Yugoslavia (1939)
Prototype Advanced Trainer – 1 Built

With the emergence of new fighter planes in the years leading up to the Second World War, it became necessary to replace the older biplane trainer aircraft, which were too slow, in order to efficiently train new pilots to fly the newest fighters. Thus, it was logical that more modern advanced trainer aircraft would be needed. The MM-2 was an experimental Yugoslavian solution to this problem.

First Steps

At the end of the thirties, the Yugoslav Air Force was equipped with modern planes, such as the German Me-109, the indigenous IK-3, and the British Hurricane, highlighting the need for an updated trainer. There were several older aircraft in use for the role, like the FP-2 and the Rogožarski PVT, with a maximum speed of around 140 mph (230 km/h) but there was a need for a much faster and modern aircraft trainer.

To fill this gap, Air Force engineer and pilot Captain 1st Class Dragutin Milošević, on his own initiative, began to work on a new advanced trainer in 1936. The first aerodynamic calculations, choice of engine, structure, and the design were done by 1937. This new plane was conceived as a two-seater with seats one behind the other, with an enclosed cockpit and dual controls. It had a low wing, mixed construction, with a single engine and retractable landing gear. The engine would have been the Renault 6Q-02, giving 162 kW (220 hp). Milošević never gave a designation for this plane, but was later simply named the M-1.

Captain Dragutin Milošević submitted this project to the Yugoslav Department of Aviation in 1937. The Department analyzed this proposal and, while on paper it would have had great flying performance, a decision was made to reject it because the parts necessary for its construction had to be imported from abroad.

This decision did not discourage Captain Milošević, and he made attempts to improve his design. He proposed replacing the Renault with the license-built Gnome-Rhone K-7 309 kW (420 hp) air-cooled 7-cylinder engine. By adding this engine, the length of the plane would be reduced from 23 ft 7 in to 20 ft 4 in (7.2 m to 6.7 m) but the total weight increased to 2,160 lbs (980 kg). To improve the landing characteristics of the aircraft, it would have been necessary to increase the distance between two front landing wheels from 6 ft 2 in to 7 ft 10 in (1.9 m to 2.39 m). All aerodynamic and statistical calculations were finished by 1939. The second version was named M-2 and it was, in essence, the basis of the future MM-2 aircraft.

One wooden model (1:10 scale) was built by the Albatros factory in Sremska Mitrovica. This model would be used to test the aerodynamic properties and accuracy of earlier calculations. Aerodynamic properties were tested in the Paris wind tunnels on the 17th and 18th of July 1939. After these trials, the fuselage length reverted to the original 23 ft 7 in (7.2 m).

Later, Captain Milošević did new calculations that showed that certain changes to the design of the aircraft were necessary. Adding weapons and increasing fuel capacity would lead to an increase of the mass of the M-2 by 242 lbs (110 kg), some 60 lbs (30 kg) in fuel and 176 lbs (80 kg) in armament. After all the other modifications, the total mass reached 2,782 lbs (1,262 kg) compared to the initial 2,160 lb (980 kg). The wing area had to be increased from 129 to 146 sq ft (12 to 13.6 m²) and the wingspan from 27 ft 10 in to 30 ft 3 in (8.5 to 9,23 m).

Adoption of a Prototype

Captain Milošević submitted a letter, together with documents, plans and calculations, to the supreme headquarters of the Yugoslavian Air Force, notifying them of the test results of the proposed M-2 aircraft. Since he did not receive any kind of response, he asked Major Đorđe Manojlović, also an aviation engineer, for help. Although Đorđe Manojlović did not have a direct impact on the design of the M-2, his great influence and connections in the Supreme Air Force Command lead to the continuation of the project. The cooperation of these two men lead to the final approval for construction of the M-2 aircraft project.

When the Air Force Headquarters of the Army of the Kingdom of Yugoslavia accepted the M-2, construction of this project was given to the Ikarus factory. The contract was signed on the 25th March 1940. It was planned to build one prototype aircraft for testing in order to ascertain if the M-2 was fit to be accepted for serial production. The project was monitored by a team composed of engineer Sava Petrović, Air Force Major Vojislav Popović and the technician Stefan Lazić. The prototype was ready by the first half of November 1940.

