IS-1 Sęp
| IS-1 Sęp | |
|---|---|
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| IS-1 Sęp prototype (SP-443) | |
| Role | Glider |
| National origin | Poland |
| Manufacturer | Glider Workshop in Jeżów Sudecki |
| Design group | Instytut Szybownictwa |
| First flight | 2 June 1947 |
| Number built | 6 |
The IS-1 Sęp was a single-seat high-performance glider designed and built in Poland from 1947. It was the first post-war Polish glider.
The IS-1 Sęp (Vulture) was designed in Instytut Szybownictwa (Gliding Institute) as part of the effort to re-invigorate Polish gliding after World War II, which included the IS-2 Mucha for training and medium performance, IS-A Salamandra transition solo trainer and IS-3 ABC primary trainer. An initial design was developed by Władysław Nowakowski and Józef Niespał.
The first flight, piloted by Piotr Mynarski, took place on 2 June 1947, but nearly ended in disaster as the ailerons were cross-connected. Mynarski abandoned the launch and landed safely. The Sęp was cleared for cloud flying, high speeds and basic aerobatics with comparable performance with foreign contemporaries such as the DFS Weihe and its derivative the Slingsby T.34 Sky. Tests were satisfactory and the prototype (markings SP-443) was taken to the international glider meet held at Samedan, Switzerland in July 1947. The glider met with an interest there, being one of the first new postwar designs, and Adam Zientek achieved eighth place, winning a speed task on a closed circuit.
Results of flight tests and reports from pilots prompted modifications to the airbrakes, increased dihedral and increased aileron range of movement as well as a more compact cockpit. A production model was named IS-1 Sęp bis. Three production IS-1 Sęp bis aircraft, and an IS-2 Mucha, were entered in the 1948 International Gliding Championship at Samedan in 1948, but were withdrawn when the Polish team was withdrawn for political reasons. Competition success came in the 1948 7th Polish National Gliding championships, taking the first three places, and many Polish national records were broken in Sęps, including the International Feminine Record for speed round a 100 km triangle set by Irena Kempówna on 10 June 1948. On 1 April 1948 A. Zientek set a record of duration 18 hours 23 min; in July 1947 I. Kempówna, A. Zientek and R. Matz flew two Sęps and a Mucha 270 km from Żar to Vienna; in December 1948 I. Kempówna set a record of 3720 m height gain; on 9 May 1949 A. Zientek flew 100 km triangle at 28.7 km/h; on 10 June 1948 I. Kempówna flew a 100 km triangle at 50 km/h for a Polish national and world record. On 23 July 1950 Tadeusz Góra achieved 5,737 m altitude (5038 m height gain); on 22 July 1950 A. Zientek flew out and return 232 km for a Polish record; on 11 May 1950 Tadeusz Góra flew a 100 km triangle at 52.63 km/h; on 23 April 1953 J. Popiel flew a 100 km triangle at 68.52 km/h.
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