Nazi Germany (1942)
Experimental Aircraft – 1 Prototype Built
Three-quarters view of the B9, note the large glazed cockpit. Colorized by Michael Jucan [airwar.ru]The Akaflieg Berlin B9 was a German experimental twin engine aircraft designed with the pilot placed in the prone position. It was designed to withstand extremely high g-forces. One prototype was built and tested by a glider production workshop in 1943 but it would not be adopted for mass production. The author would like to especially thank Carsten Karge from the Archiv Akaflieg Berlin for providing information on this generally unknown aircraft.
Why prone position?
During sharp up and down turns while flying an aircraft, strong g-forces appear that act on the pilot, potentially leading to loss of consciousness. Under normal flying conditions, the g-forces that appear are relatively harmless. The first effect of the g-force which the pilot notices is the difficulty of moving his body normally, as normal movements feel much heavier. Another effect of strong g-forces, which is much more dangerous, is the loss of oxygen flow to the brain. In some cases, the flow of oxygen and blood to the human brain can be greatly diminished, which can lead to the pilot losing consciousness momentarily. This effect lasts a short time, but it is enough for the pilot to lose control of the plane with a potentially fatal outcome.
While today, devices such as advanced anti-g suits help the pilot withstand strong g-forces, during the World War Two, other solutions had to be found. The Germans had noticed that, especially during sharp dive bombing actions, the pilots often lost consciousness. One way to tackle this was to put the pilot into a prone position, which in essence means to fly the plane while lying on the belly. In this position, the pilot has both his heart and his brain at the same level, which means that blood is no longer stopped from travelling to the brain during high-g maneuvers. Thus, this flying position allows the pilot to endure much greater g-forces than he would normally be able to if he would be in an ordinary sitting position. Other advantages of the prone position are the reduced aircraft size, smaller fuselage, less drag due to the smaller cockpit, and it would be easier for the pilot to operate the plane when conducting bomb sighting and ground attack, among other advantages.
During the war, the Germans would test several such aircraft designs, sush as the Henschel Hs 132 or B9, mostly for the ground attack role. Beside a few prototypes built, none were ever used operationally.
History
The SF 17 prone glider was the forerunner of the B9 powered aircraft [Akaflieg Stuttgart]In order to test the idea of an aircraft with the pilot in the prone-position, the Aero-Technical Group (Flugtechnische Fachgruppe/FFG) of Stuttgart designed and later built the FS 17 all-wood test glider. It was especially designed to withstand forces up to 14 G. It made its first test flight on 21st March, 1938. In the spring of 1939, FFG Stuttgart made the first design drawings and calculations for a prone-piloted aircraft. This aircraft was to be powered by two Hirth HM 50 engines with an estimated speed of 250 mph (400 km/h).
FFG Stuttgart never completed this project as it was forced, for unknown but likely politicaly reasons, to hand over the project to Akaflieg (Akademische Fliegergruppe/Academic Aviator Group) Berlin. It is possible the order came from the German Experimental Department for Aerospace (Deutsche Versuchanstalt für Luftfahrt e.V. Berlin-Aldershof) DVL or even from the Ministry of Aviation (RLM – Reichsluftfahrtministerium), but precise information is lacking. Akaflieg Berlin, founded in 1920, was one of the oldest gliding clubs in Germany and it still exists today.
The RLM designation for this aircraft was “8-341” but Akaflieg used the simpler B9 designation. The technical characteristics that the new plane was supposed to have were a good field-of-view for the pilot in the prone position, a high degree of safety for the pilot, a high speed during diving, good general flying characteristics and being able to withstand forces of up to 25 G, or 22 G depending on the sources.
Akaflieg Berlin had a small number of engineers and workers and an adequately equipped workshop to complete the task given. For this purpose, a design team was formed with Theodor Goedicke, Leo Schmidt and Martin G. Winter, which was responsible for the creation of this new aircraft design. The first prototype was to be ready by August 1942 but this was never achieved, and the prototype was only completed in early 1943. It made its first test flight on the 10th April, 1943 at the Schönefeld airfield, near Berlin.
The Design
Front view of the B9 [airwar]The B9 was a single-seat, low wing, mixed construction aircraft with the pilot in prone position. It consisted of a metal airframe, made of steel ribs, covered with wood and canvas. The main fuselage’s cross-section was trapezoidal shaped. As the B9 was specifically designed to withstand forces of up to 25 G, it had to have a strong fuselage.
The wings were made of wood covered with duralumin sheets. In order for the wooden wings to withstand the strong torsional forces which occur during high acceleration maneuvers, the spaces between the spars were heavily reinforced. The middle part of the wings viewed from above have a square shape and then narrow towards the wing tips. The wings were held in place by four bolts on each side. The rear tail design was a simple one, with standard rudder and elevators.
The B9 had a standard retractable landing gear copied from the Me-108, which consisted of two larger wheels and one smaller non-retractable wheel at the back. The landing gear was lowered and raised manually. The front wheels retracted into the engine nacelles, but they were not fully enclosed.
The B9 had a large 4.9 ft (1.5 m) long glazed cockpit with good all-around view. But, as the pilot was in a prone position, the above and the rear views were limited by the human body’s inability to turn the head in these directions. The glazed cockpit was made of two parts, the front windshield and the rear larger canopy that opened to the right side. The cockpit interior had to be especially designed for a pilot lying in the prone position. The usual flight controls were almost useless in this situation and, thus, certain changes were necessary. It was important to divide the controls on both sides of the cockpit, in order to avoid the pilot crossing hands, which could lead to complications in flight. On the right side were the controls for ailerons and elevation. The pilot would use his right hand to gain access to the harness and the canopy release mechanism. For controlling the rudders and brakes, the pilot would use his feet. Using his left hand, he would operate the remaining instruments, the throttles, flaps, ignition switches, emergency pump, fire warning, undercarriage control and others. Additional engine and flight instruments were located behind the pilot. These included, among others, the distance indicator, climb indicator, compass, oil and fuel pressure gauges and airspeed indicator. For the pilot to be able to see them, a small mirror was provided. There were also inclined and horizontal line markers on the inner windshield to help the pilot with orientation. For flying at high altitude, an oxygen supply system with a mask was provided to the pilot.
The aircraft was powered by two Hirt HM 500 air-cooled engines, with 105 hp each. The maximum speed was around 140 mph (225 km/h) but, according to some sources, it was as high as 155 mph (250 km/h). The four fuel tanks, with a total capacity of 25 gallons (95 l), were located between the spars on both engine sides. The B9’s effective operational range was 250 mi (400 km). Originally, the B9 was meant to be equipped with two variable-pitch propellers, but it was instead fitted with ordinary wooden fixed pitch propellers made by the Schäfer company.
As the B9 could be used as a ground attack aircraft, a bomb rack was meant to be installed, but it is not clear if this was ever implemented.
Operational Testing
The B9 in flight [airwar]The operational prototype was ready by the summer of 1943. The first test flights were carried out by Ing. L. Schmidt and Dipl.-lng. E. G. Friedrichs. On one flight, L. Schmidt had an accident, the details of which are not known, but the plane probably suffered only minor damage.
The B9 was meant to make a series of test flights in order to ascertain if the prone position design had any merit and to test the general flying and overall structural performance. If these proved to be successful, the B9 would serve as base for future development and be put into active service. The B9 aircraft received the ”D-ECAY” marking, which was painted on both sides of the fuselage.
The tests were carried out from July to October 1943, during which time around thirty pilots had the opportunity to fly it. The test flights were conducted without any major problems and only one accident was recorded. This accident was caused not by any mechanical problems, but by a pilot mistake during takeoff. The B9 was damaged, but it was repaired and put back into service in only a few weeks.
The pilots did not have many objections to flying in the new prone position. They described it as comfortable and that it was relatively easy to adapt to the new commands. There were some issues, like fatigue and tiredness of the neck and shoulder muscles because of the constant moving of the upper arms. There were also some complaints about the chin supporter, which was deemed as unpleasant during flight but it was essential during high g-force maneuvers. During these test flights, the control panel and the controls did receive some changes in design. The large and fully glazed cockpit provided the pilot with good front and below fields of view, while the rear and upward view was somewhat problematic due to the prone position.
These tests showed that this type of aircraft was well suited for bomber, ground attack, high speed reconnaissance and possibly even in a high-speed fighter role. But it was also noticed that, due to the somewhat restricted view, the use of low speed prone pilot aircraft without air support was not recommended. Despite being designed to withstand forces of up to 25 G, the maximum achieved was only 8.5 G. One of the reasons for this was the use of low rotational speed propellers.
For 1944 and 1945 unfortunately, there is no information about the B9’s operational use. The B9 was found abandoned at the Johannisthal airfield near Berlin after the war. In what condition it was by the time of capture is not known. What is unusual is that the B9 was captured by the Americans and not the Soviets (according to author Hans J.W.). What the Americans did with the plane is unknown to this day, but it was most likely scrapped.
Only one B9 plane prototype was ever built. By 1943 and 44, a large amount of resources were invested in the production of fighters for the defense of the Reich and there were neither the time nor the resources needed to develop and test such an aircraft.
The first Junkers D.I prototype J.9/I [Nhungdoicanh]The German Air Force was responsible for several great revolutions in the development of aviation during both World Wars. While the development of jet technology in the Second World War is probably the best known, during the First World War, one of the most important such evolutions was the development of the first all-metal planes. The man responsible for this was the famous Hugo Junkers. The corrugated metalwork first seen on the D.I would become a hallmark of later Junkers aircraft.
The first all-metal projects
Aviation technology before the First World War revolved around wood as the main building material. Wood was used as it was easy to process and was easily available in great quantities and simple carpenters could be put to work on airplane construction.
One of the first persons who ever experimented with the idea of building an all-metal plane was the well-known German aviation designer and inventor Hugo Junkers (1859-1935). While working as a professor of thermodynamics at the Technische Hochschule (Technical University) in Aachen in 1907, he met a colleague, Professor Hans J. Reissner. Professor Reissner was involved in experiments with many novel ideas, such as aerodynamics in aviation. This moment would have a big impact on Hugo Junkers, as he would develop a great interest in aviation.
