PZL-37 Łoś. History. 1936

Mielec 2012-11-01

PZL PZL-37 Łoś bomber.

History

In the history of Polish Aviation, there were several fantastic designs that aroused great interest abroad. The design solutions used in them often set standards. It is hard to believe now (2012). One of such aircraft was the PZL-37 Łoś. The PZL-37 Łoś is an excellent example of the ability of Polish designers and design offices to create modern and innovative designs. Surprisingly easy to fly. Simple technical maintenance. Resistance to extreme situations. Unfortunately, the attack of the Germans on September 1, 1939, together with its Muscovite brothers, caused the PZL-37 Łoś aircraft to share the fate of many Polish designs, prematurely ending its promising career.

Why was the construction of the PZL-37 Łoś undertaken?

The Polish Bomber Aviation at the beginning of the 1930s was based mainly on outdated Fokker F.VII 3m designs, manufactured under Dutch license. These were originally passenger planes, adapted only for bombing operations. There was a dramatic lack of a typical bomber design. An aircraft designed and manufactured in Poland, and at the same time modern. Against this background, the PZL-37 Łoś was created. It should also be remembered that the PZL-37 Łoś was not the only medium bomber design. Competing designs for the Łoś aircraft were; LWS-6 Żubr and Lublin R-XXB. The purchase of a license for the Lockheed L-10A Electra aircraft was also seriously considered, in order to adapt it to a bomber version. Several preliminary designs were submitted to the PZL Design Council. The Council issued a positive opinion on the submitted projects submitted by engineer Jerzy Dąbrowski and commissioned him to carry out further work (preliminary dimensional design and full-scale models).

The concept and design of the PZL-37 Łoś.

The concept of the aircraft was developed by the Department of Aeronautics. This body issued the initial Tactical and Technical Guidelines. Engineer Jerzy Dąbrowski became the leading designer. His deputy and right-hand man was engineer Piotr Kubicki. Franciszek Misztal was the designer of the wing. Work on the aircraft began in the autumn of 1934. This project was designated P-37/34. The designers had an important insight into foreign achievements, including designs developed in the USA, which at that time achieved speeds of over 350 km/h with a twin-engine power unit.

The aim was to develop a medium bomber aircraft, equal in speed to fighter aircraft. The basis was the engines that could be used. Another important factor was the highest possible lifting capacity, ensuring effective transport of the bomb load. Engineer Jerzy Dąbrowski used a wing with flaps in his design, which increased lift during takeoff and landing. Retractable landing gear was used. The engines received compressors that increased power at higher altitudes. The propellers received a variable rake. The fuselage itself received a shape similar to the wing profile, thanks to which it not only had less aerodynamic drag, but also participated in generating lift (which could be as much as 15%). The design of a cantilevered mid-wing, all-metal, with a carefully aerodynamic shape and functionally planned fuselage layout was assumed. A modern semi-monocoque design was used. The bomber was supposed to reach a speed of 400 km/h, i.e. it was to be faster than all fighters of the time. The range was to be 3,000 km. The bomb load capacity was 2,000 – 2,500 kg. The defensive armament was planned to be 2 machine guns in the front and 1 20 mm cannon on the back.

Laminar profile.

Engineer Jerzy Dąbrowski used a wing with a laminar flow profile in his design. Such a profile creates less aerodynamic drag than a classic flow profile. The laminar wing profile was created partly by accident. The aircraft was supposed to have bomb bays not only in the fuselage, but also in the wings. The wing design allowed for the use of retractable landing gear, which was located behind the engines. The bomb bays in the wings were to accommodate the standard 110 kg bombs. Engineer Franciszek Misztal started with a wing profile designated JD12. However, it quickly turned out that with the selected outline and dimensions of the wings, the bombs would not fit in them. Therefore, the designer increased its relative thickness from 12% to 14% and moved the maximum thickness from about 30% to over 40% of the chord. Tests in the Aerodynamic Institute tunnel showed a significant reduction in the drag coefficient Cx at its constant value within the range of angle of attack changes from -4 to 5 degrees, while for classic profiles the minimum value Cx referred only to the most favorable angle of attack. This fact surprised everyone. This means that despite the lower lift of such a profile, it retains this force over a larger range of angles of attack. It is perfectly suited for fast combat aircraft. This profile became popular among Polish aircraft designs and was used, for example, in aircraft; Jastrząb, Sum, Wilk, Miś.

Further decisions and work.

In October 1934, PZL (State Aviation Works) received permission to build a prototype, with a recommendation for further development. The program received funding. An information series of 10 units was immediately ordered. Production of the aforementioned 11 machines was to begin in the newly built PZL – WP-1 plants in Paluch, near the Okęcie airport. The new factory was ready in the autumn of 1934. The PZL factory moved there at the turn of 1934-1935. In December 1934, permission was given to make a life-size fuselage mockup. The mockup was accepted in April 1935, after which the order for the prototype (for strength tests) and the option to purchase 10 copies were confirmed. At the same time, the Aviation Technical Institute began to develop a full technical specification of the type based on the guidelines of the Department of Aeronautics, including details of armament, combat equipment and auxiliary equipment.

Due to the expected high speed of the aircraft, it was recommended to limit the armament to single machine guns in all positions. With such armament, the PZL-37 was to reach a speed of about 400 km/h, which was higher than the P.11c fighter that was equipped with it. It should be mentioned that at that time there were two conflicting views on the defensive fight of bombers. Either use the great firepower of machine guns against attacking fighters, or avoid combat, having the advantage of speed. It should be remembered that each additional machine gun and its ammunition means additional kilograms. The aircraft’s armament consisted of three movable wz. 37 machine guns of 7.9 mm caliber or Vickers F machine guns of 7.69 mm caliber, operated by the crew members. The aircraft was able to carry up to 2,242 kg of bombs in the chambers, fuselage and wings, which was a very good result, unrivaled at that time.

