Schleicher ASK-21 / TG-9
Designed by Rudolf Kaiser, the ASK-21 was Schleicher’s entry to the composite two-seat sailplane market, first flew in 1979 and is approved for a number of aerobatic maneuvers. Originally an improved version of the AS-K 13 with glassfibre wings and T-tail was studied but the requirement for a new two-seater was met instead of the AS-K 21. Differing from the AS-K 13 in having a wing span increased to 17m (55ft 9.25in), a T-tail, a more streamlined fuselage, and a non-retractable semi-recessed nose wheel, as well as a sprung fixed monowheel with drum brake and a steel-shod rubber tailskid. A tailwheel was available as an option instead of a skid. The structure is fiberglass and foam wing, fiberglass honeycomb sandwich fuselage and tail. Schempp-Hirth type airbrakes (upper surface only), ailerons and elevators are operated by pushrods in ball bearing; the rudder is cable-operated. Wings attach with a tongue- and- fork connection and two pins.
The cantilever single-spar mid-set wings have Wortmann aerofoil sections and 4° dihedral, and there are Schempp-Hirth air brakes in the upper and lower surfaces. The wing tips are turned down to reduce tip stalling. The tailplane is fixed, with a separate elevator with spring trim. Unlike the ASK13, there are two separate cockpit canopy sections, the front one opening forwards and the rear one rearwards, and the pilots sit in a semi-reclining position, with dual controls.
Production of the AS-K 21 began in 1979 and the prototype first flew in December 1978. A flight test evaluation by Dick Johnson demonstrated a best L/D of 31:1.
Span: 17 m / 55 ft 9.25 in
Length: 28 ft 10 in
Height: 5 ft 3 in
Wing area: 17.95 sq.m / 193.21 sqft
Aspect ratio: 16.1
Airfoil: Wortmann FX-S0 2-196 and FX 60 - 126
Empty weight: 360 kg / 794 lb
Gross Weight: 600 kg / 1323 lb
Wing Load: 31 kg/sq.m / 6.34 lb/sq.ft
Max speed: 136 mph
Max aero-tow speed: 96 mph
Min sinking speed: 0.65 m/s / 2.13 ft/sec at 42 mph
L/DMax: 35 85 kph / 46 kt / 53 mph
Best glide ratio: 34:1 at 59 mph