Power and energy issues in the induced-strain actuation for aerospace adaptive control

General concepts regarding power and energy in mechanical and electrical systems representing the aerodynamic control surface and the solid-state induced strain actuator are first reviewed. Power and energy management concepts in conventional flight control systems and in induced-strain actuated flight control systems are presented. The electromechanical coupling across the solid-state induced strain actuator, and the accompanying reversible flow of reactive energy and power are highlighted. Experimental results obtained in the laboratory with the HAHDIS Mk. 1 hydraulically-amplified highdisplacement induced-strain proof-of-concept demonstrator are presented and discussed. Suggestions for further work are given. INTRODUCTION Aerospace adaptive control through induced-strain actuation has been intensively researched in recent years. With the advent of high-performance electroactive and magneto-active materials and actuators at accessible prices, the road is open towards revolutionary changes in the aircraft flight control systems design and construction. Active materials technology allows the transition from conventional mechanical and/or hydraulic flight control systems to all electric concepts in which the control power and energy are transmitted across the aircraft in electrical form and are transformed into mechanical action directly at the control surface. The vulnerable of hydraulic lines are replaced by the much more robust electric conductors, while a large number of hydraulic paraphernalia (accumulators, cocks, valves, tanks, etc.) might simply disappear. The implementation of induced-strain actuating concepts for adaptive flight control, is currently pursued on twa parallel paths^ 1. Deformable aerodynamic surfaces (wings', tailplanes, rotor blades', etc.) activated by embedded induced strain active-material fibers. fi 7 R 2. Rigid control surface (ailerons, flaps '' , leading edge flaps, etc.) with induced-strain activematerial actuators replacing the conventional hydraulic cylinders or electric motors. The first direction aims at creating a deformable aerodynamic surface similar to that met in the animal world. This concept is, undoubtedly, visionary and full of attractive benefits for adaptive control and for performance and maneuverability improvement, since it allows the simultaneous use of span-wise and chord-wise control algorithms. However, the implementation of the deformable aerodynamic surface concept is not straight forward, and has encountered considerable difficulties. The building blocks of a deformable adaptive aerodynamic surface need to be first developed and individually certified. The aircraft structural design philosophy must be revised and updated as to incorporate the concept of highly deformable aerodynamic surfaces. The second direction aims at modifying existing flight control concepts by replacing the traditional actuation methods with lighter, less complex, more responsive, and more reliable induced-strain actuators. This concept retains the limitations of rigid and localized control surfaces, but its implementation is easier since it utilizes, to a large extent, existing techniques. This concept offers a gradual approach to the implementation of inducedstrain actuation principles, and its experimentation will provide practical experience into the specific behavior and limitations of induced-strain actuators. This paper pursues the study of power and energy issues connected with the implementation of induced-strain adaptive control using a conventional control surface and an induced strain actuator as prime mover. POWER AND ENERGY CONCEPTS FOR INDUCEDSTRAIN ACTUATION OF FLIGHT-CONTROL SURFACES Mechanical Power and Energy 301 Research Professor, Member AIAA, ASME "Professor and Director, Member AIAA, ASME Graduate Research Assistant © Copyright 1996 by Center for Intelligent Material Systems and Structures Published by the AIAA, Inc., with permission Figure 1a shows an aerodynamic control surface, while Figure 1b presents the equivalent massspring-damper system.