One of the few produced J 2 prototype which lead to the D.I [Wikimedia]Hugo Junkers’ initial efforts were focused on solving the problem of poor aerodynamics of already existing aircraft. In 1912, his preliminary research showed that planes had better aerodynamics properties if they were designed to have an airfoil structure. In essence, this means that the whole plane, wing, body, and control surfaces had to have curved surfaces specially designed to give the best possible ratio of lift to drag. In order to perform even more experiments in aerodynamics, Junkers financed the construction of a wind tunnel at the Frankenberg laboratory. In the following years he continued his research, and by 1914 he had performed around 4,000 different tests and built 400 test models.
In 1914, Junkers had the first indications that an all-metal monoplane with thick wings was a feasible idea. While metals, like iron, were available in large quantities, lighter metals, like duralumin, an aluminum alloy, were more desirable for this purpose. The negative aspect of duralumin was the fact that it was difficult to work with. The techniques and technology of the day were inadequate, and the process of forming duralumin was slow and crude. As this could delay his work for years, Hugo Junkers decided to use the iron plates as a replacement, as they were much easier to work with.
After having constructed one all-metal wing prototype with a 9.18 ft (2.8 m) wingspan, Hugo Junkers made a request on the 2nd of February, 1915 to the German War Ministry for funds so he could build an all-metal prototype plane. This request was rejected, but it did not discourage Junkers from continuing his research. His second request was accepted in July 1915. With these funds, Hugo Junkers was able to construct a working prototype by December 1915.
The base of the prototype was made of iron ribs which were covered with iron sheets which were only 0.1 to 0.2 mm thick, held in place by electric welding. A second layer of sheet metal was added to reinforce the whole construction. The first prototype, designated the Junkers J 1, was ready by the end of 1915. It was powered by a Mercedes D.II 125 hp engine. After some ground testing, the new plane was shipped to Döberitz, the main German aviation training and test site in December 1915. Once there, the first test flight took place on 18 January, 1916. This was the first flight of a plane with an all-metal frame. The Idflieg (Inspektion der Fliegertruppen – Inspectorate of Flying Troops) was impressed with this prototype and ordered six more all-metal planes for future testing as a fighter plane. The J 1 design was not without problems, as there were some issues with the wing connection to the fuselage. During one test landing, one of the wings separated entirely.
Hugo Junkers began working on a second improved prototype named J 2. The problem with the wing-fuselage connection was solved by changing the internal design. The wings were divided into a couple of parts. The main section was connected directly to the fuselage and the others were affixed by screws. In only a few months, the first Junkers J 2 was ready to be tested. The J 2 was powered by a single Mercedes D.II 120 hp engine which was later changed to a stronger Mercedes D.III 160 hp. It made its first flight on 11 June, 1916. However, unlike the first prototype, the flying performance of the Junkers J 2 was poor. The speed was good, but the plane was simply too heavy at 2,480 lbs (1,160 kg) and thus useless as a fighter. Some six were ordered and built for future testing but the Idflieg lost any interest in it. Despite being rejected for operational service, it was still deemed important for testing construction methods and acquiring additional research.
After Hugo Junkers and his team analysed the Junkers J 2, they concluded that the plane could be vastly improved if lighter materials were used. Their solution was to undertake a study of how to make duralumin easier to work with. In time, specialized tooling and machines were developed and designed in the hope of producing adequate duralumin parts that could be used for aircraft construction. Despite the use of the duralumin in Zeppelin construction, the Junkers team made many improvements to these processes.
Thanks to these developments with aluminum processing, Junkers tried to build a fully operational all-metal monoplane. This was a private venture marked as the Junkers J 3. It was short lived, as the Idflieg refused to finance its development and only a single incomplete airframe was built. The Idflieg was more interested in all-metal ground attack biplanes.
The improved J 7 prototype
Side view of the J 7 prototype. [Wikimedia]Hugo Junkers and his team continued to develop their own all-metal plane project. The J 4 served as a prototype for the J.I biplane and J 5 was never completed. Next in line was the Junkers J 7 as a single seat fighter and the J 8 two-seat close ground-support version. The J 8 prototype would eventually lead to the J 10 and the CL I. As the the J 7 and J 8 were developed, tests done in the wind tunnels showed that the low wing design provided good performance. One extra benefit of this design was the fact that the low wing would provide some extra protection for the pilot during a harsh landing. However, the weakest point in the design was the fuselage. Hugo and his team had significant problems designing a structure that would be strong enough to support all the necessary equipment, engine, and fuel tanks while still being light enough to maintain fighter maneuverability. They eventually reached a achieved a design that met most of the requirements.
The Junkers J 7 was constructed by using steel bars to form the structures of the plane and these were then covered in duralumin sheets. This method was copied from the J 4, with the only difference was that parts of the surface of J 4 were covered with fabric, while J 7 was all-metal. The J 7, piloted by Feldwebel Arved Schmidt, made its first test flight on 17 September, 1917. As the tests continued, Schmidt was generally pleased with how the plane behaved. In his report he said that the plane “.. made a good impression and possessed no serious fouls but the unique rotating wingtip ailerons were somewhat overbalanced…”. The J 7, despite its large front mounted radiator to accommodate the Mercedes D III 160 hp engine, managed to reach a speed of 77 mph (124 km/h). Many further trial flights were conducted, and in early October 1917 Schmidt managed to reach an altitude of 16,400 ft (5,000 m) in 17 minutes. This was a great result especially considering that the J 7 had a weight of 1,572 lbs (713 kg) and with added military equipment, the same altitude could be reached within 24 minutes.
For the next series of test flights, the J 7’s wings were equipped with conventional ailerons. These trials were held in late October 1917. The pilots were Leutnant Gotthard Sachsenberg and Theo Osterkamp. This time, the J 7 was pitted against the Albatros D.III. The J 7 proved to be a better fighter but the problems with the ailerons persisted. Both pilots gave a “green light” for the J 7 to go into production.
On 20th October, 1917 Idflieg made a decision to establish a new cooperation between Hugo Junkers and Anthony Fokker. Junkers-Fokker Werke AG was thus founded. It was hoped that the lack of production capacity of Junkers’ team would be supplemented by Fokker’s. This meant that there were two companies working on the J 7 project, Junkers (Jco) and Junkers-Fokker (Jfa). Despite the Idflieg’s hopes for good cooperation, this was never achieved as both sides sought control of the project.
Pilot and his assistant are starting the D.I. in front of the ‘Zeppelin’ hangars at Wainoden. [flyingmachines.ru]In December, new modified ailerons were tested and the large nose radiator was also changed. While flying the J 7, the pilot, Tonny Fokker, had an accident upon landing. The plane was damaged but quickly repaired in time for the inspection made by Hauptmann Schwarzenberger from the Idflieg. He gave positive reviews of this plane and suggested that it should be used in the First Fighter Competition held in Germany. For this purpose, it was equipped with a new Mercedes engine and received new aerodynamically-balanced ailerons.
This competition was held from January to February 1918. Many front line pilots flew the J 7, including the famous Red Baron. He had positive comments for the J 7, in his report the plane being rated as having better climb rate and speed than other fighters in field use. However, he also noted the presence of some oscillation in the wings during sharp turns.
In January, Fokker once again had an accident during landing, but the damage was minimal. The plane was damaged again during its flight to Dessaou for wing modifications, but was repaired and ready for further testing by early February. These accidents also proved that its construction was much more robust than that of ordinary wooden planes. In March 1918, the last tests took place, with Leutnant Krohn as the pilot. His report read “.. On take-off the aircraft accelerates quickly and leaves the ground in a short time. It reacts instantaneously to the control. After ten degrees of control-stick movement, which suffices for an 80-degree bank, the control becomes very heavy. In a spiral, the aircraft reacts quickly to the controls. On the whole, the aircraft is at least as manoeuvrable as the new Albatros D.III or D.VI when diving at 155 mph (250 km/h) airspeed without any vibration in the wings..”
The ailerons were modified for the last time, which solved all previously mentioned problems with the controls. The J 7 prototype plane was used by a Fligertruppe in late March 1918. The J 7 was also used in the Second Fighter Competition held in July 1918. Despite proving to be an adequate fighter, the J 7 would never be accepted for service.
The J 9 and the D.I
The J 9/II rear view. [Militär Wissen]At the same time as the J 7 was developed, Junkers began work on an improved model named J 9. Two prototypes were built, simply marked as J 9/I and J 9/II, the first of which was ready by April 1918. The J 9 was similar in construction to the J 7, but it was better suited for possible mass-production. By March 1918, Idflieg was negotiating with Junkers about the possible production of six planes for more testing. Hugo Junkers was disappointed with this, as he expected the signing of a major production contract. He thought it was a waste of precious time and that the plane did not need further testing. By early May, he managed to convince military officials to put the J 9 into production. A contract was signed for the production of 100 all-metal planes, including other Junkers models CL.I and the J.I, with around 20 copies of the J 9, now officially designated as the D.I. The first group was to be built by late July, with 6 in June and 14 by July.
This is the J 9/II prototype that was powered with the Benz Bz. IIIbo V-8 195 hp engine . Due to some mechanical problem with this engine prevent it from participating in the Second Fighter Competition. [Militär Wissen]The D.I (J 9/I) prototype made its first flight on 12 May, 1918 (Some sources incorrectly state April), piloted by test pilot Leutnant Krohn. The D.I prototype was ready to participate in the Second Fighter Competition. For this, it was equipped with the Mercedes D. IIIaü engine. During this competition, the D.I prototype presented itself well. The second D.I prototype (J 9/II) was equipped with the Benz Bz. IIIbo V-8 195 hp engine. Due to problems with this engine, it was not used in this competition. During these tests, the J 9/I was equipped with two Spandau machine guns located above the engine compartment, with one on each side. At the end of the Second Fighter Competition, several front fighter pilots were asked to test these new models. As most pilots, such as Oberleutnant Goering, thought that biplanes were the future, they marked the D.I as a complete failure.
