Schleicher ASK 21
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The ASK 21 is a
glass-reinforced plastic Fiberglass (American English) or fibreglass ( Commonwealth English) is a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet called a chopped strand mat, or woven into glass c ...
(GRP) two-seat
glider aircraft A glider is a fixed-wing aircraft that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose gliding flight, free flight does not depend on an engine. Most gliders do not have an engine, although mot ...
with a
T-tail A T-tail is an empennage wikt:configuration, configuration in which the tailplane of an aircraft is mounted to the top of the vertical stabilizer, fin. The arrangement looks like the capital letter T, hence the name. The T-tail differs fr ...
. The ASK 21 is designed primarily for beginner instruction, but is also suitable for
cross-country flying Cross-country flying ( XC 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 (paraglider, hang g ...
and
aerobatic Aerobatics is the practice of flying maneuvers involving aircraft attitudes that are not used in conventional passenger-carrying flights. The term is a portmanteau of "aeroplane" and "acrobatics". Aerobatics are performed in aeroplanes and gl ...
instruction.


Design and development

The ASK 21 was designed by
Rudolf Kaiser Rudolf Kaiser (10 September 1922 – 11 September 1991) 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 Schleich ...
to replace the popular ASK 13, providing 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, flying for the first time in February 1979. Production also began in 1979. In 2003 the operating time was extended to 18,000 hours. In December 2004 the ASK 21 Mi, a self-launching version, made its first flight. A revised and improved version, the ASK 21B was introduced in 2018. The ASK 21 remains in production (May 2024) with over 1000 examples completed.


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 Automotive safety is the study and practice of automotive design, construction, equipment and regulation to minimize the occurrence and consequences of traffic collisions involving motor vehicles. Road traffic safety more broadly includes roadw ...
with low weight. The two-piece, mid-set, cantilever wing is a single-spar glass-fiber construction without flaps, but with upper side
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 "Sport ...
-type air brakes. The wingtips curve downward, providing tip skids that allow take-offs without a wing helper (small wheel added with ASK-21 mi). The T-tail possesses a fixed horizontal stabilizer and an
elevator An elevator (American English) or lift (Commonwealth English) is a machine that vertically transports people or freight between levels. They are typically powered by electric motors that drive traction cables and counterweight systems suc ...
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 A disc brake is a type of brake that uses the #Calipers, calipers to squeeze pairs of #Brake pads, pads against a disc (sometimes called a
rake Rake may refer to: Common meanings * Rake (tool), a horticultural implement, a long-handled tool with tines * Rake (stock character), a man habituated to immoral conduct * Rake (poker), the commission taken by the house when hosting a poker game ...
rotor) to create friction. There are two basic types of brake pad friction mechanisms: abrasive f ...
. Checking the tire pressure is hindered by the need for removing the wheel fairing. The tail unit has a rubber skid or a
tailwheel Conventional landing gear, or tailwheel-type landing gear, is an aircraft undercarriage consisting of two main wheels forward of the center of gravity and a small wheel or skid to support the tail.Crane, Dale: ''Dictionary of Aeronautical Term ...
.


Flight characteristics

The thick wing profile gives good low-speed characteristics (nominal
stall speed In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack exceeds its critical value.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', p. 486. Aviation Supplies & Academics, 1997. ...
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. 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 neutralized ailerons, full opposite rudder until the rotation stops, centralizing the rudder and progressively moving the control column forward to reduce the angle of attack. As the glider recovers from the spin the control column is progressively moved backwards to pull out of the dive. When entering a side slip, which is not uncommon as an energy management technique, the rudder can aerodynamically over centre, requiring an input from the pilot for the rudder pedals to return to neutral.


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. ;Vanguard TX.1 :The ASK-21 acquired by the UK Ministry of Defence for use by the Air Cadet organisations. ;ASK 21B :Improved version of the original ASK 21. New features: automatic control connections, internal spin ballast, revised canopy, more effective ailerons.


