Nimbus 4 Accident [Archive]

Bert Willing

July 6th 05, 02:23 PM

I'd say that his analysis is questionable, at least.
It sounds like written by somebody who is astonished that a 26m ship might
handle in some situations differently than a 15m ship, and that if there is
any accident evolving of this, the designer of the ship should be
responsible (and not improper pilot reactions).

And to the subject of pulling the airbrakes at vne pull-ups: If the max
g-load at vne is lower with airbrakes extended than without, it's written in
the manual. In any case, coming out of a spiral dive / spin combo with such
a ship, you are pretty sure that you will come _at least_ close to vne
and/or max g-load. A pilot pulling the airbrakes _and_ pulling hard up in
such a situation hasn't thought about such a situation beforehand (not
good), or has no idea what he is playing with (also no good).
--
Bert Willing

ASW20 "TW"

"Bill" > a écrit dans le message de news:
. com...
>I posted the message below on the thread, "Nimbus 4DT accident 31 July
> 2000 in Spain." I am posting it again for better visibility.
>
> Stan Hall presented his analysis of the Nimbus-4DB accident in Minden,
> NV, 1999. Stan's analysis is scary, to say the least.
>
> The article, Probing for the Smoking Gun, was reprinted in the Soaring
> Association of Canada's free flight, 2/04. Go to the link below. Click
> on free flight on the side bar. Go to free flight back issues - 2004 -
> issue 2. Down load the PDF file.
>
> http://www.sac.ca/
>
> Bill Feldbaumer 09
>

John Sinclair

July 6th 05, 04:13 PM

I'd say Stan's analysis of this accident is right
on. He's the only one that has come up with a reasonable
sequence of events that could lead to the known results.
We hit a violent shear in the same area, the day before
this accident. It rolled our ASH-25 up on one wing.
If we hadn't taken immediate corrective action (aileron
& rudder against the roll) I could see us entering
a spiral dive. As we are learning, once the nose is
down in a big ship, you are headed for a moment of
truth.

JJ Sinclair

At 13:42 06 July 2005, Bert Willing wrote:
>I'd say that his analysis is questionable, at least.
>It sounds like written by somebody who is astonished
>that a 26m ship might
>handle in some situations differently than a 15m ship,
>and that if there is
>any accident evolving of this, the designer of the
>ship should be
>responsible (and not improper pilot reactions).
>
>And to the subject of pulling the airbrakes at vne
>pull-ups: If the max
>g-load at vne is lower with airbrakes extended than
>without, it's written in
>the manual. In any case, coming out of a spiral dive
>/ spin combo with such
>a ship, you are pretty sure that you will come _at
>least_ close to vne
>and/or max g-load. A pilot pulling the airbrakes _and_
>pulling hard up in
>such a situation hasn't thought about such a situation
>beforehand (not
>good), or has no idea what he is playing with (also
>no good).
>--
>Bert Willing
>
>ASW20 'TW'
>
>
>'Bill' a écrit dans le message de news:
. com...
>>I posted the message below on the thread, 'Nimbus 4DT
>>accident 31 July
>> 2000 in Spain.' I am posting it again for better visibility.
>>
>> Stan Hall presented his analysis of the Nimbus-4DB
>>accident in Minden,
>> NV, 1999. Stan's analysis is scary, to say the least.
>>
>> The article, Probing for the Smoking Gun, was reprinted
>>in the Soaring
>> Association of Canada's free flight, 2/04. Go to the
>>link below. Click
>> on free flight on the side bar. Go to free flight
>>back issues - 2004 -
>> issue 2. Down load the PDF file.
>>
>> http://www.sac.ca/
>>
>> Bill Feldbaumer 09
>>
>
>
>

John Galloway

July 6th 05, 04:24 PM

I wouldn't want to speculate about the sequence of
events in a specific accident but note the author's
comment:

'designers of new machines might consider the installation
of a jettisonable drogue chute in the tail as standard
equipment.'

IMHO this should not just be 'considered' - all new
high performance glider designs should have a well
engineered jettisonable tail chute or some other fuselage
sited speed limiting device. If they already had them
at least 3 lives we have discussed recently on RAS
would likely have been saved.

John Galloway

At 13:42 06 July 2005, Bert Willing wrote:
>I'd say that his analysis is questionable, at least.
>It sounds like written by somebody who is astonished
>that a 26m ship might
>handle in some situations differently than a 15m ship,
>and that if there is
>any accident evolving of this, the designer of the
>ship should be
>responsible (and not improper pilot reactions).
>
>And to the subject of pulling the airbrakes at vne
>pull-ups: If the max
>g-load at vne is lower with airbrakes extended than
>without, it's written in
>the manual. In any case, coming out of a spiral dive
>/ spin combo with such
>a ship, you are pretty sure that you will come _at
>least_ close to vne
>and/or max g-load. A pilot pulling the airbrakes _and_
>pulling hard up in
>such a situation hasn't thought about such a situation
>beforehand (not
>good), or has no idea what he is playing with (also
>no good).
>--
>Bert Willing
>
>ASW20 'TW'
>
>
>'Bill' a ï¿½crit dans le message de news:
. com...
>>I posted the message below on the thread, 'Nimbus 4DT
>>accident 31 July
>> 2000 in Spain.' I am posting it again for better visibility.
>>
>> Stan Hall presented his analysis of the Nimbus-4DB
>>accident in Minden,
>> NV, 1999. Stan's analysis is scary, to say the least.
>>
>> The article, Probing for the Smoking Gun, was reprinted
>>in the Soaring
>> Association of Canada's free flight, 2/04. Go to the
>>link below. Click
>> on free flight on the side bar. Go to free flight
>>back issues - 2004 -
>> issue 2. Down load the PDF file.
>>
>> http://www.sac.ca/
>>
>> Bill Feldbaumer 09
>>
>
>
>

Papa3

July 6th 05, 04:53 PM

Bert Willing wrote:
> It sounds like written by somebody who is astonished that a 26m ship might
> handle in some situations differently than a 15m ship, and that if there is
> any accident evolving of this, the designer of the ship should be
> responsible (and not improper pilot reactions).
>
> > Bert Willing
>
> ASW20 "TW"
>

Bert,

That's an odd comment. When someone like Stan Hall writes about
stability, control, and structures, I listen. Carefully.

I think the bottom line in his analysis is very clear. Open Class
performance comes with risks that need to be completely understood AND
there are flight regimes where the margin between recovery and disaster
is very, very thin.

Erik Mann
LS8-18 "P3"

Bert Willing

July 6th 05, 05:48 PM

Sorry, I don't care who he is, I care what he writes (and I read it
carefully).

He does make valuable points - a tail chute is not a stupid idea. His
comment on wing momentum is very good (and I don't think that people are
well aware enough of that), and I completely agree on the fact that if a
60:1 performance is breathtaking on a long glide, 60:1 performance in a
vertical dive coming out of a spin is life-taking.

What I disagree with is the underlying tune of the the disaster(s) being
designed into the ship :

"But I think one can legitimately ask if there was something inherent in the
design of the sailplane that led its occupants into a situation from which
there was no escape. My thesis is, there was."

Now if today somebody wants 60:1, he will have to go for 26m, and the
structure of these ships cannot be built otherwise - at leat not today. Even
the newest development, the Eta, will bite during the recovery from a spiral
dive as it has been shown (on purpose - those guys have some balls... and
parachutes). With such a ship, some situations are extremely dangerous
(situations which would be rather fun in 15m), and if you want to fly such a
ship, you better start to think first.