A second commission rejected the notion that it was a complete failure, referencing its demonstrated performance. One demerit marked by this commission was the lack of downward visibility from the cockpit. This was based on the German air fighting tactics which had been adopted due to Allied air superiority. This tactic involved attacking Allied planes using high speed dives from above, and thus downward vision was deemed critical. The D.I lacked this due the to the large low-placed wings, but it compensated with the metal construction that made it more resilient to low caliber rounds.
On the 21st August 1918, Idflieg place an order for 100 more Junkers all-metal planes, including the CL.I and the J.I, of which around 20 were D.I fighters. At the beginning of August 1918, three D.Is were ready for static machine gun testing. Three more were almost completed with five more to be constructed by early September 1918. For more firing tests, two were sent to Adlershof. Due to the installation of the offensive armament, some small modifications were needed.
Despite entering production, there were still some modification that were needed. The first D.I produced had a longer fuselage and larger wings. As it was tested, there were problems with vibrations of the fuselage and maneuverability. As this could endanger the entire production, a series of quick modifications were done to the remaining four, possibly five, produced aircraft. These were built with modified, shortened fuselages and smaller wingspans. In total, around nine operational fighters and two prototypes were ready by the war’s end.
Construction
The first four D.I planes still under construction. The plane on the right is the J.7 prototype. [Nhundoicahn]The D.I was designed as a single seat, all-metal low-wing fighter plane. It consisted of a metal airframe of steel ribs covered with corrugated duralumin sheets. Duralumin is a trade name for one of the earliest types of aluminum alloy. The corrugated surface of the duralumin offered increased strength, rigidity, and projectile resistance without a significant weight penalty. This method of aircraft skin construction would later be used in larger Junkers bombers in World War II becoming an iconic hallmark of the company, going on to inspire the look of the Citroen H van of the late 1940s. Aluminum construction low wing monoplane designs in would later come into widespread adoption, becoming the standard by World War II. In this way, the C.I’s design was truly ahead of its time.
The airframe was designed by Hugo Junkers, but it said that even he was never completely satisfied with its design. It nevertheless did its job and was robust, durable, and easier to maintain and repair. It offered the pilot a greater chance of survival during a forced landing than a wooden airframe. The D.I’s metal airframe provide good protection from most weather conditions in comparison to standard wooden built planes. The D.I could be left out in the elements and exposed to strong rain and wind without fear of damaging the plane. Due to use of lighter metals, the D.I’s total weight was 1,835 lbs (843 kg).
The main engine chosen for this plane was the BMW III water-cooled 6-cylinder inline, supplying 185 hp (138 kW). With this engine, the maximum speed that could be achieved was 118 mph (185 km/h).
The pilot was located behind the engine and had a good visibility of the to the front, sides, above, and rear, but the downwards visibility was somewhat limited due to the plane’s large and low wings. The wing’s design was similar to previous prototypes, as it was divided into a few parts. The central part of the wings was directly connected to the fuselage and the remaining were connected by fasteners. Under the pilot there were two fuel tanks. The total fuel capacity is not precisely known.
The landing gear was fixed, like on all planes of the era. The landing wheels were mounted on an axle that was connected to the plane by triangular-shaped steel bars. The main armament consisted of two Spandau (7.92 mm) machine guns mounted above the engine compartment.
Production
Around 40 aircraft were ordered by Idflieg to be built by Junkers, 20 in May and a second group of 20 in August. Junkers completed around 27 planes before production was stopped in February of 1919.
The Junkers-Fokker joint company was also involved in the planned production of the D.I. The exact production details are not known. The Junkers-Fokker company was given an order to produce 20 more D.I, but it only produced 13. During the production run from June 1918 to February 1919, around 40 D.I fighters were built in total by both companies in addition with two prototypes..
What is interesting is the lesser known fact that Idflieg wanted to give a contract for the production of 50 D.I planes to Hansa-Brandenburg but, as the war ended in November 1918, this never took place.
In combat
This D.I was captured on the Western Front, note the two color stripe behind the pilot cockpit, suggest that it was used in combat. [Pinterest]The war ended before more could be produced, and thus only limited numbers were sent to the front. These were given to front line units, possibly in the Flanders sector in October 1918. Later, in early 1919, during the Entente advance after the Armistice, five D.I fighters were captured. Four were found at Hombeek in Belgium. Of these four, only one was in flying condition, two were badly damaged, and the condition of the fourth is unknown. One more was found(missing half of its parts at an airfield near Brussels. There is little information about their use in combat.
However, there is evidence that gives some indication of the D.I seeing some combat. On the plane captured at Hombeek in Belgium, there were markings behind the pilot’s cockpit that may have been kill markings, but this is at best just speculation. The aircraft captured near Brussels had machine gun bullet holes, but the origin of these is unknown.
At the war’s end, the US Air Service, after analyzing the collected data and field reports, made a report “.. no one was found who had ever seen one of these airplanes in flight …. Some of the RAF pilots, however were sure that it had been used in service..”
The Junkers D.I did see combat action after the war against Soviet Bolshevik forces in the Baltic countries. The D.I was used by Kampfgeschwader Sachsenberg (under the command of Leutnant Gotthard Sachsenberg), being mostly used in the air support role, covering the German Freikorps units that remained there after the war.
Leutnant Gotthard Sachsenberg was very impressed with the D.I’s overall performance. His report reads: ”.. The Junkers aircraft have proven themselves beyond all expectations. The weather resistance of the aircraft is so great that it was possible to allow the aircraft to stand for weeks on end in the open during snow, rain, and thaw of the March season. A tarpaulin cover over the propeller and the engine sufficed to provide protection. Since neither tents nor hangars were available, no other aircraft except the Junkers would have been able to serve in Russia at that time.. the advantage of the weather resistance, the exceptional speed and the invulnerability of the aircraft outweighed the small disadvantages. In crashes and emergency landings relatively little occurred …. the Junkers aircraft, with improvement, will without doubt, take first place as a combat type…”.
Today, only a single D.I has survived the War and can been seen at the Musée de l’Air et de l’Espace near Paris.
Junkers D.I Specifications:
Wingspan
28 ft 6 in / 9 m
Length
23 ft in / 7.25 m
Height
7 ft 4 in / 2..25 m
Wing Area
159 ft² / 14.8 m²
Engine
One BMW III water-cooled 6-cylinder, 138 kW (185 hp)
This is one of the four Junkers D.I captured by the Allies in Belgium after the war. Due to the marking on the wheels, it can be ascertained that this one was built by the Junkers company. [Nhungdoicanh]This D.I was powered by a 185 hp engine and was used in the Third Fighter Competition held in October 1918. [Wikimedia]Sources
Yak-23 in Czechoslovak operational service. [airwar.ru]The Yak-23 emerged as the final step of the Yak-15 and Yak-17 development series. It made its first flight in mid-1947, powered, ironically, by a British Rolls-Royce Derwent jet-engine. By the time it entered production, the engine was changed with a Soviet-built copy. Over 300 were built, but as more advanced planes were ready for service the Yak-23s were sold to several Eastern Bloc countries. There they remained in service until replaced with the MiG-15 in the mid-1950s.
History of the Yak-23 predecessor
The Soviets began developing jet powered aircraft in the 1930s, but the process was slow with no major progress. However, by the end of World War 2, the Soviets managed to come into possession of large quantities of German war technology, engines as well as experimental and operational jet aircraft.
In April 1945, by orders of the National Defense Committee of the Soviet Union, work on a new generation of jet-powered aircraft began. In the case of jet fighters, the minimum requirement was that it had to achieve a maximum top speed of 500 mph (800 km/h). As there were a number of captured German Junkers Jumo 004B1 and BMW 003 jet engines, it was proposed to try to use them in Soviet designs. These received the new Soviet designation RD-10 Reaktinyi Dvitagatel, which is Russian for “jet engine.” The design and work on the first power plant was given to the OKB-117 Experimental Design Bureau, under the designer Vladimir Y. Klimov in late April 1945. A few months later, a second order was given to develop a new RD-20 jet engine based on the German BMW 003 jet engine. As the Soviet scientists were not familiar with this technology, the entire development ran quite slowly. The first series of these engines was ready in 1946, but the performance turned out to be limited and almost useless.
The work on the new jet fighter program was also slow and largely fruitless. Projects like the MiG-13, La-7R and Yak-3RD were built in limited numbers and proved to be unsuccessful. One of the main reasons for so many failed projects was the fact that the Soviet designers used captured and complicated German jet technology as an inspiration. There had to be a change in the way the Soviet designers and engineers approached these technologies and developments. Since time was crucial, the designers were forced to adopt simpler solutions.
The development of Yak-Jumo aircraft would later led to the Yak-23. [talkbass.com]Several new projects resulted from these decisions, one of which was the A.S.Yakovlev Yak-Jumo project. It was based on Yakovlev’s own analysis of German technology, especially the light weight, stepped fuselage and the forward position engine design. His first idea was to try to take advantage of the already existing piston engine-powered fighters and, if possible, install one or more jet engines on them. He reused one Yak-3 fighter and modified it to mount one rocket engine instead of the piston engine. Most parts of the Yak-3 were reused, wings, including the whole fuselage, tail surfaces, undercarriage and most in-built systems and equipment. The new engine was fitted in the forward part of the fuselage, but tilted at a 430’ angle with respect to the plane’s axis. Besides this, it was necessary to redesign the whole fuel system. A new redesigned cockpit was installed and the armament would consist of two 23 mm NS-23K autocannons each with 60 rounds of ammunition located above the engine. The German Jumo 004 engine was used and thus the project name was Yak-Jumo or Yak-3 Jumo (depending on the source).
The first prototype was completed and ready by late 1945. During its first several ground tests, many problems were reported. One of them was the excessive heating of the rear lower fuselage caused by the engine exhaust gases. A second complete and improved prototype was built in December 1945. It was equipped with the Soviet-built RD-10 which was a direct copy of the Jumo 004. Tests on the second prototype plane began during the second half of 1946. During these tests, several complaints were noted and the aircraft was returned to the factory in order to resolve these issues. By that time, this plane received a new military designation, the Yak-15.