Origin of the Name

In the Kingdom of Yugoslavia, there was a custom of using the initials of the names of the designers as the official designation for most of new types of aircraft in service (like the IK-2/3), and MM-2 was no exception. MM comes from the initials of the surnames of Captain Dragutin Milošević and the constructor and engineer Major Đorđe Manojlović. There is sometimes confusion about the exact name of this aircraft. It is sometimes also called MiMa-2. In some documents found after the war, it is also called M.M. 2. In this article, the MM-2 name will be used, as it is the most common.

Technical Characteristics

The MM-2 was designed as an advanced two-seater trainer, with seats one behind the other, with dual controls and a fully enclosed cockpit. It was a low wing, mixed construction, a combination of wood and metal, single engine aircraft with retractable landing gear.

The wings had a trapezoidal shape with a rounded top. They were constructed by using two racks which were made of steel tubes welded together. The racks were welded to the plane’s hull and the wooden ribs were connected to them by rivets. The wings were covered with canvas, except for the central parts, which were made of aluminum sheet. This was done so that the technicians and repair crews could have easy access to the inside of the wing. The ends of the wings were made of wood that were held in place by steel fittings. The flaps were covered in canvas and operated either manually or hydraulically.

The MM-2 hull was of mixed construction. The main body was made by using welded pipes. The front part was covered with aluminum sheet and the rear with canvas. The tail was made mostly of wood and covered with canvas.

The main engine was the Gnome-Rhone K-7, which supplied 310 kW (420 hp). It was domestically built under license from Franch aircraft manufacturer Rakovica. It was hoped to use a two-bladed metal propeller but, due to the lack of resources, wood was used. The maximum estimated speed (never achieved) was around 250 mph (400 km/h), with an effective range of 475 mi (764 km) with some 40 gallons (150 l) of fuel capacity. Climbing to 6,500 ft (2,000 m) could be achieved in 3 minutes and 9 seconds, but the maximum service ceiling was never adequately tested.

The landing gear was supposed to be of the ‘Nardi’ type imported from Italy, but it was planned to domestically build the landing gears for the production version, to avoid being dependent on foreign countries. On the prototype, no radio was installed but it was hoped to equip all future production aircraft with the FuG VII radios.

The main armament consisted of two wing-mounted 7.7 mm Darn-type machine guns with 175 rounds of ammunition for each gun. The total bomb load consisted of four 10 kg bombs carried under the wings. It must be noted that the armament was never installed on the prototype, as testing was interrupted by the beginning of the war.

First Test Flights

The first test flights were made by the beginning of the 1941 at the Zemun airport. The pilot for these flights was Vasilije Stojanović, the test pilot of the Ikarus factory. By the end of March 1941, some 45 flights had been made with a total of 20 flying hours. The pilot assessed the flying performance of this plane as excellent. The results of these tests indicated that this aircraft had good flight performance. The controls were adequate, both instructor and the students cockpits had enough room with a good field of view and, during flights, the aircraft did not present any tendencies for sudden unpredictable movements. Due to its good air brakes and flaps, take-offs and landings were quite easy. There were no major objections from the test pilot about the MM-2.

The MM-2 could very easily reach speeds of up to 217 mph (350 km/h). The design maximum speed was never tested, but calculations suggested that it could be as high as 250 mph (400 km/h). This was never confirmed due to the outbreak of the war. The MM-2 prototype had an unusual color scheme with a combination of red on most of the rear fuselage and wings, and polished aluminum on the majority of the fuselage and the engine section, with a small Yugoslav flag painted on both sides of the tail.

On the 25th of March 1941, a contract was signed between Ikarus and the Air Force. According to this contract, Ikarus was to prepare for production of MM-2 trainer planes in the near future. Before the production would begin, a last series of tests was to be conducted by a test group at an airfield near city of Kraljevo. An order was given to Stojanović to fly the MM-2 from Zemun to the Kraljevo airfield. Once there, it was planned to do some more flight performance trials in order to examine the limit of the flying characteristics of the MM-2 aircraft. Stojanović completed the flight on the 4th April. Final production was never achieved due to the German invasion of Yugoslavia that started only a few days later.

Operational Service

The MM-2 did not see any active service in the Royal Yugoslav Army because of the beginning of the April war, the German attack on Yugoslavia in April 1941. After the defeat of the Yugoslav army, the Independent State of Croatia, or NDH, was created. In order to form the new NDH military air force, it was necessary to find and obtain planes to equip these new units. Like many other former Yugoslav planes, the MM-2 was also pressed into NDH service in a very limited role.

