Long wing twisting

[JJ Sinclair]

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

[Derrick Steed]

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

[Guy Byars]

> 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..

[pawnee_pilot22]

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
------------------------------------------------------------------------
Posted via OziPilots Online [ http://www.OziPilotsOnline.com.au ]
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[Stewart Kissel]

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.

[John Sinclair]

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
>------------------------------------------------------------------
>>------
>Posted via OziPilots Online [ http://www.OziPilotsOnline.com.au
>]
>- A website for Australian Pilots regardless of when,
>why, or what they fly -
>
>

[Andy Blackburn]

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

[John Sinclair]

>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

[[email protected]]

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

[Kilo Charlie]

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

[Andy Blackburn]

At 12:30 27 June 2005, John Sinclair wrote:

>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.

We probably can't say definitively one way or the other.
Many big ships have a tendency to digging in at the
stall even without any aeroelastic (twisting) effect.
This can be exacerbated by a pilot trying to pick the
wing up through use of aileron rather than rudder.
As you say, once the nose gets pointed down in a big
ship you can have very little time to get things straightened
out before you're past some limit or other.

Generally you need pretty high Q before the aileron
can produce enough moment to twist the wing. This could
happen once the spiral is established and speed has
built up, but the root cause of the spiral is likely
related to a more common stall/wing drop sequence.
In the Minden accident there wasn't any asymmetric
wing bending reported, but there was quite pronounced
symmetric bending observed leading to structural failure.
It's not clear to me that you can un-twist a wing
without slowing down, so I'd be hard pressed to come
up with the sequence of events that would have the
glider go directly from an asymmetric wing bending
to symmetric bending/failure.

Notwithstanding the specifics of that accident, the
general warning about aeroelastic effect - particularly
in sailplanes over 20m in span - is noteworthy.

9B

[John Sinclair]

At 10:00 28 June 2005, Andy Blackburn wrote:
>At 12:30 27 June 2005, John Sinclair wrote:
>
>>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.
>
>We probably can't say definitively one way or the other.
>Many big ships have a tendency to digging in at the
>stall even without any aeroelastic (twisting) effect.
>This can be exacerbated by a pilot trying to pick the
>wing up through use of aileron rather than rudder.
> As you say, once the nose gets pointed down in a big
>ship you can have very little time to get things straightened
>out before you're past some limit or other.
>
>Generally you need pretty high Q before the aileron
>can produce enough moment to twist the wing. This could
>happen once the spiral is established and speed has
>built up, but the root cause of the spiral is likely
>related to a more common stall/wing drop sequence.
>In the Minden accident there wasn't any asymmetric
>wing bending reported, but there was quite pronounced
>symmetric bending observed leading to structural failure.
> It's not clear to me that you can un-twist a wing
>without slowing down, so I'd be hard pressed to come
>up with the sequence of events that would have the
>glider go directly from an asymmetric wing bending
>to symmetric bending/failure.
>
>Notwithstanding the specifics of that accident, the
>general warning about aeroelastic effect - particularly
>in sailplanes over 20m in span - is noteworthy.
>
>9B

That was very good, 9B. Give yourself a big hug from
old JJ. BTW, good job at Parowan. I would have given
you a run for the money if only my wheel hadn't rolled
about 12 miles short of the finish cylinder, on the
first day. I enjoyed the contest, Parowan is an awesome
place to fly. Hope the Region 9 guys will continue
to have regionals and nationals there.
Cheers,
JJ

[Papa3]

Andy Blackburn wrote:
> At 12:30 27 June 2005, John Sinclair wrote:
>
> Generally you need pretty high Q before the aileron
> can produce enough moment to twist the wing. This could
> happen once the spiral is established and speed has
> built up, but the root cause of the spiral is likely
> related to a more common stall/wing drop sequence.
> In the Minden accident there wasn't any asymmetric
> wing bending reported, but there was quite pronounced
> symmetric bending observed leading to structural failure.
> It's not clear to me that you can un-twist a wing
> without slowing down, so I'd be hard pressed to come
> up with the sequence of events that would have the
> glider go directly from an asymmetric wing bending
> to symmetric bending/failure.
>
> Notwithstanding the specifics of that accident, the
> general warning about aeroelastic effect - particularly
> in sailplanes over 20m in span - is noteworthy.
>
> 9B

Not meaning to be glib about this serious subject, but it reminds me of
a video I once saw. They were clearing out the flight research lab at
the university, and I came across a short film of flight testing on the
Goodyear Inflatoplane. For the unitiated, this was (as the name
implies) an inflatable aircraft designed to provide a platform for
forward recon to the army and potentially recovery to downed aviators.


There's an air-to-air sequence during stability tests that showcases
bending and twisting moments like nothing else I've ever seen. It
ought to be required viewing. The inflatoplane had a VNE somewhere in
the 60-70 mph range if I recall, and these tests were done near that
range. In one shot, the left wing (I think) tucks briefly like a
folded napkin. In this wing, however, the structure was elastic
enough that it basically "sproinged" back into shape. I spoke with a
guy who was a test pilot on the project, and he seemed to be of the
opinion that springy wings weren't such a great idea after all :-))

P3

[Andy Blackburn]

At 13:24 28 June 2005, John Sinclair wrote:
>That was very good, 9B. Give yourself a big hug from
>old JJ. BTW, good job at Parowan. I would have given
>you a run for the money if only my wheel hadn't rolled
>about 12 miles short of the finish cylinder, on the
>first day. I enjoyed the contest, Parowan is an awesome
>place to fly. Hope the Region 9 guys will continue
>to have regionals and nationals there.

Thanks JJ. Seems like many of the top competitors this
year could have used the 'drop a day' rule. Every day
was a different challenge.

Ditto on the continuing use of this beautiful site
for regionals and nationals - without a local club
groups from out of town will need to adopt it. I have
heard rumblings that Region 9 has an interest in Moriarty
for next year - so who will take the Parowan baton
from the very capable Mifflin group?

9B