On 12th September, 1946, an order for a limited production run was given by the Ministry of Aircraft Production. The Yak-15 and MiG-9s were first presented to the public during a military parade held in Moscow’s Red Square of that year.
Yak-23 Rear View [Avions Legendaires]Due to the rapid development of Western jet aircraft, Soviet military authorities demanded improved and more advanced jet planes. The new fighters had to be able to reach a maximum speed of 620 mph (1,000 km/h), but mostly due to lack of adequate jet engines this was only successfully implemented in later, much more improved models like the MiG-17. This was the reason why some jet fighters were put into production despite much lower top speeds.
Due to obsolescence and new problems discovered during the Yak-15’s service, most were modified to be used as advanced trainers, but some were operated as standard fighters. Yakovlev was again tasked with the development of an improved jet fighter. It was required to have a significantly better aerodynamic layout and was to be powered by an RD-10 engine. Estimated maximum speed was to be around 527 mph (850 km/h) at an altitude of 16.400 ft (5,000 m). Besides this, a novelty was the installation of an ejection seat and armored glass plate for the windscreen. By September 1946, the first Yak-17 was ready for testing. These tests were considered successful, especially by the pilots who considered it to have good flying performance. Serial production was to start in the autumn of 1947. The Yak-17 would be built in relatively small numbers as more advanced designs would replace it in the following years, designs like the Yak-23.
History of the Yak-23
Drawing of the Yak-23’s internal components. [Airwar.ru]Later development of new Yakovlev aircraft was characterized by several different methods of approaching development. One of the many Yakovlev design teams, lead by Leonid L. Selyakov, worked on a completely new design that would later lead to the Yak-25. The main goal of this project was to build a completely new aircraft. In addition to this team, a second team advocated for the improvement of the already existing Yak-15 and Yak-17 designs.
The second team’s design was a lightweight and with highly maneuverable jet fighter. This new fighter was to be powered by an RD-500 jet engine, which itself was based on a British Rolls-Royce Derwent 5 turbojet engine. The whole aerodynamic concept was taken from the older Yak-17, but improved with an all-metal construction. The new plane was a lightweight mid-wing monoplane, but with unswept wings and rear tail. The cockpit was placed at the middle of the fuselage and equipped with an ejection seat. To save weight, some modifications were done such as the omission of air brakes, the armor plate being removed, fuel tank capacity lowered, no pressurization fitted to the cockpit and decrease of the wing thickness. The calculated weight with these modifications was about 4,725 lbs (1,902 kg). By the time it entered production, there was a slight increase of weight. The main armament was also relatively light, as it consisted of only two 0.9 in (23 mm) cannons, with some 90 rounds for each cannon.
The work on this project began in the early 1947. Plant No.115 was tasked with the construction of the first operational prototype. On 17th June, 1947 the prototype, designated Yak-23-1 was completed. The first factory test flight was made on 8th July, 1947 by the test pilot M.I. Ivanov. The results of these first flights showed that the Yak-23-1 had a high rate of climb and excellent maneuverability. The maximum speed achieved was 578 mph (932 km/h) at low level. Some issues that were noted during these first flights were solved in time.
In September the same year, on the insistence of the Minister of Aircraft Production, Mikhail V. Khruniche, the Yak-23 was accepted for additional test trials. For this purpose, a second prototype was built, named Yak-23-2. For the series of new test flights, besides G.A.Sedov, the main test pilot, many more pilots were also chosen to test the Yak-23, such as A.G. Proshakov, Valentin, I. Khomvakov among others. By March 1948, these test flights were successfully completed. The Yak-23 displayed great maneuverability during flights. In contrast to other models, like Su-9 and MiG-9, the Yak-23 proved to have much better climb rate. But it was not without its problems: during acceleration, the forward fuselage tended to suddenly rise and the lack of air brakes made potential dog-fighting very difficult. At higher speeds it took a lot of time to slow down and the lack of a pressurized cockpit made the Yak-23 incapable of operating at high altitudes. The second prototype was lost on 14th July, 1948, during one of the many flight exercises for the planned military parade to be held at Tushino. During these exercises, an unknown object struck the wing of Yak-23-2 flown by M.I. Ivanov, which caused the wing to break and fall off. The pilot lost control and crashed to the ground. Ivanov died immediately and the aircraft was totally destroyed. A subsequent investigation found that the main culprit was a balance tab that was torn from the tail of one of the Tu-14 bombers that was flying above the Yak-23.
Despite these problems, the Yak-23 was considered a successful aircraft worthy of production. Plant No.31 was chosen for manufacturing. By mid-1949, the production began, however, at first, the process was slow due the lack of RD-500 engines. The first batch was not ready until October 1949. In the period of January to March 1950, some 20 aircraft were used to conduct more tests. These trials revealed that the Yak-23 had a few more problems to be worked out, such as smoke in the cockpit, among other small issues.. As these problems were considered minor and did not endanger the production of the Yak-23 at the time.
Design
Yak-23UTI Front View [Aero Concept]The Yak-23 was designed as a lightweight, all-metal, mid-wing monoplane with unswept wings and tail surfaces. The long front fuselage was designed and constructed so that it could be easily changed or removed for ease of maintenance.
The external fuselage was made of 0.039 in (1 mm) thick duralumin sheets (D16AWTL) and the inner part was made of 0.031 in (0.8 mm) sheets. To protect the main landing wheels, a special cover was installed close to the exhaust nozzle. The lower part of the Yak-23 fuselage was covered with a specially designed heat resistant plate in order to protect the plane’s inner structure from any potential thermal damage. The two unswept wings were made of 17 ribs that were covered in 0.05-0.07 in (1.3-1.8 mm) duralumin panels. At the wing’s trailing edges, ailerons and flaps were fitted. The wings were made mostly of duralumin sheet metal. The wing ends were flat and it was possible to mount two external fuel tanks that were ejectable. The rear tail had a tapered design and was made of metal covered with duralumin sheets. There were no air brakes installed and this caused the Yak-23 to have some problems with maneuvering. This would be a major problem in any potential dogfight with other fighters.
The main engine was the RD-500 turbojet engine with 3,500 lbs (1590 kg) of thrust that was fitted with a single centrifugal compressor and nine cylindrical shaped combustion chambers. The engine had a diameter of 3.58 ft (1.09 m) and 6.76 ft (2.06 m) long. It was angled downwards by 4°30’ with respect to the plane’s centerline. This was not a perfect design choice as when the pilot accelerated the plane, it tended to suddenly pitch up. The main jet fuel was kerosene, stored in five large tanks mounted in the fuselage with a capacity of 240 gallons (910 liters) and two smaller 50 gallon (190 liters) tanks located in the wings. With this fuel capacity, the maximum operational range was around 640 mi (1,030 km). The Yak-23’s flight endurance was very low, with only one hour of operational flight. With this engine, the maximum speed achieved was 606 mph (975 km/h) with a climb rate of 6,693 ft (2,041 m) per minute. The air intake was located at the front, which split into two symmetrical ducts that passed under the cockpit. There was a headlight located in the air intake to help during landings.
The landing gear was a tricycle design typical of jet planes of the era. The front nose wheel retracted forward, while the larger rear wheels retracted into the fuselage sides. A built in shock absorber mechanism with double rebound system was used for the landing gear.
The Yak-23’s operational service life in the Soviet Union was very limited due to the rapid development of better jet planes. [Wikipedia]The cockpit was located at the center of the upper fuselage. The cockpit was designed with a fixed windscreen with an armored glass panel and a rear sliding hood with non-armored glass. For the pilot to enter his seat, he had to climb on top of the wings. The Yak-23 was equipped with an ejection seat that could be used by the pilot in case of emergency. The ejection seat with parachute was activated with a command handle located next to the armrest of the seat’s right side. A small explosive charge was used to catapult the seat from the plane. The main command instruments were in the standard configuration. All instruments were placed ahead of the pilot and the rudder pedals were mounted at the floor. The pilot’s instrument panel was divided into three sections. In the central section were the main and most important flying instruments: M-46 Mach meter, PDK-45 compass, AGK-47A artificial horizon, and engine control indicators. Secondary controls were located at sides of the main control panel. An oxygen supply system with a capacity of 2.11 gal (8 l) with a KM-16 model mask was fitted in the cockpit. Electric power was provided by 1.5 kW GSK-1500 generator and 12A-10 type battery. For communication, a RSI-6K radio set and a RPKO-10M radio-direction finder/semicompass were used. Also, the SCh-ZM IFF (Identification Friend or Foe) system was used.
The offensive weapon load consisted of only two 0.9 in (23 mm) NR-23 cannons placed in the lower forward part of the fuselage. Available ammunition for these two cannons was limited with only 90 rounds per gun. The main weapons were aimed by the semi-automatic gyro gun sight placed above the pilot’s instrument panels. Additional offensive armament could consist of two 123 lb (60 kg) bombs attached in the place of the external fuel tanks.
Beside the Yak-23 fighter aircraft, a trainer version, the Yak-23 UTI, was developed. One Yak-23 (serial number 115001) was converted for this purpose. A second instructor cockpit was installed at the rear of the pilot’s seat. The prototype was tested from March to September of 1949, but this modification was ultimately deemed unsuccessful. A new attempt was made with the redesigned Yak-23 UTI-II. The fuselage was stretched by some 7.8 inches (200 mm) to the front, and this time the instructor was moved to the front. A special periscope was installed to allow the instructor to see what the pilot was doing in the rear seat. The armament was reduced to only one 0.5 in (12.7 mm) machine gun. Many more changes were made, which resulted in the third version, Yak-23 UTI-III. By this time, the more impressive MiG-15 UTI was entering production and so the Yak-23 UTI project was canceled.
