ON THE DESIGN OF A HIGH-GAIN SATURATING CONTROLnSYSTEM FOR USE AS AN ADAPTIVE AUTOPILOT

摘要

A theoretical investigation is made of the use of a high-gain saturating control system for an adaptive autopilot. The results of the study show that such a system can control an aircraft over the entire flight envelope without requiring air data measurements. The capabilities and limitations of this type of control system are explored, and it is found that difficulties may be encountered at either high or low extremes of dynamic pressure. At high dynamic pressure, the limit cycle or "chatter" which is inherent in the system may produce objectionable or intolerable effects. Analytical methods are presented for predicting the frequency and amplitude of this chatter and its effect on the low frequency performance. Methods are also given for reducing chatter amplitude and its undesirable effects on the low-frequency response. At low dynamic pressures, the performance is restricted by limiting and low aerodynamic gain. Attempts to make the system response time short for small inputs will result in a poorly damped response and, in some cases, instability for large inputs. It is shown that one way of compensating for this difficulty is to accept a sluggish response for low dynamic pressures;the closed-loop transfer function changes automatically with flight condition to take advantage of the higher aircraft capabilities at high dynamic pressures. It is also shown that the system can be designed to control unstable aircraft.