Yugoslavia (1938)

Type: Fighter aircraft

Number built: 1 prototype plus 12 production aircraft

The Kingdom of Yugoslavia, despite its rather undeveloped industry and infrastructure, still possessed several aircraft manufacturing companies. During the 1930s, these produced a series of aircraft that would be adopted for military use. These were mostly training aircraft but there were also several fighter designs that would see service with the Kingdom of Yugoslavian Royal Air Force (RYAF). Among them was the IK-3 fighter, created by the well-known Yugoslavian aircraft engineers Ljubomir Ilić, Kosta Sivčev, and Slobodan Zrnić.

History

During the 1930s, the RYAF was mainly equipped with old and obsolete biplane fighters. While this would be eventually solved by the introduction of more modern, foreign designs like the Bf 109 and the Hawker Hurricane, some Yugoslavian aircraft engineers wanted to develop domestic fighter designs. This motivated two aircraft engineers from Ikarus, Ljubomir Ilić and Kosta Sivčev, to start working on such a design. They were already involved in designing a new high-wing fighter named IK-2. This aircraft proved to be superior to older biplane fighters that were in RYAF service. But after a small production series of 12 aircraft, it became obvious that this aircraft would quickly become obsolete, in contrast to other nations’ low-wing fighters.

For this reason in 1933, Ljubomir Ilić and Kosta Sivčev began working on improved fighters on their own initiative. While initially, they tested various ideas, eventually both agreed that a low-wing design was the best option. While having experience in fighter design, these two quickly realized that this project would require more work than the two engineers could achieve on their own. So they asked another engineer Slobodan Zrnić to assist in their work. All three of them worked on this project under the veil of secrecy. Finally, in 1936 they had a finalized project which was presented to the RYAF officials. After some time spent considering this new proposal, the RYAF gave the green light for it at the end of March 1937. A deal was made for the construction of a single prototype for testing and evaluation. While the IK-2 was built by Ikarus, the construction of the new aircraft was given to Rogožarski instead. Given the experience this company had working with wooden airframes, the new fighter was to have a primarily wooden construction to reduce costs and speed up development time.

Name

This project would receive the IK-3 designation. At that time it was common practice that any newly developed aircraft was to be named based on the designer’s initials. In this case, I stood for Ilić and K for Koča, which was Kosta Sivčev’s nickname. The number 3 represents the third fighter project of these two engineers.

Construction of the Prototype

After one year of work, the first prototype was completed. In appearance and design, this was quite a modern aircraft. It was built using a mixed construction and was powered by a 925 hp V-12 Hispano-Suiza 12Y29 engine. It was flight tested for the first time on the 14th of April, 1938. An initial series of test flights were carried out near the capital of Belgrade at Zemun. The test pilot at this early stage was Captain Milan Bjelanović. These flight tests lasted up to the late summer of 1938. During this time, there were no major problems reported with its design, and the aircraft was given to the RYAF for future testing.

A commission of several RYAF officials was elected for the planned army testing and it was agreed that the whole process should last 100 flight hours. For this, the aircraft was to be fully armed which included a centerline mounted 20mm cannon which fired through the propeller hub, and two 7.92 mm machine guns placed in the upper engine cowling.

Following the conclusion of the testing by the RYAF, a report was issued in which its performance was deemed sufficient. The armament was installed and functioned without any major issues, however, it was desirable to add two more machine guns in the wings. The aircraft offered good overall flying performance though its controls were noted to be somewhat problematic and some changes were requested. To resolve this it was asked to improve the design of the flaps, by increasing their deployed angle and size. The canopy was of rather poor quality and was reflective, forcing some test pilots to fly the aircraft with open canopies. The engine had overheating problems which required extensive work before finally being solved by adding an improved cooling system. During these trials, the maximum speed achieved was slightly over 520 km/h. While not bad, the RYAF commission wanted it to be increased to at least 540 km/h, which was not achieved on this aircraft. Overall, this aircraft was deemed worth developing further by the RYAF commission, which gave a recommendation for a small series of 12 aircraft to be produced.

