The IS-4 Jastrząb was the first aerobatic glider designed in Poland after World War II. It is of wooden construction. The prototype was first flown by Piotr Mynarski on 21 December 1949.
Two prototypes of the IS-4 Jastrząb were built, followed by 35 production units at the Sports Aviation Equipment Works No. 5 in Krosno, which incorporated modifications such as a wheel, handles for lifting the rear fuselage, cockpit changes, and a hook for bungee cord launches. Three units were exported to East Germany and the People’s Republic of China.
The Jastrząb was characterised by exceptionally high structural strength and virtually unlimited permissible speed. The calculated permissible speed was 450 km/h, but in a vertical dive only 400 km/h could be achieved. Due to its heavy construction and high sink rate, it was nicknamed “the axe” by pilots.
The exhibited aircraft, serial number 09, SP-1383, manufactured in 1953, was operated by the Krakow Aeroclub from 1954 to 1969. It was donated to the Museum collection on 29 January 1970.
| Wingspan | 12.0 m |
| Length | 6.25 m |
| Wing area | 13.75 m² |
| Empty weight | 255 kg |
| Total weight | 340 kg |
| Glide ratio | 19.6 at 82 km/h |
| Sink rate | 1.08 m/s at 73 km/h |
| Minimum speed | 62.0 km/h |
| Permissible speed | 450 km/h |
