The Rogožarski IKZ / IK-3; Yugoslav Surprise

August 7, 2022

As I have said many times, the 1930s was an era when a whole host of new technologies came to fruition in aeronautics, and this helps explain the sheer number of aircraft and concepts produced in that decade. Of course, many of these proved to be dead ends but even for those designers and companies that correctly predicted how future aircraft would be, success was not guaranteed.

And this aircraft, the Rogožarski IKZ, is a great example of an aircraft that seems to have got everything right but didn’t get the opportunity to really make an impact because of circumstance. Which is a shame because it appears to have been a very capable aircraft, and had it been created sooner might have played a more important role and be better known.

 

The background to this fighter lies in a program implemented by the new Kingdom of Yugoslavia, only created in 1918 in the aftermath of the First World War, to build up their national aeronautic industry. This saw promising students and Air Force officers sent to foreign nations, principally France, to get advanced educations on the latest developments in aircraft design and production.

This program showed great potential payoff when two of the designers who participated, Ljubomir Ilić and Kosta Sivčev, designed a new fighter for the Yugoslavian Air Force essentially completely independently from the official aircraft industry.

Naturally working on this as essentially a hobby project meant that development was slow, but in 1933 their ideas and scale models, which they had even wind tunnel tested in Paris, got enough official interest to get built by the Yugoslavian Ikarus aircraft company. This was the Ikarus IK-1 prototype and ultimately the IK-2 fighter, which first flew in 1935.

IK-1 prototype with its designers

But while the IK-2 was by the standards of the day a reasonable aircraft, its designers had with great foresight recognised that the future of fighters was shifting rapidly and were working on an even more advanced aircraft. In fact, they had been developing their ideas as early as 1933, and their concept was for a low-wing monoplane that had a retractable undercarriage, full cockpit canopy, powerful water-cooled engine and a mixed armament of cannon and machine guns.

Again, the project was essentially a private development between the two men, but in 1935 they were joined by Slobodan Zrnić, Head of Production at the Yugoslavian State Aircraft Factory.

In 1936 the three men were confident enough to present their design to the Royal Yugoslav Air Force (RYAF) and authorities for consideration…and hit some scepticism.

The previous IK-2 was still undergoing testing and being examined by the Yugoslavians for potential service. To be suddenly presented with an aircraft that seemed to be right on the cutting edge, when they were still working on ironing out the kinks on the previous aircraft, created reservations about the new design.

But by this point other nations were actively adopting such aircraft and, after their initial hesitation, the Yugoslavian government signed a contract to build a prototype in late March 1937. Production was allocated to the Rogožarski factory in Belgrade, and by April 1938 this aircraft, the first IKZ was completed.

Now, I should address the issue of the IKZ / IK-3 naming convention. It seems that the original intention was to call it the IKZ, drawing an initial from each of the designer’s names. But, in the Cyrillic alphabet, “Z” looks very much like the numeral “3”, and so, especially as there already existed the previous IK-1 and -2, somewhere some confusion has crept in and the aircraft is often called the “IK-3”.

Anyway, the IKZ was a thoroughly modern aircraft that showed its French influences very strongly.

 

The aircraft was powered by a Hispano-Suiza 12Y V12 engine, which in the prototype was purchased from France but in the production models was a variant licensed built by the Czech Avia company and which produced 920hp.

The fuselage was of a mixed construction, with a steel tube superstructure and the aircraft skin being both metal and fabric, whilst the wing was made of wood with some steel internal structure.

In appearance, the IKZ looked very similar to contemporary French fighters such as the MS 406, probably not surprising as the designers had received their technical training in that country, and the armament also followed the French pattern. The prototype was armed with an HS-9 20mm cannon firing through the propeller hub and two Darne machine guns of .303 calibre mounted in the fuselage.

Flight testing began in May 1938 and showed that the aircraft was a pretty good performer. The controls were very responsive, and the aircraft proved itself to be remarkably agile, with principal complaints being the canopy design, which caused distortion, and some issues with engine heating.

The only other issue was with the armament, which was favourably commented on for its concentrated fire but was thought to be a little lightweight, and the test pilots suggested that consideration be given to adding additional machine guns in the wings.

