ASK 21

 Design Description
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ASK 21 - A Trainer like No Other!

After our very successful ASK 13 trainer we have now switched to an all fiberglass design – the legendary ASK 21.

No other 2-seater has turned a larger number of students into solo pilots and no other glider has carried more new pilots through their first flight and cross country training to competition flying.

The ASK 21’s very attractive appearance paired with a first class track record has already led to more than 750 orders for this timeless, robust and versatile aircraft. The demand is still as strong as ever – proof that the ASK 21 has set new standards and earned an enviable reputation for extreme reliability in a demanding training environment. But more than that, the ASK 21 stands for low maintenance, for pleasant flying characteristics and for retaining value like no other glider.


The backbone of every club is a reliable fleet of training aircraft. With the ASK 21 instructors get a training tool that puts enjoyment and fun back into flight training. Very docile flight characteristics combined with an easy handling - both on the ground and in the air – make the aircraft a true favorite amongst instructors. Thanks to its roomy and comfortable cockpit, excellent visibility and pleasant handling, instructors find flight training no longer a chore but an enjoyable experience.
During the design stages particular attention was paid to safety. After all, the primary role of this glider is in training and while inevitably some landings are better than others quite a few can only be described as arrivals. For exactly this reason the ASK 21 features a safety cockpit in double wall GRP honeycomb design. This robust sandwich construction not only offers an unrivalled degree of pilot protection and passive safety but also minimizes the weight of structural components. In addition the fixed undercarriage with a large diameter 5.00-5 main wheel features very generous rubber shock absorbers. They take care of the roughest of airstrips and protect the backbone of the flight instructor and student alike.

While on the subject of safety, the automatic elevator connection as well as the 5-part safety harness deserves a special mention. Additional safety features include a large two-piece canopy with structurally integrated roll cage and a smart interlock mechanism to guarantee safe locking of the rear canopy. A welcome by-product of this design is a gap-less canopy fit and a tight seal even under the most extreme temperature conditions.


The ASK 21 is also popular with trainees due to its tolerant low speed behavior and forgiving flight characteristics. While on the ground the aircraft rests on both main and nose wheel aiding directional stability during take off and landing run and easing trainee workload. When empty the glider is finely balanced on its main wheel eliminating the need for a tail dolly for ground handling. A low wing loading of only 24.5 kg/m² (at a payload of 85 kg) adds to the pleasant thermalling characteristics and gives the ASK 21 the ability to climb even in the weakest of thermals - ideal for low hour pilots.


The glide ratio of the ASK 21 was independently measured as 34:1, although we have not revised the best L/D of 33.5:1 first calculated by designer Rudolf Kaiser. Such above average performance for a training aircraft further adds to its versatility and makes the ASK 21 eminently suitable for advanced cross country training. But more important than the glide ratio in a training aircraft are operating speeds and maximum payloads. Even when flown dual the ASK 21 has a stalling speed of only 65 km/h (35kt) – quite remarkable considering that the aircraft is certified for a maximum speed of 280km/h or 151kt. A low empty weight of only approx. 360kg and maximum payloads of 110 kg for front and rear seat clearly put the ASK21 in a class of its own.



    A long list of standard features includes:
  • sturdy all fiberglass design – even for all control surfaces
  • in flight adjustable rudder pedals for front and rear seat
  • generous air vent in the nose of the fuselage
  • two large and individually adjustable air-vents on right cockpit wall
  • separate tow releases for winch launch and aerotow
  • pushrod actuation for ailerons, elevator and airbrakes
  • use of precision ball bearings for low actuating forces
  • double walled honeycomb sandwich fuselage construction
  • large 4.00-4 nose wheel
  • rubber shock absorbers for large 5.00-5 main wheel
  • very effective hydraulic disc brakes
  • removable main wheel fairing
  • adjustable backrest for front and back seat
  • interlock mechanism for canopy system
  • front hinged front canopy including lifting instrument panel
  • separate large instrument panel for rear seat
  • rear canopy hinged aft for ease of access
  • VHF antenna in the fin
  • Elevator trim via trim located next to control column
  • rubber tail skid (210 x 65 tail wheel on request)
  • cloth seat cushions and cloth side pockets for front and rear seat
  • large dive brakes on upper wing surface
  • automatic elevator control connection
  • 5-part safety harness for front and rear seat
  • maximum load for front and rear seat 110kg
  • large luggage compartments in wing roots accessible from cockpit
  • spin kit attachment available as optional extra


The versatility of the aircraft is further enhanced by its aerobatic capabilities. Maximum g-loads of +6.5 and -4.0 (for speeds up to 97kt) make the ASK 21 suitable for the entire training syllabus - including spin training.
    Approved aerobatic maneuvers include:
  • inverted flying
  • slow rolls
  • loops
  • spins
  • stall turns
  • Split ‘S’
  • Immelmann turn
  • steep climbing turn
  • Chandelle
  • Lazy Eight.

No wonder the ASK 21 is by far the world’s most popular aerobatic trainer and has introduced more glider pilots to aerobatics than any other glider.


After an extensive evaluation of the ASK 21’s service history it was recently granted a service life extension becoming the first glider ever to be certified for 18000 hours of service – clear proof of the high quality standard of Schleicher gliders in general and the ASK 21 in particular. Well over 850 ASK 21’s are already serving as basic trainers at clubs and flying schools around the world.

And best of all: ASK 21 gliders are known for spending their time in the air and not in the workshop.

Of course, such unrivalled quality and the long list of features add to the cost, but an ageless aircraft like the ASK21 is as a club’s long term investment in its future. After all, the bitterness of poor quality lingers on after the sweetness of a cheap price is long forgotten.

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Photos: Manfred Münch