Avoiding Vne

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?e...09X01702&key=1 Nimbus 4DM -
Minden - Two killed.

the link is actually
http://www.ntsb.gov/NTSB/brief.asp?e...12X19310&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.

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?e...09X01702&key=1 Nimbus
4DM - Minden - Two killed.


the link is actually
http://www.ntsb.gov/NTSB/brief.asp?e...12X19310&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

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 ?

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

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 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

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

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

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 ?