PZL 37/I Łoś – first prototype.

The construction of the aircraft began at the PZL Prototype Department in the autumn of 1935. The aircraft with the factory number 0001 was to be used for static tests, but it is very likely that this number was given to a mock-up that had already been completed. The fact is that due to the lack of sufficient funds, the number of prototypes ordered changed.

The aircraft with the factory number 0002 was a flight prototype. At that time, it was also given the name Łoś, and the military number was “72”. The model had a mechanical system for retracting the landing gear and extending the flaps. To retract or extend the landing gear, the radio operator made 200 turns of the crank. A hydraulic system was eventually used.

In January 1936, design errors were detected in the control system and the landing gear in the prototype under construction, which slowed down the work. Another problem turned out to be the deformation of the skin. The cause was the cabin floor, made of 2.5 mm thick sheet metal, which was also a power element, which was too sparsely riveted. The faults were rectified within two months and in April 1936, aircraft 0002 was ready.

In the spring of 1936, various tests were carried out at the Institute of Technical and Aviation Research. As a result, reservations were raised regarding the starting and control of the engines and the reinforcement of the internal structure of the wings (spars). Therefore, aircraft no. 0002 was returned to the hall. The defects were corrected by the end of May 1936. (Other sources indicate the end of September 1936). It is worth mentioning that during the construction of the first flight prototype, over 600 corrections were made to the initial design, which is completely normal. Remember that this was a highly innovative design.

The first flight prototype PZL-37/I no. 0002 was completed in May 1936. It was ready for flight in September 1936. The first flight of prototype no. 0002 was planned for October 22, 1936. However, on that day, one of the Bristol X engines stopped working. It turned out that a metal pin had been thrown through the hole for screwing in the spark plug. It was not possible to explain the matter; whether it was sabotage or an accident. The problems with the engines repeated themselves once again. Even before the first flight, in December 1936, the Bristol Pegasus X engines were replaced with the newer Bristol Pegasus XII.

In the literature, you can find information that the first flight was performed already in June 1936, which is possible, but not very likely. Possible, because the aircraft began to be assembled in the autumn of 1935 and the Bristol Pegasus X engines were already available. However, it should be assumed that the given date was the plan for the first flight and was already being distributed for advertising purposes.

The PZL-37/I prototype is distinguished by: Main landing gear with single wheels on double legs. Single vertical tail. No propeller hubs. The aircraft had a measuring probe in the glazed nose.

The first flight was performed on December 13, 1936. The pilot was Jerzy Widawski. The flight was without any major problems, although slight vibrations of the tail section were observed. The landing gear was not retracted during the flight. The vibrations were repeated in subsequent flights. As a result, the engine mount frame cracked. The exhaust pipes of both engines also cracked. The engine reducers were damaged. Another problem was the insufficient cooling of the engines, which, due to the winter season, boded even worse for the summer period. The prototype had a single tail in the tail section. It was powered by 9-cylinder Bristol Pegasus XII B engines, with a power of 2 x 873 HP each. Three-blade metal propellers. The aircraft had a structural strength with a safety factor of 3, which allowed the use of 2 engines with a power of 2 x 800 HP to 2 x 1,200 HP. The prototype was made with a main landing gear with single wheels on double legs. However, during landings in random terrain, it turned out that the landing gear was hard and the aircraft did not tolerate all unevenness well. Therefore, the landing gear was redesigned. Engineer Piotr Kubicki developed a new landing gear. For the first time in the world, an independent suspension system for twin wheels was used. This meant that they could work independently in uneven terrain. Each wheel could be tilted individually. It allowed not only typical operations from field airports, but also safe landings even in a potato field. The landing gear turned out to be sensational and was patented by PZL; Polish Patent No. 29090.

The overall assessment of the aircraft was positive. It was stated that the aircraft would meet the recipient’s expectations after improvements. The Air Force Command changed the order from 10 to 30 aircraft, with a delivery date by the end of 1938. As part of this order, 29 units were to be received by the Polish Army, and one aircraft, in the form of the second prototype, was to be used to test the dual tailplane improving the field of fire in the rear hemisphere, which the army wanted. It was also assessed that the dual vertical tailplane would completely eliminate vibrations in the rear part of the fuselage.

With the arrival of spring 1937, further research and development projects were initiated. Weapon tests were commenced at the Aviation Technical Institute and a series of test flights were conducted. A speed of 420 km/h was achieved at that time. The tests were completed with a flight time of 200 hours. In August 1937, the aircraft was once again returned to PZL for a few modifications. The modified prototype was transferred to the Independent Experimental Squadron of the ITL for another 200 hours of operational tests.

PZL-37/II Łoś – the second prototype, and also the second flying aircraft. The aircraft bore the number 0003. It had the military number 72.2. Assembly began before the first prototype flew, also in the Prototype Department. The aircraft was to be a model for serial construction. Changes and modernisations resulting from tests of aircraft no. 0002 were introduced on an ongoing basis. The first flight was probably performed in November 1937. In terms of design, the aircraft differed from the first prototype in having a double tailplane and a different landing gear (mentioned above). The aircraft was powered by Bristol Pegasus XX engines with 2 x 918 hp. The aircraft had a rebuilt crew compartment and Meisser hydraulic systems. Additionally, the observer’s cabin could be fitted with a removable control panel, and the lower gunner’s position was fitted with a manually operated cover covering the fuselage cutout.