What I also think being pure speculations is the stiffness of the ailerons
due to flexing (and in this situation, you don't loose time fiddling with
ailerons anyway), and when and how the airbrakes have been deployed. There
is a chance that the pilot pulled the airbrakes before reaching vne and
pulled to hard, and there is a chance that he pulled them after having
exceeded vne and tried to pull up (and at a certain point beyond the v-n
diagramm, any glider will brake up) - we will never know at which speed and
at how many g's the wings came off. In this light, his comment

"What the AFM didn't say of course was, "if you exceed the maximum permitted
speed and open
the brakes be prepared to have the wings come off."

is plain stupid.

However, his last paragraph is very good.
--
Bert Willing

ASW20 "TW"

"Papa3" > a écrit dans le message de news:
om...
>
>
> Bert Willing wrote:
>> It sounds like written by somebody who is astonished that a 26m ship
>> might
>> handle in some situations differently than a 15m ship, and that if there
>> is
>> any accident evolving of this, the designer of the ship should be
>> responsible (and not improper pilot reactions).
>>
>> > Bert Willing
>>
>> ASW20 "TW"
>>
>
> Bert,
>
> That's an odd comment. When someone like Stan Hall writes about
> stability, control, and structures, I listen. Carefully.
>
> I think the bottom line in his analysis is very clear. Open Class
> performance comes with risks that need to be completely understood AND
> there are flight regimes where the margin between recovery and disaster
> is very, very thin.
>
> Erik Mann
> LS8-18 "P3"
>

Roy Bourgeois

July 6th 05, 08:06 PM

I read all of this stuff with interest since I've spent most of my soaring
career in long wing gliders (18 years in an 20m ASW-17 and 5 in a 24.5m
Nimbus 3). While I respect Stan and his extensive resume - he acknowledges
that he has no experience flying the open class ships. I have not found
that the long wing gliders are any more or less susceptible to spiral
dives, spins or unexpected acceleration as opposed to 15m ships. If
anything, they are more stable tend to telegraph the stall pretty early and
spin pretty slowly. The Nimbus does have a remarkably short span
stabilizer which when stalled can cause pitch down - but this is pretty
rare and easily recovered from. I also confess that I do not understand the
second hand comment about "extreme rudder sensitivity" (all open class
pilots wish it were so!). It should also be noted that most of these break
ups seem to happen in the 2 place ships (or 2 place with engine versions)
where the fuselage is hanging more weight on the same wing that is fitted
in the single place pure glider model. While single place N3s and 4s have
crashed, I don't think any have come apart in the air. This tells me the
problem is more complex than just wingspan.

What is clear is that opening the dive brakes at high loads and high wing
flexion is the last step before disaster. It suddenly increases the bending
moment outboard of the brakes and pushes the wing to failure. This was
found in both the Spain and Minden accidents. Stan spends a great deal of
time talking about what happens to aileron loads at high wing flexion. It
would be more interesting to study what happens to the dive brakes when the
wings are flexed at 45 degrees. Do they pop open because of forces on the
control rods (or forces on the caps caused by the flexion)? I don't think
that there is any real data or experimentation on this issue (and I'm not
volunteering to be the first!). When the factory does their stress load
testing - I do not believe that they actuate the dive brakes and the issue
cannot be studied by merely stressing a wing with a dive brake rod
unconnected to the fuselage. Also, there is no scientific study as to
what pilots do in sailplanes when surprised by high angle dives and high G
pull outs. My my own experience (32 years soaring , 2000 hrs, active
CFI-G) leads me to doubt that the pilot reaches for the dive brake while
plummeting down in a dive. More likely, he over stresses by a too dramatic
pull out during which an un commanded dive brake pop out occurs that
destroys the wing. Because of the location of the dive brakes on the
Nimbus 2 and 4 (they are quite far inboard) - this creates loads that would
not be found on a 15m ship pulling the same G load.

This is not to be critical of anybody - all of this is good for all of us.
So I thank Stan for his article.

Roy B.

tel: 508 798 8801
fax: 508 754 1943

F.L. Whiteley

July 6th 05, 08:41 PM

Roy Bourgeois wrote:

> I read all of this stuff with interest since I've spent most of my soaring
> career in long wing gliders (18 years in an 20m ASW-17 and 5 in a 24.5m
> Nimbus 3). While I respect Stan and his extensive resume - he acknowledges
> that he has no experience flying the open class ships. I have not found
> that the long wing gliders are any more or less susceptible to spiral
> dives, spins or unexpected acceleration as opposed to 15m ships. If
> anything, they are more stable tend to telegraph the stall pretty early
> and spin pretty slowly. The Nimbus does have a remarkably short span
> stabilizer which when stalled can cause pitch down - but this is pretty
> rare and easily recovered from. I also confess that I do not understand
> the second hand comment about "extreme rudder sensitivity" (all open class
> pilots wish it were so!). It should also be noted that most of these
> break ups seem to happen in the 2 place ships (or 2 place with engine
> versions) where the fuselage is hanging more weight on the same wing that
> is fitted
> in the single place pure glider model. While single place N3s and 4s have
> crashed, I don't think any have come apart in the air. This tells me the
> problem is more complex than just wingspan.
>
> What is clear is that opening the dive brakes at high loads and high wing
> flexion is the last step before disaster. It suddenly increases the
> bending
> moment outboard of the brakes and pushes the wing to failure. This was
> found in both the Spain and Minden accidents. Stan spends a great deal of
> time talking about what happens to aileron loads at high wing flexion. It
> would be more interesting to study what happens to the dive brakes when
> the wings are flexed at 45 degrees. Do they pop open because of forces on
> the
> control rods (or forces on the caps caused by the flexion)? I don't think
> that there is any real data or experimentation on this issue (and I'm not
> volunteering to be the first!). When the factory does their stress load
> testing - I do not believe that they actuate the dive brakes and the issue
> cannot be studied by merely stressing a wing with a dive brake rod
> unconnected to the fuselage. Also, there is no scientific study as to
> what pilots do in sailplanes when surprised by high angle dives and high G
> pull outs. My my own experience (32 years soaring , 2000 hrs, active
> CFI-G) leads me to doubt that the pilot reaches for the dive brake while
> plummeting down in a dive. More likely, he over stresses by a too
> dramatic pull out during which an un commanded dive brake pop out occurs
> that
> destroys the wing. Because of the location of the dive brakes on the
> Nimbus 2 and 4 (they are quite far inboard) - this creates loads that
> would not be found on a 15m ship pulling the same G load.
>
> This is not to be critical of anybody - all of this is good for all of us.
> So I thank Stan for his article.
>
> Roy B.
>
>
> tel: 508 798 8801
> fax: 508 754 1943
Wasn't the 4 breakup in the NZ world's a single place?

Frank

Roy Bourgeois

July 6th 05, 10:12 PM

Yes - But the pilot flew at high speed into the primary wave rotor. Not
the N4's fault I think.

Roy

Roy A. Bourgeois

Denis

July 7th 05, 09:57 PM

Papa3 a écrit :

> That's an odd comment. When someone like Stan Hall writes about
> stability, control, and structures, I listen. Carefully.

Even the best pilots may have accidents, and even a well known engineer
may write obvious stupidities. Obviously Stan Hall did make statements
that are completely false. He admits himself that he never flew an open
class glider, and that should have led him to be more prudent in his
analysis.

> I think the bottom line in his analysis is very clear. Open Class
> performance comes with risks that need to be completely understood AND
> there are flight regimes where the margin between recovery and disaster
> is very, very thin.

*That* is right. As it has already been discussed here, that the load
factor admissible with airbrakes out is much lower than without
airbrakes. This is obviously not easy when recovering from a spin not to
apply too much g-factor, especially above VNE or near the ground, but it
may save your live !