The production of the IK-3

Following the production orders for the IK-3, an accident happened that threatened the realization of the project. On the 19th of January 1939, an accident occurred during a test flight, and test pilot Captain Milan Pokorni was killed, and the plane was lost. A commission was formed to examine what went wrong. After analyzing the wreckage it was determined that the IK-3 prototype’s structural design was not at fault, nor did the pilot make any mistakes. Prior to this accident another pilot Dragutin Rubčić, had a harsh landing, damaging the aircraft in the process. Why this was not properly examined before another take-off by Captain Milan Pokorni is unclear. In another account, during a dive, the canopy broke free which probably made the pilot enter a climb. This seemingly caused enough force to be put on the already damaged aircraft, resulting in structural failure.

While this accident did not lead to the cancellation of the whole project, it did cause huge delays in the delivery of new aircraft. The RYAF officials wanted the aircraft to be thoroughly examined and tested before any further production order was given. Finally, in November 1939, the project received a green light again.

The second prototype, which was also the first aircraft of the first production series, was completed in December 1939. This aircraft was examined in detail over the next few months. As no major issues with the prototype were found, the production of additional 5 aircraft was completed by the 17th of April 1940. The other six aircraft could not be completed as the IK-3’s propellers had to be imported. As there were delivery problems with the last six aircraft, instead of the hydraulically controlled Hispano-type propeller, they were equipped instead with Chauviere-type propellers. It used pneumatic commands which necessitated changes to the engine and its compartment. These were finally completed in July 1940. Once all were available these were allocated to the 51st Fighter Group in July 1940. These were divided into two six-aircraft strong squadrons (the 161st and 162nd) stationed at Zemun airfield near the capital Belgrade.

Second series proposal

In march 1940, the Rogožarski company proposed to the RYAF another production run of 25 to 50 new IK-3 aircraft. It was to incorporate a number of improvements like self-sealing fuel tanks, a redesigned radiator, adding radio equipment, armor for the pilot seat, an aerodynamically improved engine cowling, and a new gunsight. The company proposed that these could be completed in a period of 9 months. To speed up the developing process, one IK-3 (serial number 7) was selected to be converted as the prototype of this new series. This aircraft was completed by the end of March 1941. It was flown in early April, managing to reach a speed some 15 to 20 km faster than the standard IK-3. Its further development was stopped due to the outbreak of the war.

Further IK-3 modification proposals

Some accounts claim that the aircraft was tested with a DB 601 from one of the RYAF’s imported German fighters. According to eyewitness accounts, this model was fully completed and tested. If this was true, it was not confirmed by any historical documentation or photographic evidence. At the same time a Hurricane aircraft was tested with this engine (known as LVT-1). It is possible that an eyewitness simply confused these two.

Another proposed project was the IK-3/2 two-seater trainer. It was planned to add another position to the rear of the pilot, reduce the armament to two machine guns, and move the cooling radiator some 50 cm to the rear. As a number of modern Bf 108 aircraft were acquired, this project was dropped with no prototype ever constructed.

In service, prior to the war

The newly produced IK-3 entered service at the end of 1940 and was used primarily in training flights. They were especially used to test their performance against the Bf 109, which was also in service with the RYAF. The Bf 109 offered better horizontal and climbing speed. In comparison, the IK-3 possessed better horizontal maneuverability, possessing a smaller turning radius of 260 m, the Bf 109 on the other hand had a turning radius of 320 m. The IK-3 also had a somewhat more stable armament installation, providing better accuracy during firing. As the pilots who flew on the IK-3 were not entirely accustomed to flying on modern airplanes, harsh landings were quite common. This necessitated that many IK-3 were often in workshops awaiting repairs of their landing gear units.

