aileron reversal
 

BEAgle,
thanks for the correction ref the 'Whistling Wheelbarrow ' accident, memory is a fallible thing.

For the slightly dense amongst us (me !) could someone explain what causes aileron reversal and what the effects are.

I'm assuming that its due to the wing twisting when the ailerons are deflected at high speed - the ailerons remain fixed in space and the wing twists.

Does this actually reverse the control input from the pilot ie a left bank rolls the a/c to the right, or does the term 'aileron reversal' refer purely to the structural effect.

Partial aileron reversal means that the torisonal stiffness of the wing (resistance to twist) is inadequate at high IAS and that aileron deflexion will indeed twist the wing, reducing the effective roll rate due to the reduced AoA change over the section concerned.

Taken to extremes, it might become so twisted that the effective AoA would cause a rolling moment in the opposite direction to that intended by the pilot.

Torsional flutter problems can also occur when a wing is disturbed in turbulence and twists, it's the effect you hear when a venetian blind buzzes in a strong draught!

Yes and yes.

Generally what happens is that aileron effectiveness steadily reduces with increasing speed until the aileron reversal speed is reached (when actually you have no roll control at-all), above that the control works in the reverse sense.

G

Not strictly aileron reversal in the sense you describe, but Delmar Benjanin's replica GeeBee racer had some telling scrapes on the wing tip from the first time he tried to 3-point it onto the runway.
Apparently, in the 3-point attitude, the angle of attack was sufficient to stall a wing tip if any down-aileron was applied, with ensuing entertainment.

From then on it was wheelers only (at about 110mph).

G
I understand aileron reversal was endemic at surprisingly low airspeeds in some vintage gliders of the 30's and was accommodated by their pilots through deft and positive footwork. A trawl though VGC might be worth the effort.
W

I think what's surprised me here (plus scouting around I found out a few other things - for example that the prototype C141 had a serious aileron reversal problem) is not that aileron reversal is there, but that it seems to have happened so much, on so many aeroplanes, and is apparently still cropping up.

I *thought* that the basic theory and solution had been cracked 40 years ago, but that wouldn't appear to be true. It also appears true from Wunper's post that it was known well before the Spitfire as well, which surprises me somewhat.

Interesting, very interesting.

G

N.B. Wunper, on the one aeroplane I've ever flown with a serious aileron reversal problem, a development of the CFM shadow that was eventually, and rightly, abandoned before certification, it was certainly true that heavy use of rudder was the only way to achieve anything resembling a useable roll rate at most speeds.

Without scanning back, I think that some wise soul (maybe BEagle?) posted about the F-4, which apparently also needed heavy bootfuls of rudder to roll in certain regimes. I remember this being said by msny others, though I think it was more to do with AoA than anything.

Conan

See reply No 18



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Not quite aileron reversal, but....
Shortly after buying a DH82 I was interested to note that as the stick was moved to one side the appropriate ailerons would go up and down in the correct sense, but further movement caused the upgoing one to go further up, while the (previously) downgoing one would start to come back up. Close to full travel, one would be well up, the other back to neutral. At full travel, one was fully up, the other very slightly up! Believe this is normal behaviour for a Tiger, no doubt designed to reduce adverse yaw. Also no doubt contributes to the leisurely roll rate!

Sailing, think DH developed (and patented?) the differential aileron for the Moth family, as you say, to reduce adverse yaw. Never knew it was that extreme though!