Actuation of flight surfaces in aircraft have evolved over the last century from systems using simple mechanical linkages actuated by the pilot to complex electronic systems that maneuver large loads and have some form of redundancy. The latest form of flight surface actuation uses Power-By-Wire (PBW) systems, which are modulated, lean and fault tolerant actuators embedded in the flight surface that require only the attachment of power and control wires. This research will focus on a specific form of PBW system called an Electro-Hydrostatic Actuator (EHA), which is seen on modern aircraft such as the Lockheed F-35 Lightning and the Airbus A380. An EHA is a closed-loop form of hydraulic system which controls an actuator's movement by routing fluid to it via a fixed-displacement pump attached to a servomotor. The two primary components of the EHA's hydraulic circuit are a bi-directional external gear pump and an actuator, but the system incorporates an accumulator, a bi-directional relief valve, a by-pass valve and a series of check valves for full functionality. The minimal components and the closed-loop architecture lend itself to be lightweight, modular and independent of other hydraulic systems on an aircraft. This research will focus on developing a design based on a dual EHA system used for the rudder of the F-35. The design objective is to reduce the comparative weight. The dual EHA allows for continued actuation of the airfoil in the event that one of the EHA's malfunction. The design produced in this research incorporates a new inner-circuit which allowed the system to be 12% lighter than the F35 rudder EHA. A prototype developed from this design was produced but was augmented with additional components that allow for simulation of fault conditions in the future. With a prototype produced several experiments were performed to determine the level of internal leakage and damping inside the system. Experiments showed that internal leakage increases linearly with the increase of back pressure on the pump and that the bulk of the leakage occurs at the pump itself. Experiments also showed that the damping in the system is non-linear and that it is best described by a LuGre friction model. Black-box system identification techniques were applied to the EHA to determine piece-wise linear models. These trials showed that the non-linear friction as well as the seals in the actuator forced the system to have two major piece-wise linear regions. These experiments also showed that when the mean velocity of the actuator increases so does the system bandwidth. Enclosed in this dissertation are details of the design of the dual EHA and the experimental results performed on it.

Master of Applied Science (MASc)