View source for Schleicher ASK 21

{{Short description|German two-seat traning glider, 1979}}
{{Refimprove|date=May 2025}}
<!-- This article is a part of [[Wikipedia:WikiProject Aircraft]]. Please see [[Wikipedia:WikiProject Aircraft/page content]] for recommended layout. -->
{{Infobox aircraft
| name = ASK 21
| image = File:Schleicher ASK 21 (D-0721) 02.jpg
| caption = Schleicher ASK 21
| type = [[FAI Two Seater Class|Two Seater-class]] Or [[FAI Club Class|Club-class]] sailplane
| national_origin = Germany
| manufacturer = [[Alexander Schleicher GmbH & Co]]
| designer = [[Rudolf Kaiser]]
| first_flight = February 1979
| introduction = 1979
| number_built = Over 1000
| developed_from = 
| variants = 
}}

The '''ASK 21''' is a [[glass-reinforced plastic]] (GRP) two-seat [[glider aircraft]] with a [[T-tail]]. The ASK 21 is designed primarily for beginner instruction, but is also suitable for [[cross-country flying]] and [[aerobatics|aerobatic]] instruction.

==Design and development==
The ASK 21 was designed by [[Rudolf Kaiser]] to replace the popular [[Alexander Schleicher ASK 13|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 [[Alexander Schleicher GmbH & Co|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.<ref>[http://www.alexander-schleicher.de/wp-content/uploads/2015/03/210_TM29_E.pdf Technical note No. 29, Extension of service life beyond 12000 operation hours.]</ref> 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.<ref name="ReferenceA">{{Cite web|url=https://www.alexander-schleicher.de/en/neu-b-version-der-ask-21|title=New: B-Version of the ASK 21 &#124; ASSegelflug|date=12 July 2018}}</ref>

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]] with low weight. The two-piece, mid-set, cantilever wing is a single-spar glass-fiber construction without [[Flap (aircraft)|flaps]], but with upper side [[Schempp-Hirth]]-type [[Air brake (aeronautics)|air brakes]]. The wingtips curve downward, providing tip skids that allow take-offs without a wing helper (small wheel added with ASK-21&nbsp;mi). The T-tail possesses a fixed horizontal stabilizer and an [[Elevator (aircraft)|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. The tail unit has a rubber skid or a [[Conventional landing gear|tailwheel]].

==Flight characteristics==
The thick wing profile gives good low-speed characteristics (nominal [[stall speed]] approximately 65&nbsp;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.

[[File:Spin kit on an ASK-21.JPG|thumb|Spin kit installation on the tail of C-FASK at the Bromont Airport in Quebec]]

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.<ref name="ReferenceA"/>

==Operators==

===Military===

====Current====
;{{AUS}}
*[[Royal Australian Air Force]]
**[[Australian Air Force Cadets]] - 11<ref name=alexander-schleicher.de>{{cite web|url=http://www.alexander-schleicher.de/neuigkeiten/aktuell_128_e.htm |title=Alexander Schleicher: AAFC |publisher=alexander-schleicher.de/ |access-date=2014-02-28}}</ref>
;{{POR}}
*[[Portuguese Air Force]]
**[[Portuguese Air Force Academy]]

====Former====
;{{UK}}
*[[Royal Air Force]] for [[Air Training Corps]] (Vanguard TX.1)

===Civilian===
;{{CAN}}
*Association de Vol à Voile Champlain - 2<ref name=SAC.ca>{{cite web |url=https://www.sac.ca/index.php/en/documents-en/info-general/694-canadian-glider-fleet-february-2022/file |title=Canadian glider fleet 2022 |last=Burton |first=Tony |date=July 2022 |website=SAC.ca |publisher=Soaring Association of Canada |access-date=16 November 2022 |quote=}}</ref>
*Cu Nim Gliding Club<ref name=SAC.ca/>
*Great lakes Gliding Club<ref name=SAC.ca/>
*Rideau Valley Soaring School<ref name=SAC.ca/>
*Southern Ontario Soaring Association - 3<ref name=SAC.ca/>
*York Soaring<ref name=SAC.ca/>
*Youth Flight Canada<ref name=SAC.ca/>