PZL-37/II Łoś No. 0003 Okęcie Airport. Preparations for series production.

After conducting ground and flight tests, the Military Adjudicating Commission issued permission to commence series production of the PZL-37 Łoś aircraft. The test flight of the prototype was slightly delayed and took place in November 1937, at Okęcie, just after the test flight of prototype no. 0003.

It turned out that at low speeds and landing, the rear of the aircraft would flutter. This defect was eliminated by riveting duralumin pads that increased the stiffness of the horizontal stabilizer spars.

The test results confirmed that the requirements had been met and the aircraft received a good assessment. At the end of the year, the prototype was transferred to the Prototype Squadron of the Independent Experimental Squadron of the ITL. The aircraft was to be powered by two engines; 9-cylinder, radial, air-cooled, with power ranging from 2 x 837 HP in version A to 2 x 1,050 HP in a single copy of the D series.

PZL 37 A Łoś (Łoś I).

PZL 37 A Łoś (Łoś I) – the first series version of the Łoś. In August 1937, a series of 30 PZL-37 aircraft was ordered, with delivery starting in January 1938. Initially, the model for this series was to be aircraft no. 0003, the P-37/I prototype, which after changes took on the features and name of the P-37/II prototype. The army wanted the PZL-37/II version. Since PZL was ready to start production, but of the P-37/I version, the Air Force Command agreed that the ordered batch would include 10 A-version aircraft based on the first prototype, i.e. with a single tail, but with a new undercarriage. Their construction was simply already far advanced. The aircraft had Bristol Pegasus XII B engines with 2 x 873 hp. 10 aircraft of this version bore military numbers from 72.3 to 72.12.

There were also disagreements between the manufacturer and the user regarding the engines. The second prototype of the PZL-37/II aircraft was already flying with Bristol Pegasus XX engines. However, the final first examples had Bristol Pegasus XII engines. Production of the aircraft began in the autumn of 1937, at PZL-Okęcie. These aircraft were completed at the beginning of 1938, initially they did not have propeller hub caps and, with the exception of one example, remained unarmed until the end of the year. They were never equipped with bombardier machines, and therefore had the only option of mechanically dropping the entire bomb load.

PZL-37 A Łoś.

On June 20, 1938, during tests conducted by the Aviation Technical Institute, a disaster occurred. During a task – a flight for higher piloting, i.e. aerobatics, the wing of the aircraft fell apart in a loop. The aircraft crashed to the ground near Piaseczno, burying the crew in its wreckage. The pilot in this flight was platoon pilot Stanisław Macka. The wreck of the aircraft was transported to Mokotów Airport. The investigation showed that the cause of the accident was faulty riveting, caused by the imprecision of the Junkers corrugated sheet metal. This resulted in the need to unrivet 20 ready sets of wings to check the quality of their riveting. Later, the wreck was used by cadets from the Aviation Cadet School (technical group) at Mokotów Airport as a teaching aid.

PZL 37 A bis Łoś (Łoś I bis).

PZL 37 A bis Łoś (Łoś I bis) – these were the remaining 20 machines of the A version. These aircraft were already based on the P-37/II prototype. They had a double tail. From the A bis series, 17 machines had Bristol Pegasus XII B engines. The rest received Pegasus XX engines. The aircraft in the PZL-37 A bis version were made by July 1938.

The first two copies with military numbers 72.13 and 72.14 received civil registration SP-BNK and SP-BNL respectively. They served as demonstration copies. SP-BNL received Pegasus XX engines and the official designation Łoś A bis on the tail. The first flight was made at the beginning of May 1938 and sent to the international aviation exhibition in Belgrade. The exhibition was held from 28 May 1938 to 13 June 1938. The aircraft aroused great interest there. In December 1938, this aircraft was shown at the 16th Paris Air Show, where it was also successful. It was admired and positively commented on by Colonel Pilot Charles Lindberg, the first to fly across the Atlantic in 1927.

PZL 37/III Łoś.

PZL 37/III Łoś – the third prototype. It was Łoś A bis, which was given the civil registration SP-BNK. Although the construction of serial machines was to begin, numerous tests were carried out on it in the period 1937-1938. According to sources, it was the A bis version adapted for tests. This aircraft was tested in flight with, among others, Gnôme-Rhône 14N00/01 engines (with power of 2 x 751 kW and 2 x 1,020 hp) and was to serve as a model for the export version of the P-37 C bomber. During the tests, it reached a speed of 453 km/h at an altitude of 4,250 m. This prototype was to be used for a series of tests with various radial engines: Renault 14T, Gnőme-Rhőne 14N, and Fiat A-80 RC41, 3 of which were given to PZL by Fiat together with offer documentation, wishing to interest Poland in its engines. Various versions of gun and bomb armament were also tested on this aircraft.

The first PZL-37 A models were sent to units for operation. Since these aircraft were not fully armed, they were not transferred to combat units. They were sent to training units, which was a very good solution. The entire logistics could be worked out. The PZL-37 is a modern aircraft that requires greater skills from pilots, which is why training was slow and fraught with difficulties. In addition, fatal accidents occurred. The first of them involving the PZL 37 A was described above.

