Avoiding Vne

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

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

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

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

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

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

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

"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

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 ?

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 ?