Avoiding Vne

No, it is only one point.

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

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

You can also read about the Nimbus 4DM at Minden; 99.07.13 - LAX99MA251 -
http://www.ntsb.gov/NTSB/brief.asp?e...09X01702&key=1 Nimbus 4DM -
Minden - Two killed.

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

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


"Stefan" wrote in message
...


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

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


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

Stefan.

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

--
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.

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.

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

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

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

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

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

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

Excessive-g may
not.

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

The trick is to stay within the limits as long as possible.
Therefore it's necessary to know the limits and their use. In
abovementioned Nimbus 4 incident it seems that pilot exchausted
g-limits before the Vne arrived. But no-one knows what really
happened.

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

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


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

Eric Greenwell
Washington State
USA

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

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



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

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

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

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

Excessive-g may
not.

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

The trick is to stay within the limits as long as possible.
Therefore it's necessary to know the limits and their use. In
abovementioned Nimbus 4 incident it seems that pilot exchausted
g-limits before the Vne arrived. But no-one knows what really
happened.

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

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


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

Eric Greenwell
Washington State
USA

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