How does aileron reversal work?

  • How does aileron reversal work? igen5

    I want to know how aileron reversal takes place when control reversal velocity is higher than divergence speed and operating speed is in between them (for conventional wing)

  • Control reversal speed is way lower than divergence speed. It may actually lower than operating speed for some aircraft, which is why they have inboard ailerons/flapperons and/or use spoilers (that don't suffer control reversal) for roll control at high speeds.

    Control reversal (at high speed; there is also control reversal at stall, which is different) occurs because the force generated by ailerons twists the wing sufficiently so that the aileron starts to act more like trim tab. For that the wing has to flex, but it does not have to flutter at all.

    Spoilers act closer to the wing mid-chord, so they don't twist it much and thus don't suffer reversal. In fact they twist the wing a bit, because pre-stall lift acts more forward than post-stall lift, but this twists the wing forward and thus further reduces the lift, so still no control reversal.

  • As I understand it, aileron reversal can occur in two regimes of flight, high speed and near stall.

    Near stall, the wing is very near it's critical angle of attack. When the pilot inputs let's say a left turn, the right aileron will deflect downward. This downward deflection increases the AOA of the outboard portion of the right wing such that the lift generated by that outboard portion is lower (drag higher as well) than the lift generated on the opposite wing.

    You can kind-of visualize this by thinking of a wing operating on the backside of the lift curve.

    Aileron reversal at high speed, (again, as I understand it) can occur when the wing isn't stiff enough tortionally to prevent twisting about the aircraft's lateral axis when a control input is made. Some old warplanes had this characteristic at high speeds.

    For example, the pilot makes a control input to the left. The right aileron deflects downward, and instead of raising the overall AOA of the wing, it lowers it because the aileron acts like a trim tab, twisting the wing's leading edge downward.

    Your question is asking: If the control reversal velocity is calculated to be higher than the divergence velocity, (When the wing breaks apart), how then can control reversal take place in flight?

    The answer would be when it occurs near a stall.

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