 2) that the wing design met pertinent certification standards for strength safety margins; and 3) whether or not the failures occurred in overload beyond the ultimate load limits of the structure. While production control type discrepancies were found in the structure that differed from drawing specifications, none contributed to the failures. The testing established that the structure as built exceeded the minimum safety margin requirements. All the wing failures were overload in character and occurred at loadings well above the ultimate design load limits.
>
> The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
> The pilot's excessive use of the elevator control during recovery from an inadvertently entered spin and/or spiral dive during which the glider exceeded the maximum permissible speed, which resulted in the overload failure of the wings at loadings beyond the structure's ultimate design loads.
>
> Full narrative available
>
> Index for Jul1999 | Index of months

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Denis

April 6th 04, 08:13 AM

K.P. Termaat wrote:

> Started this thread (Avoiding Vne) some weeks ago with a kind invitation to
> respond to the idea of pulling the airbrakes while still in the rotating
> mode of a spin. The idea behind it is when rotation has been stopped with
> the glider at a pitch angle of say 60° or more this will be at a lower speed
> then when the airbrakes stay closed all the time. Possibly a build up of
> speed to over Vne can then be avoided after that. Of course airbrakes should
> be closed again in the following pull up manouvre.
> Any comments?

well... after 114 answers, I think you have good specimens of the very
diverse opinions that have been expressed so far ;-)

in short, mine is : apply full airbrakes just after applying the initial
spin recovery control inputs, and keep them out during dive (gentle)
pull out...

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

K.P. Termaat

April 6th 04, 10:22 AM

Hi Denis,

If I understand you well you will wait with pulling the airbrakes until the
glider has stopped its rotation and then carefully put some back pressure on
the stick. I was considering the idea of pulling the brakes with the glider
still in its rotation mode in order to keep forward speed as low as possible
at any time. However this may frustrate the spin recovery action; I just
don't know. What's your idea about this. Of course handbooks do not say
anything about this.
B.t.w. my provisional handbook for the Ventus-2cxT forbids spin exercises.
My idea is to avoid spins with this glider any time anyway; however I will
try to get some feeling about the glider's behaviour close to entering this
"acrobatic" flying mode.

Karel, NL

"Denis" > schreef in bericht
...
> K.P. Termaat wrote:
>
> > Started this thread (Avoiding Vne) some weeks ago with a kind invitation
to
> > respond to the idea of pulling the airbrakes while still in the rotating
> > mode of a spin. The idea behind it is when rotation has been stopped
with
> > the glider at a pitch angle of say 60° or more this will be at a lower
speed
> > then when the airbrakes stay closed all the time. Possibly a build up of
> > speed to over Vne can then be avoided after that. Of course airbrakes
should
> > be closed again in the following pull up manouvre.
> > Any comments?
>
> well... after 114 answers, I think you have good specimens of the very
> diverse opinions that have been expressed so far ;-)
>
> in short, mine is : apply full airbrakes just after applying the initial
> spin recovery control inputs, and keep them out during dive (gentle)
> pull out...
>
> --
> Denis
>
> R. Parce que ça rompt le cours normal de la conversation !!!
> Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

