The IS-3 was the basis of a family of high performance gliders designed by Iosif Șilimon and built in Romania in the 1950s at the URMV-3 (Rom: Uzinele de Reparatii Material Volant-3 - Glider repair and manufacture factory) factory at Brașov.[1]
The IS-3 was designed as a high performance sailplane for record-breaking and international competition flying. The development of the IS-3 was in four distinct phases with differences in wing position and construction as well as fuselage design. The original glider, first flown on 19 August 1953, was built primarily of wood with a pod and boom style fuselage and high-set wings. The streamlined pod contained the enclosed cockpit with flush fitting canopy and supported the wings and the Duralumin sheet tubular tailboom which supported the conventional tail surfaces at its extremity. The tapered wings were built with plywood-covered torsion box leading edges with fabric covering aft of the main spar, incorporating spoilers for approach control and differential ailerons to reduce adverse yaw. With the exception of the IS-3c and IS-3d the IS-3 family followed the pod and boom arrangement with variations in wing position, span, wing construction and undercarriage arrangement.[1]
All versions had a single mainwheel with nose and tail skids, varying in skid sizes and mainwheel position. The IS-3c and IS-3d were drastically different in having a conventional wooden fuselage and further minor variations in wing construction and roll controls.[1]
Data from: Romanian Aeronautical Constructions 1905-1974[1]
IS-3
Original prototype with high-set 16 m (52.5 ft) span wings on a pod and boom fuselage, with two part differential ailerons and non-speed-limiting airbrakes/spoilers.
IS-3a
A revised IS-3 with wings lowered to the mid position and tailboom also lowered. The IS-3a wings were similar to the plywood D-box and fabric covered aft section of the IS-3 but incorporated flaps with two part differential ailerons and non-speed-limiting airbrakes/spoilers.
IS-3b
The IS-3b was essentially identical to the IS-3a with the exception of having no flaps and having plywood skinned wings throughout.
IS-3c
The IS-3c was markedly different from its predecessors in having high-set 17 m (55.8 ft) span wings, skinned throughout with plywood, with three section differential ailerons and introducing speed-limiting airbrakes. The new long span wing was supported by a conventional fuselage, incorporating the streamlined enclosed cockpit and a conventional tail unit.
IS-3d
Essentially similar to the IS-3c, but with a 15.3 m (50.2 ft) wing, single-section ailerons and streamlined wing-tip fairings and speed limiting airbrakes.
IS-3e
Reverting to the pod and boom layout the IS-3e had high-set 17 m (55.8 ft) span wings, with plywood D-box and fabric covered aft section, two section ailerons and speed limiting airbrakes.
IS-3f
A variant with a 15.3 m (50.2 ft) wing completely skinned with plywood, otherwise similar to the IS-3e.
^ abcdefghijklmGudju, Ion; Gheorghe Iacobescu; Ovidiu Ionescu (1974). Romanian Aeronautical Constructions 1905-1974. Bucharest.{{cite book}}: CS1 maint: location missing publisher (link)
^Shenstone, B.S.; K.G. Wilkinson (1963). The World's Sailplanes:Die Segelflugzeuge der Welt:Les Planeurs du Monde Volume II (in English, French, and German) (1st ed.). Zurich: Organisation Scientifique et Technique Internationale du Vol a Voile (OSTIV) and Schweizer Aero-Revue. pp. 180–191.
Shenstone, B.S.; K.G. Wilkinson (1963). The World's Sailplanes:Die Segelflugzeuge der Welt:Les Planeurs du Monde Volume II (in English, French, and German) (1st ed.). Zurich: Organisation Scientifique et Technique Internationale du Vol a Voile (OSTIV) and Schweizer Aero-Revue. pp. 180–191.
Gudju, Ion; Gheorghe Iacobescu; Ovidiu Ionescu (1974). Romanian Aeronautical Constructions 1905-1974. Bucharest.{{cite book}}: CS1 maint: location missing publisher (link)
