Avoiding Vne

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