Control Strategy for Electro-Mechanical Actuators Versus Hydraulic Actuation Systems for Aerospace Applications

Actuators are critical engine and flight control components used in aerospace applications for motion and fuel controls. All aircraft today contain three primary types of actuators; electro-mechanical actuators (EMA), electro-hydraulic actuators (EHA), hydraulic actuators. Actuators control thrust vectoring of the main engines during powered ascent, movement of the aerodynamic control surfaces, and the positioning of propulsion system geometry and fuel/air control valves. EMAs consist of an electric motor and gear-train to reduce speed, translate motion, and provide appropriate load torque. Electro-hydraulic actuators are self contained systems that combine the benefits of an electric system with the benefits of hydraulic systems. EHAs use an electric motor to drive a hydraulic pump which develops hydraulic pressure to act on a cylinder to provide the mechanical actuation energy. Hydraulic actuators use a centralized hydraulic pump that supplies the required pressure. EHAs avoid the operability issues associated with a central hydraulic supply and distribution system. They also have weight and integration benefits. Aerospace actuation has historically been dominated by hydraulic and fluid power systems. Sales of hydraulic actuation systems today accounts for more than several billion dollars per year of business for the major vendors. These systems comprise about 19% of the cost of a commercial aircraft. However, as entrenched as hydraulics are in flight applications, the emergence and maturation of electrical actuation promises to encroach significantly on hydraulic technology over the next several decades. This paper focuses on the potential of EMAs for aerospace applications and compares their qualities and benefits with hydra-mechanical actuators (HMA) and hydraulic actuators. Emerging industry trends have demanded compact, accurate, actuation for turbine fuel and geometry control. The EMA provides these benefits for applications where high-precision rapid actuation is desired. EMAs maintain the same high performance capability as hydraulic actuators and the potential for enhanced reliability and controllability in a compact package. The EMA will lend itself to high levels of diagnostics and fault prediction capability using algorithms in the engine/aircraft control system. Adaptive engines of the future will demand a variety of actuation solutions which may be a combination of EMAs, EHAs, and others. Their use requires careful system considerations to achieve optimal integration in the engine and air vehicle.