;{{UK}}
*[[Yorkshire Gliding Club]] - 2<ref>{{Cite web|title=Our Fleet|url=https://www.ygc.co.uk/info/our-fleet|access-date=2021-12-30|website=Yorkshire Gliding Club|language=en}}</ref>
*[[Devon and Somerset Gliding Club]]
*[[Edgehill Gliding Club]] -1
*[[Cambridge Gliding Centre]] - 2 
*[[London Gliding Club]] - 7<ref>{{Cite web|title=Fleet & Facilities|url=https://www.londonglidingclub.co.uk/about-us/fleet-and-facilities|access-date=2023-02-19|website=London Gliding Club|language=en}}</ref>
*Booker Gliding Club - 2
*Buckminster Gliding Club
*Midland Gliding Club
*Cranwell Gliding Club
*Kent Gliding Club<ref>{{cite web | url=https://www.kent-gliding-club.co.uk/glider-fleet-2/ | title=Glider Fleet }}</ref>
*Scottish Gliding Union<ref>{{cite web | url=https://en.wikipedia.org/wiki/Scottish_Gliding_Union | title=Scottish Gliding Union }}</ref>{{Circular reference|date=September 2023}}
;{{US}}
*Mid Atlantic Soaring Association - 2<ref name="midatlanticsoaring.org">{{cite web|url=https://midatlanticsoaring.org/content.aspx?page_id=22&club_id=218612&module_id=291910|title=Our Fleet|publisher=midatlanticsoaring.org|access-date=2020-06-03}}</ref>
*Texas Soaring Association<ref name="texassoaring.org">{{cite web|url=https://texassoaring.org/about|title=About TSA|publisher=texassoaring.org|access-date=2023-05-02|website=Texas Soaring Association|language=en}}</ref>
*Caesar Creek Soaring Club - 2
*Blue Ridge Soaring Society - 3<ref name="brss.net">{{cite web|url=https://www.brss.net/|title=About|website=brss.net/|access-date=2024-07-26}}</ref>
*Soaring Society of Boulder
*Greater Boston Soaring Club - 2<ref>{{Cite web |title=Greater Boston Soaring Club |url=https://soargbsc.com/fleet.php |access-date=2024-10-14 |website=soargbsc.com}}</ref>
;{{AUS}}
*Bathurst Soaring Club - 2 (1 ASK 21, 1 ASK 21 Mi) <ref name="bathurstgliding.com.au">{{cite web|url=https://bathurstgliding.com.au/bsc-fleet/|title=BSC Fleet - Bathurst Gliding Club|publisher=bathurstgliding.com.au|access-date=2024-10-13}}</ref>

==Specifications (ASK 21)==
[[File:Schleicher ASK 21 Three-view.svg|thumb|K21 Three-view drawing]]
{{Aircraft specs
|ref=''Jane's All the World's Aircraft 1988-89''<ref name=JAWA88-89>{{cite book |title=Jane's All the World's Aircraft 1988-89 |year=1988 |publisher=Jane's Information Group |location=London |isbn=0-7106-0867-5 |editor=John W.R. Taylor|pages=630}}</ref>
|prime units?=met
<!--
        General characteristics
-->
|crew=1 student, 1 instructor
|length m=8.35
|span m=17
|height m=1.55
|wing area sqm=17.95
|aspect ratio=16:1
|airfoil=FX S02-196 / FX 60-126
|empty weight kg=360
|max takeoff weight kg=600
|more general=
<!--
        Performance
-->
|stall speed kmh=65

|never exceed speed kmh=280
|never exceed speed note=in smooth air
::::{{convert|200|kph|kn|abbr=on}} in rough air
::::{{convert|180|kph|kn|abbr=on}} on aero-tow
::::{{convert|150|kph|kn|abbr=on}} on winch launch
|g limits=+6.5 -4 at {{convert|180|kph|kn|abbr=on}}
|glide ratio=34 at {{convert|90|kph|kn|abbr=on}}
|sink rate ms=0.64
|sink rate note= at {{convert|67|kph|kn|abbr=on}}
|lift to drag=
|wing loading kg/m2=33.4
|more performance=
|avionics=
}}

==See also==
*[[ICA IS-28|IS 28 B2]]
*[[Schleicher ASK 23]]
*[[Politechnika Warszawska PW-6|ZS Jezow PW-6U]]
*[[Grob G103a Twin II]]
*[[PZL Bielsko SZD-50]]

==References==
{{Reflist}}

==Further reading==
*{{cite book|last1=Thomas|first1=Fred|last2=Milgram|first2=Judah|title=Fundamentals of sailplane design|date=1999|publisher=College Park Press|location=College Park, MD|isbn=978-0966955309|edition=3rd}}
* {{cite book |last=Simons |first=Martin |title=Sailplanes 1965-2000 |year=2005 |publisher=EQIP Werbung und Verlag G.m.b.H. |location=Königswinter |isbn=978-3-9808838-1-8 |edition=2nd revised}}

==External links==
{{Commons category|Schleicher ASK 21}}
*[https://www.alexander-schleicher.de/en/ Alexander Schleicher GmbH & Co] English version 
*[https://web.archive.org/web/20010331183137/http://www.ssa.org/Magazines/Johnson.asp Johnson R, A Flight Test Evaluation of the ASK 21], Soaring, July 1985
*[http://easa.europa.eu/system/files/dfu/EASA-TCDS-A.221_Schleicher_ASK_21-04-07022010.pdf European Aviation Safety Agency Type Certificate Data Sheet]

{{Schleicher}}
{{US glider aircraft}}

[[Category:Schleicher aircraft]]
[[Category:1970s German sailplanes]]
[[Category:Mid-wing aircraft]]
[[Category:Aircraft first flown in 1979]]
[[Category:T-tail aircraft]]