From about 1950 to his death in February 1981, Iosif Silimon was Romania's most prominent glider designer, his aircraft distinguished by his initials.
Mounted with 3° of dihedral, they were straight tapered in plan and built around a single spar with a forward torsion box between it and the leading edge.
It carried a fabric covered, rounded, unbalanced rudder, broad at its heel, as well as the straight edged tailplane placed just above the boom.
There were rounded, spring balanced elevators with gaps at their roots to clear the fin and a small cut out for rudder movement; these control surfaces were ply skinned and fabric covered like the ailerons.
The IS-5 had a short, rubber sprung skid under the cockpit and a fixed, unsprung monowheel under the wing, fitted with a brake.