Helicopters

Gyroplane developer Groen Brothers Aviation (GBA) has begun designing a high-speed, long-range vertical take-off and landing (VTOL) aircraft under a US Defense Advanced Research Projects Agency (DARPA) contract. The Heliplane revives the concept of the UK’s Fairey Rotodyne, last flown in the early 1960s.

The contract, potentially worth $40 million, could lead to flight testing of a technology demonstrator based on Adam Aircraft’s A700 very-light jet by mid-2008. “We are reviving a 40-year-old concept to see if we can get performance out of a rotary-wing aircraft that is comparable with fixed-wing aircraft in speed and efficiency,” says DARPA Heliplane programme manager Donald Woodbury.

The objective for the proof-of-concept demonstrator is a two-fold improvement in forward-flight performance over a conventional combat search-and-rescue helicopter, including a 350kt (645km/h) cruise speed and 1,850km (1,000nm) unrefuelled range with a 455kg (1,000kg) payload. The goal is a lift/drag ratio greater than 10, compared with 5-6 for a helicopter and 15-plus for a fixed-wing aircraft, says Woodbury.

Groen’s concept uses a reaction-drive rotor, with tip jets powered by gas from an engine mounted in the belly of the aircraft. The rotor will be powered for vertical take-off and landing, but will autorotate in forward flight. To reduce drag, the rotor will be slowed, and lift transferred to the wing, as forward speed increases. The Heliplane will be powered by a pair of Williams turbofans, although turboprops are still be studied, says Woodbury.

The Salt Lake City, Utah-based company is working under a 15-month, $6.4 million first-phase contract that covers preliminary design of the rotor system, a full-scale blade section windtunnel test, rotating-arm tip jet test, and subscale fuselage windtunnel and rotor download tests. The second phase will involve full-scale rotor system testing in a large windtunnel. The Heliplane demonstrator is planned to be constructed in the third phase and flight tested in the fourth and final phase, says Woodbury.

GRAHAM WARWICK/WASHINGTON DC