Abstract: To simulate, for testing purposes, the subsystems of an aircraft that electrohydraulically position the movable control surfaces of an aircraft, circuitry is provided for receiving input control signals, generated, for example, by an autopilot, and for transforming such signals into electrical output signals that are the analogs of signals produced by linear variable differential transformers (LVDT) feedback devices that track the actual movements and positions of the aircraft control surfaces. The relatively slow acting hydraulic components of the aircraft control subsystems are simulated by integrating circuitry and the resulting integrated signals are used to modulate an AC reference signal, which is then applied to the primaries of isolation transformers, the secondaries of which produce the simulated, analog LVDT feedback signals and also present a load impedance to the autopilot that closely matches the output windings of the simulated LVTDs.