[1] 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.

[2] 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.

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.

[2] The cantilever gulled wings followed normal practice with a plywood-covered torsion box leading edge, mainspar, ribs and false rear spar to support the full-span flaps and ailerons.

[1] Six IS-1 Sęps were built, including a prototype, with several continuing to fly into the 1960s with one surviving at the Polish Aviation Museum in Kraków.