IS-1 Sęp

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IS-1 Sęp is a Polish single-seat high-performance glider built starting in 1947. It was the first post-war Polish glider, designed at the Gliding Institute (Instytut Szybownictwa) by Władysław Nowakowski and Józef Niespał. Six were built, including the prototype SP-443.

The first flight was on 2 June 1947, piloted by Piotr Mynarski. The launch nearly failed because the ailerons were cross-connected, but Mynarski landed safely. The Sęp was cleared for cloud flying, high speeds and basic aerobatics, with performance similar to the DFS Weihe and the Slingsby T.34 Sky.

Prototype SP-443 went to the international gliding meet at Samedan, Switzerland in July 1947. Adam Zientek finished eighth and won a speed task. After flight tests, adjustments were made to airbrakes, dihedral, aileron range and cockpit design. A production version named IS-1 Sęp bis followed.

Three IS-1 Sęp bis aircraft and an IS-2 Mucha were entered in the 1948 International Gliding Championship at Samedan, but were withdrawn for political reasons.

In Poland, the Sęp helped set many records and dominated the 1948 Polish National Gliding Championships. Notable achievements include Irena Kempówna’s world record for fastest 100 km triangle in June 1948, and several distance and altitude records through the late 1940s and early 1950s, such as altitude gains over 3,700 m and 100 km triangle records.

Construction: the glider was made of wood with a plywood-covered fuselage and a fixed, integrated fin and tailplane. It had a plexiglass canopy, a nose skid with a jettisonable two-wheeled dolly for take-off, and various hooks for winches and tow. The wings were cantilever gull wings with full-span flaps and ailerons, and DFS-style airbrakes at the rear of the wing.

Six IS-1 Sęps were built, with some flying into the 1960s; one example survives in the Polish Aviation Museum in Kraków.