During the use of the first aircraft, other accidents involving casualties also occurred. Three accidents occurred in the 1st Air Regiment. All of them occurred on the A bis, during which the controls were jammed. In six other cases, the crews were to blame. Usually, during a tight turn, at too low a speed, with a strong lean to the wing, the aircraft would go into a sideways skid. A delayed reaction by the pilot led to a disaster. The designers blocked the rudder deflection to +/- 20 degrees. This meant that such an accident did not happen again. The designers also improved the rudder compensation, but the outbreak of World War II blocked the introduction of this modernization in all aircraft. The fact is that in the period from November 1938 to June 1939, a total of 21 personnel died and 8 aircraft were lost. During production, 250 design changes were made and about 4,000 defects were fixed.

PZL 37 B Łoś (Łoś II)

PZL 37 B Łoś (Łoś II) – a new version of the aircraft. They began to be produced from August 1938, (according to other sources from autumn 1938) based on the PZL 37/II with corrections from the PZL 37 A and A bis. Aircraft of this version had two Bristol Pegasus XX engines with a power of 2 x 918 HP each. Work on the licensed production of PZL-Pegasus IX/XX engines in Poland was advanced. During the tests of version B in November 1938, the issues of bomber and gunnery armament were finally established, which were to be used as targets.

PZL-37 B Łoś. 1938.

General pilot Ludomił Rayski wanted to order 180 machines, in order to create a strong bomber group consisting of 21 squadrons of 6 planes each. A total of 126 machines, plus a reserve. This was to be a deterrent for a quick riposte to offensive actions of a potential enemy, the Germans. After numerous discussions and consultations, in October 1936, a plan was adopted to create 21 bomber squadrons of 7 planes each, a total of 147 bomber planes. Interestingly, in addition to 130 PZL-37 Łoś planes, there were to be 17 LWS-6 Żubr machines. Looking a little into the future, it should be mentioned that due to the low budget of the Republic of Poland, in the project of expenditure on the purchase of equipment for aviation in the budget year 1938-1939, the number of squadrons was limited to 8, 7 machines each. That is 56 machines plus 74 reserves (repairs, training squadrons). In total 130 aircraft.

The factory offer price of the PZL-37 was initially PLN 420,000 + PLN 150,000 for engines, later reduced to PLN 400,000 (equipped airframe without engines – the cost of equipment and instruments was about PLN 125,000). This price was considered too high by the army. The recalculation of costs by the Air Armament Committee gave the amount of PLN 320,000, after which the PZL-Okęcie factory reduced the offer price to PLN 280,000 for the airframe. This raised serious doubts as to the reliability of the factory cost estimates and the material management at the factory. In 1938, after the final cost calculation, PZL received the total cost of the PZL-37 B at the level of PLN 319,600.

The Military Aviation (as mentioned above) initially placed an order for 180 B version aircraft. An advance payment was also made for the equivalent of 108 aircraft. The delivery completion date was set for March 31, 1939.

The first PZL 37 B bombers began to receive units from the spring of 1939. They were met with recognition, as there was no more aircraft accident involving them in the Polish Air Force caused by equipment failure or technical defects. PZL repaired only one aircraft, in which the on-board instruments were replaced and a leak in the air system was reported. Finally, on November 30, 1938, 124 PZL-37s were ordered. By July 31, 1938, 10 PZL-37 A, 17 PZL-37 A bis, 1 PZL-37/II, 1 PZL-37/III, 1 exhibition aircraft had been produced, a total of 30 units. The remaining 95 PZL-37 B aircraft were to be produced by March 31, 1939. In March 1939, General Pilot Ludomił Rayski was replaced by General Pilot Władysław Kalkus, who became the commander of the air force. He reduced the order from 180 to 108 aircraft. PZL reacted quickly and referred to the fact that production of components for the crossed-out aircraft had already started. The army agreed to 130 PZL-37 B Łoś aircraft. Ultimately, 104 PZL-37s were built in Warsaw in WP No. 1 (WP-1). In order to mislead the Germans, the aircraft serial numbers were not assigned consecutively. The high numbers were to suggest that many more aircraft had been built than in reality.

At the beginning of 1939, the production load of WP-1 was very high. The assembly of PZL-43 aircraft for Bulgaria began. (PZL-43 Czajka is an export version of the bomber-reconnaissance PZL-23 Karaś.) Preparations were made for the production of the PZL-50 Jastrząb and PZL-46 Sum. The pace of production of the PZL-37 slowed down. Therefore, preparations for the production of the PZL-37 in Mielec were accelerated, as discussed below.

According to various researchers, a total of 124 to 134 machines were built. These discrepancies result from the fact that a large percentage of the machines were in the production phase, at various stages of advancement. There were also about 20 airframes under construction on August 31, 1939. By September 2, 1939, over 120 aircraft had been built. This was a huge number, considering the weakness of the Polish economy, ruined for 123 years by the occupiers, and then by the Great World War and the Polish-Bolshevik War. The purchase of PZL-37 bombers was largely financed by voluntary donations from Poles within the National Defense Fund. The enormous sacrifice of Poles in the interwar period can be appreciated by looking at the numbers. By 1939, a total of 1,264.7 million złoty had been spent, which was the equivalent of almost twice the annual budget of Poland for armaments. Apart from the bomber in question, the O.R.P. Orzeł ship project was also financed from this voluntary donation.

Encouraged by the bomber’s success, engineer Jerzy Dąbrowski and his team developed a preliminary design for a twin-engine, two-seater high-altitude reconnaissance aircraft, considered a new trend at the time. The aircraft was similar in design and layout to the PZL-37. It was the later PZL-38 Wilk fighter aircraft. In April 1939, Major Eng. Franciszek Suchos, Deputy Head of the Technical Department at the Air Command, came up with the concept of developing a two-seater version of the PZL-37 Łoś as a heavy pursuit aircraft. The idea was related to preventing fast Germanic aircraft from flying over Pomerania and Silesia. The designer planned to permanently mount 8 PWU wz. 37 machine guns in the full rounded nose. The project was not implemented.

