Roll control problems

In low speed flight, where the wing may be close to the stall angle, the down­ward deflection of an aileron will produce an increase in drag associated with the increased camber and onset of stalling, while the upgoing aileron will pro­duce a reduction. This causes the aircraft to turn towards the lowered aileron, which is the reverse of the normal response described earlier. The problem can be partially overcome by the design of the control surfaces, as in the Frize aileron design shown in Fig. 10.14. Alternatively, the ailerons may be geared, so that the upgoing surface moves more than the downgoing one.

Spoilers present another, and sometimes preferable solution. The operation of a spoiler causes a loss of lift, and the required rise in drag on the downgoing wing. Spoilers are also used for control in high subsonic and supersonic flight, where conventional ailerons may either lose their effectiveness, or become too effective.