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The P.Z.L. P.50 Jastrzab (Hawk) was a radial engine powered fighter that was let down by the lack of a suitable engine, and that had been cancelled a few months before the German invasion of Poland.
In the mid 1930s the Poles realised that they would soon need a replacement for the gull winged P.Z.L. P.11, which had been an advanced design when first introduced, but that was becoming obsolete. At first the plan was to replace it with the twin engined P.Z.L. P.39 Wilk, a multi-role aircraft that was also to serve as a high altitude attack aircraft and escort fighter as the P.38. However this aircraft was to have been powered by the Polish designed Foka engine, which ran into problems after its designer was killed in a climbing accident in the summer of 1936.
Soon after this accident (but before the problems with the Foka engine had emerged) the Polish government revised its plans for a new fighter. The P.39 was cancelled, and it was decided to replace the P.11 with a new single engined fighter. The existing P.24, an export version of the P.11, was briefly considered, presumably because it was already in production, but was rejected because it was no better than later versions of the P.11.
Wsiewolod Jakimiuk, the head of P.Z.L,’s fighter team, produced a design for the new requirement. This was for a sturdy low wing monoplane fighter, powered by a radial engine, and large enough to take more powerful engines when they appeared. This design was given the company designation P.50, and was in competition with another P.Z.L. design, the lightweight P.45.
The P.50 was selected by the Polish Aviation Command and given the name Jastrzab (Hawk). The first production version, the P.50A Jastrzab A, was to be powered by a 840hp Mercury VIII engine, armed with four wing mounted 7.7mm machine guns, and was expected to reach a top speed of 310mph at 14,107ft. Production of a mock-up was approved in the autumn of 1937, and this was soon followed by the construction of two prototypes and a static test airframe. The first prototype, the P.50/I Jastrzab I, was to be able to take engines up to 1,200hp. The P.50/II Jastrzab II was to take radial engines up to 1,600hp.
In 1938 the Aviation Command ordered 300 Jastrzab As before the prototype had been completed, and paid for the first 100 in advance. The first fifty were to be delivered by September 1939. In an attempt to speed up work on the first prototype the British Dowty company was given a contract to produce the undercarriage, but this backfired, and the prototype was actually completed in September 1938, four months before the undercarriage arrived. As a result the prototype wasn’t able to make its maiden flight until February 1939.
When the first prototype did take to the air it proved disappointing. The Bristol Mercury VIII simply wasn’t powerful enough for the large fighter, and its top speed was only 274.4mph, 35 mph slower than expected. It was also unstable in low speed turns and suffered from tail flutter at higher speeds. Part of the problem turned out to be with the carburettor air intake, which had been designed for a different engine, and with a larger intake the Mercury produced more power. In August the modified P.50/I reached its expected speed of 310.6mph. However it was still not considered to be entirely satisfactory, and was still undergoing airworthiness trials when the Germans invaded.
The second prototype, P.50/II, evolved into a more capable design, and was eventually re-designated as the P.53 Jastrzab II. It was given an early example of an all-round vision cockpit canopy, with a cut down rear fuselage (although still with cockpit frames). It could carry more fuel, and a 661lb bomb under the fuselage, It was to be armed with the same four machine guns, and two 20mm cannon in the wing roots. However once again it suffered from engine problems. This time the problems were with the Polish designed P.Z.L. Waran radial, which was meant to produce 1,200-1,400hp, allowing the P.50/II to reach 347.9mph. However the Waran was behind schedule, and so a 1,375hp Bristol Hercules engine was selected to test the prototype.
By this point the Air Force was beginning to lose trust in the radial engine, and work began on a version of the P.50 that would have been powered by the 1,000-1,200hp Hispano-Suiza 12Y and 1,400-1,600hp 12Z inline engines. By the spring of 1939 this version of the aircraft had been designated as the P.56 Kania (Kite). However this project may have been cancelled in the summer of 1939 in favour of another, rather obscure P.Z.L. design.
In the spring of 1939 General Rayski was replaced as head of the air force by General Zajac. He decided to cancel production of the P.50, although did allow work to continue on 30 aircraft that had already been started at P.Z.L.’s W.P.1 factory at Okecie. One of these aircraft was being given a 870hp Gnome-Rhone 14Kirs radial engine when the Germans invaded. A series of other engines were also considered including the Pratt & Whitney Twin Wasp, but none of these ideas had produced anything when the Germans invaded.
When the Germans invaded Jerzy Widawski, the P.Z.L. factory test pilot, attempted to fly the prototype to Lwow, but it was shot down by a Polish anti-aircraft gun. The five pre-production aircraft that were most advanced were later taken by the Germans, but probably only to be scrapped.
Estimates for Jastrzab A
Engine: Bristol Mercury VIII nine cylinder air cooled radial engine
Power: 810-840hp
Crew: 1
Span: 31ft 10.75in
Length: 25ft 3in
Empty Weight: 3,747lb
Gross Weight: 5,511lb
Maximum Speed: 310.6mph at 14,107ft
Range: 466 miles
Guns: Four 7.7mm KM Wz 36 machine guns