Central Industrial District.

The Central Industrial District (COP) is closely associated with the PZL-37 Łoś aircraft. In October 1936, the Committee for Armament and Equipment (KSUS) passed a resolution to build the COP, with the guiding idea of ​​the defense industry needs. Location was important. Efforts were made to select a location far from our eternal enemies; Germans and Muscovites. The best location turned out to be Subcarpathia, naturally protected from the south by the Carpathian Mountains. It included 27 counties; Biłgoraj, Brzesko, Brzozów, Dobromil, Dabrowa, Gorlice, Janów Lubelski, Jarosław, Kolbuszowa, Krasnystaw, Krosno, Lesk, Lubartów, Lublin, Łańcut, Mielec, Nizniów, Przemyśl, Przeworsk, Rzeszów, Robczyce, Sandomierz, Sanok, Tarnobrzeg and Tarnów. This area was poorly developed urbanly. The road and rail network was poor. There was no water supply or sewage system. However, there were many willing and able workers. Technical deficiencies turned out to be beneficial, because it was possible to design from the beginning for specific needs for the newly reborn Republic of Poland. The COP construction plan was approved in February 1937. It was planned to build about 30 factories and supporting plants. Most of them were not built, because their construction was interrupted by the attack of the Germans, supported by the attack of the Muscovite brothers. A large part of the future factories was still on the drawing boards.

However, the aircraft factories were among the first to be implemented. These were: State Aviation Works – Airframe Factory 2 (WP-2) in Mielec and Engine Factory 2 (WS-2) in Rzeszów. Both were organizationally related to PZL WP-1 and WS-1 in Warsaw. Both new factories were to be at least 1.5 times larger than the plants in Warsaw.

Already in mid-1937, in the town of Cyranka, located on the outskirts of Mielec, the locations for future facilities began to be marked out. On September 1, 1937, the construction of the factory officially began. The construction of the factory resulted in the development of the city’s infrastructure. A housing estate for employees and single-family houses for the management staff were built. Many new paved streets were built. The construction of the factory itself was completed in 1938. Already in 1938, the organization of aircraft production began. It was decided to place the production of PZL-37 Łoś bombers in Mielec. In May 1939, the factory received parts for 30 aircraft from Warsaw. By the end of 1939, 130 bombers were to leave the factory. Annual production was to amount to 228 bombers. In June 1939, the first Mielec PZL-37 Łoś aircraft was flown. By the time the Germans attacked the Republic of Poland, on September 2, 1939, the construction of 6 bombers had been completed, and the remaining 10 machines were waiting for the remaining equipment to be installed and for flights. Only 3 of them flew to combat units. None of these 6 bombers were officially accepted by the Polish Army, there was no time for that.

The PZL-37 Łoś bomber was not the only aircraft to be produced at PZL Mielec. The second was to be the PZL-46 Sum light reconnaissance bomber. The aircraft was designed by the talented Polish designer and engineer Stanisław Prauss, and the first flight was performed by the test pilot Jerzy Widawski in August 1938. The PZL Warszawa plant built only two prototypes. The next aircraft were built by the new PZL-Mielec plant. The aircraft proved successful and was presented in 1938 at the Paris Salon. At the end of 1938, the Polish Air Force Command ordered 160 aircraft, to be reduced to 300 on 28 March 1939. At the same time, Bulgaria held talks on purchasing 12 PZL-46 Sum aircraft. PZL Mielec was of course chosen as the production site. However, preparations for production were slow, because priority was given to the production of fighter aircraft, and Mielec was busy with the production of the PZL-37 Łoś. Nevertheless, in July 1939, the PZL-46 production line in Mielec was ready and the first elements were started to be manufactured.

The Germanic attack on the Republic of Poland caused the occupation of the factory in Mielec and the interruption of the construction of both the PZL-37 Łoś and the PZL-46 Sum, the first flight of which was expected in September 1939.

The construction of the WS-2 plant in Rzeszów took place in the period 1937-1939. In 1939, the production of parts for Walter Junior and Minor engines (Czechoslovak license) and Bristol Pegasus-IX (British license) began. This was a department producing rolling bearings under British license. The target was to build 600 engines per year.

It is worth adding that the equipment of the factories in Mielec and Rzeszów was very modern. The machines came from France, the UK and the USA. Mielec had around 150 machine tools and employed 700 workers. Rzeszów had around 400 machine tools and employed around 1,200 workers. Both plants were bombed on 1-2 September 1939.

PZL-37 Łoś for export.

Successful foreign shows gave a chance to find buyers for the PZL-37 to customers other than the Polish Army. An export version designated PZL-37 C Łoś (Łoś III) was built relatively quickly. The main change was the use of Gnome-Rhone 14N00/01 engines with 2 x 970 HP. It was also planned to replace some of the avionics equipment to meet the needs of local users. The PZL-37/III prototype was shown in Greece as the PZL-37 C.

Soon another export version appeared, designated PZL-37 D Łoś (Łoś IV). Again, the basic change was the use of the most powerful Gnome-Rhone 14N20/21 engines available at the time, with an output of 2 x 1,050 hp.

In August 1938, the P-37/III aircraft with the registration SP-BNK, made a promotional flight in several countries. Piloted by Bolesław Orliński and Stanisław Riess. Bulgaria, Greece and Turkey were visited. Romania was also planned. In Greece, the aircraft was viewed by the highest officers of the Greek Air Force and government representatives. The display took place at Tatoi Airport. Greece placed an order for the PZL-37 Łoś.