The sixth produced IK-3 would be lost in an accident that happened on the 3rd of September 1940. During a mock dogfight with a Potez 25, pilot Anton Ercigoj lost control of the fighter and fell into the Danube river. The pilot was killed on the spot and the aircraft could not be salvaged. While it was not clear how the accident happened, it was speculated that it did occur due to the pilot being too tired from previous flights.

In War

Just prior to the outbreak of the so-called April war, from the 6th to 17th April 1941, between the Kingdom of Yugoslavia and the Axis forces, only 6 IK-3 were combat-ready. The remaining 5 aircraft were awaiting repairs. Three were located at the Rogožanski workshop in Bežanijska Kosa, and two more at the Zemun Airfield. The war began with massive Luftwaffe bombing raids on vital military, communication, infrastructure, and civilian targets. The capital, Belgrade, was a primary target of strategic bombing and was majorly hit. The whole 6th Fighter Regiment, to which the 51st Fighter Group belonged, was tasked to defend Northern Serbia and parts of Croatia and Bosnia from any potential enemy attacks. The 51st Fighter Group reinforced the 102nd Fighter Squadron equipped with Bf 109 and was tasked with defending the Northern sector. Its primary defense point was the capital Belgrade.

The 51st Fighter Group was informed of a possible enemy attack almost an hour before it occurred. At 0645, the unit was informed of two approaching enemy aircraft formations. Five minutes later, all available IK-3s took to the sky to defend the capital. One aircraft, due to engine problems, had to abort the flight and went back to the base.

During the first engagement, some 5 to 6 enemy aircraft (at least one Ju 87) were shot down. One IK-3 was shot down and three more were damaged. Two of these were badly damaged and they were not used in combat after this point. The defenders were then left with only three operational IK-3 aircraft. Late that morning, another bombing raid was launched by the enemy. While only three IK-3 were available at this point, their attack was supported by the Bf 109s from the 51st Group. While the Yugoslavian fighters reported no losses, they managed to take down one Bf 109 and damaged two Ju 87. During the first day of combat, the Germans used nearly 500 bombers which dropped some 360 tonnes of bombs on Belgrade.

The following day, enemy activity came in the form of smaller formations that attacked specific targets. The Ik-3s once again saw action, managing to shoot down more enemy aircraft. While they received no losses, many aircraft were badly damaged by enemy return fire. For example, the IK-3 fighter piloted by Milisav Semiz received 56 hits. The engine itself received some 20 direct hits. While fully covered in engine oil the pilot managed to land safely at the Zamun airfield, the aircraft had to be written off. This unit was reinforced with one IK-3 of the second series. Due to heavy enemy activity, the unit was repositioned some 50 km away from Belgrade at Ruma. For the next few days due to bad weather, the IK-3 was not used. On the 11th of April, the Yugoslavian positions were discovered by a Me 110, which proceeded to attack the airfield. It failed to do any damage, but one IK-3 began a pursuit of it. Eventually, it managed to close in on it and shoot it down. Later that day, two IK-3s took to the sky and managed to shoot down two Ju 87s.

At 1700 hours, due to an enemy ground advance, it was decided to move the available units to Bosnia. The retreat was to commence on the 12th of April, but due to sudden enemy advances and poor weather, the evacuation could not be achieved. The unit commander and pilots agreed to burn down any surviving aircraft to prevent them from falling into enemy hands. This action basically marked the end of the IK-3 service with the RYAF.

In total both the 161st and 162nd squadrons reported some 15 air victories. These included two Ju 88, one Do 17, two Ju 87, two Bf 109, three Me 110, and one He 111. The remaining claims remain a mystery.

In German hands

The victorious Germans managed to capture a number of operational and damaged IK-3s fighters. Most were captured at Rogoarski repair workshops, with a few more at the Zemun airfield, all being abandoned. This included the IK-3 with serial numbers 2151 (which was actually the second prototype) 2152, 2153, 2157, 2158, 2160, and 2161. Most of these would be left exposed to the elements, near the capital Belgrade, until 1942 when they and many other captured aircraft were scrapped. At least one IK-3 was transported back to Germany. It is unlikely that it was used for testing, and some sources suggested but instead placed in the Berlin Aviation Museum. Its fate is unknown but likely lost when the museum was bombed by the Allies in 1944.