--
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

July 7th 05, 10:11 PM

Roy Bourgeois a écrit :
> My my own experience (32 years soaring , 2000 hrs, active
> CFI-G) leads me to doubt that the pilot reaches for the dive brake while
> plummeting down in a dive. More likely, he over stresses by a too dramatic
> pull out during which an un commanded dive brake pop out occurs that
> destroys the wing. Because of the location of the dive brakes on the
> Nimbus 2 and 4 (they are quite far inboard) - this creates loads that would
> not be found on a 15m ship pulling the same G load.

It is not unlikely that speed be very close to VNE increasing and in
such a case most pilots would extend the airbrakes if not all. That's
what airbrakes are for.

The wisest manouever in such case would be to extend the airbrakes as
soon as the glider is nose down, that would avoid the need for too much
g-load on recovery.

Note that in the case of an uncommanded pop out the airbrakes do *not*
increase the loads on the wing because they *decrease* the g-load - only
for the same g-load factor the wing root bending stress is increased.
Therefore, if there is a pop-up and the pilot does not pull more to get
the same g-load again, there should be no increased risk.

--
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 \(U.K.\).

July 8th 05, 12:05 AM

I have never flown a glider of more than about 20 metres span (ASW 17,
Jantar 2).

However, I am in the process of asking for other pilots' experience.

One such pilot's reply includes the following:

>From your experience of big Nimbi do you think there is merit in Stan's
>ideas?

"Only to the extent that you fly a big glider like a big glider, not like
a Spitfire. You adjust all your flying to the fact that you are flying
a big ship. For instance to adjusting your thermalling technique to
gradual bank angle changes rather than spirited use of controls to roll
in and out of thermals.

"I have always said about large span gliders, of whatever make, that you
regard them like flying a 747 Jumbo. Not like an agile 15m glider.

"For instance, in a very turbulent thermal such as what you often get
over power stations, I often am reluctant to put on over about 15
degrees of bank. Yes, fifteen degrees. I do not wish to be sucked in
to a "loss of control" situation like Ivans and Engen or the Levers.

>Which particular brand of Nimbus do you fly?

"4DM. I am entirely happy with it but I fly it like the big glider that
it is."

I would like to add the following:

On the question of use of air-brakes, it would appear that they were not
opened in the case of the Spanish accident.

In the case of the Minden accident, there was correspondence on Rec.
Aviation Soaring when the report was published by others who had experience
of the inadvertent deployment of the brakes at high speed in turbulence;
the suggestion was that deployment may have been uncommanded.

In addition, Dick Johnson posted that with the Minden accident there may
have been a problem with the oxygen system undiscoverable after the crash,
such as oxygen tanks filled with Nitrogen (not entirely unknown I am
afraid).

It is also notable that whereas there seems to have been no attempt to bale
out with the Minden accident, with the Spanish accident both pilots did bale
out and deploy there parachutes, but unfortunately one of them had his
canopy foul of the wreckage which brought him down with it.

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

>
> "Bill" > wrote in message
> oups.com...
>
> I posted the message below on the thread, "Nimbus 4DT accident 31 July
> 2000 in Spain." I am posting it again for better visibility.
>
> Stan Hall presented his analysis of the Nimbus-4DB accident in Minden,
> NV, 1999. Stan's analysis is scary, to say the least.
>
> The article, Probing for the Smoking Gun, was reprinted in the Soaring
> Association of Canada's free flight, 2/04. Go to the link below. Click
> on free flight on the side bar. Go to free flight back issues - 2004 -
> issue 2. Down load the PDF file.
>
> http://www.sac.ca/
>
> Bill Feldbaumer 09
>

Udo Rumpf

July 8th 05, 01:00 AM

>
> In the case of the Minden accident, there was correspondence on Rec.
> Aviation Soaring when the report was published by others who had
> experience
> of the inadvertent deployment of the brakes at high speed in turbulence;
> the suggestion was that deployment may have been uncommanded.

I had an unintentional airbrake opening on my ASW24.
I asked other ASW 24 owners on our Yahoo group if anybody experienced the
same thing. Apparently I was the only one, so far.
Very scary indeed. I installed a lock to prevent it from happening again.
The flight was through many vertical gust for many miles.
On one very powerful one it let go.
Regards
Udo

Don Johnstone

July 8th 05, 10:23 AM

I think we have to accept that there are occasions
when the finding of an accident report should be 'I
don't know but........'
In the case of the Nimbus 4 accident(s) there are so
many factors which 'may' have occurred that a definitive
conclusion is almost impossible, the best that anyone
can do is speculate, and this applies to most glider
accidents where there are no living witnesses. It is
very easy to attribute the cause to human factors and
in many cases this may be true but there is always
the possibility that there is an unknown factor. What
I have taken from these reports is that it would appear
that there is a point at which a situation becomes
irrecoverable and this point maybe reached quicker
in big wing gliders thatn in small ones and the response
must be to act to prevent the situation ever arising.
To me this means that care should be taken to never
spin or enter a spiral dive which may mean smaller
bank angles and higher airspeed in turbulent conditions
even if this means that some performance is lost.
There are plenty of examples of problems with aircraft
getting into irrecoverable situations, The DH Chipmunk
was just one such example. Modern aircraft, designed
for performance at the expense of handling such as
the SEPECAT Jaguar are know to be almost irrecoverable
if they depart from flight. In the case of the Jaguar
this was discovered during testing and the pilot had
the option of departing the aircraft, survived and
was able to tell the story. While not wishing to digress
the discussion too much we have a similar situation
involving the Puchaz where there have been several
fatal spin ins. It has been found in most cases that
the pilot must have mishandled the controls and this
may indeed be the case however this has to be speculative.
It is not beyond the realms of possibility that there
are some loading conditions and other circumstances
which make recovery from the spin impossible, we cannot
know for certain as there are no living witnesses to
these events. While this may be thought unlikely the
DH Chipmunk is an example of this and several pilots
died before the true problem was realised and anti
spin strakes were added. Test flying can never duplicate
every loading condition or minor difference in construction
and I believe it is very dangerous to assume, that
in the absence of any other cause, the pilot must have
been at fault.
Perhaps the lesson to be learned from all this is that
we know less that we think we do and 'exploring the
envelope' can bring us closer to disaster. It is a
matter of personal choice as to whether we accept this
risk.
In this context Stans assessment has cogent arguments
but must be speculative, we simply will never know.
Not knowing is propbably the most difficult thing that
we as human beings have to accept.