The next flight led to Turkey. On August 15, 1938, a flight was made from Athens to Ankara. Unfortunately, due to bad weather, the pilots deviated from the route. The extended route led to the exhaustion of the fuel supply and a forced landing. The landing in an unfamiliar area ended with serious damage to the aircraft. The potential costs of transporting the aircraft to Poland and its repair turned out to be too high. Therefore, the decision was made to leave the airframe. Only engines, armament and avionics were taken.

In August 1938, three PZL-37 A bis (Łoś I bis) and one PZL-37 A (Łoś I) aircraft made another advertising flight through Romania to Bulgaria. The team was led by General Pilot Ludomił Rayski. On August 26, 1938, at Sofia’s Buzurishte Airport, the aircraft was presented to representatives of the Bulgarian army. Bulgaria expressed interest in purchasing initially 30, later 12-15 aircraft with Italian FIAT engines. Further talks were held with Romania. Romanian sources report that a contract had been signed for the delivery of 30 PZL-37 D aircraft. Turkey wanted to buy 10 PZL-37 D aircraft and components for the assembly of another 15 aircraft. They also wanted help in organizing a factory. As for the sale of the PZL-37 to Greece, negotiations lasted until August 1939 and were far advanced. Nevertheless, the contract was not signed. The Germanic attack on the Republic of Poland prevented it. 1 or 2 PZL-37 aircraft were to be built for Egypt.

In 1938, the license for the production of the PZL-37 was sold to the Belgian company Constructuins Aeronautiques G. Renard for 400,000 złoty (the company operated in the period 1923-1970). Additionally, for each airframe built, the company was to pay a fixed fee to the Polish side. It was planned to build machines for the Republicans during the civil war in Spain. However, production did not take place. At the same time, talks were also held on the sale of the first version of the PZL-37 A to Spain, for the Republican side. Negotiations were carried out using intermediaries in England, France, the Netherlands, and Denmark. For the Germans, the Chinese embassy was the intermediary. The agreement was not concluded because the war in Spain had ended.

In total, by August 1, 1939, 55 PZL-37 export orders had been collected, and the same number was to come from Romania and Turkey. Today we would describe most of these orders as options. There is no doubt that the most interested countries were; Romania, Bulgaria, Greece and Turkey. Requests for proposals were received from Belgium, Finland and Estonia. There was a chance of selling 200 to 400 units.

Łoś in the Polish Army.

The first PZL-37 aircraft were delivered to the established Training Squadron. The first were of course the A versions, not fully armed. The first combat machines were delivered to the units at the turn of 1938-1939. The first to receive them was the 1st Air Regiment. They were divided into 4 bomber squadrons: 211, 212, 216 and 217, grouped in two squadrons. Each received 9 B type machines, i.e. there were 36 machines on duty. Most of these aircraft were based at Okęcie Airport. It was a part of the Bomber Brigade at the disposal of the Commander-in-Chief, under the command of Col. Dipl. Observer Władysław Heller. Each squadron additionally had two transport Fokkers at its disposal. On August 31, 1939, the squadron was relocated from Okęcie Airport to Ułęż Airport near Dęblin. The commander of the 211th Squadron was Captain Observer Franciszek Omylak. On August 31, 1939, the 212th Squadron (12) was also relocated to Ułęż Airport near Dęblin. The commander of the 212th Squadron was Captain Pilot Stanisław Taras-Wołkowiński. At the end of August 1939, the 216th Squadron (16) was not fully completed. It lacked 6 on-board gunners and technical personnel. The squadron was intended for the second wave. Despite this, on August 31, 1939, the 216th Squadron was relocated from Okęcie Airport to Podlodów Airport near Dęblin. The commander was captain observer Władysław Dukszto. Squadron 217 (17) The Squadron on August 31, 1939, was relocated to Podlodów Airport near Dęblin. The commander was captain observer Eugeniusz Prusiecki.

A large number of PZL-37s were stationed at Małaszewicze Airport waiting to be armed. Małaszewicze Airport, or rather a large military base with an airport, was an important element of the Polish military base. It was far from the borders of the Republic of Poland, but not far from Warsaw. 31 aircraft were based there, which were included in the XX Training Squadron. Almost all PZL-37 A and PZL-37 A bis were stationed there. In the first days of the war, 8-17 more machines arrived there. 5 PZL-37 Łoś aircraft were sent to the Independent Experimental Squadron.

The use of PZL-37 bombers in combat, according to the regulations in force at the time, was decided by the Commander-in-Chief through the Supreme Air Command. The commander of the Bomber Brigade could only have 2 squadrons at the same time. This made the chain of issuing orders difficult. During the first months of operation, it turned out that locating the center of buoyancy of the wing, close to the center of gravity of the aircraft, allowed for performing aerobatics and conducting maneuverable air combat when the aircraft was not loaded with bombs. This was a defect that was easy to eliminate, but in the conditions of the rapidly approaching war, it was impossible to eliminate. In normal conditions, after eliminating this problem, the PZL-37 could even be a heavy fighter.

The problem was certainly the limited experience of the crews. There was not enough time to conduct training in this area. The aircraft was difficult for older pilots. They were not used to the retractable landing gear or adjustable propellers. Older pilots were also unfavorable about the cockpit, which they believed was located too high. Entering the cockpit took some time, because you got in from the back, climbing up the wing to the front cockpit. A different opinion on the PZL-37’s piloting was held by the younger generation of pilots, praising the design for its great ease of piloting, which even surpassed Polish fighter planes of the time. Engine control required attention. The throttle levers had to be pulled back to increase thrust, which was a rather unintuitive solution. The PZL-37 engines were supplied with fuel from 5 tanks in a rather complicated way, and refueling was only possible using a pump.

