Avoiding Vne

To put the record straight
1. When I referred to idiots and exceeding VNE I meant
those who had done so deliberately, not those who had
done so inadvertantly.
2. Pulling excess G can damage the airframe, however
the damage is likely to be far less than the damage
caused by flutter. I am not sure that enough G could
be pulled at speeds below VNE to cause serious catastrophic
failure as there is a margin between the placarded
limit and the design limit of most gliders. (We are
talking about avoiding exceeding VNE) For example from
memory the Grob 103 Acro is placarded +3G -1G in the
UK. (This might be the LBA limit). If I remember correctly
Grob place a limit of +8G -3.5G for the airframe. I
stand to be corrected but I suspect it is unlikely
that 8G could be attained at an airspeed less than
VNE. Other design limits may of course be closer to
the placarded limit but again I suspect it may be difficult
to exceed the design limit at speeds below VNE.
3. Airframe flutter can occur at less than VNE. The
likelyhood of flutter increases dramatically above
VNE and the severity increases with the speed. The
flutter may mean that there is no control of the aircraft
and therefore no way to recover. Aerodynamic flutter
breaks airplanes (and bridges) and the failure is almost
always catastrophic. The N really does stand for never.

Excess G is the lesser of 2 evils, I know which i would
choose.

However whatever floats your boat but if you intend
to exceed VNE I would be grateful if you did not do
it over my head, all thos falling bits can really spoil
your day.

Yes Bert, you were indeed lucky if you exceeded VNE
but read my first paragraph as to the rest. I have
spun a large span glider (ASW17) and I have to say
I have never got anywhere near VNE or the placarded
G limit in the recovery. Will airbrakes effect the
recovery from a spin, I don't know yet, I will let
you know.



At 11:48 26 March 2004, Bert Willing wrote:
Well, your contribution does make me assume than you
never did a spin in a
large span glider. I once had to choose between exceeding
Vne and pulling
the airbrakes, and I didn't pull them. As someone said
earlier, I was one of
the lucky idiots who got away with it.

--
Bert Willing

ASW20 'TW'


'Stefan' a écrit dans le message de
...
K.P. Termaat wrote:

Thanks for the discussion. Once one has exceeded
Vne ...

This whole discussion is somewhat bizarre. I've been
doing spins on a
regular basis and exceeding Vne has never been an
issue. Certainly not
when still spinning (no acceleration in spinning mode),
but not during
pull out either. I can't help assuming that no one
contributing to this
thread has ever done a spin himself.

Stefan

Once I was in that situation I didn't behave as an idiot. But to get there,
I did all to qualify as an idiot.

What speed you build up during recovery largely depends on how long the ship
continues to turn after the counter measures. In my case the ship (26m)
passed from spin through a form of spiral dive, and that makes builing up of
speed very fast. Vne in this case was 200 km/h.

What happens if you step outside the flight enveloppe - your guess is as
good as mine. Flutter test on modern gliders is done up to Vne + 10%, but
10% is not very much in such a situation. If flutter starts, your day is
spoiled.
If you exceed g-loads during pull-up, you have a 1.5 design factor for a
clean wing (that's more than 10%...), but pulling the airbrakes will shift
the load distribution on the wing dramatically.

So, you have to make a choice between two sub-optimal solutions. But, in a
certified glider there is basically no reason to get there.

--
Bert Willing

ASW20 "TW"