Don Johnstone

April 6th 04, 11:04 AM

At the risk of flogging this subject to death it should
be remembered that this thread was started with the
question on how to avoid reaching excessive speeds.
While extending airbrakes and/or dropping the wheel
may help the only really effective way is to use gravity
to slow down the glider as opposed to accelerating
it. The priority is to prevent reaching excessive speeds,
not necessarily what to do if they are reached, when
options may be very limited.
Those who have said that pulling excessive G beyond
the design limits can cause failure are right.
Those who have said that exceeding VNE and getting
into the flutter envelope can cause failure are right.
The title of this thread is 'Avoiding VNE' and what
I have said has always been directed at this.
It is clear that at very high speeds in excess of VNE
you are in danger of flutter and catostrophic overstress
and the Nimbus accident shows that. The accident report
only gives a probable cause, did the wing fail because
of the excess G or did flutter cause the break up,
I suspect no one really knows.
What we do know is that the higher the airspeed the
more G can be applied. Bearing in mind that we are
trying to avoid VNE, because of flutter and the danger
of excessive G forces the sooner the speed can be reduced
the better. The lower the airspeed when full control
is applied the less the load which can be applied.
(The report of the Nimbus accident seems to indicate
that the airspeed was very high indeed) I advocated
using the elevator to prevent further acceleration
even if this applied a G load in excess of the placarded
limit to reduce airspeed or at least prevent further
acceleration.
What we do know is that flutter can and has caused
the breakup of aircraft (and as I have said before,
bridges). Flutter is the result of high speed.
We also know that the higher the airspeed the greater
the load that can be applied and I accept that at speeds
in excess of VNE these loads can exceed the ultimate
design load. Conversely at lower airspeeds it may not
be possible to apply a loading above the placarded
limit. Ergo, pulling hard before the speed gets excessive
is better than allowing the speed to build and then
trying to do something about it, especially when the
situation could be complicated by the onset of flutter
with total loss of control (see comments made earlier
by manufacturer). It may be possible to exceed the
design G limit of the airframe at VNE but it will be
almost impossible at 60kts. I re-stress my suggestion
was directed at avoiding high speeds, given the choice
of having to apply excessive load or exceeding VNE
I would choose the former. The risks involved in allowing
the airspeed to increase are far greater than the risks
involved in controlling the airspeed by a smaller excessive
loading at the lower speed.

It really is a case of the lesser of two evils, best
to avoid the situation in the first place.