Operational use
Despite its good flying characteristics the Yak-23, also known by its NATO designation “Flora,” was built in small numbers, 310 planes in total. Its operational service life in the Soviet Union was very limited, as it was operated by only a few fighter regiments located in the Caucasus and Volga military districts. As more modern planes were becoming available, the Yak-23 would be sold off to Eastern bloc countries such as Czechoslovakia, Bulgaria, Romania and Poland.
In Czechoslovak Service
Czechoslovakia had extensively negotiated with Soviet military officials in the 1950s about the purchase of new jet-powered fighters. These negotiations had been preceded by earlier ones, from which Czechoslovakia received one older Yak-17 under designation S-100. This sole aircraft was to be used as a basis for future local production. However, since this plan went nowhere, the Yak-17 was sent to a military museum and it was never used operationally. An agreement was made in November 1950 for a possible license production of the Yak-23 under a new name, S-101, and also for the engine under the M-02 name. The first group of 12 Yak-23s arrived in Czechoslovakia in late 1950. Their first public appearance of nine planes were used in a military parade on 6th May, 1951, the anniversary of the liberation of Czechoslovakia by the Soviet Red Army in WW2. A second group of 9 Yak-23s was allegedly received, possibly in 1951 or 1952, but precise information is lacking.
The Yak’s were first used by the 3rd Fighter Division, but as the more advanced MiG-15 arrived, the Yak-23s were given to the 11th Fighter Regiment, part of the 5th Fighter Division, from June to August 1951. By early 1952, this unit had 11 operational Yak-23s in total. One Yak-23 was lost in an accident on 16 October, 1952. In 1953, all available Yaks were given to the 51st Air Regiment, which was renamed as the 7th Air Regiment in October. By early 1954, there were 12 Yak-23s reported in service, of which 11 were operational.
Due to the purchase of newer types of aircraft, the Czechoslovakian military authorities thought that the Yak-23 plane was inadequate and outdated and so the original plans for a license production were dropped. By 1956, a decision was made to withdraw all Yak-23s from operational service. Only a small number of Yak-23s where ever used by the Czech Air Force, thought to be around 21, but the exact number is unknown. Most of these were sold, 10 to Poland in 1953, possibly 7 to Bulgaria, with one given to a military museum and at least one was lost in an accident.
In Bulgarian Service
Yak-23 put on display at the Bulgarian Air Force Museum [Deano’s Travels]Bulgarian military officials purchased several Yak-17 UTI training variants and 12 Yak-23s from the Soviet Union in early 1951. These were used to form the 19th Fighter Regiment in March 1951. The first pilot to fly on one of the Yak-23s was Major Vasil Velichkov. On his first take-off, the engine suddenly stopped working and he was forced to land in a field near the airfield. Because it was necessary to train new pilots to fly the Yaks, some planes were supplied to the 2nd Training Combat Air Regiment, located at the Georgi Benkovski Flying School. In order to increase the number of units equipped with the Yak-23s, some 72 new planes were purchased from the Soviet Union in 1952. Around 7 Yak-23s were sold to Bulgaria by Czechoslovakia in early 1956. As in Czechoslovakia, the Yak-23 would not stay long in service, and by 1959 all were retired.
In Romanian Service
After the Second World War, the Romanian Military leadership had great plans for the revival of their shattered air force and acquiring modern jet planes. Some 60 Yak-23s were bought from the Soviet Union during the fifties, with the first 12 planes reaching Romania in early 1951. The total number of planes used is not known. As the more modern MiG-15 was received during 1953, the Yak-23 was considered obsolete and only small numbers were ever used. One Yak-23 was modified by the Romanian air engineers of the AEMV-2 (Atelierele de Reparații / Material Volant) to be used as a dual-command trainer aircraft. A new instructor cockpit was installed. This new modified plane was designated as Yak-23 DC (Dublă Comandă / double command), but only a single prototype was built.
On the 24th June, 1953, Romanian pilot Mihail Diaconu escaped to Yugoslavia in Yak-23, where he sought asylum. Not long afterwards, another pilot flying a MiG-15 flew over and later landed onto Yugoslav territory, most likely due to a navigation error. Both planes were thoroughly researched and tested. Pilots Todorović and Prebeg both flew the Yak-23 with more than 4 flight hours. Beside the flying performance, the weapon systems were also tested during 1954. According to the agreement between US and Yugoslav military officials (code name ‘Zeta’), the Yak-23 was disassembled and sent to the Wright-Patterson Air Force Base in order to test the progress of Soviet aviation technology. Test flights were conducted on 4th November and, by 25 November, it was ready to be sent back to Yugoslavia. The Yak-23 was disassembled, and loaded onto a C-124 and later flown to Pančevo airfield. The whole operation was a complete success as it remained a secret for nearly 40 years. After several months, this Yak-23 was returned to Romania, without the Soviets ever realizing where it was the whole time.
In Polish Service
A few of the Polish Yak-23s would be put in Museums. [Wikipedia]After the Second World War, Poland was economically and militarily devastated. It took several years before the beginning of the renewal of Polish military power. The new Polish military leadership wanted to built up the shattered air force and, despite their plans to acquire a new jet fighter by 1948, this was not possible. The process of acquiring new jet fighters began only in the spring of 1950. The first negotiations with the Soviet Union focused on the acquisition of Yak-15s, but this was later changed to the Yak-17. Due to outbreak of the Korean war, Soviet authorities decided to supply their allies with larger numbers of newer jet fighters. On 6th January, 1951, Poland received its first Yak-23 planes. The planned production of the older Yak-17s was suspended in favor of the Yak-23 under the Polish designation G-3.
Besides the 1st Fighter Aviation Regiment (PLM for short in Polish) which had some 16 Yak-23, a second unit, the 2nd PLM was also supplied with this plane. To train the new pilots, Yak-17 UTI training planes were used. In mid-1952, all operational Yaks were used by five Fighter Regiments: 2nd PLM with 26, the 39th PLM with 19, the 40th PLM with 19, the 26th PLM with around 11 and the 29th PLM with 14 Yak-23. From 1953 onwards, according to the new Polish military strategy, the first line fighter units would be equipped with the new MiG-15, while second-line units received all available Yak-23s.
In the early fifties, the Western Allies were eager to examine and spy on the military power of the East. A simple way to do this was by using various types of balloons. They were used for propaganda, meteorological, and reconnaissance duties. The Polish Air Force was heavily engaged with shooting down these balloons.
The final fate of Polish Yak-23s was sealed by the start of licenced production of the MiG-15 (under the name Lim-1). The remaining Yak-23s were gradually phased out of service. All operational Yak planes were allocated to training units at Radom, where they were used for training new officers and pilots. Some Yak-23s were temporarily used as reconnaissance aircraft in the 21st PLZ (21st Scout Aviation Regiment). By late August 1954, all Yak-23s were moved to Radom. The ones that were not operational were cannibalized for spare parts. On 1st September, 1959, the remaining 39 Yak-23s were removed from the Polish Air Force and a few would be used as memorials. During its operational service in the Polish Air Force, several planes were lost in crashes but, in most cases, the pilots escaped without any injuries.
Albanian Yak-23
Albanian Air Force allegedly operated a unknown number of Yak-23. Possibly bought from Poland sometime after 1951, according to author Yefim G.
Hungary and the Yak-23
Hungary allegedly also used the Yak-17 and 23, but there is no documentation or any information to confirm this (Source Marian M.). But according to author Yefim G. an unknown number of Yak 23 were operated by the Hungarian Air Force during the 1955 to 1956. But this author does not specify the number of planes used nor describes in more detail operational service life.
Production and modifications
A relatively small number of planes of this type were ever produced. As more advanced planes were becoming rapidly available, there was no need to continue the production of the old Yak-23. Most of the Yak-23s produced would be later sold to Eastern bloc countries.
In total, 310 aircraft plus three prototypes were built by Plant No.31. The plant produced these in twelve series, with 25 to 26 aircraft in each batch. Production was stopped by the end of 1950.
Variants
Yak-23 – Main production aircraft
Yak-23 UTI – One Yak-23 was modified to be used as a fighter trainer. It did not enter production.
Yak-23 DC (Dublă Comandă) – Romanian experimental dual control trainer, only one tested.
Operators
Bulgaria – Used over 70 Yak-23s
Soviet Union – Operated only two fighter regiments equipped with the Yak-23
Romania – Some 60 Yak-23 were bought from the Soviet Union during the fifties
Poland – Used around 101 planes, under the designation G-3
Czechoslovakia – Operated around 21 aircraft (possibly more) under the designation S-101
Yugoslavia – Used one Romanian interned plane for experimenting with flying performance and weaponry
USA – Briefly tested one aircraft that was supplied by Yugoslavia
Hungary – Allegedly used this type of aircraft, but proof is lacking
Albania – Possibly operated a small numbers of Yak-23
Conclusion
The Yak-23, despite proving that it had good flying performance and good handling, had a rudimentary design and was produced too late to have any great impact or role in the Soviet fighter force. Due to the rapid development of jet technology, more advanced planes were soon ready for service like the La-15 or MiG-15. The Yak-23 finished its career in service with many Eastern Block air forces.
Although its operational service life was short and its significance was negligible, the Yak-23 was an example of how, with only a short time and using limited resources, a solid jet fighter could be designed and built by the Soviets.
Yakovlev Yak-23 Specifications
Wingspan
28 ft 7 in / 8.73 m
Length
26 ft 7.8 in / 8.12 m
Height
10 ft 10.3 in / 3,31 m
Wing Area
145.32 ft² / 13.5 m²
Engine
One Klimov 3,505 lbs/1,590 kg thrust RD-500 turbojet engine
One dual control Yak-23 was tested but the development was stopped, mostly due to production of more advanced MiG-based trainers. [Krasnayazvezda]Yak-23 under construction in Plant No. 35 [Krasnayazvezda]Yak-23 Side View [Aviastar]
Yugoslavia (1939)
Prototype Advanced Trainer – 1 Built
The MM-2 prototype had an unusual color scheme with a combination of red and polished aluminum.
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.
The designer of the MM-2 trainer, Captain Dragutin Milošević.
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.
