All-Electric Airplanes Prove Efficient
ngineers at NASA's
Dryden Flight Research Center in Edwards, California, have completed tests
on a device that paves the way for developing future all-electric airplanes.
These planes could be safer and more fuel efficient than today's aircraft.
Called the Electro-Hydrostatic Actuator (EHA), the device eliminates or minimizes airborne dependence on pneumatic, hydraulic and mechanical systems. Along with related electrical systems, it also could lead to a 5- to 9-percent fuel savings on an all-electric passenger plane, a 30- to 50-percent reduction in ground equipment, and a reduction in the vulnerability of military aircraft in combat situations.
The EHA uses an electric motor to drive a hydraulic pump and relies on local hydraulics for force transmission without using or interfering with the aircraft's central hydraulics. The EHA contains its own hydraulic fluid reservoir/accumulator. Its two back-to-back check valves allows the reservoir to replenish fluid in the balanced actuator cylinder. The EHA performed as well as a standard actuator and completed 36 hours of flight, said Robert Navarro, Dryden's principal investigator.
The actuator does not require active cooling and has a solenoid-operated bypass shutoff valve that reverts to cycling the fluid through one orifice. It also has components that provide measurements and position feedback.
The device, designed as part of a joint Air Force-Navy-NASA effort, was tested on the left aileron of NASA's F/A-18 Systems Research Aircraft.
Taking its signals from the aircraft's flight-control computers, the EHA uses its electronics to "fool" aircraft computers into thinking a standard actuator is on board. The device contains a small amount of hydraulic fluid and uses an electric motor to drive its pump, creating a force that moves the aileron.
For many years, NASA, the U.S. Air Force and the U.S. Navy have sought to eliminate sophisticated but heavy hydraulic systems in aircraft in favor of electrical "power-by-wire" systems for operating flight controls. Besides savings in costs and support, electrical systems promise diminished vulnerability in combat by eliminating hydraulic lines in the fuselage and wing box. The power-by-wire arrangement also will reduce complexity and improve reliability.
The EHA is part of the Electrically Powered Actuation Design Program. The U.S. Air Force Research Laboratory, located at Wright-Patterson Air Force Base in Ohio, manages the overall program. Dryden is responsible for flight safety and provided ground testing for the actuator and the necessary data acquisition systems. Dryden also installed and integrated it in the F/A-18.
The device is the second of three actuators being tested. It will continue to fly aboard the F/A-18 until it is replaced by the Electro-Mechanical Actuator. The Air Force is sponsoring this mechanical actuator, which is powered by electronics.
For more information, contact Robert Navarro at Dryden Flight Research
Center. Call (805) 258-3193,
E-mail: Robert.Navarro@mail.dfrc.nasa.gov
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Ice Spacecraft
Elevates Commercial Applications
Results from the Laser Altimetry Mission could result in commercial applications.
The Laser Altimetry Mission is scheduled to be launched in a near-polar orbit in July 2001. The Greenland and Antarctic ice sheets cover 10 percent of Earth's land area, and they contain 77 percent of Earth's fresh water and 99 percent of its glacier ice. Measurements of the ice sheets are essential for assessing whether future changes in ice volume will add to the sea-level rise, which is already occurring, or whether the ice sheets might grow and absorb a significant part of the predicted sea-level rise. The laser altimeter, being developed at Goddard Space Flight Center, will provide precise elevation of the land, ice and clouds that are overflown. The laser transmits short pulses of infrared light and visible-green light to measure ice sheet elevation and land topography (infrared light) to measure clouds and aerosols (green light). The distance from the spacecraft to clouds and to Earth's surface will be determined from measurements of the time taken for the laser pulses to travel to these targets and return. For more information,
contact Joe Dezio at Goddard Space Flight Center. Call (301) 286-5102,
Fax: (301) 286-1736 |
laser
study about the growth or shrinking of the Earth's polar ice sheets
and the future rise and fall of global sea level will also measure
land topography for a variety of scientific and potential commercial
applications. The Laser Altimetry Mission, recently known as ICESAT—for
Ice, Cloud and land Elevation Satellite—will accurately measure
the elevations of Earth's ice sheets, clouds and land, as well as
the heights of clouds for studies of Earth's temperature balance.