At 07:12 06 April 2004, Denis wrote:
>Don Johnstone wrote:
>> OK taking your point about the Nimbus 4. Exactly why
>> did the wing break, because of pilot induced overstress
>> or because of overstress caused by flutter? What did
>> the crew say in evidence?
>
>I have no information except the link that have been
>provided by Bill
>earlier in this thread :
>http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19310&key=1
>
>The likliest cause of the outer wings failure seems
>to be pulling out of
>the dive beyond extreme load, since the observed wing
>bending (45°)
>correspond to that expected by the manufacturer for
>ultimate load limit
>
>> NTSB Identification: LAX99MA251. The docket is stored
>>on NTSB microfiche number DMS.
>> 14 CFR Part 91: General Aviation
>> Accident occurred Tuesday, July 13, 1999 in MINDEN,
>>NV
>> Probable Cause Approval Date: 9/30/02
>> Aircraft: Schempp-Hirth NIMBUS 4DM, registration:
>>N807BB
>> Injuries: 2 Fatal.
>>
>> The glider broke up in flight during the recovery
>>phase after a departure from controlled flight while
maneuvering in thermal lift conditions. Airborne witnesses
in other gliders who saw the beginning of the sequence
said the glider was in a tight turn, as if climbing
in a thermal, when it entered a spiral or a spin. With
a 45-degree nose down attitude, the speed quickly built
up as the glider completed two full rotations. The
rotation then stopped, the flight stabilized on a northeasterly
heading, and the nose pitched further down to a near
vertical attitude (this is consistent with the spin
recovery technique specified in the Flight Manual).
The glider was observed to be pulling out of the dive,
with the wings bending upward and the wing tips coning
higher, when the outboard wing tip panels departed
from the glider, the wings disintegrated, and the fuselage
dove into the ground. Several witnesses estimated the
wing deflection reached 45-degrees or more before the
wings f
>ailed. Examination of the wreckage disclosed that the
>left and right outboard wing sections failed symmetrically
at 2 locations.
>>
>> The glider is a high performance sailplane with an
>>87-foot wingspan and is constructed from fiber reinforced
plastic (FRP) composites. The manufacturing process
uses a hand lay-up of carbon and glass materials with
applied epoxy resins. The glider is certificated in
the normal category in Germany under the provisions
of the European Joint Airworthiness Regulations.
>>
>> Pilots with experience in the Nimbus 4 series gliders
>>stated that the glider was particularly sensitive to
over input of the rudder control during turns due to
the 87-foot wingspan, with a resulting tendency for
unwanted rolling moments. The manufacturer reported
that to avoid undesired rolling moments once the bank
is established the ailerons must be deflected against
the bank.
>>
>> Maneuvering speed (Va) is 180 km/h (97 kts) and the
>>AFM notes that full control surface deflections may
only be applied at this speed and below. Never exceed
speed (Vne) is 285 km/h (154 kts) and control deflections
are limited to one third of the full range at this
speed and a bold print cautionary note reads, 'Avoid
especially sudden elevator control movements.' The
manufacturer reported that design dive speed (Vd) is
324 km/h (175 kts). The manufacturer also said that,
assuming a 45-degree nose down attitude with airbrakes
closed, the glider would accelerate from stall speed
to Vne in 8.6 seconds, with an additional 1.8 seconds
to accelerate from Vne to Vd. While no specific information
on stick force per 'g' was available, certification
flight test data showed that the elevator control stick
forces were relatively light, with only 11.9 pounds
of force (nose down) required to hold a fixed attitude
at Vne versus the neutral stick force trim speed of
135 km/h (72.89 kts).
>
>>
>> Detailed examination of witness marks and other evidence
>>in the wreckage established that the pilot extended
the airbrakes at some point in an attempt to slow the
glider during the descent prior to the break-up. Concerning
limitations on use of the airbrakes, the AFM notes
that while airbrakes may be extended up to Vne they
should only be used at such high speeds in emergency
or if the maximum permitted speeds are being exceeded
inadvertently. The manufacturer noted that the airbrakes
function like spoilers and have the effect of shifting
the aerodynamic loads outboard on the wings. The control
linkages for the airbrakes and flaps are interconnected
so that when full airbrake deployment is achieved,
the flaps are extended to their full down limit.
>>
>> The maximum maneuvering load factor limits (in units
>>of gravity or g's) change with variations in glider
speed and flap/airbrake configuration. From a 'flaps
up' configuration at Va to the condition of airbrakes
and flaps extended at Vne, the maximum maneuvering
load factor limits decrease from positive 5.3 to a
positive 3.5.
>>
>> The pertinent certification regulations require a
>>minimum safety margin of 1.5 above the design limit
load, which is defined as ultimate load. Review of
the manufacturers data on safety margins in the wing
spar disclosed that in the area of the primary wing
failures, the structural design safety margin ranged
between 1.55 and 1.75.
>>
>> The manufacturer supplied data of the wing deflections
>>under various load and aerodynamic conditions. At the
design load limit (3.5g's) with airbrakes extended
and at Vd, the wings were deflected to a 31-degree
angle. At the ultimate load limit, the deflection was
46.5-degrees, similar to the witness observations of
the wing deflection just prior to the break up.
>>
>> An extensive series of scientific investigations were
>>undertaken to establish: 1) if the structure as built
conformed with the approved production drawings; 2)
that the wing design met pertinent certification standards
for strength safety margins; and 3) whether or not
the failures occurred in overload beyond the ultimate
load limits of the structure. While production control
type discrepancies were found in the structure that
differed from drawing specifications, none contributed
to the failures. The testing established that the structure
as built exceeded the minimum safety margin requirements.
All the wing failures were overload in character and
occurred at loadings well above the ultimate design
load limits.
>>
>> The National Transportation Safety Board determines
>>the probable cause(s) of this accident as follows:
>> The pilot's excessive use of the elevator control
>>during recovery from an inadvertently entered spin
and/or spiral dive during which the glider exceeded
the maximum permissible speed, which resulted in the
overload failure of the wings at loadings beyond the
structure's ultimate design loads.
>>
>> Full narrative available
>>
>> Index for Jul1999 | Index of months
>
>
>
>
>
>--
>Denis
>
>R. Parce que ça rompt le cours normal de la conversation
>!!!
>Q. Pourquoi ne faut-il pas répondre au-dessus de la
>question ?
>

Denis

April 6th 04, 11:54 AM

K.P. Termaat wrote:

> Hi Denis,
>
> If I understand you well you will wait with pulling the airbrakes until the
> glider has stopped its rotation and then carefully put some back pressure on
> the stick. I was considering the idea of pulling the brakes with the glider
> still in its rotation mode in order to keep forward speed as low as possible
> at any time. However this may frustrate the spin recovery action; I just
> don't know. What's your idea about this. Of course handbooks do not say
> anything about this.

