The Use of Power–Adaptive and Power–Reversible Flight Control Actuation Systems to Achieve Hydraulic Power and System Weight Savings

New generations of aircraft, both commercial and military are expected to utilize active controls to reduce trim drag and enhance fuel economy. When such active controls are accepted, the practice of designing surface actuators to torque saturate will almost certainly be abandoned. This conclusion is unavoidable; since when flight safety, through dynamic stability requires active controls, and a negative passive stability margin is present on the aircraft we can no longer allow the response of actuators to go to zero. Additional actuator capacity and power required by the elimination of torque saturation will have to be charged as a weight penalty to counterbalance the obvious advantage of lesser trim drag. This penalty will apply unless we devise other means to reduce actuation power requirements.

The power reversible actuator concept offers a promise of a fully active non-stalling surface control system which will require less installed hydraulic power than the torque saturating systems in current use. The power adaptable actuator concept constitutes a less drastic step in the same direction.

This paper defines the terms power adaptable and reversible with respect to the application of hydraulic or electrical power to the positioning of a loaded aircraft control surface. Examples of each type of system are taken from those systems in current use with discussion of the limitations of each specific system. Systems of each type are then described which have not yet come into use and which circumvent many of the disadvantages of the systems already in use. Both the electrohydraulic stepping motor “D.E.H.A.”* type rotary geared output system and the staged sequential valved ram type system are described as examples of advanced systems which are, to a large degree, both power adaptable and reversible.