An aerobatic glider of wooden construction. The design of the Kobuz aerobatic glider, initially named Sokol, was created in the late 1950s by a team led by Eng. Jerzy Trzeciak to replace the Jastrzab glider designed in 1949.
The prototype SZD-21 Kobuz 1 glider made its maiden flight on 3 June 1961. It did not have good flying characteristics and was modified to the SZD-21-2 Kobuz 2 version, which also proved unsuccessful. Then another version was created, designated Kobuz 2A. During flight testing of this glider on 20 April 1963, test pilot Slawomir Makaruk was killed.
Only the third version, SZD-21-2B Kobuz 3, developed under the direction of Jerzy Trzeciak and Marian Gracz with a redesigned forward fuselage and wings, first flown on 10 December 1964 by Eng. Stanislaw Skrzydlewski, proved successful and entered serial production. 31 examples were built at the Glider Works in Wroclaw.
Polish pilots achieved many successes in international glider aerobatics competitions flying Kobuz 3 gliders. However, the end of the Kobuz’s career was tragic. During the World Glider Aerobatic Championships in 1989 in Hockenheim, West Germany, pilot Krzysztof Wyskiel was killed when the wings separated in flight due to moisture-induced weakening of the wooden structure. After this disaster, the Kobuz gliders were withdrawn from service. They were soon replaced by Swift gliders designed by E. Marganski.
| Wingspan | 14.0 m |
| Length | 7.2 m |
| Wing area | 13.5 m2 |
| Empty weight | 311 kg |
| Takeoff weight | 401 kg |
| Glide ratio | 30.5 at optimum speed of 100 km/h |
| Sink rate | min. 0.9 m/s at economy speed of 100 km/h |
| Minimum speed | 73 km/h |
| Max. dive speed | 350 km/h |
