The IIL IS-4 was a single seat, high performance sailplane designed by Iosif Șilimon and built in Romania in the late 1950s.
From about 1950 to his death in February 1981, Iosif Șilimon was Romania's most prominent glider designer, his aircraft distinguished by his initials.
Ply and fabric covered ailerons ran from the tips over the more tapered outboard panels, with mid-chord spoilers immediately inboard, opening above and below the wing.
A narrow fin with a small forward fillet rose above the tailplane to the full height of the rudder, which was broad with a rounded heel, flat tipped and also unbalanced.
The IS-4 had a short, rubber sprung skid reaching from the nose to under about mid-canopy and a fixed, unsprung monowheel under the wing, fitted with a brake.