Design and Flight Testing of Incremental Backstepping based Control Laws with Angular Accelerometer Feedback

This paper discusses the design, implementation and flight testing of an incremental Backstepping (IBS) based manual flight control law with angular accelerometer (AA) feedback. The main advantages of incremental control laws are that they only require a partial model of the system and are of low complexity. Incremental control laws for aircraft rotational motion, however, need angular acceleration measurements to compute the control increments. Previously, estimates based on angular rate measurements were used for this. The newly implemented AA feedback is expected to improve the performance of the controller by decreasing the sensor delay. The manual control laws command roll rate/angle, vertical load factor, and side slip angle and have been implemented on a Cessna Citation II aircraft, equipped with an experimental fly-by-wire system. The IBS based control law has an integrated integral control term and uses Pseudo Control Hedging to handle actuator saturations. The IBS based control law is shown to have highly satisfactory performance in flight. Test manoeuvres included standard roll and load factor commands and asymmetric thrust handling. Robustness to model mismatch has been compared in a nonlinear simulation for the controllers with and without AA feedback. In general, the AA feedback improved the tolerance to mismatch substantially