Schleicher ASK 21
Encyclopedia
{
The ASK 21 is a glass-reinforced plastic
(GRP) two-seater mid-wing glider aircraft
with a T-tail
. The ASK 21 is designed primarily for beginner instruction, but is also suitable for cross-country flying
and aerobatic
instruction.
as an improvement of the popular ASK 13, to provide a modern two-seat aircraft bridging the gap between initial training and single-seat performance flying. The ASK 21 is the first full-GRP two-seater produced by Schleicher
. The prototype first flew in December 1978 and production began in 1979. It remains in production to this day, with nearly 900 units completed. In December 2004 the ASK 21 Mi, a self-launching version, made its first flight.
, but with upper side Schempp-Hirth
-type spoilers
. The wingtips curve downward, providing tip skids that allow take-offs without a wing helper(small wheel added with ASK-21mi). The T-tail possesses a fixed horizontal stabilizer and an elevator
with spring trim and automatic connections. The undercarriage consists of two or three fixed wheels. The main wheel lies behind the centre of gravity and has a hydraulically operated disc brake
. Checking the tire pressure is hindered by the need for removing the wheel fairing (which many gliding clubs remove permanently to aid regular maintenance and to reduce the risk of trapped grass being ignited by the wheel brake as it dissipates kinetic energy as heat). The tail unit has a rubber skid or a tailwheel
.
The glider has little tendency to enter a spin. In order to make spinning possible for training purposes or demonstrations a spin kit
is available from the manufacturer. It consists of ballast discs applied to the tail to change the center of gravity according to the weight of the crew. With this device the ASK 21 when slowed to stall speed with rudder input drops one wing and begins to rotate. Recovery is standard, utilizing opposite rudder and release of stick pressure.
Flown as a single-seater, the ASK 21 climbs in thermals as well as a K 8.
ASK 21 Mi
The ASK 21 is a glass-reinforced plastic
Glass-reinforced plastic
Fiberglass , is a fiber reinforced polymer made of a plastic matrix reinforced by fine fibers of glass. It is also known as GFK ....
(GRP) two-seater mid-wing glider aircraft
Glider aircraft
Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...
with a T-tail
T-tail
thumb|right|Grob motor gliderA T-tail is an aircraft tail stabilizer configuration in which the horizontal surfaces are mounted to the top of the vertical stabilizer. Traditionally, the horizontal control surfaces are mounted to the fuselage at the base of the vertical stabilizer...
. The ASK 21 is designed primarily for beginner instruction, but is also suitable for cross-country flying
Cross-country flying
Cross-Country flying is a type of distance flying which is performed in a powered aircraft on legs over a given distance and in operations between two points using navigational techniques; and an unpowered aircraft by using upcurrents to gain altitude for extended flying time...
and aerobatic
Aerobatics
Aerobatics is the practice of flying maneuvers involving aircraft attitudes that are not used in normal flight. Aerobatics are performed in airplanes and gliders for training, recreation, entertainment and sport...
instruction.
Design and development
The ASK 21 was designed by Rudolf KaiserRudolf Kaiser
Rudolf Kaiser was a designer of gliders who worked for Alexander Schleicher GmbH & Co.The designs of Rudolf Kaiser have proven themselves for over 50 years all over the world. His designs for Schleichers can be recognised by the K in the ASK designation...
as an improvement of the popular ASK 13, to provide a modern two-seat aircraft bridging the gap between initial training and single-seat performance flying. The ASK 21 is the first full-GRP two-seater produced by Schleicher
Alexander Schleicher GmbH & Co
Alexander Schleicher GmbH & Co is a major manufacturer of sailplanes located in Poppenhausen, near Fulda in Germany. It is also the oldest sailplane manufacturer in the world....
. The prototype first flew in December 1978 and production began in 1979. It remains in production to this day, with nearly 900 units completed. In December 2004 the ASK 21 Mi, a self-launching version, made its first flight.
Construction
The two seats are in a tandem arrangement with dual controls, adjustable rudder pedals and seatbacks. The fuselage consists of a tubular sandwich and thus offers passive safety with low weight. The two-piece, mid-set, cantilever wing is a single-spar glass-fiber construction without flapsFlap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
, but with upper side Schempp-Hirth
Schempp-Hirth
Schempp-Hirth Flugzeugbau GmbH is a glider manufacturer based in Kirchheim unter Teck, Germany.-History:Martin Schempp founded his own company in Göppingen in 1935, with the assistance of Wolf Hirth. The company was initially called "Sportflugzeugbau Göppingen Martin Schempp"...
-type spoilers
Spoiler (aeronautics)
In aeronautics, a spoiler is a device intended to reduce lift in an aircraft. Spoilers are plates on the top surface of a wing which can be extended upward into the airflow and spoil it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly...
. The wingtips curve downward, providing tip skids that allow take-offs without a wing helper(small wheel added with ASK-21mi). The T-tail possesses a fixed horizontal stabilizer and an elevator
Elevator (aircraft)
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's orientation by changing the pitch of the aircraft, and so also the angle of attack of the wing. In simplified terms, they make the aircraft nose-up or nose-down...
with spring trim and automatic connections. The undercarriage consists of two or three fixed wheels. The main wheel lies behind the centre of gravity and has a hydraulically operated disc brake
Disc brake
The disc brake or disk brake is a device for slowing or stopping the rotation of a wheel while it is in motion.A brake disc is usually made of cast iron, but may in some cases be made of composites such as reinforced carbon–carbon or ceramic matrix composites. This is connected to the wheel and/or...
. Checking the tire pressure is hindered by the need for removing the wheel fairing (which many gliding clubs remove permanently to aid regular maintenance and to reduce the risk of trapped grass being ignited by the wheel brake as it dissipates kinetic energy as heat). The tail unit has a rubber skid or a tailwheel
Conventional landing gear
thumb|The [[Piper PA-18|Piper Super Cub]] is a popular taildragger aircraft.thumb|right|A [[Cessna 150]] converted to taildragger configuration by installation of an after-market modification kit....
.
Flight characteristics
The thick wing profile gives good low-speed characteristics (nominal stall speed approximately 65 km/h or 35 knots). The flight characteristics are docile; its stall is gentle, with ample vibration warning, and is easily recoverable. The nose does not noticeably drop, but the variometer indicates a high rate of descent and the vibration continues until back pressure is released and stall recovery is initiated.Spin kit
A few sailplanes are very difficult, if not impossible, to spin under normal conditions.To make these sailplanes spin easily for training purposes or demonstrations a spin kit is available from the manufacturer....
is available from the manufacturer. It consists of ballast discs applied to the tail to change the center of gravity according to the weight of the crew. With this device the ASK 21 when slowed to stall speed with rudder input drops one wing and begins to rotate. Recovery is standard, utilizing opposite rudder and release of stick pressure.
Flown as a single-seater, the ASK 21 climbs in thermals as well as a K 8.
Variants
ASK-21- Production sailplane
ASK 21 Mi
- Self-launching sailplane, as ASK 21 with a retractable IAE R50-AA rotary engine with a fixed pitch propeller mounted behind the wing.
Specifications (ASK 21)
See also
- Schleicher ASK 23
- ZS Jezow PW-6U
- Grob G103a Twin II
- PZL Bielsko SZD-50PZL Bielsko SZD-50|-References:* * *-External links:*...