DAJ ASW17 401
At 00:00 08 July 2005, W.J. \bill\ Dean \u.K.\. wrote:
>I have never flown a glider of more than about 20 metres
>span (ASW 17,
>Jantar 2).
>
>However, I am in the process of asking for other pilots'
>experience.
>
>One such pilot's reply includes the following:
>
>>From your experience of big Nimbi do you think there
>>is merit in Stan's
>>ideas?
>
>'Only to the extent that you fly a big glider like
>a big glider, not like
>a Spitfire. You adjust all your flying to the fact
>that you are flying
>a big ship. For instance to adjusting your thermalling
>technique to
>gradual bank angle changes rather than spirited use
>of controls to roll
>in and out of thermals.
>
>'I have always said about large span gliders, of whatever
>make, that you
>regard them like flying a 747 Jumbo. Not like an agile
>15m glider.
>
>'For instance, in a very turbulent thermal such as
>what you often get
>over power stations, I often am reluctant to put on
>over about 15
>degrees of bank. Yes, fifteen degrees. I do not wish
>to be sucked in
>to a 'loss of control' situation like Ivans and Engen
>or the Levers.
>
>>Which particular brand of Nimbus do you fly?
>
>'4DM. I am entirely happy with it but I fly it like
>the big glider that
>it is.'
>
>I would like to add the following:
>
>On the question of use of air-brakes, it would appear
>that they were not
>opened in the case of the Spanish accident.
>
>In the case of the Minden accident, there was correspondence
>on Rec.
>Aviation Soaring when the report was published by others
>who had experience
>of the inadvertent deployment of the brakes at high
>speed in turbulence;
>the suggestion was that deployment may have been uncommanded.
>
>In addition, Dick Johnson posted that with the Minden
>accident there may
>have been a problem with the oxygen system undiscoverable
>after the crash,
>such as oxygen tanks filled with Nitrogen (not entirely
>unknown I am
>afraid).
>
>It is also notable that whereas there seems to have
>been no attempt to bale
>out with the Minden accident, with the Spanish accident
>both pilots did bale
>out and deploy there parachutes, but unfortunately
>one of them had his
>canopy foul of the wreckage which brought him down
>with it.
>
>W.J. (Bill) Dean (U.K.).
>Remove 'ic' to reply.
>
>>
>> 'Bill' wrote in message
>> oups.com...
>>
>> I posted the message below on the thread, 'Nimbus
>>4DT accident 31 July
>> 2000 in Spain.' I am posting it again for better
>>visibility.
>>
>> Stan Hall presented his analysis of the Nimbus-4DB
>>accident in Minden,
>> NV, 1999. Stan's analysis is scary, to say the least.
>>
>> The article, Probing for the Smoking Gun, was reprinted
>>in the Soaring
>> Association of Canada's free flight, 2/04. Go to
>>the link below. Click
>> on free flight on the side bar. Go to free flight
>>back issues - 2004 -
>> issue 2. Down load the PDF file.
>>
>> http://www.sac.ca/
>>
>> Bill Feldbaumer 09
>>
>
>
>
>
>
>
>
>

Bob Kuykendall

July 8th 05, 06:02 PM

Earlier, Bill wrote:

> ...Stan Hall presented his analysis
> of the Nimbus-4DB accident in Minden,
> NV, 1999...

One aspect of Hall's report with which I will take issue is what is
meant by a "45-degree bend" in the wing. The report shows a diagram
that depicts a 45-degree bend as the wing bend at which the pilot must
looks upwards 45 degrees from the lateral axis to see the wingtip.

I don't doubt that that might be what witnesses reported seeing. What I
do doubt is whether that is what the factory meant when they said that
under static test their wing deflected about 45 degrees (46.5, to be
exact) at 8g.

When I was doing deflection calculations for the wing spar in my HP-24
project, it seemed that the most useful measures of deflection were the
angular deflection at any point on the wing, and ultimately the total
accumulated angular deflection at the wingtip.

This figure compares 45-degree bends as defined by Stan Hall and by me:

http://www.hpaircraft.com/misc/nimbus_bend.GIF

I'm not privy to what definition of deflection the Schempp-Hirth
factory used in saying that their Nimbus wing would bend 46.5 degrees
at 8g. However, if their definition is similar to mine, and what
witnesses saw matched Stan's definition, it would mean that the
aircraft was seen at a loading substantially greater than 8g.

Also, I will submit that witnesses often over-report wing bending, and
that photos often seem to exaggerate it. What happens is that the
witness or camera viewpoint is rarely very close to the aircraft
longitudinal axis, and the oblique angle of the view tends to
"compress" the wings laterally, exaggerating the dihedral and wing
bend.

Thanks, and best regards to all

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

Derek Copeland

July 9th 05, 06:50 PM

I have not flown a Nimbus 4D, but have several hundred hours experience in
its' early predecessor the Nimbus 2.

A couple of points that might be relevant to this accident:

1) With flapped gliders there is usually a positive flap limiting speed,
often way below Vne. If you are thermalling you are likely to be in a
positive flap setting, so if a loss of control occurs that leads to a spiral
dive, it is very easy to exceed the flap limiting speed and risk twisting
the wings off.

2) With large span gliders, opening the airbrakes causes the wingtips to
bend up. We fitted a second paddle to our Nimbus 2 airbrakes and I did the
test flight in which I was supposed to fly up to Vne (135 knots) with the
brakes extended. By 95 knots the wings were bending up so much that I
started to fear for the structure and didn't go any faster! I resolved that
should I ever lose control of the speed, I would slow it down by pulling g
rather than opening the airbrakes. It also had a tail-chute that could be
deployed in extremis.

I can only recommend that the first action in any loss of control situation
should be to select neutral or negative flap, and then sort things out.

Derek Copeland

Denis

July 10th 05, 10:29 PM

Derek Copeland a écrit :

> 2) With large span gliders, opening the airbrakes causes the wingtips to
> bend up. We fitted a second paddle to our Nimbus 2 airbrakes and I did the
> test flight in which I was supposed to fly up to Vne (135 knots) with the
> brakes extended. By 95 knots the wings were bending up so much that I
> started to fear for the structure and didn't go any faster! I resolved that
> should I ever lose control of the speed, I would slow it down by pulling g
> rather than opening the airbrakes.

I don't understand your choice ! if there is a risk at high speeds, the
best choice to avoid it is to avoid these speeds, and that's what the
airbrakes are for, aren't it ? Pulling g's after loosing control is the
best way to break any aircraft...

--
Denis

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

[email protected]

July 10th 05, 10:44 PM

Denis a Nimbus 4 does not have airbrakes. It has spoilers. These are
two different animals alltogether

Bob Kuykendall

July 11th 05, 01:06 AM

Earlier, wrote:

> Denis a Nimbus 4 does not have airbrakes. It has spoilers. These are
> two different animals alltogether

I'm not one to be a sticker about such things, but I generally observe
this system: If the boards hinge out of the wing surface like on a
Schweizer, I call them spoilers. If they slide out of slots in the wing
like on most European ships, I call them airbrakes.

Anyhow, the factory calls them airbrakes, specifically "Schempp-Hirth
type airbrakes." From the Schempp-Hirth Web site:

> The wing (six pices for easier rigging)
> has full span camber-changing flaps and
> double-panel Schempp-Hirth type airbrakes
> on the upper surface of the inboard panels.

The standard text on sailplane design, _Fundamentals of Sailplane
Design_ by Fred Thomas (translated by Judah Milgram), generally applies
the term "dive brake" to any flat nasty that comes out of a glider
wing. It does mention in passing that hinged panels are often referred
to as "spoilers," but that is the only use of the term.

Thanks, and best regards to all

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

Bert Willing

July 11th 05, 08:28 AM

A Nimbus 4 has airbrakes.
And as for different animals: A glider certified under JAR22 needs to have
means which limit a dive to 45 deg at vne. Whatever you call them, you can
use them to limit your speed and deploy at any speed up to vne.

--
Bert Willing

ASW20 "TW"

> a écrit dans le message de news:
. com...
> Denis a Nimbus 4 does not have airbrakes. It has spoilers. These are
> two different animals alltogether
>

Stefan

July 11th 05, 09:02 AM

Bert Willing wrote:

> A Nimbus 4 has airbrakes.
> And as for different animals: A glider certified under JAR22 needs to have
> means which limit a dive to 45 deg at vne.

Just nitpicking: JAR22 asks for a dive angle of 30 degrees. 45 degrees
are only needed to be certificated for cloud flying or aerobatics.

Stefan

Bert Willing

July 11th 05, 11:06 AM

So it seems to be right that Scotch affects the memory...

