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During high speed flight, any aileron deflection may cause the wing to twist about its torsional axis (aileron reversal).
Is it dangerous?
In what kind of conditions this occurs, what have I do as a pilot to deal with it or prevent it?
What speed should be for aileron reversal in transport type of aircraft(average)

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    $\begingroup$ I reckon this should be the aircraft designer's concern rather than the pilot's. As far as I know big airliners use spoilers instead of ailerons at high speeds to avoid aeroelastic issues, but this should be managed automatically by the flight control system. Smaller aircraft should not encounter such issues within their allowed flight envelope. $\endgroup$ – mezzanaccio Mar 8 '17 at 10:06
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    $\begingroup$ @mezzanaccio or they use a different sets of ailerons (high-speed ailerons) usually located nearer to the fuselage, sometimes over the engines (look at B767, B777 or MD-11 for example) :-) $\endgroup$ – Marco Sanfilippo Mar 8 '17 at 11:15
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    $\begingroup$ Unless you're a test pilot, you're unlikely to encounter such situation when you fly. The operating limitations are established for a reason. You have to be way outside the certified flight envelope for this to occur. $\endgroup$ – kevin Mar 8 '17 at 14:39
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Yes, this is dangerous and must be avoided.

Consider this: Between the low speed range where the aileron works as intended and the high speed range where it works like a Flettner flap there is one speed point where the rolling moments of the aileron and the wing twist cancel each other out. There the aircraft is uncontrollable in roll. No sane pilot would fly such an aircraft voluntarily.

Set the speed at which full aileron deflection produces only a quarter of the rolling moment coefficient as the never exceed speed.

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