Devices for avoiding VNE?

These reports led you to the wrong conclusion.
Overstress is the key here, weahter with or without airbrakes.

It's a lot easier to overstress the structure or eventually even cause
flutter by trying to recover from a high speed dive without using the
brakes.

"Todd Pattist" wrote in message
...
"Arnold Pieper" wrote:

Don't be affraid to open the airbrakes at high speed, believe me, the
manufacturer is just a little smarter than that.

I'm not afraid to open them at high speed, I'm afraid to
lower the G-limit when I need G-s to recover. I've seen too
many accident reports where structural failure was
attributed to overstressing with the brakes open.

You have to be careful at high speed just because they tend to jump out
more
easily, so, have a firm hand on it.

Real aerobatic training (as opposed to some occasional loops) will
clarify a
lot of this.

Although it's been long time, my training was by a national
glider aerobatic champion.


Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

I thought you flew an ASW20 (might be mistaken)? This
is one ship where the wing twist at high speed results
in a subtle trim change that you might not even notice.
At high speed the stick eventually needs to be brought
slightly back to avoid continuing acceleration. The
faster you go the further back it needs to come. Don't
get me wrong, it is VERY subtle and you probably wouldnt
ever notice it. But there was some speculation that
the ASW20 accident mentioned earlier was the result
of a speed being reached (above VNE) where the trim
change was such that the stick was on the back stop
and the sailplane was still pitching nose down.

The reason that this behaviour is allowed is because
it isn't dangerous (or even noticable) unless you exceed
VNE.

This is just stuff I have heard around, so not sure
if it is 100% true. But I have heard it from some pretty
reliable people.


At 23:42 01 April 2004, Arnold Pieper wrote:
I don't know where you guys get these things from,
but this behaviour means
these gliders should have their certifications cancelled.

I've never flown anything with these characteristics.

'Mark Navarre' wrote in message
...
From: 'Arnold Pieper'
Date: 3/31/2004 1:16 PM Pacific Standard Time
Message-id:

Maybe true if 'near vertical', however, staying at
a near vertical dive
is
something that requires a conscient effort.
The glider won't just stay there on its own.
To remain in a 90 degree vertical dive requires a
significant amount of
forward stick force and concentration.
As speed increases, the nose will come up (away from
vertical) even if
you
don't want it to, and even with full forward trim,
it would still require
an
honest push on the stick to maintain that attitude.

Not true with all gliders. Several modern racing
ships will, when trimmed
within CG limits for best climb performance, 'tuck'
or pitch down with
increasing airspeed, resulting in a large outside
loop or exceeding VNE
without
pilot input. The crossover speed for this in my own
ship is about 115
kts,
above which slight back pressure is needed to maintain
speed.

-
Mark Navarre
2/5 black ace
LoCal, USA
-

I own and fly an ASW 20, and the behaviour you describe is definitively
complete nonsense.
Even approaching Vne you need to positively push the stick to maintain
speed.

--
Bert Willing

ASW20 "TW"


"Jon Meyer" a écrit dans le message
de ...
I thought you flew an ASW20 (might be mistaken)? This
is one ship where the wing twist at high speed results
in a subtle trim change that you might not even notice.
At high speed the stick eventually needs to be brought
slightly back to avoid continuing acceleration. The
faster you go the further back it needs to come. Don't
get me wrong, it is VERY subtle and you probably wouldnt
ever notice it. But there was some speculation that
the ASW20 accident mentioned earlier was the result
of a speed being reached (above VNE) where the trim
change was such that the stick was on the back stop
and the sailplane was still pitching nose down.

The reason that this behaviour is allowed is because
it isn't dangerous (or even noticable) unless you exceed
VNE.

This is just stuff I have heard around, so not sure
if it is 100% true. But I have heard it from some pretty
reliable people.


At 23:42 01 April 2004, Arnold Pieper wrote:
I don't know where you guys get these things from,
but this behaviour means
these gliders should have their certifications cancelled.

I've never flown anything with these characteristics.

'Mark Navarre' wrote in message
...
From: 'Arnold Pieper'
Date: 3/31/2004 1:16 PM Pacific Standard Time
Message-id:

Maybe true if 'near vertical', however, staying at
a near vertical dive
is
something that requires a conscient effort.
The glider won't just stay there on its own.
To remain in a 90 degree vertical dive requires a
significant amount of
forward stick force and concentration.
As speed increases, the nose will come up (away from
vertical) even if
you
don't want it to, and even with full forward trim,
it would still require
an
honest push on the stick to maintain that attitude.

Not true with all gliders. Several modern racing
ships will, when trimmed
within CG limits for best climb performance, 'tuck'
or pitch down with
increasing airspeed, resulting in a large outside
loop or exceeding VNE
without
pilot input. The crossover speed for this in my own
ship is about 115
kts,
above which slight back pressure is needed to maintain
speed.

-
Mark Navarre
2/5 black ace
LoCal, USA
-

On 2 Apr 2004 09:26:34 GMT, Jon Meyer
wrote:


This is just stuff I have heard around, so not sure
if it is 100% true. But I have heard it from some pretty
reliable people.

Basic rule #1 about aviation rumours:
Never believe anything as long as you have not seen it yourself.

The behaviour described above is, as Bert alreay pointed out, absolute
nonsense and exactly the contrary of how a 20 behavies in reality.


Bye
Andreas

The behaviour described above is, as Bert alreay pointed out, absolute
nonsense and exactly the contrary of how a 20 behavies in reality.