It seems that the MM-2 had some engine problems (possibly sabotaged) when it was captured by the Germans at airfield near Kraljevo. It is possible that it was in a bad condition since the Germans did not even bother to repair it and put it into operational use.

The MM-2, together with other Yugoslav captured aircraft, was collected and handed over to the NDH. After a while, the MM-2 was repaired under code name No. 6301, and returned to active service. Additional flight tests were conducted by Georgije Jankovski, a test pilot for Dornier-Werke. In September 1941, the plane was transferred to the Zemun airport and handed over to Croatian Major Ivan Pupis for future use. Major Pupis was the leader of the group responsible for the repair, reception and later transfer of all Yugoslavian aircraft captured during the April war. When the MM-2 was repaired and ready for active service, Pupis to keep it for his personal use rather than handing it over to the military.

The MM-2 was ‘owned’ by Pupis until March 23rd, 1942, when he received a direct order from the Croatian Aviation Command to transfer the MM-2 to the ‘Rajlovac’ airfield near the city of Sarajevo in Bosnia. The aircraft arrived at the beginning of April 1942. The MM-2 was given to the 17th Squadron (Jato) which was part of the 6th group (Skupina) under the Command of the Major Romeo Adum. The MM-2 was used mostly for limited test flights. On May 13, 1942 while piloted by Vid Saić (from the 18th Squadron), the plane crashed. The pilot survived the crash with no injuries. A commission was formed to investigate the causes of the crash and found several irregularities: The pilot did not ask for permission and had no orders to fly on the MM-2 that day, and he also did not know anything about the flying characteristics or the condition of the plane. The conclusion was that the pilot was guilty for the accident and, as punishment, Vid Saić lost his Pilot rank. The damage to the MM-2 was estimated to be around 90%. There was no point to try to rebuild it from scratch and the remaining parts were destroyed. There is no information whether it was equipped with any armament in Croatian military service.

Production

Due to the outbreak of war on April 6th, 1941, except for the prototype, no other specimen of this aircraft was ever built. In some documents and letters found after the Second World War, it was discovered that the Ministry of Aviation planned to order around 50 copies of the MM-2 aircraft. Along with this, the Yugoslav military negotiated with Germany for the purchase of Arado Ar 96 training planes, but nothing came of this.

After the war, the new communist Ministry of Aviation and the Ikarus factory representatives were also interested in restarting the production of this aircraft but, as the chief designer had died in one of the many German prison camps and the necessary machines and tools were lost during the war, this was too difficult and was abandoned.

Operators

• Kingdom of Yugoslavia – Built and tested the single prototype.
• Independent State of Croatia NDH – Used the MM-2 captured during the April war, but it was lost in an accident.

MM-2 Specifications
Wingspan	30 ft 6 in / 9.23 m
Length	23 ft 7 in / 7.20 m
Height	9 ft 6 in / 2.89 m
Wing Area	14.6 ft² / 13.60 m²
Engine	One Gnome-Rhone K-7, 309 kW (420 hp) air-cooled 7-cylinder engine
Empty Weight	1,071 lbs / 894 kg
Maximum Takeoff Weight	2,290 lbs / 1,330 kg
Fuel Capacity	150-160 l
Maximum Speed	250 mph / 400 km/h
Cruising Speed	390 mph / 630 km/h
Range	475 mi / 764 km
Maximum (estimated) Service Ceiling	6,600 ft / 2,000 m
Climb speed	Climb to 2,000 m in 3 minutes and 9 seconds
Crew	Two, instructor and student pilot
Armament	Two Darn M30 7.7 mm machine guns in wings Total bomb load around 40 kg.

Gallery

Illustration by Haryo Panji https://www.deviantart.com/haryopanji

Sources

• http://www.letletlet-warplanes.com/2008/06/01/ikarus-mm2/
• http://www.vazduhoplovnetradicijesrbije.rs/index.php/istorija/76-ikarus-mm-2
• Military Magazine Arsenal, 41-50, 2011 Belgrade,
• Tihomir L. and Danko Č. (1998), The Croatian Air Force In The WWII, Nacionalna i sveučilišna knjižnica, Zagreb
• Vojislav V. Mikić (2000) Zrakoplovstvo Nezavisne Države Hrvatske 1941-1945, Vojno istorijski institut Vojske Jugoslavije.