--
Bert Willing

ASW20 "TW"

"Stefan" > a écrit dans le message de news:
...
> Bert Willing wrote:
>
>> A Nimbus 4 has airbrakes.
>> And as for different animals: A glider certified under JAR22 needs to
>> have means which limit a dive to 45 deg at vne.
>
> Just nitpicking: JAR22 asks for a dive angle of 30 degrees. 45 degrees are
> only needed to be certificated for cloud flying or aerobatics.
>
> Stefan

Derek Copeland

July 11th 05, 01:28 PM

At 21:48 10 July 2005, Denis posted the message 'Re: Nimbus 4 Accident'
I don't understand your choice ! if there is a risk at high speeds, the
best choice to avoid it is to avoid these speeds, and that's what the
airbrakes are for, aren't it ? Pulling g's after loosing control is the
best way to break any aircraft...
------------------------------------------
Denis
The point that I was trying to make was that exceeding the positive flap
limiting speed and then opening the airbrakes is also likely to cause damage
to the wing structure. Gliders are certified to withstand +5.3g with the
brakes shut, but only +3.5g with them open.

Derek Copeland

__________________________________________________ ____________________
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Bert Willing

July 11th 05, 01:49 PM

Derek,

you're mixing up things. Speed limits for positive flap settings have
nothing to do with g-load; they are to limit the forces on the flap.

With a constant speed, a wing produces always the same lift - disregarding
speed or deployed/undeployed airbrakes. If you pull the airbreaks at any
given speed, the load factor of the wing will momentarily be less than 1 g
(you just destroyed a part of the lift and are vertically accelerating), and
then return to 1 g, but now with a different load distribution accross the
wing. Pulling the airbrakes alone will _never_ get you more than 1 g load
factor.

Only when you start to pull up, you have to think about max load factor with
airbrakes deployed.

--
Bert Willing

ASW20 "TW"

"Derek Copeland" > a écrit dans le
message de news: ...
> At 21:48 10 July 2005, Denis posted the message 'Re: Nimbus 4 Accident'
> I don't understand your choice ! if there is a risk at high speeds, the
> best choice to avoid it is to avoid these speeds, and that's what the
> airbrakes are for, aren't it ? Pulling g's after loosing control is the
> best way to break any aircraft...
> ------------------------------------------
> Denis
> The point that I was trying to make was that exceeding the positive flap
> limiting speed and then opening the airbrakes is also likely to cause
> damage
> to the wing structure. Gliders are certified to withstand +5.3g with the
> brakes shut, but only +3.5g with them open.
>
> Derek Copeland
>
>
>
> __________________________________________________ ____________________
> This email has been scanned by the MessageLabs Email Security System.
> For more information please visit http://www.messagelabs.com/email
> __________________________________________________ ____________________
>
>
>

Roy Bourgeois

July 11th 05, 07:09 PM

I think what Bert says is technically correct (wing load doesn't change
when you open the air brakes) - but the distribution does change a lot -
especially on a ship like the N3 & N4 where the brakes are located inboard
on the inner panels. Stated differently, when the brakes are opened the
outer panels are being asked to do more work supporting the fuselage (and
non flying portions or the inner panels) than before the dive brakes were
opened. The Nimbus 3 and 4 are placarded against carrying water ballast
in the inner panel tanks with the outer panel tanks empty for structural
reasons. You also must dump the inner tanks first. The same structural
problem occurs when the dive brakes are open and that part of the inner
panel becomes "dead weight". So - while the brakes should be used to
prevent the glider getting to extreme speeds - we need to be cautious about
suggesting that nothing bad is going to happen if you open them at extreme
speeds.

Roy B. (Nimbus 3 # 65)

Derek Copeland

July 12th 05, 02:08 PM

I'll try again.

Positive flap limiting speeds have two justifications:
1) To prevent damage to the flaps themselves or more likely to their hinges.
2) To stop the wings producing more lift than is good for them at high
speeds, remembering that lift increases with the square of the speed for a
given angle of attack, and that flaps increase the camber and therefore lift
produced by the wings.

Airbrakes (when open) reduce the amount of lift produced over the portion of
the wing they occupy and increase the drag. The rest of the wing (mostly
outboard of the brakes) has to produce more lift to support the weight of
the glider and hence the bending moment on the wingspar is increased. The
fact that some stressing is taking place in the region of the airbrakes is
often witnessed by the gel coat cracks that tend to appear in this area.
Please also re-read my account of my test flight to check the double paddle
airbrake mod!

There have been two N4D break-up accidents where the common factor is that
control has been lost in a thermal, either a spin followed by a spiral dive,
or just a straight spiral dive. It is likely that in both cases that
thermalling (ie positive) flap was selected and speed and g. increased very
rapidly. In at least one case the pilot tried opening the airbrakes, but the
glider still broke up.

We had a fatality in the UK involving an ASW20 that dived vertically at very
high speed into the ground after a similar thermalling upset. The flaps also
to some extent act as elevators and it was thought that the pilot was unable
to overcome the nose down pitch tendency by pulling back on the stick.

My main original point was that the first action in any sort of loss of
control situation in a flapped glider must be to select neutral or negative
flap. If you have to open the brakes, do so before Vne is reached.

Derek Copeland
--------------------------------------------------------------------------
----

Bert Willing wrote:
you're mixing up things. Speed limits for positive flap settings have
nothing to do with g-load; they are to limit the forces on the flap.

================================================== ==========================
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--

Don Johnstone

July 12th 05, 02:40 PM

At 13:30 12 July 2005, Derek Copeland wrote:
>
>We had a fatality in the UK involving an ASW20 that
>dived vertically at very
>high speed into the ground after a similar thermalling
>upset. The flaps also
>to some extent act as elevators and it was thought
>that the pilot was unable
>to overcome the nose down pitch tendency by pulling
>back on the stick.

Not sure that is exactly right, the flaps tend to cause
the fuselage and tailplane to 'pitch down'. Ergo the
higher the ias the greater the angle of attack of the
tailplane and elevator. (The AoA of the tailplance
increases as the AoA of the wing reduces as the tailplane
is trying to produce lift 'down' rather than up relative
to the pilot). Pulling back on the stick increases
the AoA of the tailplane which could become stalled
and this would certainly cause it to be ineffective
as you describe.
>
>My main original point was that the first action in
>any sort of loss of
>control situation in a flapped glider must be to select
>neutral or negative
>flap. If you have to open the brakes, do so before
>Vne is reached

Absolutely correct, carve that in stone.

>Derek Copeland
>------------------------------------------------------------------
>>--------
>----
>
>Bert Willing wrote:
>you're mixing up things. Speed limits for positive
>flap settings have
>nothing to do with g-load; they are to limit the forces
>on the flap.
>
>
>
>

Bert Willing

July 12th 05, 05:11 PM

You're point number two doesn't hold: At constant speed (whichever speed), a
wing of a sailplane will never produce more lift than corresponds to the
weight of the glider. Otherwise you would be climbing.

Your main original point is absolutely right.

