NASA HAS temporarily halted test-flights of an electrically powered actuator on its McDonnell Douglas F-18 Systems Research Aircraft after encountering problems on its initial flight.

Despite this, the flight of the electro-hydrostatic actuator (EHA) is considered a milestone in the development of an all-electric aircraft. The tests are part of the electrically powered actuation design (EPAD) validation programme. NASA says that the problems, believed to concern the control of the EHA, "...need to be ironed out before flight-tests restart".

The EHA operates the F-18's left aileron without using the aircraft's standard hydraulic system, taking signals from the flight control computer and using electrical power generated by the engines to drive a pump containing a small amount of internal hydraulic fluid.

The EHA effort, is part of a joint NASA, US Air Force and US Navy study into eliminating heavy hydraulic systems in favour of "power-by-wire" systems. The study suggests that all-electric systems could result in fuel and weight savings, as well as reducing vulnerability to cannon fire.

The EHA ram, is moved by an integrated motor and hydraulic pump, receiving commands from a power control and monitoring electronics unit. This accepts analogue position commands from EPAD interface boxes which act as intermediaries between the actuator and the flight-control computer.

The EHA is the second of three actuators being tested in the EPAD programme, all built by three different manufacturers. The first "smart actuator" was tested in May 1993. The third, an electro-mechanical actuator, is to be flown by mid-1996, according to NASA. The third actuator differs from the EHA in having a ball-screw ram driven by a rotary gear train.

Source: Flight International