Avoiding Vne

Don Johnstone wrote:

OK the answer to this one is very simple, VNE stands
for 'Velocity never exceed' the never is not optional.
Pulling the airbrakes or pulling back hard on the stick
may cause structural damage to the glider, however
this structural damage is not likely to be catastrophic.

Why not?


Exceeding VNE may induce aerodynamic flutter, this
can and almost certainly will cause catastrophic failure
of the airframe. Put simply try and avoid both but
if the choice is exceed the placarded G loading or
VNE the G loading is the only choice. The potential
for catastophic failure is much much greater if VNE
is exceeded,

Why?

exceeding VNE is therefore not an option.

Isn't there a built in safety margin for both G's and VNE?


I have no doubt there will now be lots of postings
from people who say they have exceeded VNE and got
away with it. Even idiots can be lucky sometimes.

Exceeding VNE may induce aerodynamic flutter, this
can and almost certainly will cause catastrophic failure
of the airframe. Put simply try and avoid both but
if the choice is exceed the placarded G loading or
VNE the G loading is the only choice. The potential
for catastophic failure is much much greater if VNE
is exceeded,


Why?

exceeding VNE is therefore not an option.

Isn't there a built in safety margin for both G's and VNE?

A modern sailplane is built to withstand a sudden updraft of 10 m/s at
Vne. If you pull at the same time, it is more than likely that the wing
won't make it.

Don Johnstone wrote:
OK the answer to this one is very simple, VNE stands
for 'Velocity never exceed' the never is not optional.
Pulling the airbrakes or pulling back hard on the stick
may cause structural damage to the glider, however
this structural damage is not likely to be catastrophic.

"May"? At Vne, "pulling back hard on the stick" will guarantee
catastrophic structural failure, not just "damage". Even "pulling back
modestly" (like one-third of the stick travel) can get you very close to
the limits.

Exceeding VNE may induce aerodynamic flutter, this
can and almost certainly will cause catastrophic failure
of the airframe.

References? The majority of people I know that have suffered flutter did
so without catastrophic failure. The glider often had damage to a
control surface or linkage, but not structural damage.

Put simply try and avoid both but
if the choice is exceed the placarded G loading or
VNE the G loading is the only choice. The potential
for catastophic failure is much much greater if VNE
is exceeded, exceeding VNE is therefore not an option.

References?

I have no doubt there will now be lots of postings
from people who say they have exceeded VNE and got
away with it. Even idiots can be lucky sometimes.

Inadvertently exceeding Vne doesn't automatically make the pilot an
idiot. Most of these "idiots" will be good pilots that got caught in a
bad situation; some might be pilots that took exceptional risks. Anyway,
we are talking about what to do when caught between a rock and hard
place, not what led to it. Let's not prejudge anyone.


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Eric Greenwell
Washington State
USA

Nonsense. Exceed the structural g-load limit and you fly without wings.

--
Bert Willing

ASW20 "TW"


"Don Johnstone" a écrit dans le
message de ...
OK the answer to this one is very simple, VNE stands
for 'Velocity never exceed' the never is not optional.
Pulling the airbrakes or pulling back hard on the stick
may cause structural damage to the glider, however
this structural damage is not likely to be catastrophic.
Exceeding VNE may induce aerodynamic flutter, this
can and almost certainly will cause catastrophic failure
of the airframe. Put simply try and avoid both but
if the choice is exceed the placarded G loading or
VNE the G loading is the only choice. The potential
for catastophic failure is much much greater if VNE
is exceeded, exceeding VNE is therefore not an option.

I have no doubt there will now be lots of postings
from people who say they have exceeded VNE and got
away with it. Even idiots can be lucky sometimes.

At 11:30 25 March 2004, Bert Willing wrote:
If you are already very fast and pull the airbrakes,
you have to be very
careful during the pull up because the wing won't stand
the same g-load as
without airbrakes.

--
Bert Willing

ASW20 'TW'


'Erik Braun' a écrit dans le message de
...
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.

Karel, NL



Pulling the airbrakes is what most handbooks say on
this subject. But if
you're already very fast I'd do this carefully.

Bert Willing wrote:
Nonsense. Exceed the structural g-load limit and you fly without wings.

Not so much fly as.... plummet.

Tony V. :-)

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!

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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