LONGITUDINAL STABILITY OF AN AIRPLANE WITH DELAYED ACTION AUTOPILOT,

An investigation was made with the aid of asymptotic methods by Krylov and Bogolyubov of longitudinal stability of an aircraft with an autopilot which is making short-period movements. The presence of delay in the autopilot has a substantial effect on the stability of the airplane. This effect is expressed in the first place in considerable narrowind down of the area of stability of the system constructed in the plane for the transmittable numbers of the autopilot. Not to take into account the delay may lead to the choice of designs of autopilot outside the area of the asymptotic stability of the system, i.e., to instability. The permissible value for the delay in the autopilot depends on and is determined by the value of the aerodynamic coefficients. With a given value of delay the aerodynamic coefficients determined the permissible adjusting of the autopilot. The periodic oscillations occurring natural oscillations which are set up on the boundary of the area of the asymptotic stability of the system under consideration are stable for small values, i.e., according to Bautin the boundary is safe for small magnitudes. Author