Tandem two-seat single-engined high-wing monoplane with conventional three-axis control. Wing has unswept leading and trailing edges, and constant chord; cruciform tail. Pitch control by elevator on tail; yaw control by fin-mounted rudder; roll control by half-span ailerons; control inputs through stick for pitch/roll and pedals for yaw. Wing braced from above by kingpost and cables, from below by cables; wing profile Gardan (high-lift airfoil); double-surface. Undercarriage has three wheels in tail-dragger formation; steel-spring suspension on tailwheel and rubber suspension on main wheels. Push-right go -right tailwheel steering connected to yaw control. Optional brakes on main wheels. Aluminium-tube framework, with optional pod. Engine mounted below wing driving tractor propeller. All-aluminium airframe with Dacron covering.
For his first ULM, Yves Gardan opted for an all-metal construc-tion covered in Dacron in order to make industrial manufacture easier. With a high lift airfoil which he has designed himself, the wing of his GY-120 is also fitted with flaps covering most of the span, which are separate from the ailerons and have three positions: 10, 20 and 30 degree depression. It is worth noting that the load sheet for this aircraft complies to the FAR23 Utility category applicable to aircraft of less than 3.70 tonne (4.08 US ton, 3.64 Imp ton) according to international law.
Design work started in June 1982 and the building of the prototype in October of the same year, its first flight being programmed for the 15 May 1983. The motor on the prototype is a Hirth 270R-03E of 40hp, but the aircraft is designed to receive any engine usable as a tractor and developing 35-60 hp. Options include a fuselage fairing, complete dual control equipment, differential brakes on the main wheels, floats and skis specifically designed for the GY-120, an instrument panel and load carrying pods (agricultural or military).
Engine: Hirth 270R-03E, 40 hp at 7000 rpm.
Propeller diameter: 55 in (1.40m).
Toothed-belt reduction, ratio 2.71-1.
Power per unit area 0.21 hp/sq.ft, 2.3 hp/sq.m.
Fuel capacity 7.9 US gal, 6.6 Imp gal, 30.0 litre in main tank; 7.9 US gal, 6.6 Imp gal, 30.0 litre in reserve.
Length overall 19.0 ft, 5.80 m.
Height overall 8.211, 2.50m.
Wing span 32.9ft, 10.00m.
Constant chord 5.9ft, 1.75m.
Dihedral 2 deg.
Sweepback 0 deg.
Tailplane span 9.2ft, 2.80m.
Fin height 4.3ft, 1.30m.
Total wing area 189 sq.ft, 17.5sq.m.
Total aileron area 20.5 sq,ft, 1.90sq.m.
Fin area 7.5 sq.ft, 0.70sq.m.
Rudder area: 7.0 sq.ft, 0.65sq.m.
Tailplane area: 15.3 sq.ft, 1.42sq.m.
Total elevator area: 14.0 sq.ft, 1.30sq.m.
Wing aspect ratio 5.711.
Wheel track 5.9 ft,1.80 m.
Wheelbase 14.9 ft, 4.50 m.
Tailwheel diameter overall 5 inch, 13 cm.
Main wheels diameter overall 16 inch, 40 cm.
Empty weight 320 lb, 145 kg.
Max take-off weight 751 lb, 340 kg.
Payload 431 lb, 195 kg .
Max wing loading 3.97 lb/sq.ft, 19.4 kg/sq.m.
Max power loading 18.77 lb/hp, 8.503kg/hp.
Load factors design; +6.6, -3.3 ultimate.
Max level speed 75 mph, 120 kph.
Never exceed speed 87 mph, 140kph.
Max cruising speed 68mph, 110 kph.
Economic cruising speed 47mph, 75kph.
Stalling speed 24 mph, 38 kph.
Max climb rate at sea level 500 ft/min, 2.5 m/s.
Min sink rate 370 ft/min at 40 mph, 1.8 m/s at 65 kph.
Best glide ratio with power off 10/1 at 40mph, 65 kph.
Take-off distance 130 ft, 40 m.
Land-ing distance 115ft, 35m.
Service ceiling 8200ft, 2500m.
Range at average cruising speed 240 mile, 400 km.