In one mode of operation, the autopilot of a jet transport is used to control altitude. For the
purpose of designing the altitude portion of the autopilot loop, only the long-period airplane
dynamics are important. Assume that the linearized relationship between altitude and elevator
angle for the long-period dynamics is
?(?) =
?(?)
?(?)
250
?(? + 5)(? + 50)
ft/sec
deg
The autopilot receives from the altimeter an electrical signal proportional to altitude. This signal
is compared with a command signal (proportional to the altitude selected by the pilot), and the
difference provides an error signal. The error signal is processed through compensation, and the
result is used to command the elevator actuators. A block diagram of this system is shown in figure
below. You have been given the task of analysing the frequency response and stability of this
system. Begin by considering a proportional control law D(s) = K.
- Draw a Bode plot of the open-loop system for D(s) = K = 1
- Find the approximate gain and phase margins of this system.
Assoc. Prof. Dr. Güleser K. Demir
Asst. Prof. Dr. Hatice Doğan
Sample Solution