The ASK21 is a tandem-seater glass-fibre glider constructed by Roland Kaiser and first flown in the later 1970s. It is still produced by the glider manufacturer "Alexander Schleicher Flugzeugbau". As it has very good-natured flight and stall characteristics, it is often used in flying schools and for aerobatic training.
This model for flightgear is based on an older ASK21 by Heiko Schulz and AJ MacLeod with help by Detlef Faber, but was mostly redone and updated in FDM, exterior model, textures, systems and cockpit by Viktor Radnai, Gilberto Agostinho, Thomas Polzer and Benedikt Wolf.
Here are some screenshots, please note that these might not reflect the current version, as there is progress ongoing.