World War II.

Unfortunately, the Germanic army, on September 1, 1939, at 4:40, attacked the Republic of Poland. The Polish Army had 84 operational machines at its disposal. Most of them were not ready to take immediate military action. This was due to minor faults, such as a failure of the on-board intercom or compasses. The Germans had relatively good reconnaissance of the aircraft’s base locations. Therefore, on September 1, 1939, Okęcie Airport and Małaszewicze Airport were bombed several times. At Małaszewicze Airport, they destroyed about 7 bombers. In the following days, at least 10 machines of version A and B were evacuated to Romania.

In the Defensive War of 1939, PZL-37s were used to combat German armored weapons in the area of ​​Wieluń, Sieradz, Piotrków Trybunalski, Radomsko, Pułtusk, Różany, in the areas of Przeworsk, Jarosław and Jaworów and east of Zamość, Hrubieszów and Włodawa. The wartime task of the Łoś was to bomb heavily defended, German armored columns. The bombing was carried out without fighter cover, with variable luck, losing many machines, as a result of enemy fighters. The attacks were carried out by a small number of machines. It should also be noted that these were tasks for attack aviation rather than bomber aviation. The squadrons also recorded six Messerschmitt Bf 109 and 110 aircraft shot down. About 30 aircraft were lost in combat. 27 PZL-37 machines were evacuated to Romania. It turned out that the system of evacuating the crew from the aircraft during the flight was very difficult. This was certainly an element that should have been improved, but due to the total war it was impossible to implement.

PZL-37 Łoś performed 135 bombing and reconnaissance missions, dropping about 120 tons of bombs and achieving 5 defensive shootdowns. 47 machines took part in the Bomber Brigade operations, including 11 from the reinforcements. 30 machines were lost in the process, and 17-19 were evacuated to Romania. From the remaining units, 6-10 machines were evacuated to Romania. The Muscovites took over 4-8 machines, 3 of which were airworthy. Two were transferred to the Scientific and Research Institute in Moscow. About 50 damaged PZL-37 bombers were seized by the Germans. At least two planes were renovated. The first one was sent for tests at the Luftwaffe center in Rechlin. The plane was crashed there in May 1940. The second one was shown at an exhibition of captured equipment in Vienna (from September 17, 1940 to December 30, 1940). Several destroyed (set on fire) PZL-37s were used in 1940, during the production of the propaganda film “Kampfgeschwader Lützow”.

Very often, experts on the subject compare the PZL-37 Łoś with the He-111. In our opinion, this comparison is a misunderstanding. The Germanic designs that were in the equipment of combat units on September 1, 1939 were inferior in every respect to the Polish PZL-37 Łoś. However, the Germanic offices continued to work intensively, and the factories built more improved planes. The Polish offices and factories were destroyed.

The Łoś passed a tough test, although they were not prepared for it at all, it should be assessed that they passed it with flying colors. 30 machines were lost in combat. The crews of the PZL-37 aircraft performed excellently, demonstrating courage and bravery. 9 pilots died, 6 were wounded, and a total of 42 did not return from the flights (including prisoners and missing in action). Honor the memory of those who died defending the independent and sovereign Republic of Poland.

In foreign service.

The defensive war has ended. Two enemies have destroyed the Republic of Poland. But the history of the PZL-37 Łoś has not ended. Sources provide different numbers of aircraft that ended up abroad. 17 B-type machines were evacuated to Romania from the Bomber Brigade. It is unclear how many from the XX Training Squadron. Most likely, these were 6 machines. In total, 23 or 27 machines ended up in Romania.

The Łoś machines were interned in Romania and incorporated into its air force, despite the strong protests of the Polish authorities supported by France and England. They were incorporated into the 76th and 77th Squadrons. A total of 23-27 aircraft were evacuated to Romania. They crashed one machine on November 18, 1939, at the airport in Iaşi. According to preserved Romanian materials, they were re-armed with Germanic 7.92 mm MG 15 machine guns and 20 mm MG FF cannons. They were used in combat against the CCCP from 1941 to 1944. They bombed cities in Ukraine, among other places. They were also used to train crews flying the Ju-88. It is possible that 3 PZL-37B aircraft bombed Kosice on June 26, 1941, as a provocation to the Hungarians, so that they would declare war on the CCCP. The sources do not fully determine whether they were Łoś or perhaps SB-2s. The provocation was successful, but Romania paid for this action in August 1944, when the Hungarians found an opportunity to repay the Romanians by bombing the Cimpia Turzii airport and destroyed many PZL-37Bs there. Supposedly, several were destroyed by Hungarian partisans in August 1944. It is possible that the few remaining machines took part in the fight this time against the Germanic troops. The news reaching Poland after the war that the Romanians still had PZL-37s turned out to be untrue.

The Łoś did not make a great career in Romania. There, the PZL-37 Łoś gained the nickname of a flying coffin. Many machines crashed, burying their crews. However, the blame for this situation cannot be placed on the plane. The Romanian pilots were not trained by Polish instructors who knew the strengths and weaknesses of the Łoś. Moreover, the Romanians were not given flight instructions, as a result of which the rather complicated system of switching fuel taps remained a mystery to them and that is why cases of sudden engine failure were not uncommon there.

