In 1926 it was becoming obvious that the hayday of the biplane and high- wing monoplane configurations for single –seat high-speed fighters was passing, and all major aircraft manufacturing nations were turning their attentionton low-wing monoplane with a fully-retractable undercarriage. Influenced by this trend, the designers of IK-1 and IK-2 Ljubomir Ilic and Kosta Sivcev, were joined by Ing. Zrnic and initiated work on a new fighter project, the low-wing IK-3 of mixed construction and featuring a retractable undercarriage. All preparatory work was undertaken in strict secrecy, model was tested in Eiffel wind tunnel in Paris before the design was submitted to the Yugoslav Air Ministry. The Rogozarski A.D. at Belgrade was instructed to proceed with the construction of a prototype that flew for the first time in the spring of 1938 with Captain M. Bjelanovic at the controls.
The prototype IK-3 was powered by Hispano-Suiza 12Y-29 liquid-cooled engine rated at 890 h. p. for take-off and 920 h.p. at 11,810 ft., and carried an armament of one 20 mm. Hispano-Suiza HS-404 cannon between the cylinder banks and two 7.92 mm. FN Browning machine guns over the engine. The fuselage was a steel –tube structure with ply wood and fabric covering, the wings were of wooden construction with plywood skinning, metal-framed, fabric-covered ailerons and dural flaps, and the fully-retractable under-carriage was of Messerschmitt design. Initial flight trials were extremely successful, demanding only minor modifications to the undercarriage and engine installation. Five other pilots flight –tested the IK-3 before, on January 19,1939, the machine was destroyed. The pilot Captain Pokorni, took-off from Zemun airfield performed a series of acrobatics and then put a prototype into a terminal velocity dive from which he failed to recover. A Subsequent investigation of the accident completely exonerated the aircraft, and the Yugoslav Air Ministry placed an order with the Rogozarski Company for an initial batch of twelve IK-3 fighters.
The production IK-3 different in few respects from prototype. Additional frames were added to the sliding cockpit canopy, a bulletproof Windscreen was fitted, and the engine was a Czech –built version of the Hispano-Suiza, the Avia H.S. 12Ycrs. The first IK-3 were delivered in summer of 1940 to the experimental unit, the 52nd Fighter Squadron, whose pilots preferred the indigenous design to both Bf-109 E-3 and the Hurricane I. The IK-3 was appreciably more maneuverable then the German fighter and could turn inside the Hurricane with ease. Its controls were exceptionally well co-ordinate and maintenance proved simple despite the fighter’s experimental status, a factor of extreme importance in view of the poor equipment of most Yugoslav service airfields.
Negotiations were conducted with the Turkish government who were considering the license manufacture of the IK-3, and plans were made by Rogozarski to accelerate production of the fighter despite the fact that, together with the Zmaj concern, the company was engaged in the license manufacture of one hundred Hurricanes. Rogozarski`s part in the Hurricane program was forty machines, and with the completion of these the Belgrade factory was to build a further twenty-five IK-3s for the Yugoslav Air Force. In the event the second batch of IK-3s had only just been started when, on the April 6, 1941, German forces invaded Yugoslavia.
In the mean time, the design team had been working on improved versions of the IK-3. It had originally been planed to power later IK-3s with new 1,100 h.p. Hispano-Suiza 12Y-51 engine, the German occupation of France had frustrated this plan, and it therefore become necessary to consider a British or German engine. The Air Ministry favored the DB 601 A, and as part of IK-3 development program, the Daimler-Benz engine was installed experimentally in a Hurricane airframe in 1940. The conversion was extremely successful, and experimental aircraft displayed better take-off performance and climb rate than either the standard Hurricane or the Bf 109 E-3 and was only slightly slower than the latter. At the same time, a 1,030 h.p. Rolls-Royce Merlin III was installed in one of the IK-3 airframes, but this machine had only just been completed at the time of the German attack, and as enemy forces neared Belgrade it was destroyed by the factory workers, together with four other IK-3s undergoing overhaul or modification.
One IK-3 was destroyed when it dived under full power into the Danube, subsequent investigations indicating that the pilot had black out, and the remaining six were being operated by the 52nd Squadron which, together with ten Bf 109 E-3s of the 32nd Squadron, formed the 6th Fighter Regiment for the aerial defense of Belegrade.Based at Zemun, the IK-3s put up a valiant resistance against the Luftwaffe, scoring a number of “kills” before they were finally destroyed in combat.
It is of interest to note that Rogozarski were working on the further fighter design at the time that German forces occupied Belgrade. This, the IK-5, was to be powered by two Hispano-Suiza 12Y engines and was projected in two versions: a single-seat interceptor and a two-seat long-range “destroyer” with exceptionally heavy nose-mounted armament. Wind tunnel test with models of the IK-5 had been completed, and prototype construction had commenced.
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