--
Bert Willing

ASW20 "TW"

"Derek Copeland" > a écrit dans le
message de news: ...
> I'll try again.
>
> Positive flap limiting speeds have two justifications:
> 1) To prevent damage to the flaps themselves or more likely to their
> hinges.
> 2) To stop the wings producing more lift than is good for them at high
> speeds, remembering that lift increases with the square of the speed for a
> given angle of attack, and that flaps increase the camber and therefore
> lift
> produced by the wings.
>
> Airbrakes (when open) reduce the amount of lift produced over the portion
> of
> the wing they occupy and increase the drag. The rest of the wing (mostly
> outboard of the brakes) has to produce more lift to support the weight of
> the glider and hence the bending moment on the wingspar is increased. The
> fact that some stressing is taking place in the region of the airbrakes is
> often witnessed by the gel coat cracks that tend to appear in this area.
> Please also re-read my account of my test flight to check the double
> paddle
> airbrake mod!
>
> There have been two N4D break-up accidents where the common factor is that
> control has been lost in a thermal, either a spin followed by a spiral
> dive,
> or just a straight spiral dive. It is likely that in both cases that
> thermalling (ie positive) flap was selected and speed and g. increased
> very
> rapidly. In at least one case the pilot tried opening the airbrakes, but
> the
> glider still broke up.
>
> We had a fatality in the UK involving an ASW20 that dived vertically at
> very
> high speed into the ground after a similar thermalling upset. The flaps
> also
> to some extent act as elevators and it was thought that the pilot was
> unable
> to overcome the nose down pitch tendency by pulling back on the stick.
>
> My main original point was that the first action in any sort of loss of
> control situation in a flapped glider must be to select neutral or
> negative
> flap. If you have to open the brakes, do so before Vne is reached.
>
> Derek Copeland
> --------------------------------------------------------------------------
> ----
>
> Bert Willing wrote:
> you're mixing up things. Speed limits for positive flap settings have
> nothing to do with g-load; they are to limit the forces on the flap.
>
>
>
>
> ================================================== ==========================
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> necessarily those of ADT Fire and Security.
> Any prices for the supply of goods or services are only valid if supported
> by a formal written quotation.
> This e-mail and any files transmitted with it, including replies and
> forwarded copies (which may contain alterations) subsequently transmitted
> from ADT Fire and Security are confidential and solely for the use of the
> intended recipient.
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> delivery
> to the intended recipient, be advised that you have received this e-mail
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> notify
> us via e-mail at ' or telephone on 0121 255 6499 and
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> ================================================== ==========================
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>
> --
>
>
>
>

Derek Copeland

July 12th 05, 06:37 PM

Bert Willing wrote on 12th July.
You're point number two doesn't hold: At constant speed (whichever speed), a

wing of a sailplane will never produce more lift than corresponds to the
weight of the glider. Otherwise you would be climbing.

Your main original point is absolutely right.
--------------------------------------------------------------

Er, I'm only a humble gliding instructor, so what do I know about things?

You are also right in that in steady flight lift must equal the weight of
the glider. However in a spiral dive you are in accelerated flight and the
glider could effectively weigh several times its own weight, and the wings
(if not stalled) have to produce the equivalent extra amount of lift to
balance this. If you are pulling more than 3.5 g at high speeds, opening the
airbrakes could just be enough to finish things off, due to the extra
bending load on the wings this entails. The correct recovery from a spiral
dive is just to carefully reduce the angle of bank while keeping the stick
fairly well back, by the way.

As an instructor I do lots of spins and spiral dives, so can easily
recognise what is going on. Many good cross-country pilots haven't done
either for years, so could be caught out should either occur unexpectedly .
The recovery actions are quite different. I also understand that Nimbus 4s
have a non-standard spin recovery procedure, which further complicates the
issue.

Derek Copeland

================================================== ==========================
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necessarily those of ADT Fire and Security.
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This e-mail and any files transmitted with it, including replies and
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--

Bert Willing

July 12th 05, 07:14 PM

Ok - you've got a point :-)

--
Bert Willing

ASW20 "TW"

"Derek Copeland" > a écrit dans le
message de news: ...
> Bert Willing wrote on 12th July.
> You're point number two doesn't hold: At constant speed (whichever speed),
> a
>
> wing of a sailplane will never produce more lift than corresponds to the
> weight of the glider. Otherwise you would be climbing.
>
> Your main original point is absolutely right.
> --------------------------------------------------------------
>
> Er, I'm only a humble gliding instructor, so what do I know about things?
>
> You are also right in that in steady flight lift must equal the weight of
> the glider. However in a spiral dive you are in accelerated flight and the
> glider could effectively weigh several times its own weight, and the wings
> (if not stalled) have to produce the equivalent extra amount of lift to
> balance this. If you are pulling more than 3.5 g at high speeds, opening
> the
> airbrakes could just be enough to finish things off, due to the extra
> bending load on the wings this entails. The correct recovery from a
> spiral
> dive is just to carefully reduce the angle of bank while keeping the stick
> fairly well back, by the way.
>
> As an instructor I do lots of spins and spiral dives, so can easily
> recognise what is going on. Many good cross-country pilots haven't done
> either for years, so could be caught out should either occur unexpectedly
> .
> The recovery actions are quite different. I also understand that Nimbus 4s
> have a non-standard spin recovery procedure, which further complicates the
> issue.
>
> Derek Copeland
>
>
> ================================================== ==========================
> Any opinions expressed in this e-mail are those of the individual and not
> necessarily those of ADT Fire and Security.
> Any prices for the supply of goods or services are only valid if supported
> by a formal written quotation.
> This e-mail and any files transmitted with it, including replies and
> forwarded copies (which may contain alterations) subsequently transmitted
> from ADT Fire and Security are confidential and solely for the use of the
> intended recipient.
> If you are not the intended recipient or the person responsible for
> delivery
> to the intended recipient, be advised that you have received this e-mail
> in
> error and that any use is strictly prohibited. In this event, please
> notify
> us via e-mail at ' or telephone on 0121 255 6499 and
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> ================================================== ==========================
>
>
> --
>
>
>
>

Michael Clarke

July 13th 05, 12:43 AM

Er, I'm only a humble Nimbus 4 pilot (not an instructor),
so what do I know about things?

'I also understand that Nimbus 4s have a non-standard
spin recovery procedure, which further complicates
the issue. '

Derek, my Nimbus 4 flight manual says:

'a) Apply opposite rudder.

b) Hold ailerons neutral.

c) Ease control sick forward until roation ceases and
the airflow is restored.

d) Centralise rudder and pull gently out of the dive.

Recovery speeds are between 70 - 113 knots - depending
on the flap setting. If necessary, flaps must therefore
be reset at '0' or '-1' so as to avoid exceeding their
speed limits.'

Sounds to me very similar to what Mr Piggott taught
me all those years ago?

At 17:54 12 July 2005, Derek Copeland wrote:
>Bert Willing wrote on 12th July.
>You're point number two doesn't hold: At constant speed
>(whichever speed), a
>
>wing of a sailplane will never produce more lift than
>corresponds to the
>weight of the glider. Otherwise you would be climbing.
>
>Your main original point is absolutely right.
>--------------------------------------------------------------
>
>Er, I'm only a humble gliding instructor, so what do
>I know about things?
>
>You are also right in that in steady flight lift must
>equal the weight of
>the glider. However in a spiral dive you are in accelerated
>flight and the
>glider could effectively weigh several times its own
>weight, and the wings
>(if not stalled) have to produce the equivalent extra
>amount of lift to
>balance this. If you are pulling more than 3.5 g at
>high speeds, opening the
>airbrakes could just be enough to finish things off,
>due to the extra
>bending load on the wings this entails. The correct
>recovery from a spiral
>dive is just to carefully reduce the angle of bank
>while keeping the stick
>fairly well back, by the way.
>
>As an instructor I do lots of spins and spiral dives,
>so can easily
>recognise what is going on. Many good cross-country
>pilots haven't done
>either for years, so could be caught out should either
>occur unexpectedly .
>The recovery actions are quite different. I also understand
>that Nimbus 4s
>have a non-standard spin recovery procedure, which
>further complicates the
>issue.
>
>Derek Copeland
>
>
>================================================== ================
>>==========
>Any opinions expressed in this e-mail are those of
>the individual and not
>necessarily those of ADT Fire and Security.
>Any prices for the supply of goods or services are
>only valid if supported
>by a formal written quotation.
>This e-mail and any files transmitted with it, including
>replies and
>forwarded copies (which may contain alterations) subsequently
>transmitted
>from ADT Fire and Security are confidential and solely
>for the use of the
>intended recipient.
>If you are not the intended recipient or the person
>responsible for delivery
>to the intended recipient, be advised that you have
>received this e-mail in
>error and that any use is strictly prohibited. In
>this event, please notify
>us via e-mail at ' or telephone
>on 0121 255 6499 and then
>delete the e-mail and any copies of it. WebSite:
>www.adt-fire-and-security.co.uk
>================================================== ================
>>==========
>
>
>--
>
>
>
>
>

Michael Clarke

July 13th 05, 12:50 AM

Just for general clarification, Section 4.5.6 of my
Nimbus 4T flight manual says:

“Note:

In order to achieve a high maneuverability, a favourable
c/g position (when using the fin tank) and a maximum
in ground clearance of the wing tips on take-off and
landing, it is always recommended to fill the inboard
water tanks first.”