Technical characteristics

The IK-3 was a low-wing, mixed-construction single-seat fighter. Its fuselage consisted of welded chrome-molybdenum tubes supported with wooden stringers, and covered in duralumin skin. The rear part of the fuselage was covered in plywood and canvas. The wings were mostly made of wood with some metal links added for better structural stability. The IK-3 wings were covered with birch plywood which was in turn covered in bakelite. The ailerons were made of metal, but covered with canvas. While the trailing edge flaps were made of duralumin, assembly was made using the same materials as the wings.

The IK-3 was powered by a 925 hp, V-12 Hispano-Suiza 12Y29 liquid-cooled engine. It used a Hamilton-type constant-speed propeller. The cooling airflow was adjustable by changing the angle of the grills located on the radiator intakes.

The canopy initially was made by using concave-convex side panels. These proved to be problematic as they distorted the pilot’s vision and were replaced with simpler flat sides. The instrument controls panel and command were directly copied from French designs. The first prototype and the later first-moved aircraft of the second series were only equipped with radios.

The landing gear was of a conventional design consisting of two front legs which retracted outwards, with the tail wheel being fully retractable. To provide better landing, the front landing gear units had shock absorbers. The IK-3 landing gear was of rather poor quality and it often broke down during landing, and led to many aircraft being constantly under repair.

Initially, the armament consisted of one 2 cm HS 404 cannon placed behind the engine, and two 7.7 mm M.31 Darne machine guns, positioned above the engine. This was used on the prototype for firing testing. Later production models were rearmed with one 2 cm Oerlikon M.39 cannon supplied with 60 rounds of ammunition. The 7.7 mm machine guns were replaced with two 7.92 mm Browning machine guns. The ammunition load for each machine gun consisted of 500 rounds.

Production

Despite its advanced design, only one prototype and 12 aircraft would be built. This took an extended period of time to be completed from December 1939 to July 1940. While proving to be one of the better domestically developed aircraft, the RYAF was reluctant to order more IK-3 fighters as it was heavily dependent on imported parts.

Production Versions

• IK-3 Prototypes – Two prototypes were completed
• IK-3 – Production version
• IK-3 II Series – One aircraft converted to this version
• IK-3 powered by a DB 601 engine – Allegedly one aircraft was modified this way, but the evidence is lacking
• IK-3/2 Series – Proposal for a two-seater trainer, none ever completed

Conclusion

Despite being a very capable design, the IK-3 saw only limited production. This was mainly the case due to many of its parts having to be imported, something that could not be easily done in war-torn Europe. When used in combat, despite the limited number of operational aircraft, they performed well, with claims for 10 enemy aircraft at the loss of only one IK-3. Ultimately they could do little to turn the tide of the war, and most were either captured or destroyed by their own crews to avoid being captured.

IK-3 Specifications
Wingspans	10.3 m / 33 ft 4 in
Length	8 m / 26 ft 3 in
Height	3.5 m / 10 ft 9 in
Wing Area	16.5 m² / 178 ft²
Engine	925 hp V-12 Hispano-Suiza 12Y29 liquid-cooled engine
Empty Weight	2.070 kg / 4.560 lbs
Maximum Takeoff Weight	2.630 kg / 5.800 lbs
Maximum Speed	520 km/h / 325 mph
Cruising speed	400 km/h / 250 mph
Range	600 km / 370 miles
Maximum Service Ceiling	9,400 m
Fuel	330 Liters
Crew	1 pilot
Armament	One 2 cm cannon and two 7.92 mm machine guns

Gallery

Credits

• Article written by Marko P.
• Edited by  Henry H. and Medicman11
• Ported by Marko P.
• Illustrations by Ed Jackson

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