Development of Helios and Pathfinder electric motor proposed for Lockheed high-altitude surveillance platform
AeroVironment, the California-based unmanned air vehicle specialist, is proposing development of a flight-weight ironless core electric motor for Lockheed Martin's High Altitude Airship (HAA) surveillance platform, after successfully developing a prototype version.
The HAA, which is designed to act as a quasi-geostationary high-altitude surveillance UAV to watch for ballistic missiles and air threats approaching the continental USA, is being evaluated under a Missile Defense Agency (MDA) contract. The prototype airship is being designed to loiter with a 1,815kg (4,000lb) surveillance payload at altitudes around 65,000ft (19,800m) for periods of up to a month. A production version would be designed to loiter for up to a year.
Four motors will be needed to power the helium-filled airship, which is 152.4m long and 48.7m in diameter, with a volume of 1.5 million m3 (52.9 million ft3). The electric motors will drive large twin-bladed propellers, two on each side of the vehicle, with thin-film photovoltaic cells covering the airship's skin, generating power from sunlight for the vehicle's propulsion and the additional 10kW necessary to operate the airship's payload.
AeroVironment business development manager Charlie Botsford says the new design builds on earlier 3-5kW ironless core electric motors developed for the Helios and Pathfinder high-altitude flying- wing UAVs, but is significantly more powerful, with a rating up to 50kW.
"For the Pathfinder and Helios we had to develop our own motors because of the high-altitude conditions they operated at where thermal issues are critical. With the high-altitude airship this is even more critical because the motors are much larger," says Botsford. Unlike conventional iron core-based electric motors, the AeroVironment design uses permanent magnets to set up a magnetic field through "highly efficient packing of the copper wire", says Botsford.
Other design challenges included meeting equally critical "low-speed torque requirements, especially at sea level for take-off and manoeuvring", as well as part-load efficiencies greater than 98%. "That's one of the constraints of the HAA, where you are cruising with lower power levels of 5-10kW at 60,000ft. We had to have high efficiency at around 5kW, whereas a regular motor's efficiency drops off at lower loads." AeroVironment is also supplying the propulsion motor control electronics, propellers, and propeller pitch control.
GUY NORRIS/LOS ANGELES
Source: Flight International
