Limitations of block-decentralized control with implications for ASTOVL aircraft

Abstract

Limitations of block-decentralized control laws are investigated for an Advanced Short Take Off and Vertical Landing (ASTOVL) vehicle. The vehicle configuration selected is similar to those proposed for the Joint Strike Fighter (JSF) program. For the model considered, no block-decentralized control law can achieve acceptable performance as defined herein. This result follows from necessary conditions for the existence of a block-decentralized control law that achieves specified performance. One of these conditions is violated for the case study. To achieve the required decoupling, block-decentralized control requires an engine feedback gain that is larger than actuation constraints allow. The performance specifications and actuation constraints are considered realistic estimates for this class of vehicles, and the case study demonstrates possible limitations of block-decentralized control for ASTOVL vehicles, in general. Introduction Advanced Short Take Off and Vertical Landing (ASTOVL) aircraft configurations are of current interest. These aircraft configurations frequently exhibit significant airframe/propulsion subsystem 8-9 dynamic interactions. Fig. 1 displays a generic ASTOVL vehicle. The airframe's must be generated by the propulsion subsystem during low speed flight and hover. The is generated by re-directed aft thrust and thrust from an auxiliary lift system. Some proposed designs call for the system to possess both fan and turbine, and possibly even a burner. However, the primary thrust of the system is typically provided by either main engine by-pass and/or core flow. Secondary thrust is generated by airflow from intakes located on top of the fuselage. Nozzle vectoring and Reaction Control System (RCS) jets will generate t Presented at the AIAA GNC Conf., San Diego, 1996, AIAA Paper No. 96-3921. t Research Associate, Student Member, AIAA. * Prof, and Director, Associate Fellow, AIAA. Copyright © 1996 by J. Schierman and D. Schmidt. Published by American Institute of Aeronautics and Astronautics, Inc. with permission. moments to enable attitude control of the airframe during hover, low speed, and high angle of attack flight. RCS thrust is typically generated by some manner of engine bleed.