The Selection of Actuation Devices for Aircraft Pneumatic Valves in Systems Under Computer Control 891456
The advent of lightweight, inexpensive digital computers has substantially enhanced the capabilities of the valves that control the flow of air through airborne pneumatic systems. Control algorithms which were once implemented via mechanical devices are now being performed by on-board computers. As the computer takes over more of the function of valve control, the problem arises as to the best method for providing the power required to position the valve modulating element. Traditionally, this power has been provided through the use of pressurized hydraulic fluid or bleed air. With computers taking over the valve control functions, should valve actuation also be purely electrical?
This paper discusses the performance requirements for valves in four different aircraft pneumatic systems. It examines the power needs for each type of valve and provides a method for calculating the actuation power needed to ensure that the valve will perform properly. It then evaluates the various actuation technologies available and examines the relative merits of each with regard to overall system weight. The four actuation methods are: 1) Electrohydraulic, 2) Electropneumatic, 3) Servomotor Electromechanical, and 4) Stepper Motor Electromechanical. Finally, a graph is presented which compares the weight of each type of actuator for existing aircraft valve requirements.