Long wing twisting

I survived an unexpected twisting of my ASH-25 wing a few years back.
The situation was as follows; speed 145 knots, altitude 50 feet (finish
line). After receiving my "Good Finish JJ", I initiated a climbing left
turn to exchange speed for altitude, about 30 degrees nose up and
banked 45 degrees left to reverse my track, to land on the ramp 1/2
mile behind me. To my surprise the ship kept rolling left. I applied
full right aileron and rudder and it stopped rolling left, but fill
right control input didn't make the ship roll back to level flight. As
I climbed and speed decayed, my right turn command eventually became
effective and the ship rolled out to level flight.

The next day I spoke to the fellow that was on the finish gate. He said
the inboard portion of my wing was bent up in the normal high speed
bow, but my left wing tip was bent down. He said my wing looked like a
sine wave!

Why did this happen? I believe the left wing tip dug in as I applied
left turn control at high speed. The aileron input caused the outboard
section of the left wing to twist (L/E down) resulting in the tip
digging in and giving me much more roll than I had commanded.

Why did I survive? Because I was in a climb and my airspeed was
decreasing. As speed decayed, the wing un-twisted and normal control
was restored. Had this happened from level flight, I believe the wing
twist (digging in) would have quickly resulted in a nose down attitude
and I don't believe it would be possiable to recover from this
situation. The wing tip is dug in and causing an un-commanded roll
which will shortly cause the nose to drop resulting in even more speed.
Opposite aileron won't (can't) make it roll out and back stick won't
(can't) make it slow down, it will only tighten the spiral dive.

After this experience I placed a personal maximum speed on the ship of
120 knots and was careful to limit my aileron input to about 50% of
full throw at that speed. I told the new owner about my experience and
recommended he adopt these limits.

Is this what happened to Ivans and Egan?

JJ Sinclair

I seem to recall on my assistant instructors course in '95 that above
maneuvreing speed one should not use any more than 1/3 of full
deflection on any control, and in combination even less than that, since
that would overstress the aircraft. Isn't it likely that in doing what
you did at VNE you were flying the aircraft outside of it's design
limits and therefore ran into an aeroelastic phenomenon which caused the
wing twisting you observed because the wing had been stressed outside
the limits of its torsional stiffness?

Rgds,

Derrick Steed

line). After receiving my "Good Finish JJ", I initiated a climbing left
turn to exchange speed for altitude, about 30 degrees nose up and
banked 45 degrees left to reverse my track, to land on the ramp 1/2
mile behind me. To my surprise the ship kept rolling left. I applied
full right aileron and rudder and it stopped rolling left, but fill
right control input didn't make the ship roll back to level flight. As
I climbed and speed decayed, my right turn command eventually became
effective and the ship rolled out to level flight.

You should have practiced this maneuver at 5000 feet first. That way you
have the altitude to recover in case of something unexpected happening..

What is the manoevring speed of an ASH25?
Any control deflection above this speed should be a max of one t hird
of the total movement


--
pawnee_pilot22
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Well what JJ was asking was not the groups opinion
on what he did...rather was this a possible scenario
for the Ivans/Engen accident.

An interesting theory...how would the spoilers being
deployed have helped/hindered this condition? Interestingly
in both these Nimbus crashes, spoilers and/or flaps
were deployed to help recover...contrary to the POH.
Although no one will really know what happened in
the case of the Minden accident. My guess is for a
brief few moments...the two pilots may have thought
the other had the stick.

At 23:06 26 June 2005, Pawnee_Pilot22 wrote:

What is the manoevring speed of an ASH25?
Any control deflection above this speed should be a
max of one t hird
of the total movement


--
pawnee_pilot22

My control input was about 1/3 full throw as I started
the climbing left turn. Full opposite input was applied
only after it wouldn't stop rolling left.

My purpose in posting this was to alert other long
wing drivers to this potential problem area.
JJ
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At 21:00 26 June 2005, Jj Sinclair wrote:

Is this what happened to Ivans and Egan?

That's Don Engen.

The accident reports indicated that the outer wing
panels departed following a (more or less) symmetric
pull-up, probably out of a spiral dive. It's unlikely
that there was much asymmetric twisting at work.

The twisting aeroelastic effect comes from high aileron
hinge moments associated with high speeds and large
control deflections. Happened to my Dad in an F-86
doing max-Q testing below sea level. It's less common
at glider speeds, but long, floppy wings might permit
it.

I consider it a good idea to execute the symmetric
maneuver (pull-up) before the asymmetric one (roll),
particularly at high speed. This helps to avoid JJ's
experience.

9B

The accident reports indicated that the outer wing
panels departed following a (more or less) symmetric
pull-up, probably out of a spiral dive. It's unlikely
that there was much asymmetric twisting at work.


My thought was that wing twisting (digging in) might
have gotten them (Ivens & Engen) into the spiral dive
in the first place. Once you get a big ship pointed
down with the speed near red-line and increasing, you
might very well have already had the snitz.
JJ

Great input there JJ.

I dont like flying my ASW22 much above 120knots.
There really isnt much point to it either.

Wasnt there an ASW17 crash along similar lines to what you describe.
Washout over powering the wings structural integrity.

Al

Thanks for the heads up JJ. I have flown the Nimbus 3D a bit above 120 kts
but it really doesn't like to go that fast (lots of very hard forward
pressure required which makes me nervous in that a hiccup ends up in a loop
at best and broken wings at worst) so I think that I'll be sticking to less
than that for the future. I was taught years ago that smooth control
movements not only make aerodynamic sense (less drag) but also make safety
sense due to less stress on the aircraft. I don't do strong pulls in
anything anymore....I'll leave those to the powered aerobatic dudes.
Besides that I've forgotten how to do the tensing excercises so would
probably get syncopal!

Casey Lenox
KC
Phoenix