It's not all BS, there was this Doctor that extended the wing span on his ship,
back in the '70's. He brought a new meaning to the term, *final glide* as the
wing tips dug-in and he almost completed an outside loop, with the stick full
back, but the ground got in the way. Wing twist at high speed is real.
JJ Sinclair

Subject: Devices for avoiding VNE?
From: Andreas Maurer
Date: 4/2/2004 5:48 AM Pacific Standard Time
Message-id:
Basic rule #1 about aviation rumours:
Never believe anything as long as you have not seen it yourself.

The behaviour described above is, as Bert alreay pointed out, absolute
nonsense and exactly the contrary of how a 20 behavies in reality.

I have seen it myself, my ship was not out of CG limits, the effect is subtle,
but present nevertheless. Other pliots with AS-W20's may not experience the
tuck due to flying with a further forward CG and resulting trim speed change,
thereby canceling the aeroelastic twist of the wings. 20 B's have stiffer
wings than the A or C, by the way, and may not twist as much.
The speed at which this begins to occur on my ship is out of the normal range
of efficient cruising speed anyway. Just fly the plane...put the stick where
it gives you the speed you want and keep it there until you want a different
speed. It's not autopilot!


-
Mark Navarre
2/5 black ace
LoCal, USA
-

JJ Sinclair wrote:
The behaviour described above is, as Bert alreay pointed out, absolute
nonsense and exactly the contrary of how a 20 behavies in reality.


It's not all BS, there was this Doctor that extended the wing span on his ship,
back in the '70's. He brought a new meaning to the term, *final glide* as the
wing tips dug-in and he almost completed an outside loop, with the stick full
back, but the ground got in the way. Wing twist at high speed is real.
JJ Sinclair

I think the context here is "certified gliders" operated within their
limits, are supposed to have positive stability at Vne. If you have one
that doesn't, this suggests there is something wrong with your glider.

I'm sure we all agree that wing twist can happen, and we are not
surprised it might happen to someone that extended the span on his
glider, or exceeds Vne by 40 or 50 knots.
--
-----
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Eric Greenwell
Washington State
USA

I a bit suspicious of this whole wing twist thing.
Since the center of lift for most airfoils is at about
0.25 chord, which is generally a bit haead of the spar,
you'd expect the natural aerodynamic forces to generate
neutral to positive twisting with loading. The only
counter-examples I know of are in jet fighters. The
F-100 was known to have aileron reversal at maximum
dynamic pressure (transonic at low altitude) under
high Gs.

On a glider you would have to have a lot of washout
built into the tips to get it to twist because you
would need to generate negative angle of attack at
the tip. I guess this is possible if you modify your
glider extensively, or maybe if do an aggressive negative-G
pushover at a high enough speed. Neither of those
are in my bag of tricks so I'll consider myself relatively
safe for now.

At 16:54 02 April 2004, Eric Greenwell wrote:
JJ Sinclair wrote:
The behaviour described above is, as Bert alreay pointed
out, absolute
nonsense and exactly the contrary of how a 20 behavies
in reality.


It's not all BS, there was this Doctor that extended
the wing span on his ship,
back in the '70's. He brought a new meaning to the
term, *final glide* as the
wing tips dug-in and he almost completed an outside
loop, with the stick full
back, but the ground got in the way. Wing twist at
high speed is real.
JJ Sinclair

I think the context here is 'certified gliders' operated
within their
limits, are supposed to have positive stability at
Vne. If you have one
that doesn't, this suggests there is something wrong
with your glider.

I'm sure we all agree that wing twist can happen, and
we are not
surprised it might happen to someone that extended
the span on his
glider, or exceeds Vne by 40 or 50 knots.
--
-----
change 'netto' to 'net' to email me directly

Eric Greenwell
Washington State
USA

I a bit suspicious of this whole wing twist thing.

Take a K-6 up to 100 and look at the tips.

Take an ASH-25 up to 80 with landing flaps on and look at the tips.

In the case of the K-6, she does have a few degrees of tip wash-out (leading
edge down)

In the case of the ASH-25 with landing flaps on, Only the inboard flaps go
down, the outboard flaps and ailerons go up to produce a negative angle of
attack.

So why do the wings in both cases bend down?

Why does the B-52 use spoilers instead of ailerons? Because at higher airspeeds
an aileron input causes the wing to bend and can cause the ship to turn in the
opposite direction (wing twist)

Even in a *certified* ship, if the wings start to tuck under and you don't
catch it right away, you could find yourself in a situation where elevator
won't stop the pitch down action. Now, all of this is at or above VNE, so if we
are flying our glass slippers within limits, we should be OK.
JJ Sinclair

Andy Blackburn wrote:
I a bit suspicious of this whole wing twist thing.
Since the center of lift for most airfoils is at about
0.25 chord, which is generally a bit haead of the spar,
you'd expect the natural aerodynamic forces to generate
neutral to positive twisting with loading.

I think you are right to be suspicious about the importance of wing
twist in a certified glider, but not for your reason. Most gliders do
have wing twist built into them, and the pitching momemt of the airfoil
also is twisting the wing in the same direction. The reason we don't
have worry about it is the designer knows about these factors, used
sufficent structure to avoid excessive twisting, then validated his
design with structural and flight tests.

A glider operated well outside it's limits, a damaged one, or a modified
one... Plenty to worry about then.

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

Eric Greenwell
Washington State
USA