A theoretical study of lateral stability with an automatic pilot

The influence of automatic operation of the aileron and rudder controls on the lateral stability of an airplane is discussed. The control deflections are assumed to be proportional to the deviations and to the rates of deviation of the airplane from steady-flight conditions. The effects of changes in the types of deviation governing control application are considered. For one simple method of control in which the aileron deflection is proportional to the angle of bank and the rudder deflection is proportional to the angle of yaw, the effect of lag in control application is studied and regions of stability with and without lag are given. For the simple control with lag, curves are included that show the variations in the roots of the stability equation with changes in the amount of control applied. It is concluded that, although the simple control provides a satisfactory means of varying most of the lateral stability characteristics, the stability in azimuth will always be poor for such a control.