AIRCRAFT LATERAL CONTROL OFFSETS DUE TO CONTROL SYSTEM THRESHOLD AND SPIRAL DIVERGENCE.

Lateral control offsets are possible in control systems due to the combination of control system threshold and spiral divergence. The offsets can occur during straight and level flight when roll attitude is the feedback parameter and the spiral divergence is very pronounced. These offsets are a result of the variation in the position error constant with the location of the spiral mode root. As the spiral divergence increases, the closed loop system changes from what is essentially a Type One system to a Type Zero system. The divergence combined with the threshold then produces a steady state offset in both roll attitude and lateral control position that is proportional to the threshold value times an inverse function of the roots. This problem can be eliminated by minimizing system threshold or by adding a proper combination of integral and rate feedback, although the latter method results in a rather complex system. Author