A missile adaptive roll autopilot with a new dither principle

The design, theory, and simulation are described for a new adaptive roll autopilot in a typical air-to-air cruciform interceptor missile with a range of 55.4 to 1 in aileron-moment effectiveness. The adaptive loop injects a sinusoidal dither signal (at 3.5 c/s) into the main roll loop, measures the in-phase component of the return signal (not its amplitude, as in the Smyth [1], [2] system), and adjusts the gain of a multiplier in the main roll loop. The system maintains unity loop gain of the roll loop at the dither frequency without cross-coupling effects, and is believed to have good inherent rejection of noise. The analysis of the system is satisfactory for preliminary design, but stability limits of the adaptive loop must be tested by simulation. Successful simulation results are presented for flights at three altitudes with different Mach histories. This type of system appears to be practical for the roll autopilot of an interceptor missile with tail control, particularly if ground-launched. The roll multiplier gain setting can be used to adjust analogous gains in the pitch and yaw autopliots. Further analysis of stability and noise rejection would be desirable.