"Don Johnstone" a écrit dans le
message de ...
To put the record straight
1. When I referred to idiots and exceeding VNE I meant
those who had done so deliberately, not those who had
done so inadvertantly.
2. Pulling excess G can damage the airframe, however
the damage is likely to be far less than the damage
caused by flutter. I am not sure that enough G could
be pulled at speeds below VNE to cause serious catastrophic
failure as there is a margin between the placarded
limit and the design limit of most gliders. (We are
talking about avoiding exceeding VNE) For example from
memory the Grob 103 Acro is placarded +3G -1G in the
UK. (This might be the LBA limit). If I remember correctly
Grob place a limit of +8G -3.5G for the airframe. I
stand to be corrected but I suspect it is unlikely
that 8G could be attained at an airspeed less than
VNE. Other design limits may of course be closer to
the placarded limit but again I suspect it may be difficult
to exceed the design limit at speeds below VNE.
3. Airframe flutter can occur at less than VNE. The
likelyhood of flutter increases dramatically above
VNE and the severity increases with the speed. The
flutter may mean that there is no control of the aircraft
and therefore no way to recover. Aerodynamic flutter
breaks airplanes (and bridges) and the failure is almost
always catastrophic. The N really does stand for never.

Excess G is the lesser of 2 evils, I know which i would
choose.

However whatever floats your boat but if you intend
to exceed VNE I would be grateful if you did not do
it over my head, all thos falling bits can really spoil
your day.

Yes Bert, you were indeed lucky if you exceeded VNE
but read my first paragraph as to the rest. I have
spun a large span glider (ASW17) and I have to say
I have never got anywhere near VNE or the placarded
G limit in the recovery. Will airbrakes effect the
recovery from a spin, I don't know yet, I will let
you know.



At 11:48 26 March 2004, Bert Willing wrote:
Well, your contribution does make me assume than you
never did a spin in a
large span glider. I once had to choose between exceeding
Vne and pulling
the airbrakes, and I didn't pull them. As someone said
earlier, I was one of
the lucky idiots who got away with it.

--
Bert Willing

ASW20 'TW'


'Stefan' a écrit dans le message de
...
K.P. Termaat wrote:

Thanks for the discussion. Once one has exceeded
Vne ...

This whole discussion is somewhat bizarre. I've been
doing spins on a
regular basis and exceeding Vne has never been an
issue. Certainly not
when still spinning (no acceleration in spinning mode),
but not during
pull out either. I can't help assuming that no one
contributing to this
thread has ever done a spin himself.

Stefan

Don Johnstone wrote:

I am not sure that enough G could
be pulled at speeds below VNE to cause serious catastrophic
failure as there is a margin between the placarded
limit and the design limit of most gliders.

IIRC, JAR requires a safety margin of 1.5

Stefan

Stefan wrote:
Don Johnstone wrote:

I am not sure that enough G could
be pulled at speeds below VNE to cause serious catastrophic
failure as there is a margin between the placarded
limit and the design limit of most gliders.


IIRC, JAR requires a safety margin of 1.5

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.

Further, At Vne (47% higher than Va), you could pull 2.2 times the
flight limits!

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

Eric Greenwell
Washington State
USA

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

Don Johnstone wrote:

2. Pulling excess G can damage the airframe, however
the damage is likely to be far less than the damage
caused by flutter.

Both may cause the same damage : loosing the wings (and both have)

I am not sure that enough G could
be pulled at speeds below VNE to cause serious catastrophic
failure

Below manouevreing speed, no. Above it (and below VNE) yes !

I stand to be corrected but I suspect it is unlikely
that 8G could be attained at an airspeed less than
VNE.

If 8 g is the extreme limit this includes a safety margin and the real
limit is what is placarded (in most gliders it's about 5 or 5.5 g). And
this limit is only valid at manouevering speed, at VNE it is much lower.

yes 8 g may be attained well below VNE (if stalling speed is 70 km/h,
you may exceed 8 g at 198 km/h, as lift depends on square of speed.) At
270 km/h you'd reach 14.9 g !!!

3. Airframe flutter can occur at less than VNE. The
likelyhood of flutter increases dramatically above
VNE and the severity increases with the speed.

Nonsense. Flutter cannot appear under Vc, a design speed that is just
above VNE.

Not all modes of flutter are catastrophic (it depends of the damping)
but most are explosive. At any speed above flutter speed.

The N really does stand for never.

Yes, but the G limits are *never* to be exceeded too, even if nobody has
thought to call it GNE. It is exactly the same.

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 !

--
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 3/26/04 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

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 ?