PZL.55

PZL.55 was a Polish pre-war project of a fighter aircraft, created at Państwowe Zakłady Lotnicze by Jerzy Dąbrowski. The design was for a single-seat low-wing all-metal monoplane. It was planned that the plane would replace obsolete fighters and lead to a significant increase in the capabilities of Polish Military Aviation.

Design and development
At the end of the 1930s, Polish Military Aviation urgently needed a modern high-performance fighter with strong armament that could put up an equal fight with the latest German designs such as the Bf 109 and Fw 190. In the summer of 1939, the PZL.55 defeated the PZL.53 and PZL.56 designs in the competition for a future fighter aircraft and completed a series of tests in the wind tunnel, giving promising results. The aviation command showed great interest in the PZL.55 project. In August 1939, the design and model of the fighter were approved and two prototypes were ordered. Due to the German-Soviet invasion in September 1939, the implementation of the PZL.55 project was stopped shortly after it had started.

The project was developed using experience with the PZL.26 sports plane and a private sports plane built by Dąbrowski for his own use. It was intended to use several very modern solutions for the Polish conditions at that time. The fighter was to have a fully retractable landing gear with air-oil shock absorbers, and powerful armament consisting of 6-8 machine guns was to be placed in the wings. The rest of the internal wing structure was to be taken up by integral fuel tanks. The wings were also equipped with flaps and automatic Handley Page slats. The wing armament was to be complemented by an autocannon firing through the propeller shaft. A retractable engine coolant radiator was placed under the fuselage, but it is possible that this rather problematic solution would be abandoned in later stages of development. The pilot's cabin was fully adapted to night flights and had heating, air conditioning and instruments for piloting without ground visibility. The plane was also equipped with a transmitting and receiving radio station, an oxygen installation and armored pilot's seat. The windshield was also to be made of thick armored glass. Some of these solutions have already been used in PZL P.24 and PZL.50.

The first prototype PZL.55/I was designed for the Hispano-Suiza 12Y49 inline engine but the final production version was to be powered by the more powerful, license-built Hispano-Suiza 12Z series engines which were still in development at the time. In 1939, Hispano-Suiza provided the PZL with information that the 12Z engines were to ultimately achieve a maximum power of 1,400-1,600 hp. The approved design assumed that such power would translate into a maximum speed of 650-700 km/h, which was an unprecedented speed at that time. Ultimately, the surrender of France during World War II halted development of the 12Z engines and full-scale production did not begin until the end of the war. The Allison V-1710-23 engine was also considered, which, however, was not very realistic because deliveries from the USA would be long, expensive and prone to delays, and the Americans did not license the production of aircraft engines to other countries.