Avoiding Vne

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.

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

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.

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

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

Bert Willing wrote:

Well, your contribution does make me assume than you never did a spin in a
large span glider.

I did spins up and including a Duo. I've never flown an ASH 25 or a
Nimbus 4, so I can't comment these from my own experience. However, JAR
requires that they can be safely spun up to 5 full rotations. To my
undertanding, "safely" means that they can be recovered without dirty
tricks and without exceeding their operation limits.

Stefan

Why don't you check your glider's flight manual ?
Jean
"K.P. Termaat" a écrit dans le message de
...
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

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

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

Unless you are the designer, you don't know what was the limiting factor
which sets the limit speed.

I once saw the wreck of an ASW20C just after it crashed at about 200 knots.
It turns out that the stability and control characteristics of that type are
such that above a certain speed it is impossible to recover from a dive even
with the stick on the back stop; this is because the wing twists.

I also saw the wreckage of a Vega where the trailing edge brakes had been
deployed at too high a speed.

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.

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.

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


"Bert Willing" wrote in
message ...

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"