Mr Yanagisawa, whose nickname is "Gen", developed a small, but comparatively high-powered, horizontally opposed two-cylinder engine while working for the Zenoa company. By 1985, this had been tested in a hang-glider, para-glider and model aircraft, but failed to find a market. Tests of a coaxial rotor RPV in 1987 were unsuccessful because of control problems, while a manned twin-engined design in 1992 failed to produce sufficient lift. By 1994, however, this had evolved into the BDH-1 (Boy's Dream Helicopter 1), exhibited at that year's Japan Aerospace Show. A three-engined BDH-2 followed in 1996 and was further modified as the BDH-3 which, although successful, was unable to sustain height with one engine inoperative. The BDH-4 was shown at AirVenture, Oshkosh, USA, in 1997 and continues to be refined. Manufacture is by ESCO, a general engineering company headed by Mr Yanagisawa, which has produced over 400 types of equipment since being founded in 1971. The assistance of a US agent was enlisted to collaborate on H-4 trials, such as ballistic parachutes and high-speed cruising, which are prohibited by Japanese air law.

YANAGISAWA GEN H-4

TYPE: Exoskelitor flying vehicle.

PROGRAMME: Four-engined development of BDH-3; basic version shown at AirVenture, Oshkosh, 1997; yaw control by small, electrically powered, auxiliary propellers; by 1998, yaw accomplished by differentiation of rotor rpm. Current configuration first flew in 1999. Marketed in kit form.

CURRENT VERSIONS:

H-4: As described.

H-4 UAV: Radio-controlled version, first flown 22 March 2002.

COSTS: Kit US$50,000 (2002).

DESIGN FEATURES: "Strap-on" personal helicopter with contrarotating twin blades of tapered planform and fixed pitch (thus no autorotation capability - replaced by ballistic parachute, if desired). Seat, with fuel tank at rear supported by triangular tube framework landing gear and footrest. Gimballed platform above occupant's head houses four small motors, central transmission and rotor assembly with gears. Combined hand-grip control column and instrument panel attached to front of platform. Rotor speed 800 to 900 rpm. Quoted build time 40 hours.

FLYING CONTROLS: Two-axis control by tilting of engine/rotor platform; yaw control effected by thumb switch on instrument panel, operating electric motor which differentiates speed of rotors by 1%.

STRUCTURE: Framework of 5cm aluminium tube; glass fibre seat and backpack; rotors of carbon fibre and Kevlar, with foam core.

LANDING GEAR: Four small "wheels" each comprise multiple rollers in circular arrangement.

POWER PLANT: Four 124cc Gen 125 two-stroke, horizontally opposed, two-cylinder piston engines with independent ignition, positioned symmetrically on pivoting platform, each developing 7.5kW at 8,500 rpm. Fuel, of 30:1 petrol and oil premix, in seatback tank, capacity up to maximum of 19 litres.

Jane's All the World's Aircraft, 2004-2005

Technical data for Gen H-4

Rotor diameter: 4.00m, max take-off weight: 220kg, empty weight: 70kg, never-exceed speed: 90km/h, cruising speed: 80km/h, service ceiling: 3000m, endurance: 1h