An Introduction to Aircraft Hydraulic Systems

Abstract This paper traces the evolution of hydraulic systems for airplanes, from the hand-actuated piston pump and “motor” piston, through the stage of motor-driven gear pumps, down to the present-day systems which derive their power directly from the airplane engine. Three general methods of pump control have been developed which permit rotation of the pump but prevent build-up in the hydraulic system, since the pump operates continuously. These methods include “the constant-pressure,” the “manual by-pass,” and the “automatic by-pass,” all of which are in wide use. Special applications of hydraulic control are described in the “power-amplifier” or “load-feel” system, the “follow-up” system, “follow-up plus load-feel” system, and the “full-automatic” system.