Schleicher ASW 20
The AS-W20, like the AS-W 19, was designed by Dipl-lng Gerhard Waibel and is a 15m Unrestricted Class version of the AS-W 19 fitted with camber changing flaps to take advantage of the new March 1975 CIVV regulations for this class of sailplane. It has an additional high drag range of flap movement incorporating a special mechanism to eliminate pitch and airspeed changes when the flap position is changed between 30° and 55°. The AS-W 20 also has a new device, developed by Wil Schuemann, that automatically co-ordinates and optimises the flap position to the prevailing airspeed so as to give optimum glide performance and to reduce the pilot's workload. This device also eliminates the need for underwing air brakes, although the AS-W 20 has larger spoilers in the wing upper surfaces than the AS-W 19.
Apart from its flaps, the AS-W 20 is very similar to the AS-W 19, with longer ailerons of narrower chord, which rise to -8° when the flaps are lowered to 55° for landing, and with the same glassfibre sandwich construction and T-tail; up to 265lb of water ballast can be carried, and the cockpit canopy hinges to open upward like the AS-W 19's.
The fiberglass ASW-20 prototype first flew on 29 January 1977 and was a success, winning numerous world and national championships. Built for the 15 m racing class, it features trailing edge flaps which interconnect with the ailerons and allow the entire trailing edge to operate as a flap between -9 and +5 degrees. The flaps also act as ailerons, but deflect only half of the aileron amount. The fuselage is similar to that of the ASW-19. Schempp-Hirth type airbrakes are provided on the upper wing surface only and operate in conjunction with the flaps at approach setting.
The -20B model was introduced in 1983 incorporating new aerodynamic developments in the form of pneumatic jets (about 860) placed in the lower wing surface, drawing impact air from pitot inlets and exhausting it into the boundary layer to delay underwing flow separation. The B model has its gross weight increased to 525 kg / 1,157 lb. Other changes include automatic elevator hookup, an instrument cluster attached to the forward-hinged canopy, and a hydraulic disc brake.
The -20C model has a slightly modified cockpit, an maximum gross weight of 454 kg / 1,001 lb and water ballast of 120 kg / 264 lb.
Schleicher also introduced an ASW-20L variant (the L denoting Lang, or long), with span extended to 16.59 m (54ft 1.5in) by use of detachable tip extensions, making the ASW- 20L, -20BL and 20CL for Open Class competition. 48 of this variant had been built by the beginning of 1980. In these, water ballast is restricted to 50 kg / 110 lb and gross weight is 430 kg / 948 lb (BL) and 380 kg / 837 lb and no ballast (CL). With the extended tips, best glide ratio goes up to about 46.
The Schleicher ASW 20-L is a high performance single-seat competition glider of all-composite construction with a mid-wing layout and T-tail. The L version indicates optional extended wing tips from 15 to 16.59 metres.
The glider’s flight controls consist of a cable operated rudder and push-pull rods for the elevator, ailerons, flaps and the upper wing surface airbrakes. The flap system incorporates a mechanical mixing unit that provides partial flap movement to augment aileron control when the control stick is moved laterally. In addition, the flaps have five selectable positions that are designed to maximise laminar flow over a variety of speed ranges. The flap positions that provide the low drag performance are position one to four. Flap five is a high drag configuration and used for landing.
The range of speeds to fly, at particular flap positions and various wing loadings are provided in the Flight Manual. For example, flap position four is recommended when thermalling. At a wing loading of 1.3g, (40 degrees angle of bank), the best low drag speeds are between 49 and 55 kts.
The Flight Manual also provides minimum speeds to fly for the various flap configurations. At 454 kg MAUW, in a wings level attitude at flap position four, the recommended minimum speed is 43 kts.
It is claimed the glider spins easier and flatter in the Flap 4 and 5 configurations than with negative (up) flap settings. The explanation goes on further to point out that negative flap should be used to prevent wing drops and spins but recognises that this is impossible when thermalling at low level. In that regard, the Flight Manual recommends the use of safety speeds in excess of the minimum recommended.
For spin recovery, the Flight Manual includes a recommended recovery technique and some additional remarks:
‘(1) Apply opposite rudder, i.e. against the direction of rotation of the spin.
(2) Short pause.
(3) Ease the control column forward, until the rotation ceases and sound airflow is established again.
(4) Centralise rudder and allow sailplane to dive out.
Recovery from spin can be easier achieved if the flaps are set in negative position.
Extending the airbrakes slows down rotational speed but needs more height for recovery and therefor is less recommended.
If the Schleicher ASW 20 recovers itself from a spin, it starts a spiral like side-slip with high increase in speed. Recovery from this flight attitude is done by usual control inputs.
At forward C. of G. positions the ASW 20 -L spins very steeply and starts a spiral dive in less than one turn, whereas at rear C. of G. positions the gliders pitch becomes steeper and steeper after an initial flat and slow turn (approximately 30 degrees negative pitch) until the transition into a spiral-dive develops after five to seven turns.’
The ASW-20 was also license built by Centrair in France in three variants. The ASW-20F and ASW-20FL are the Centrair equivalents to the 20 B and 20BL model while the 20 FP is an F model with NASA winglets designed to improve performance in weak conditions. The Centrair ASW 20F is said to have improved water ballast and wheel brake systems, as well as a better cockpit finish.This received its French certification on 31 March 1978.
Two AS-W 20s at the 1981 World Gliding Championships were fitted with winglets for improved performance. ASW-20’s won 2nd and 3rd places in the 15 m class at the 1983 World Championships at Hobbs, NM. Roy Mcmaster, Karl Striedeck and John Seymour won jointly, with others, the world triangle distance record of 1,435 km / 891.6 miles in 1994 in an ASW-20B.
Span: 49 ft 2.5 in
Length: 22 ft 4.5 in
Height: 4 ft 9 in
Wing area: 113.0 sqft
Aspect ratio: 21.43
Empty weight: 551 lb
Max weight: 1,000 lb
Max speed: 168 mph (in smooth air)
Max useful load: 450 b
Water ballast: 265 lb
Wing loading: 8.8 lb/sq.ft
Max speed: 143 kt
Max aero-tow speed: 112 mph
Min sinking speed: 1.97 ft/sec at 45.5 mph
Stall speed: 35 kt
Rough air airspeed: 91 kt
Best glide ratio: 43:1 at 62 mph
Glide ratio (L/D): 42:1 at 54 kt