The US Air Force is planning to flight test a power-by-wire controlled aircraft following the successful test of advanced electrically powered actuators on NASA Dryden's Systems Research Aircraft (SRA) Boeing F-18.

The tests were part of the electrically powered actuation design (EPAD) programme, a jointly funded development effort conducted by the US Air Force Research Laboratory at Wright Patterson AFB, the Naval Air Warfare Center, Patuxent River, and NASA Dryden. The EPAD forms a critical element of the USAF's "more electric aircraft" initiative, which is aimed at the development of power-by-wire flight control systems for combat and utility aircraft.

As well as saving weight, an electrically actuated aircraft would be less vulnerable to battle damage. With the central hydraulic system replaced or made smaller, EPAD officials believe the vulnerable area would be reduced by up to 14%.

The first EPAD element, tested in 1993-4 on the F-18's left wing in place of the standard hydraulic actuator, drove the aileron using a "smart" actuator. The hybrid unit, developed by the Naval Air Warfare Centre and built by Hydraulic Research Textron, incorporated a standard hydraulic actuator with self-contained electronics.

The second test, involving the electro-hydrostatic actuator (EHA), was the first true power-by-wire device with no connection to the hydraulic system. The tests, undertaken between 1996 and 1998, also included an intermediate power, control and monitoring electronics (PCME) unit, an interface box and power conversion unit. These processed the flight-control computer's commands, powered the actuator and monitored their operation. The EHA, designed and built with the PCME by Lockheed Martin Control Systems, used a brushless 270V DC motor to drive a hydraulic pump located beside the actuator.

The final test was conducted in 1998 on an electromechanical actuator (EMA) made by MPC Products.

Source: Flight International