I know it is the opposite for the Nimbus 3, I assume
the wings are just that much stronger on the 4. In
my experience it does make take off less fraught and
handling a bit nicer on the 4 than the 3.

Mike

At 18:30 11 July 2005, Roy Bourgeois wrote:
>I think what Bert says is technically correct (wing
>load doesn't change
>when you open the air brakes) - but the distribution
>does change a lot -
>especially on a ship like the N3 & N4 where the brakes
>are located inboard
>on the inner panels. Stated differently, when the
>brakes are opened the
>outer panels are being asked to do more work supporting
>the fuselage (and
>non flying portions or the inner panels) than before
>the dive brakes were
>opened. The Nimbus 3 and 4 are placarded against
>carrying water ballast
>in the inner panel tanks with the outer panel tanks
>empty for structural
>reasons. You also must dump the inner tanks first.
>The same structural
>problem occurs when the dive brakes are open and that
>part of the inner
>panel becomes 'dead weight'. So - while the brakes
>should be used to
>prevent the glider getting to extreme speeds - we need
>to be cautious about
>suggesting that nothing bad is going to happen if you
>open them at extreme
>speeds.
>
>Roy B. (Nimbus 3 # 65)
>
>
>
>
>
>
>

Stefan

July 13th 05, 08:07 AM

Michael Clarke wrote:

> Derek, my Nimbus 4 flight manual says:
>
> a) Apply opposite rudder.
> b) Hold ailerons neutral.
> c) Ease control sick forward until roation ceases and
> the airflow is restored.
> d) Centralise rudder and pull gently out of the dive.

No surprize: JAR22 explicitely demands "standard spin recovery". And it
must demonstrated from a spin of "at least 5 turns" and with "the most
unfavorable configuration". (Cited from memory, so the exact wording may
be different.)

Stefan

Don Johnstone

July 13th 05, 10:50 PM

At 20:18 13 July 2005, T O D D P A T T I S T wrote:
>Don Johnstone
>wrote:
>
>>>If you have to open the brakes, do so before Vne is
>>>reached
>>
>>Absolutely correct, carve that in stone.
>
>The implication here is that if you find yourself extremely
>nose down, but at an initially low speed, opening the
>brakes
>is a desirable action. I disagree.
>
>Opening the brakes might be advisable if brakes were
>able to
>produce large amounts of drag - sufficient to limit
>you to
>speeds below Vne - but that is generally not true.
> So, your
>only other option is to get the nose back up to stop
>the
>acceleration. The only way to do that is to apply
>the
>maximum force possible in a direction perpendicular
>to the
>downwardly angled path of the aircraft to curve it
>back
>towards level.
>
>A force perpendicular to the path of the aircraft is
>called
>'lift' and by opening the brakes you prevent much of
>the
>wing from producing the lift you desperately need to
>bring
>you back to level flight. This delays the critical
>recovery. Up until you reach Va, you can operate the
>wings
>at maximum lift coefficient and produce maximum lift
>without
>risk of structural damage, and that's exactly what
>you want
>to do to get the nose back up.
>
>In addition, by opening the brakes, you seriously increase
>the risk that the pilot will overstress the aircraft
>at
>higher speeds. With brakes open, the max G load for
>many
>gliders is so low that the pilot simply does not think
>he's
>about to break anything. His built in warning system
>does
>not begin to go off until much higher G loads are felt.
>
>Finally, if you open the brakes, you increase the altitude
>loss significantly, a potentially critical factor in
>a low
>altitude recovery.
>
>The proposal to use a tail chute does not suffer from
>these
>problems, as a tail chute does not decrease lift or
>max G
>limits. It also has the advantage of allowing recovery
>from
>otherwise unrecoverable spin modes.

I accept what you say my original reponse was to the
whole paragraph 'My main original point was that the
first action in
>any sort of loss of control situation in a flapped
>glider must be to select neutral or negative flap.
If you have to open the brakes, do so before Vne is
reached'

I standby that. It is important to select a non positive
flap setting and if the brakes are going to be used
it should be before VNE is reached.
>

Denis

August 14th 05, 10:41 PM

T o d d P a t t i s t a écrit :

> The implication here is that if you find yourself extremely
> nose down, but at an initially low speed, opening the brakes
> is a desirable action. I disagree.

> A force perpendicular to the path of the aircraft is called
> "lift" and by opening the brakes you prevent much of the
> wing from producing the lift you desperately need to bring
> you back to level flight. This delays the critical
> recovery.

No. The radius of curvature of your recovery trajectory is proportionnal
to lift, but inversly proportionnal to the square of speed. Thus, even
with less lift, the radius may be smaller with airbrakes out.

> Finally, if you open the brakes, you increase the altitude
> loss significantly, a potentially critical factor in a low
> altitude recovery.

No. Smaller radius means smaller altitude loss (though smaller speed
means less altitude gain after the low point, but this is not likely to
be a problem)

--
Denis

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

Ian

August 15th 05, 08:57 PM

On Mon, 15 Aug 2005 10:15:22 -0400, T o d d P a t t i s t wrote:

> are trying to decide what to do at the point when brakes are
> closed and speed is fixed at some speed V1. If pilot 1
> leaves the brakes closed and pulls to max G for brakes
> closed, and pilot 2 opens the brakes and pulls to max G for
> brakes open, pilot 1 will have a smaller radius of
> curvature, since both are at speed V1.

If you are in a situation (perhaps recovering from a spin) with your nose
pointing 60 deg down below the horizontal and the ASI reading 180 km/h and
accelerating rapidly. You could try:

- Pull full airbrakes, and raise the nose by 15 degrees keeping the G
force below 2G. In this new attitude (45 degrees nose down) many gliders
airbrakes will be speed limiting below VNE. The acceleration will stop and
you can pull out of the dive being careful to limit the G force to 2G.

- Or, you could leave the dive brakes closed, and attempt to raise the
nose by 55 degrees to 5 degrees below the horizon without pulling
more than 4G.

I have not worked out the maths of the two options but I think that in
a clean glass ship, you would have a better chanced completing the first
manoeuvre without exceeding VNE than the second.

Ian

Bruce Hoult

August 16th 05, 02:42 AM

In article >,
Ian > wrote:

> On Mon, 15 Aug 2005 10:15:22 -0400, T o d d P a t t i s t wrote:
>
> > are trying to decide what to do at the point when brakes are
> > closed and speed is fixed at some speed V1. If pilot 1
> > leaves the brakes closed and pulls to max G for brakes
> > closed, and pilot 2 opens the brakes and pulls to max G for
> > brakes open, pilot 1 will have a smaller radius of
> > curvature, since both are at speed V1.
>
> If you are in a situation (perhaps recovering from a spin) with your nose
> pointing 60 deg down below the horizontal and the ASI reading 180 km/h and
> accelerating rapidly. You could try:
>
> - Pull full airbrakes, and raise the nose by 15 degrees keeping the G
> force below 2G. In this new attitude (45 degrees nose down) many gliders
> airbrakes will be speed limiting below VNE. The acceleration will stop and
> you can pull out of the dive being careful to limit the G force to 2G.
>
> - Or, you could leave the dive brakes closed, and attempt to raise the
> nose by 55 degrees to 5 degrees below the horizon without pulling
> more than 4G.
>
> I have not worked out the maths of the two options but I think that in
> a clean glass ship, you would have a better chanced completing the first
> manoeuvre without exceeding VNE than the second.