But generally, the reviews were extremely positive. Most of the test pilots had experience flying a range of types, from the Fury biplane then in service with the RYAF to many foreign designs that had been assessed for potential purchase, including the Hawker Hurricane, the Heinkel He 112 and the MS 405. They reported that the IKZ was a match to all of these and better in some regards.

The successful test program and praise from the pilots meant that the Royal Yugoslavian Air Force was happy to take the new design into service, and in November 1938 an order was placed for twelve production aircraft.

Tragedy then struck the following January when the prototype was lost during a flight. During a dive test the windscreen tore loose, causing the pilot to try to pull up too hard, which in turn tore the starboard wing off, causing the aircraft to crash.

This caused a delay while further examinations of the design were conducted, but the aircraft was still recognised as a fine fighter. Plus, the Yugoslavs was now trying to build up its strength as the tensions in Europe rushed towards breaking point.

Unfortunately, the reliance on certain components from foreign suppliers also became an issue, as well as strikes at the aircraft factory, and so the twelve production aircraft would only be delivered gradually between December 1939 and July 1940. These aircraft were equipped with a 20 mm Oerlikon FFM cannon and two 7.92 mm FN Browning machine guns.

 

In the preservice tests that the RYAF conducted, the top speed of the aircraft was recorded as 327mph (526kp/h) and the IKZ would be considered a match for both the Hawker Hurricane, which the Yugoslavs were building under licence, and the Bf 109E, seventy-three of which were by this point in service with the RYAF and represented its most formidable fighter. Against the Bf 109 the IKZ was found to be more agile in level flight, being able to outturn the Messerschmitt.

And it was hoped more could be wrung out of the design. The seventh aircraft on the production line was retained to have modifications, with improvements being made to the aerodynamic design and canopy, a more powerful version of the engine, armour being fitted for the pilot and self-sealing tanks. The changes do appear to have indeed improved performance, with the testing showing that the aircraft was capable of 340mph (547 km/h).

But though the RYAF wanted as many aircraft as they could get, the issues of obtaining parts from foreign suppliers as war had now broken out was recognised as a significant issue. So only twenty-five of the improved IKZs were ordered in March 1940, this being thought the maximum that it would be possible to build with available parts.

Indeed, the concerns over the supply of engines led to work being conducted to examine the possibility of fitting either Rolls Royce Merlin or Daimler Benz DB 601 engines to the IKZ. Nothing came of this, because the clock was ticking for Yugoslavia and on the 6th of April 1941 the Germans and their allies attacked.

On the RYAF strength were eleven IKZ’s, one of the production aircraft having been lost in an accident in 1940, but of the remaining aircraft only six were available for combat. These were thrown into the maelstrom from the very beginning.

Defending Belgrade, five of the IKZs attacked the first German air raid on the city – a force comprising of 234 bombers and 120 fighters. Needless to say, against these sorts of odds losses were heavy, and by the end of the first day only three of these aircraft were operational. But they were credited with eight kills.

The IKZs continued to fight, with desperate attempts made to get the damaged or non-operational aircraft available for use, including the improved variant prototype, but continuous action in trying to repel the assault meant that often only three of the aircraft were ever available at any one time.

By the evening of the 11th of April German troops were close to the airfield that the operational IKZ’s were based at and, with the end in sight, on the morning of the 12th the crews burnt their aircraft to prevent them failing into enemy hands.

With the fall of Yugoslavia a few days later two IKZ’s were apparently captured by the Germans, probably aircraft under repair at the factory, and were reportedly used for flight tests.

 

But ultimately, they too were scrapped, and that was the end of the IKZ.

However, they did leave a legacy. Though heavily outnumbered, the IKZs were credited with shooting down eleven enemy aircraft, an impressive feat considering the opposition they faced.

But additionally, after the war the design team were able to dust off their plans and incorporate new ideas into the design to produce a new fighter, the S-49, which would also go on to serve the Yugoslavian Air Force, though this time in somewhat larger numbers.

Sources/Related:

https://plane-encyclopedia.com/ww2/rogozarski-IKZ/

https://en.wikipedia.org/wiki/Rogo%C5%BEarski_IKZ

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