the ASH 26 handbook does say "spinning is not noticeably affected by
extending the airbrakes paddles, but it will increase the height loss
when pulling out, and is therefore less advisable"

I suppose the last sentence refers to loss of total energy (i.e. after
recovery you will re-gain more height if you made it without airbrakes
than with). It is not true of height loss down to lowest point (you will
loose less height with airbrakes because the diving speed is diminished
and the curving radius is reduced by the square of the speed -- even
with 3.5 G allowed w/ airbrakes instead of 4 G w/o the height loss
should be lesser with airbrakes out --

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

iPilot

April 6th 04, 04:15 PM

Yes, but we still don't know, whether there was any speed margin left. It seems very much that the
major factor in destroying the craft was fear of exceeding Vne and consequently pulling up too hard.
But nobody knows now.

One interesting thing is written there about airbrakes:

"Detailed examination of witness marks and other evidence in the wreckage established that the pilot
extended the airbrakes at some point in an attempt to slow the glider during the descent prior to
the break-up. Concerning limitations on use of the airbrakes, the AFM notes that while airbrakes may
be extended up to Vne they should only be used at such high speeds in emergency or if the maximum
permitted speeds are being exceeded inadvertently. The manufacturer noted that the airbrakes
function like spoilers and have the effect of shifting the aerodynamic loads outboard on the wings.
The control linkages for the airbrakes and flaps are interconnected so that when full airbrake
deployment is achieved, the flaps are extended to their full down limit."

Outboard is where the wing broke

"Denis" > wrote in message
...
> Don Johnstone wrote:
> > OK taking your point about the Nimbus 4. Exactly why
> > did the wing break, because of pilot induced overstress
> > or because of overstress caused by flutter? What did
> > the crew say in evidence?
>
> I have no information except the link that have been provided by Bill
> earlier in this thread :
> http://www.ntsb.gov/NTSB/brief.asp?ev_id=20001212X19310&key=1
>
> The likliest cause of the outer wings failure seems to be pulling out of
> the dive beyond extreme load, since the observed wing bending (45°)
> correspond to that expected by the manufacturer for ultimate load limit
>

ADP

April 6th 04, 05:26 PM

At the risk of reviving a flogged horse, does anyone find this part of the
analysis strange:

"The control linkages for the airbrakes and flaps are interconnected so that
when full airbrake
deployment is achieved, the flaps are extended to their full down limit."

What do you think the extension of full flaps at hight speed does to the
load distribution and the strength of the wing structure?

Allan

D.A.L

April 6th 04, 06:28 PM

> I believe that with the airbrakes open your safe positive
> G-limit reduces to +2.5G. This is because you are forcing
> most of the lift to be produced near the tip and thereby
> increasing the wing bending moment at the root, and
> there is also a hell of a shear force produced. God
> knows what happens if you open them suddenly above
> Va while pulling 3.5g but i suspect it would not be
> pretty. (I also suspect that it may be this that caused
> several big gliders to have wings come off in spin
> recovery)

I once saw a discus, 'A' I beleive, due a high speed low pass and half
way through his pull up, which seemed to be agressive, deploy his
airbreak/spoiler (?). I thought for sure his wings from the airbreaks
out were going to snap off as they had a significant greater angle of
'bend' than the rest of the wing. I don't know why, but I know what I
saw.

Don

Eric Greenwell

April 6th 04, 09:29 PM

ADP wrote:

> At the risk of reviving a flogged horse, does anyone find this part of the
> analysis strange:
>
> "The control linkages for the airbrakes and flaps are interconnected so that
> when full airbrake
> deployment is achieved, the flaps are extended to their full down limit."
>
> What do you think the extension of full flaps at hight speed does to the
> load distribution and the strength of the wing structure?

If the ailerons follow the flaps, this would cause the G loading to
increase (higher lift configuration), while shifting the load towards
the tips (not instantaneously, but very soon thereafter) because the
spoiler effect.

