Flight tests of an unmanned air vehicle, which is neither a fixed- wing aircraft nor a rotorcraft, resume next week with the installation of a new, more-powerful engine.

Unveiled by its US inventor at the Farnborough air show with a two-cycle alcohol engine, the Fanwing will now use a four-cycle petrol engine to give a short-take-off and landing capability.

The Fanwing uses a bladed rotor on a horizontal axis, which effectively acts as a thick wing. These blades, rotated by an engine at up to 2,000RPM, suck in air and push it up and over the wing, providing lift.

The 2.2m (7.2ft) -wingspan aircraft uses control flaps instead of ailerons. To turn, a flap is tilted forward, reducing thrust and lift. Winglets on the end of each wing are also used to boost airflow and add about 20% to lift. With a powerful enough motor, it may be possible that enough lift could be generated for vertical take-off.

"It will never be as efficient as a helicopter for straight vertical lift, but we think it will have a much faster transition [from vertical to horizontal flight]. It can also go beyond the theoretical speed of a helicopter," says its inventor, US born Patrick Peebles, who is based in Italy.

While helicopters achieve lift to power ratio of 50N/kW in hover and 75N/kW in horizontal flight, the Fanwing design, which was windtunnel tested at Imperial College in London in 2002, achieved 30N/kW for hovering and 280N/kW in forward flight mode.

Peebles adds that he expects a Fanwing aircraft to use from half to a fifth of the fuel used by helicopters in forward flight because of these efficiency gains.



Source: Flight International