The only MM-2 prototype during its construction by Ikarus.
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
Captain Dragutin Milošević’s first drawing of the MM-2. Note that the engine nose design appears to be for an inline engine, different from the actual prototype.
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
MM-2 Side View
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.
On the May 13 1942 pilot Vid Saić, he lost control of the aircraft and crashed due to inexperience. The MM-2 was deemed too complicated and expensive to repair.
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
Nazi Germany (1942)
Light Transport and Trainer – 1,216 Built
The Siebel Si 204 was a twin engined light transport and trainer aircraft built by Siebel for the Luftwaffe in World War II.
History
Si204s under construction
The story of the “Siebel” factory starts in the 1934, with the founding of “Hans Klemm – Flugzeugwerke Halle“ that was a branch of “Leichtflugzeugbau Klemmin Böblingen”. In December 1937 the name changed to “Siebel Flugzeugwerke“ when it was taken over by Friedrich Siebel.
Initially Siebel had a license to produce the Focke-Wulf Fw 44 “Stieglitz” and later during the war Heinkel He 46, Dornier Do 17 and the Junkers Ju-88. In addition to the production of licensed aircraft, in 1937, “Siebel” produced its own aircraft under the name Fh 104. It had its first test flight that same year, and some 46 planes where build during the period of 1938-42. The Fh 104 made a number of notewortly flights:
In March of 1939 flying a 39975 km tour of Africa,
Winning the “Littorio rally in Italy”,
And flying a 6200 km across 12 countries in 1938 (Europa Rundflug).
Color photo of Luftwaffe Si204
By the end of 1930, “Siebel” company was commissioned by the Luftwaffe to design a new type of all-metal twin-light light transport aircraft with a capacity of eight persons with two crew members. In 1940 the first prototype of the twin engine and larger and also heavier Si 204 appeared with originally a conventional stepped cockpit and a powerplant of two 360 hp (268 kW) Argus As 410 engines . The prototype made its first flight during the period of May to September 1940. Second prototype made it first test flight in early 1941. The third prototype was re-designed as a trainer aircraft for blind flying. Because of this, its first test flight was only possible at the end of 1941 or the beginning of 1942. The other 12 planes produced by “Siebel” were used for general flight evaluation. After this small production run Siebel stopped building this aircraft, and future planes would be built in France and Czechoslovakia.
Model A was build in relatively small number by the French “SNCAC” (Société Nationale de Constructions Aéronautiques du Nord) factory. It was designed as a transport and communication aircraft.
Si204A
The next model D appeared in 1942, with a new glazed nose and cockpit with no separate flat windscreen for the pilot. Almost all German bomber aircraft during the war shared this design. The D model also had more powerful 600 hp As 411 engines. The D model was used for radio navigation and for training. This model was mostly used during the war.
The production of the D-3 version start in October 1944 by the “Aero” company. The D-3 had wooden wings and a tail-plane made of wood because due to material shortages. In France, production of this aircraft was stopped in August 1944 as a result of the Liberation.
“BMM” produced the aircraft until October 1944 and then changed to producing spare parts for the Si 204. The “Aero” was scheduled to cease production of the D-1 in March 1945 after building 486 aircraft and then switch to D-3 only. The E version was built in limited numbers and can be considered as an experimental series.
After the war, production of Si 204 continued in Czechoslovakia and France. Czechoslovakia produced some 179 Si 204D, developed into military trainer variants Aero C-3A, passenger variant C-103 and military transport variant D-44. France produced 240 transport NC.701 Martinets and a number of passenger NC.702 Martinets.
Si204 in French Service
Operational history
Si204D Armed Version
During the war the Luftwaffe put the plane to use for transport, communication while also seeing use as an advanced trainer and blind flying trainer.
It was generally regarded as a good plane, but with some drawbacks like the lack of any armament, which prevented many exercises for the combat training program and possible use as a combat aircraft, although for this role it is not designed.
Designers in Halle had developed few different military projects, like installing bomb racks, machine gun turrets and other necessary equipment, but none of these plans were ever realized. This problem was attempted to be solved with some modified Si 204D airplanes with three 13mm MG 131 machine guns, intended to be used as a night combat aircraft but this model was not used in combat and was built in limited numbers.
Despite these unsuccessful attempts, Germans tried to make a new bomber variant, in order to be used in anti guerrilla fighting with a built to this specification. Three Si-204E were sent to the military tests in Belarus. They were treated as special anti-guerrilla aircraft. The scope of the actions of the Belarusian partisans forced the Germans to throw against them not only regular troops, but armored vehicles and aircraft. The extent to which they were used in this role remains unknown.
Si 204 is reported to has the “honor”, of being the last German aircraft shot down on the Western Front. On May 8, 1945 an Si 204 was shot down by an American P-38 Lightning, three miles southeast of Rodach, Bavaria.
Production variants
Closeup of Si204 Engine Nacelle
Because Siebel produced the Junkers Ju-88 under licence and the need for as many military aircraft as possible, Germans decided to increase the volume of production for this aircraft. This was done by moving the production to French “SNCAC” and Czechoslovakian “Aero”, and “ČKD-BMM” factories. The “SNCAC” produced some 168 aircraft and the “Aero” and “ČKD-BMM” produced 1033 aircraft, Siebel produced only the first 15 prototype Aircraft, before the production was stop in favor of Ju-88. In total some 1,216 aircraft of this type where build, during the war.
During WW2
Si 204 – Prototype version with 15 plane build by Siebel (Number V1 to V15),
Si 204A – Model A was a transport and a communication aircraft, with crew of two and eight passengers.
A-0 – Passenger plane version,
A-1 – French built version.
Si 204B and C – Were paper projects
Si 204D – Model with a new glazed nose and cockpit and with two 600 hp As 411 engines. Model D was used for radio navigation and for flying training.
D-0 – Blind flying trainer,
D-1 – Czechoslovakian production version,
D-3 – This model had wooden wings and tailplanes, in order to save on metal.
204E – Experimental night fighter plane. This model had on its nose two 13mm MG 131 machine guns plus one more machine gun (same caliber) in a glazed cupola on the upper hull of the plane. This model was not used in combat and was build in limited number using rebuild Si 204D planes.
E-3 – Proposed version to be armed with bombs, and to be used in anty guerrilla fighting, possibly only few were build.
Flying carrier – Paper project that was originally intended to carry one DM-1 (Doctor Alexander Lippisch plane) on the back of a Siebel Si 204. Little is known about this project
Postwar
Czechoslovakia Version:
Aero C-3 – Used for flying and crew training,
Aero C-103 – Used for Civilian transport,
Aero D-44 – Military transport version.
France versions:
SNCAC NC.701 Martinet – Military transport version with SNECMA 12S-00 air-cooled V-12 engines,
SNCAC NC.702 Martinet – Improved Passenger transport version.
Operators
Germany – Most produced planes where used by the Luftwaffe as advanced schools training, transport, blind flying trainer (usage in this role was at best was sporadic) and communication. There were plans for arming this plane for night fighter and anti-partisan operatons, but it all left on paper only with few model build and not a single one was used in combat.
Czechoslovakia – Used German build planes and the new Aero C-3 version after the war.
France – Used some captured German planes and also the NC. 701 version which was build by France after the war.
Hungary – Operated some C-3 Aero version after the war.
Poland – Used six NC.701 version.
Soviet Union –They were captured in some numbers at the end of the war. At first, the captured Si-204 was mostly used by the military. The headquarters of many regiments and divisions stationed in Germany used the Siebel for official flights, but only for short period.
Sweden – Operated five NC.701 (1962-1970) for mapping photography.
Switzerland – Operated some Si.204 D planes.
Specifications (Si 204D)
Wingspan
70 ft / 21.33 m
Length
39 ft 3 in / 12 m
Height
14 ft / 4.25 m
Wing Area
495 ft² / 46 m²
Engine
2x Two Argus As 411 12 cylinder inverted piston engines (447kW/600 hp)
The first domestic aircraft factory in Yugoslavia was established in Novi Sad under the name “Ikarus” on November 20, 1923. In 1924, Ikarus delivered two new training planes for the armies of the Kingdom of Serbs, Croats, and Slovenes which were designed in the factory. The first trainer model was delivered in April 1924 designated the “Мали Брандербург-Serb” (Small Brandenburg), which was a direct copy of Brandenburg B.I. The second plane was delivered in June 1924, a copy of school hydroplanes “IIIM” (School Mercedes/Школски Мерцедес-Serb.). Both of these aircraft did not fall far behind foreign aircraft in terms of its technical and flying characteristics, of the same intended roles which strengthened the morale of the Army and the domestic constructors, opening prospects for the domestic production of new planes.
In April 1924, another aeroplane factory was built in Belgrade: “The first Serbian aeroplane factory Živojin Rogožarski – Прва Српска фабрика аероплана Живојин Рогожарски-Serb.” They joined Ikarus as the only aircraft factories in Yugoslavia. Živojin Rogožarski was initially only building parts for the aircraft but later they began to build entire planes. From 1928, these two factories supplied around 100 training aircraft and seaplanes to the army of the Kingdom of Serbs, Croats and Slovenes and Maritime Aviation.
During the late 1930’s and early 1940’s, the company Ikarus started to design and later produce two new types of fighter aircraft, the IK-2 and IK-3. The IK-2 was a “high wing” plane, with the wings set on top of the fuselage, equipped with the Hispano-Suiza 860 hp engine and armed with one 20 mm cannon and two machine guns set above the engine. The machine guns were initially Darn type caliber 7.7 mm but this was later replaced with the new Browning 7.92 mm. The IK-2 was constructed by a team of engineers Ljubomir Ilić and Kosta Sivčevićem. Ikarus built small batch of 12 aircraft plus two prototypes in 1939. While in production the IK-2 was considered obsolete and production of the fighter ceased, nevertheless, the IK-2 saw some use in World War ll but all the planes were lost.
