Lateral Control at High Angles of Attack

I spite of the general improvement of airplane design methods and of aerodynamic research technique, the airplane designer is not much better off than his prewar predecessor in dealing with the troublesome question of lateral control at high angles of attack. Although there are available much data concerning the rolling and yawing moments of numerous types of ailerons, there are no corresponding methods of using these data. There is, for instance, no established basis for choosing between two types of lateral control devices; no way of deciding whether the one having the largest rolling moment will provide better control than the one having the smallest yawing moment; no way of deciding whether the choice will be the same for all airplanes. Although yawing moments are brought into every discussion of aileron control, the aileron control criterion tha t is most widely used deals only with rolling moment. It is evidently assumed that the rudder control will be sufficiently powerful to counteract the aileron yawing moment. Such dependence upon the use of the rudder is dangerous; too much responsibility is placed upon the pilot who might not only use an insufficient amount of rudder with the ailerons, but in cases of emergency might actually use opposite rudder, with disastrous results. In addition to providing insufficient design information, the method now used does not direct research into the proper channels. The motion assumed for the calculation of control power is entirely fictitious; the simple relation between aileron rolling moment and angular acceleration of roll does not exist at high angles of attack. The difficulty is that the yawing moment of the ailerons, and the yawing moment of the airplane due to an angular velocity of roll produce a yawing velocity. This yawing velocity induces