A total of 4 machines landed in the CCCP by mistake. In total, the Muscovites took over 4-8 machines, 3 of which were fit for flight. Two were transferred to the Scientific and Research Institute in Moscow.

The Germans in Warsaw, Mielec, Małaszewicze captured 41-50 machines. Some were destroyed for the previously mentioned propaganda purposes. Polish workers employed to clean the Okęcie and Mielec airports destroyed most of them, under the pretext of scrapping them, before the Germans had time to figure out what kind of aircraft they were. As a result, only 2 aircraft were fully operational. They were transported to Rechtlin for testing. One of them crashed in May 1940, killing the entire crew. That is, four more Germanic pilots in a corner of PZL-37 Łoś aircraft. The second one was sent to a show, and after that the fate of the aircraft is unknown. The Germans also captured 50 brand new PZL Pegasus XX engines, which they sold to Sweden and installed in Ju-86K-13 aircraft.

Replica of the PZL-37 Łoś bomber. 2012.

Despite the relatively large number of PZL-37 Łoś aircraft built, not a single one has survived to this day. And if any model survived the Second World War, it was deliberately destroyed. Remember that the machines were owned by: Romanians, Muscovites and Germans. During the Polish People’s Republic, no one was interested in acquiring even a wreck. Despite this, the history of the aircraft cultivated in the underground circulation did not allow for erasing this excellent aircraft from memory. And there came a time when in Mielec, two young engineers Jakub Skrzypek and Kazimierz Nowakowski, were fired up by the desire to revive at least a model in 1:4 scale. With this idea, at the beginning of 2010, they went to the Director of PZL-Mielec Sikorsky. The proposal was accepted and modified – the scale is to be 1:1.

The reconstruction was not easy, because no technical plans survived and there were only a few dozen photos and films. Technical documentation was created from the beginning based on the fragmentary materials that survived. Model plans were helpful, although made on a smaller scale. It was planned to build a replica in the open air, near the pedestal on which it was to stand. However, this plan evolved. It was decided that it would be good to be able to transport the replica to shows or to the hall for repairs or paint corrections. The management of the PZL-Mielec Sikorsky plant, which has been owned by Americans since 2007, was very supportive of this program. The model was created in the same hall no. 2, where PZL-37 Łoś bombers were produced before the attack of the German and Muscovite enemies. The construction of the model took 2.5 years and consumed 5,000 working hours. These 5,000 hours are the private time devoted by passionate patriots. In total, 70 people worked on the construction of the model. The construction used 5 tons of aluminum and almost a ton of steel, 20,000 rivets, 400 square meters of sheet metal for the skin and 70 liters of paint. The Łoś has a span of 17 meters, a length of 13 meters and weighs about 6 tons.

The presentation ceremony of the non-flying replica was organized for VIPs and the media on September 29, 2012 (Saturday). The ceremony had a military-patriotic character. To the sounds of the “Aviators’ March”, the Łoś was led out of the same hall where it was produced in 1939. Accompanied by an honor guard, the Mazurek Dąbrowskiego sounded, and the flag was hoisted up the mast. The presentation was led by Andrzej Tułowiecki from the Promotion Department of the Polish Army Museum in Warsaw. During the ceremony, the S-92 Black Hawk helicopter and the TS-8 Bies aircraft added an air tribute to the legendary bomber. On September 30, 2012 (Sunday), the model was presented to the residents of Mielec. The problem is that the model stands on the premises of the plant and access to it is difficult. Therefore, it is possible that in the future the model will be temporarily loaned, for example, to the Polish Army Museum in Warsaw. The permanent place of its presentation is to be the area in front of the factory, among other structures built in Mielec. If there are sponsors, a temporary presentation in other museum facilities is possible.

Over the decades, the PZL-37 Łoś aircraft has become a legend. It is mentioned immediately when we ask about Polish aircraft in the defensive war of 1939. It was and is undoubtedly the pride of the Polish Aviation Industry. The PZL-37 Łoś was designed as a modern, even innovative design, ahead of almost all others. But perhaps most importantly, it was a completely Polish design. The genius of Polish designers, technicians and workers.

The controversy surrounding the PZL-37 aircraft does not concern the design itself. The problem was the direction of aviation development and this problem did not concern only the Republic of Poland. In the 1930s, one of the directions of development was the theory of the Italian general, which grew out of the experiences of the Great World War. He believed that bombers were the main force of modern aviation. It was not until the Second World War that the theories of the use of aviation, including bombers, were verified. Giulio Douheta himself evolved in the strategy of using aviation and became a supporter of creating universal aircraft.

Many experts on the subject claim that the fast, twin-engine bomber with a large payload did not prove itself in the defensive war of 1939. However, it would have proved itself (if there had been such an opportunity) in attacks on targets in German territory. If these planes had been used as intended, they could have probably achieved great success.

The defensive armament was subjected to unjustified criticism. It was claimed that three machine guns were not enough. However, they forgot that the PZL-37 Łoś should have operated in the cover of PZL-50 Jastrząb fighters. And that would have looked completely different. Now, when we know the outcome of the struggle with the German army and the stab in the back of the Red Army, it is easy to say that a modest budget should have been allocated to the construction of fighters. The successor of General Pilot Ludomił Rayski (a great patriot), General Pilot Józef Zając, planned to end the production of the PZL-37 and direct all efforts to the production of a fighter, which was more needed in the defensive war. There were also plans to rebuild the PZL-37 into heavy fighters. It is easy to judge with hindsight. So let’s not look for the downsides of the PZL-37. Let’s be proud of our history, because currently (2012) we are no longer building any combat aircraft.

Written by Karol Placha Hetman