From about 1950 to his death in February 1981, Iosif Silimon was Romania's most prominent glider designer, his aircraft distinguished by his initials.
It was built around a single spar with a plywood covered torsion box ahead of it around the leading edge.
The IS-11 had short span spoilers, opening both above and below the wing, mounted at mid-chord just inboard of the ailerons.
The wing tips carried the small, streamlined bodies known as salmons, common at the time.
Its undercarriage comprised a very short, rubber sprung skid under the nose and a fixed, unsprung monowheel semi-recessed into the fuselage under the forward wing and fitted with a brake.