Operators


Military


Current

; *
Royal Australian Air Force The Royal Australian Air Force (RAAF) is the principal Air force, aerial warfare force of Australia, a part of the Australian Defence Force (ADF) along with the Royal Australian Navy and the Australian Army. Constitutionally the Governor-Gener ...
**
Australian Air Force Cadets The Australian Air Force Cadets (AAFC), known as the Air Training Corps (AIRTC) until 2001, is a Federal Government funded youth organisation. The parent force of the AAFC is the Royal Australian Air Force (RAAF). Along with the Australian Ar ...
- 11 ; *
Portuguese Air Force The Portuguese Air Force () is the air force, aerial warfare force of Portugal. Locally it is referred to by the acronym FAP but internationally is often referred to by the acronym PRTAF. It is the youngest of the three branches of the Portuguese ...
**
Portuguese Air Force Academy The Portuguese Air Force Academy (AFA, ''Academia da Força Aérea'' in Portuguese) is a Portuguese military higher education institution whose aim is to provide all its students with the training and the experience that will enable them to gr ...


Former

; *
Royal Air Force The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
for
Air Training Corps The Air Training Corps (ATC) is a British Youth organisations in the United Kingdom, volunteer youth organisation; aligned to, and fostering the knowledge and learning of military values, primarily focusing on military aviation. Part of the ...
(Vanguard TX.1)


Civilian

; *Association de Vol à Voile Champlain - 2 *Cu Nim Gliding Club *Great lakes Gliding Club *Rideau Valley Soaring School *Southern Ontario Soaring Association - 3 *York Soaring *Youth Flight Canada ; *
Yorkshire Gliding Club The Yorkshire Gliding Club (YGC) operate from an airfieldSutton Bank was mentioned in the House of Lords in the year 2000 as being an ''aerodrome'' as this would restrict open access to the site on the grounds that the flying activity on the site ...
- 2 * Devon and Somerset Gliding Club * Edgehill Gliding Club -1 *
Cambridge Gliding Centre Cambridge Gliding Centre is a gliding club based near Cambridge in the United Kingdom on the Bedfordshire/Cambridgeshire county border. Nearby major towns include Bedford, Cambourne, Huntingdon, Royston, Sandy, St Ives and St Neots. The club ...
- 2 *
London Gliding Club The London Gliding Club (LGC) is a members' club whose airfield is located at the foot of the Dunstable Downs. Many privately owned gliders are based there. It has the facilities to train pilots in powerless flight, and in the skills necessary t ...
- 7 *Booker Gliding Club - 2 *Buckminster Gliding Club *Midland Gliding Club *Cranwell Gliding Club *Kent Gliding Club *Scottish Gliding Union ; *Mid Atlantic Soaring Association - 2 *Texas Soaring Association *Caesar Creek Soaring Club - 2 *Blue Ridge Soaring Society - 3 *Soaring Society of Boulder *Greater Boston Soaring Club - 2 ; *Bathurst Soaring Club - 2 (1 ASK 21, 1 ASK 21 Mi)


Specifications (ASK 21)


See also

* IS 28 B2 *
Schleicher ASK 23 The Schleicher ASK 23 is a single-seat Club Class sailplane that was built by the German manufacturer Alexander Schleicher GmbH & Co. Design The ASK 23 was the last glider to be designed by Rudolf Kaiser. It is an early-solo sailplane with doci ...
* ZS Jezow PW-6U *
Grob G103a Twin II The G103 Twin II (originally designated the G 118) is a high-performance two-seat sailplane manufactured in Germany by Grob Aircraft. The aircraft is of T-tail configuration, and is fitted with upper-surface airbrakes and a non-retractable under ...
* PZL Bielsko SZD-50


References


Further reading

* *


External links


Alexander Schleicher GmbH & Co
English version
Johnson R, A Flight Test Evaluation of the ASK 21
Soaring, July 1985
European Aviation Safety Agency Type Certificate Data Sheet
{{US glider aircraft Schleicher aircraft 1970s German sailplanes Mid-wing aircraft Aircraft first flown in 1979 T-tail aircraft