Another option is to raise the nose 15 degrees with the airbrakes
closed, keeping below 4G, and *then* pull the airbrakes.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------

Gerhard Wesp

August 16th 05, 05:47 AM

Ian > wrote:
> If you are in a situation (perhaps recovering from a spin) with your nose
> pointing 60 deg down below the horizontal and the ASI reading 180 km/h and
> accelerating rapidly. You could try:

[ leave A/B closed and pull 4G ...]

> I have not worked out the maths of the two options but I think that in
> a clean glass ship, you would have a better chanced completing the first
> manoeuvre without exceeding VNE than the second.

I couldn't resist the temptation and did the maths. I kind of lost the
habit, so it took me 20 minutes. The result is: My intuition was
right: Do *not* use the airbrakes.

Even in an ideal ship (zero drag) and with the nose pointing vertically
down initially, the peak speed is only 240km/h under your assumptions
(4g pull-up and 180km/h initially). In a real ship and with only 60
degrees down, the peak speed would of course be lower.

Here's the script with the phugoid equation (Mathematica). Feel free to
modify the initial conditions and parameters and play around. The
unknowns are v1, v2, the horizontal and vertical component of the speed
vector.

kmh = 1 / 3.6
Ng = 4
g = 9.81
v0 = 180 kmh
tmax = 8
dt = .1

v =
NDSolve[
{
v1'[ t ] == Ng g * v2[ t ] / Sqrt[ v1[ t ]^2 + v2[ t ]^2 ] ,
v2'[ t ] == Ng g * -v1[ t ] / Sqrt[ v1[ t ]^2 + v2[ t ]^2 ] - g ,
v1[ 0 ] == 0 ,
v2[ 0 ] == -v0
} ,
{ v1 , v2 } ,
{ t , 0 , tmax }
][[ 1 ]]

Table[ ( Sqrt[ v1[ t ]^2 + v2[ t ]^2 ] /. v ) / kmh , { t , 0 , tmax , dt } ]

Regards
-Gerhard
--
o o
Gerhard Wesp | http://www.cosy.sbg.ac.at/~gwesp/
\_/ See homepage for email address!

Don Johnstone

August 16th 05, 10:07 AM

At 04:48 16 August 2005, Gerhard Wesp wrote:
>Ian wrote:
>> If you are in a situation (perhaps recovering from
>>a spin) with your nose
>> pointing 60 deg down below the horizontal and the
>>ASI reading 180 km/h and
>> accelerating rapidly. You could try:
>
>[ leave A/B closed and pull 4G ...]
>
>> I have not worked out the maths of the two options
>>but I think that in
>> a clean glass ship, you would have a better chanced
>>completing the first
>> manoeuvre without exceeding VNE than the second.
>
>I couldn't resist the temptation and did the maths.
> I kind of lost the
>habit, so it took me 20 minutes. The result is: My
>intuition was
>right: Do *not* use the airbrakes.
>
>Even in an ideal ship (zero drag) and with the nose
>pointing vertically
>down initially, the peak speed is only 240km/h under
>your assumptions
>(4g pull-up and 180km/h initially). In a real ship
>and with only 60
>degrees down, the peak speed would of course be lower.
>
>Here's the script with the phugoid equation (Mathematica).
> Feel free to
>modify the initial conditions and parameters and play
>around. The
>unknowns are v1, v2, the horizontal and vertical component
>of the speed
>vector.
>
>kmh = 1 / 3.6
>Ng = 4
>g = 9.81
>v0 = 180 kmh
>tmax = 8
>dt = .1
>
>v =
>NDSolve[
> {
> v1'[ t ] == Ng g * v2[ t ] / Sqrt[ v1[ t ]^2 +
>v2[ t ]^2 ] ,
> v2'[ t ] == Ng g * -v1[ t ] / Sqrt[ v1[ t ]^2 +
>v2[ t ]^2 ] - g ,
> v1[ 0 ] == 0 ,
> v2[ 0 ] == -v0
> } ,
> { v1 , v2 } ,
> { t , 0 , tmax }
>][[ 1 ]]
>
>Table[ ( Sqrt[ v1[ t ]^2 + v2[ t ]^2 ] /. v ) / kmh
>, { t , 0 , tmax , dt } ]
>
>Regards
>-Gerhard

I think the ground might get in the way before I have
done the sums :-)

Denis

August 16th 05, 10:46 PM

T o d d P a t t i s t a écrit :

> Last, I'm relying on my recollection of the physics of a
> pull-out which I calculated long ago. It's not peer
> reviewed work, and I'm quite far from infallible :-) If I
> get some time, I'll pull out my old notes. I'd love to have
> someone put this into Mathematica and verify my recollection
> of the results.

I have no calculation neither, and it would be great to help us compare
our guesses...

What we need to do so is knowing the airbrakes drag. At 1 g it limits
speed to VNE at 30° dive angle, which means that if you get twice this
drag at 4 g, even at 90° dive angle the speed will be kept under VNE.
Which is not unlikely, since induced drag increase due to airbrakes is
high, but once again I have no precise figure yet to prove it. If
someone has, please give it...

--
Denis

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

Derrick Steed

August 16th 05, 10:57 PM

since induced drag increase due to airbrakes is=20
high=20

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Don't you mean "form" drag? I thought induced drag resulted (crudely)
from the wingtip vortices.

Also, are you sure that drag is proportional to lift?

Rgds,

Derrick Steed

Denis

August 18th 05, 02:18 PM

Derrick Steed a écrit :
> since induced drag increase due to airbrakes is=20
> high=20
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Don't you mean "form" drag? I thought induced drag resulted (crudely)
> from the wingtip vortices.

No. Wingtip vortices are only the visible part of the iceberg ;-)

Induced drag is the result of lift itself and is lower when the span is
higher and when the spanwise lift repartition is close to elliptic. And
with the airbrakes out, the lift repartition is very bad, closer to 3
wings of 5 m of span separated by no lift (at the airbrakes) than to 1
27 m wing !

> Also, are you sure that drag is proportional to lift?

Induced drag is proportionnal to square of lift, while form drag don't
vary much with lift. Total drag definitely increases with lift, but to
quantify it that's where we need the proportion of induced drag...

--
Denis

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

Bruce Hoult

August 25th 05, 05:57 AM

In article >,
Denis > wrote:

> Derrick Steed a écrit :
> > since induced drag increase due to airbrakes is=20
> > high=20
> >
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Don't you mean "form" drag? I thought induced drag resulted (crudely)
> > from the wingtip vortices.
>
> No. Wingtip vortices are only the visible part of the iceberg ;-)
>
> Induced drag is the result of lift itself and is lower when the span is
> higher and when the spanwise lift repartition is close to elliptic. And
> with the airbrakes out, the lift repartition is very bad, closer to 3
> wings of 5 m of span separated by no lift (at the airbrakes) than to 1
> 27 m wing !

This appears to be confused.

> > Also, are you sure that drag is proportional to lift?
>
> Induced drag is proportionnal to square of lift, while form drag don't
> vary much with lift. Total drag definitely increases with lift, but to
> quantify it that's where we need the proportion of induced drag...

And this is clearly totally mistaken, or misspoken. Two gliders flying
have twice as much lift as one glider, but they have four times as much
induced drag as one glider? And ten gliders have one hundred times as
much induced ddrag as one?

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------