If the ailerons don't follow the flaps, the G loading would increase but
not as much, and the load may or may not be shifted to the tips, because
the inner section would have the higher lift configuration.

I don't think the strength of the structure would be changed by the flap
deflection.
--
-----
change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Denis

April 6th 04, 11:15 PM

Todd Pattist wrote:

> I don't think you can, but I admit I haven't gotten out my
> Matlab and done the equations. Anyone else want to do it?

Depends on what you bet ;-)

--
Denis

R. Parce que ça rompt le cours normal de la conversation !!!
Q. Pourquoi ne faut-il pas répondre au-dessus de la question ?

F.L. Whiteley

April 7th 04, 07:42 PM

"Andy Blackburn" > wrote in message
...
<snip>
> I've heard of several cases of control surface flutter
> in sailplanes (often older ones with looser control
> circuits - and Grobs with poor mass balancing). I've
> not heard of sailplanes fluttered apart in flight (though
> this isn't to say it has never happened). Maybe it's
> because everyone who has been forced to make a choice
> pulls the wings off first.
>
> Something to think about...
>
IIRC, Yugo built Open Cirrus at Inkpen UK. Pilot bailed successfully low
while ascending (believe it was Irvin EB80 parachute) following a beatup as
the glider fluttered to pieces (horizontal stab?). Think this was the
incident that resulted in AD for the lowering the Vne on all the Yugo built
Open Cirruses to something like 95 knots. Don't recall it ever being
modified. There was also an AD to fit the original Open Cirruses with a
rudder damper to prevent flutter. Wings were once tested to 11g's I've
heard.

Frank Whiteley

F.L. Whiteley

April 7th 04, 07:56 PM

That's what I recall causing the dive in values. The quick fix was to
tighten the speed envelopes I thought. But that was 1999.

This is now.

One of our CFI-G/Tow pilots starts his Navy BPT next month. He said all
T-34B's(? or civilian use?) were grounded a couple of weeks ago and there
will be spar mods required. Don't know how the A differs from the B, but
the Navy trainers are still flying for now. He's looking forward to flying
with a turbo. He thinks his winch launching experiences have him ready for
carrier ops:^)

Frank

"Mark James Boyd" > wrote in message
news:406b0c5e$1@darkstar...
> I'd recommend reading about the asymmetric loading arguments
> presented at:
>
> http://www.avweb.com/news/columns/182086-1.html
>
> The meat of the matter starts about halfway down
> the page. Essentially it says full aileron and full elevator
> when applied simultaneously create a much greater chance of wing
> failure at a lower airspeed than just applying either one independently.
>
> I'm not aware of how this may or may not apply to
> gliders. Perhaps some expert in wing construction
> can give most welcome educated opinion... :)
>
> F.L. Whiteley > wrote:
> >
> >"Mark James Boyd" > wrote in message
> >news:4064994c$1@darkstar...
> >> K.P. Termaat > wrote:
> >> >Yesterday evening I talked with a friend about avoiding excessive
speed
> >when
> >> >recovering from a spin in a modern low drag glider with the somewhat
> >larger
> >> >span.
> >>
> >> A lot has been written here about G loads. I recall that the
> >> T-34 (an aerobatic power plane I have a little time in
> >> which is sortof a tandem Beech 33) had some issues with wings
> >> coming off during aerobatics. The recorded G loads and mauevers
> >> indicated the aircraft wasn't flown outside of G limits.
> >>
> >> How did the wings separate? Some smarty folks said it was
> >> because the twisting G load that the wing could endure was
> >> much less than the static tested load. If the ailerons were
> >> deflected and the thing was in a steep spiral (as opposed
> >> to straight dive) there were twisting loads.
> >>
> >Thought I heard that inspections showed T-34 wings were suffering from
> >fatigue cracks. Kind of shot down some of the 'fighter dude' thrill
rides
> >(we have/had one in Colorado). We have a disassembled T-34 wrapped in
> >plastic in our hangar. I recall a conversation about the value dropping
by
> >about 50% when the crack problem was discovered.
> --
>
> ------------+
> Mark Boyd
> Avenal, California, USA