Effect of Hysteresis on the Performance of a Highly Augmented Flight Control System

With advances in control system and sensor technology, higher levels of augmentation are being integrated into the basic aircraft controls. Often, designers neglect non-linearities in the hydromechanical elements of the control system during the desiqn and simulation phases of development. This paper demonstrates the effect of hysteresis on the performance of a highly auqmented fly-by-wire helicopter control. system and shows that hysteresis need not be a problem with lower levels of augmentation. A describing function analysis demonstrates that the highly auqmented system is more sensitive to hysteresis effects than the conventional rate command system because of its added integrations. These non-linearities can become the limiting factor in attainable automatic, hover hold precision. 4 linear compensation ' technique for non-linearities is described and its effect on control system perforaance is demonstrated.