Designed as a successor to the older IK-2, the IK-3 was Yugoslavia’s first modern single-seat fighter. It was conceived in 1933 as a fighter utilizing the cantilever low-wing with a cockpit that was fully enclosed as well was fully retractable landing gear. On the tail or fuselage, the planes would carry a small black military-tracking number. The IK-2 used numbers from 2,101 to 2,112 and the IK-3 used 2.151 to 2.163. At the time of its construction, the IK-3 was equally matched to its contemporaries, representing a very advanced solution behind which stood a team of ambitious and young engineers Ljubomir Ilić, Kosta Sivčevićem, and Slobodan Zrnić j.
Prototype
IK-3 Prototype
After some statistical and aerodynamic calculations in 1936 were completed, a 1:10 wooden scale model of the IK-3 was built. The model was tested in the Eiffel wind tunnel in Paris. The planned Hispano-Suiza 12Y Engine had already been tested in earlier IK-2 aircraft. The contract to build the prototype IK-3 was signed on March 31, 1937 with Rogožarski. The first prototype IK-3 was completed on 14 April 1938, piloted by Captain Milan Bjelanović. By the end of 1938, the first factory tests were completed. Despite the good flying qualities, the pilots noticed some problems. The complaint by pilots was related to the shape of the windshield and canopy of the cockpit, while the army suggested adding two additional machine-guns in the wings. Some additional problems cropped up including engine overheating and unsuitable landing gear doors. The majority of these problems were corrected in the first batch of planes produced.
On 19 January 1939, an accident occurred while examining the behavior of the plane in flight, the right wing completely separated from the fuselage. This accident claimed the life of pilot, Captain Milan Pokorni. No domestic or foreign investigators were able to clearly determine the exact cause of the crash. In any case, the wings were reinforced during wing construction and production continued.
Production
IK-3 fresh after construction without camouflage
The loss of the IK-3 prototype did not postpone the production of new fighters. On 26 November 1938, a contract between the state and the factory was signed which authorized the production for a new batch of 12 aircraft. Delivery of the planes was planned for the end of 1939, but the beginning of World War II affected the production process. Delays in deliveries and the rising costs of raw materials postponed the completion of the first batch. The first aircraft of the series were delivered on 15 December 1939. The deliveries and production were again postponed due to a worker strike in the aviation industry, lasting until July 1940.
In March of 1940, the factory offered an improved version of the IK-3 called the IK-3 ll. The factory originally offered the production of 50 new aircraft but this was rejected by the state who instead ordered production for only 25 aircraft. It was thought that the production of 50 aircraft could not be achieved because it was impossible to obtain the necessary materials and equipment from abroad due to the war. The Command of the Royal Yugoslav Army demanded improved aerodynamics, a more powerful engine, self-sealing fuel tanks, armored glass, armored seats etc. In the end, only one plane (number 7) from the first series was modified into a prototype for the second series.
Prior to the War
51st Independent Fighter Group, Belgrade-Zemoun, April 1941
After the end of production, all operational aircraft were allocated to the 51st Independent Fighter Group at Zemun which was part of the 6th Fighter regiment. Squadrons 161 and 162 were both given 6 aircraft.
In its first year of service, an IK-3 was lost when one of the squadron commanders, Captain Anton Ercigoj, was making a “mock attack” on a Potez Po.25 over the Sava and Danube rivers. After passing below the Potez, he went into a climb with the intention of performing a loop. His rate of climb was too steep and the aircraft fell into a spin at low altitude and hit the water. Caption Anton Ercigoj did not survive the crash.
The introduction of new planes offered the opportunity for pilots of the IK-3 to test it against the Yugoslav Messerschmitt Bf 109E in “mock dogfights”. The evaluation after the dogfight concluded that the IK-3 had several advantages over the Bf 109E. The IK-3 was more maneuverable in level flight, enabling it to quickly get behind a pursuing Bf 109E by making tight horizontal turns.
In combat
IK-3 No. 2158
For the attack on Yugoslavia, the Axis forces amassed around 2236 warplanes in Austria, Hungary, Italy, Bulgaria, and Romania with some 1062 bombers, 289 reconnaissance planes, and 885 fighter planes.
The Yugoslavian Air Force had around 420 combat aircraft, in various conditions. They had about 147 modern bombers including the German Do. 17, Britain Bristol Blenheim, and the Italian SM.79. There were also about 131 reconnaissance planes, including 11 British Bristol Blenheims, about 120 outdated Brege 19 and Potez Po.25 aircraft, and over 100 combat aircraft including 61 German Me-109E, 35 British Hawker Hurricanes, some of which had been built in the “Zmaj” factory in Zemun. Yugoslavia also had a whole series of IK-3 aircraft, minus one lost in pilot training. In addition to these forces, Yugoslavia also controlled 30 two-engine Hawker Furys, 8 IK-2’s, 2 Avia BH-33’s, and 2 two-engine Potez Po.63’s. In essence Yugoslavia controlled a much smaller force than Germany but it was made up of some of the most modern aircraft of the time.
Out of the 12 IK-3 of the first series, only 6 were fully operational by 5 April 1941. One aircraft was lost in the 1940 accident, and 5 were in different states of repair: 3 in the Rogožarski factory, and two in the aviation workshop at Zemun airport. The units equipped with the IK-3 had the task of preventing the deployment of the enemy air force above the territories of Northern Serbia and parts of Vojvodina. The majority of the IK-3’s were used in the defense of the capital Belgrade, bolstered by fighters from the 102nd fighter squadron equipped with Me-109E’s.
On 6 April 1941, at about 0600, the commander of the First Air Base, Major Marko Konrad, informed the commander of the 6th Fighter Regiment that the Germans attacked Yugoslavia and that air attacks on Belgrade should be anticipated. At about 0645, the observation service TVO (teritorijalne vazdušne osmatračke službe-Territorial airborne observation services) reported two large formations of aircraft were flying in from the north towards Belgrade. At about 0650, commander of the 6th Fighter Regiment, Major Adum, ordered all three squadrons 161, 162, and 102 up for patrols. These patrols were led by First Class Captain Gogić, Sergeant Semiz, First class Captain Poljanec, Sergeant Vujić, and Lieutenant Borčić.
In their first battle, pilots with their IK-3’s shot down six German planes while only losing one IK-3, in which Lieutenant Dusan Borčić was killed, and one lightly and two heavily damaged aircraft that did not participate in any further combat. By the end of the day, two more German bombers were shot down, but this group remained with only three operational IK-3 aircraft.
IK-3 during Summer of 1940, flown by Savo Poljanec, commander of 162nd Squadron
On April 7, Sergeant Semiz, during an intercept with German bombers, was hit by German machine guns fire. 36 bullets hit his plane and 20 bullets hit his engine and ignited it. Although he was wounded, he managed to return to the airport in Zemun. The loss of his aircraft was compensated by the IK-3 ll (the only aircraft of the second series to be constructed) that was under repair in the Rogožarski factory. The combat state of this unit remained at three operational aircraft.
By the end of the day on April 7, the remaining aircraft were relocated to the auxiliary airport, Veliki Radenci II. Commander Major Adum was replaced, and Captain First Class Gogić was promoted to this position. In the following days, there was no action due to bad weather. On 11 April, at around 1000, one German Me-110 attacked Veliki Radenci II but did not cause any damage. Sergeant Samiz with his plane pursued and managed to shoot it down. On the same day at around 1200, a group of about 20 Me-110’s were attacking the airport Veliki Radenci I. Several of the 51st group took off, the pilots were First Class Captain Gogić and Sergeant Vujičić, managing to shoot down two attacking German planes.
At around 1700 on 11 April, a German armored column was spotted approaching from the North. Part of the non-flying group of the Yugoslavian Air Force had been ordered to withdraw in the direction of Sarajevo, airplanes and pilots stayed at the airport. On 12 April, they were supposed to be transferred to Sarajevo, but this did not happen. Because of the speed of the German attack and the inability of pilots to fly in time, they decided to destroy all the remaining planes in order to prevent them from falling into German hands.
Operators
Kingdom of Yugoslavia (Kraljevina Jugoslavija) – Were used during the “April War” and most were lost in combat or were destroyed
Nazi Germany – Captured at least 5 to 7 planes in different states. One complete surviving IK-3 was used for flying test performance.
Turkey – Was considering the possibility of buying the license for the production of the IK-3, but World War II prevented any plans for this program.
IK-3 Specifications
Wingspan
33 ft 10 in / 10.3 m
Length
26 ft 3 in / 8 m
Height
10 ft 8 in / 3.25 m
Wing Area
178 ft² / 16.5 m²
Wing Loading
32.6 lb/ft² / 159.4 kg/m²
Engine
One 980hp (731kW) Avia-built Hispano-Suiza 12Y29 liquid-cooled V-12 piston engine
Maximum Take-Off Weight
5799 lb / 2630 kg
Empty Weight
4560 lb / 2068 kg
Fuel Capacity
330 L
Climb Rate
16,000 ft / 5,000 m in 7 minutes
Maximum Speed
328 mph / 527 kmh
Cruising Speed
249mph / 400kmh
Range
488 mi / 785 km
Maximum Service Ceiling
30,800 ft / 9,460 m
Crew
1 (pilot)
Armament
One Oerlikon FF 20 mm cannon – fixed forward-firing cannon in the propeller hub
Two 7.92 mm Browning/FN machine guns with 500 rounds per gun – fixed forward-firing machine guns in the upper part of the forward fuselage
Gallery
IK-3 Prototype – 1940IK-3 51.Grupa, 6.Lovacki Puk No.2158 Br.9 April 1941IK-3 161.Eskadrilla, 51.Grupa No.218 April 1941IK-3 161.Eskadrilla, 51.Grupa No.2159 Br.10 – April 1941Possible markings for captured IK-3 being tested by a German research unitIK-3 PrototypeIK-3 Prototype51st Independant Fighter Group, Belgrade-Zemoun, April 1941IK-3 without camouflageIK-3 No. 2158IK-3 fresh after construction without camouflageIK-3 during Summer of 1940, flown by Savo Poljanec, commander of 162nd Squadron
Germany (1932)
Trainer & Sport Plane – 3,000 Built
The Focke-Wulf 44 (Fw 44) was the most famous Focke-Wulf design after the famous Fw 190 fighter. The aircraft was a biplane with a fabric-covered welded steel-tube fuselage sporting wooden wings with fabric and plywood coverings, powered by a 140hp (104kW) Simens Sh 14 radial engine. This aircraft was primarily designed as a two-seat aerobatic civilian training aircraft but was later used for military purposes.
