Microprocessor Control of Low Speed VSTOL Flight

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Microprocessor Control of Low Speed VSTOL Flight

R. V. Walters

The objective of this project has been to design an improved three-axis stability augmentation system (SAS) for the AV-8B Advanced Harrier VSTOL aircraft using microprocessor-based digital control. The research focuses on improving the handling qualities of the airplane through SAS redesign in the low speed flight regime. Particular attention is paid to the so-called weather-cocking instability encountered in transition (hover to conventional and vice versa) flight. Until quite recently, there has been a dearth of information about the flight characteristics of the Harrier. A major breakthrough in this field was achieved by the development of MCAIR's X22A AV-8B mathematical model, which yielded a set of linearized stability derivatives for the aircraft. The first step toward the improvement of the AV-8B SAS requires the utilization of these coefficients in the development of an analog/hybrid model of both the aircraft itself and of the unmodified SAS. The controller design employs digital state feedback control to relocate the system closed loop poles. The conclusion reached is that this method of control represents a valid approach to the final solution of the Harrier's stability and control problems. A long range goal of this research is that this controller design concept be applied to future aerospace vehicles.