History
Fw 44 Taxiing
The origin of the Fw 44 Stieglitz (Goldfinch) started in 1932 when designer Kurt Tank, conceived the two-seater double-decker of mixed construction. In its prototype stage it had a number of unacceptable flight characteristics. The frst prototype was making its first flight in the late summer of that year with pilot Gerd Achgelis at the controls who problems with oscillations.
Kurt Tank had joined The Focke-Wulf Company in November 1931 from BFW, later Messerschmitt, and headed the design and flight test department for Focke-Wulf at the same time, replacing Heinrich Focke who was preoccupied with rotary-wing activities. Tank would remain in the position until the end of the World War II.
After further extensive flight testing, undertaken by Kurt Tank himself, he found the root of the problem. While flying the prototype back from a test flight, he happened to be looking at the shadow of the plane on the ground and he noted that the tail’s shadow blurred which indicated some kind of vibration in that area. Then the whole aircraft shook. Having landed he and his engineers check the tail of the aircraft and they found that the vibrations were being caused by separate cables operating the elevators. By joining these together to make the elevators act as one unit, the vibration problem was eliminated.
With this issue solved the Focke-Wulf 44 “Stieglitz” soon proved to have excellent handling characteristics and powerful aerobatic capabilities that won many prizes in numerous competitions, such as the Artificial Flying World Championship. The Fw 44 was popular, and known aircraft all over the world as a simple training glider. Following many successful aerobatic displays around Germany, demand for this aircraft was so great that other German manufacturers manufactured the Fw 44 under license. In addition to the export models, production began in several other countries, such as Argentina, Austria, Brazil, Bulgaria and Sweden. It served as a standard training aircraft at the German transport school and the Luftwaffe.
One interesting fact about Fw 44 is that the body of one plane, the design retaining both the fuselage and engine, was used as the basis for the world’s first “practical” helicopter known as Focke-Wulf Fw 61.
Stieglitz’s Sporting Success
The Fw 44 was known for participation in numerous flight competitions, especially in the 1930s and always scored high, thanks to pilots Gerd Achgelis and Count Otto von Hagenburg.
1935 Stuttgart Seventh German Art Flying Championship Gerd Achgelis achieved second place after Willi Stor who flew in a Messerschmitt M35 plane.
1936 Eighth German Aerobatics Championship at Munich-Oberwiesenfeld Count Otto von Hagenburg won second place. Willi Stor was victorious again with his Me. M35 plane.
1936 Summer Olympic Games in Berlin
Perhaps the most publicized aviation event in pre-World War II Germany was held in conjunction with the 1936 Olympic Games. Adolf Hitler, who wished to impress the world with the strength of Germany’s aviation industry, arranged the 1936 Berlin Summer Olympics Games to include the first ever aerobatics competition. This flying event took place within the track and field stadium. Graf Otto von Hagenburg as a pilot won the men’s competition, flying the new Fw 44. It’s very likely that the aerobatics competition was staged in a way to enhance Germany’s potential results. Either way, the German built planes and their pilots were well regarded as exceptional.
1934 Paris World Championship
An enormous event, with some 150,000 spectators crowded into the military parade-ground at Vincennes which had been modified for this occasion.
Fw 44 Stieglitz in Flight – 2008
The initial compulsory competition required a list of manuevers to be performed within a time limit of eight minutes, including a right-hand and a left-hand spin, a bunt, a negative loop forward and upward, and an inverted 360 degree turn. Each contestant was also afforded the opportunity to fly their own routine for ten minutes. The sequence was to be submitted in advance to the judges, and each maneuver was assigned a difficulty coefficient set in the rules. New maneuvers were also awarded appropriate coefficients, but most were found to be already in the catalogue of 87 maneuvers. The judges’ task was to assign each figure a mark between 1 and 5 points for quality of performance, with a zero for figures not executed. These were then multiplied by the difficulty coefficients, the totals of all the judges were then averaged to obtain the final score.
Gerd Achgelis achieved third place with a score of 527.6 points. The winner was the German pilot Gerhard Fieseler, designer of the Fieseler Storch, with a score of 645.5 points.
Production Variants
Thanks to its exceptional flying characteristics, it was ordered by many nations around the world. In addition to export orders from Turkey, Switzerland, Bolivia, Chile, China, Czechoslovakia, Finland and Romania, it was produced under license in Argentina, Austria, Brazil, Bulgaria and Sweden. The Fw 44 was built in substantial numbers for the Luftwaffe, serving as a trainer until the end of the World War II. It was also in use by the Deutsche Luftsportverband and Deutsche Verkehrfliegerschule. Exact production numbers are not known, due to production in Germany by Focke-Wulf and and many other subcontractors such as AGO, Bucker and Siebel, in addition to other license agreements worldwide. It is assumed that the production numbers are between 1900 to more than 3000 planes. Focke-Wulf had to build another factory just to keep up with demand for the plane.
The production variants differed from each other in minor equipment details. The most numerous variants were the Fw 44C, Fw 44D and Fw 44F, with all three models utilizing the same Siemens Sh 14a engine. The final production Fw44J model had a 160 hp Siemens Sh 14a-4 seven-cylinder radial engine.
Fw 44A The Fw 44A was powered by a 150hp Siemens Sh14a engine, and was used for flight tests. This model was in production until the end of 1932.
Fw 44B The improved Fw 44B first appeared in 1933, with production commencing in 1934. The Fw 44B, had an Argus As 8 four-cylinder inverted inline air-cooled engine of 90 kW (120 hp). The cowling for this engine gave the plane a more slender, aerodynamic nose. The other change was in the extension of the fuselage from 6.6 to 7.3 meters, which was tested on this model.
Fw 44C This model was used extensively by the Luftwaffe at advanced training schools throughout the Second World War. The Fw 44C, was powered by the Siemens Sh 14a engine, which offered the best overall performance.
Fw 44D The D model was same as the Fw as 44 C, but with different exhaust manifold. The plane got a small luggage compartment made of fabric, which was attached to the rear cockpit. From 1934 onwards, improvements were taken into series production. Due to the high demand for this model, it was temporarily produced in other plants (Bücker Flugzeugbau – 85, AGO – 121, and an additional 515 planes under license). The Luftwaffe ordered some 1,600 examples of this model.
Fw 44E Basically identical with to the D model, it was equipped with an Argus As 8 engine. It was built in limited number, only 20, in 1934.
Fw 44F An upgrade of the D model. With some luggage compartment modifications, and the replacement of the rear pad with a landing wheel.
Fw 44H Only one plane of this model was produced in 1936, and was used only for testing. This model was equipped with a six-cylinder engine (118hp).
Fw44J The J model was mainly intended for export and was equipped with the 160 hp Siemens Sh 14a-4 seven-cylinder radial engine. This model was demonstrated in Sweden in late 1935, and in February 1936. The testing resulted in a license agreement between the Swedish aviation administration and Focke-Wulf on September 29, 1936. Two test aircraft were ordered, receiving the Swedish designation P2.
Operators
Germany The Luftwaffe used the Fw 44 until the end of the World War II, mainly as a trainer aircraft in the Flugzeugführerschulen. The Germans used more than 1,600 planes. Many famous German aerobatic pilots flew the Fw 44 aircraft, including Gerd Achgelis, Adolf Galland, Emil Kopf, Ernst Udet and perhaps most famously Hanna Reitsch, who flew on almost all aircraft models.
China China purchased around twenty Fw 44’s which were all used during the Second Sino-Japanese War where all were lost in action. Some of them were modified for combat missions.
Bulgaria In November 1936, the first six Fw 44 J were delivered and in May 1939 ten more followed. By February 1940 twenty more planes were delivered to Bulgaria, making a total of 46 J models. After the war surviving planes were handed over to Yugoslavia.
Sweden In late 1936, 14 aircraft were ordered from Focke-Wulf. ASJA, AB Svenska Järnvägsverkstädernas Aeroplanavdelning, and the Swedish Railway Workshops Aircraft Department placed an order for 20 more aircraft in June 1937, while the Central Verkstaden at Västeras (CVV) placed an order for 37 more aircraft in 1939. Another 12 were ordered from Focke-Wulf in 1940, however, these were produced by Flugzeugwerke CKD at Prague, Czechoslovakia.
These were used for elementary and aerobatic training. Other training units flew this plane, and after withdrawn from basic training in 1946-1947, it was used for liaison, observation, glider-tug, and other ancillary roles. After being withdrawn from use, many came ended up on the civil registries in Sweden and Germany.
Turkey 8 planes were ordered and delivered in 1939.
Finland As the Fw 44 was suitable for operation in polar regions, Finland required the aircraft for basic pilot training. In April 1940, a contract was signed between Finland and Focke-Wulf, for delivery of 30 Fw 44 J models.
Norway Norway placed an order for ten Fw 44 Js, which were delivered in April 1940.
Austria From 1936 onwards Austria’s Federal Army used the Fw 44 as a basic school training aircraft, with some ten aircraft were purchased from Focke-Wulf. The Fw 44 was also produced under license. Some 40 Fw 44J models were produced by Hirtenberger Patronenfabrik, (Wiener Neustadt).
Argentina Argentina ordered fifteen Fw 44 Js in January 1937, and built another 60 under license.
Brazil Built a production facility to produce the plane in some numbers.
Chile In September 1937, Chile signed an agreement to buy 15 Fw 44 J models.
Yugoslavia Some war trophy aircraft were taken from the Bulgarians as war reparations and used after the war as trainers.
Nazi Germany (1942)
German Empire (1918)
USSR (1947)
Yugoslavia (1939)
Nazi Germany (1942)
Yugoslavia (1940)
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