Design and development
The history of the PZL P.7 began in 1928, when a talented designer named Zygmunt Puławski designed an all-metal, metal-covered monoplane fighter, the PZL P.1. It introduced a high gull wing, giving a pilot an optimal view. The wing design was called the "Polish wing" or "Pulawski wing." The P.1 was powered by an inline engine and developed a speed of 302 km/h. But it remained a prototype because a decision was made to use a licence-produced radial engine in the Polish Air Force fighters. So the next model, the PZL P.6, flown in August 1930, was powered by the Bristol Jupiter VI FH radial engine. Both aircraft were well received in the aviation world, with the press recognizing the P.6 as one of the world's top fighters; it won the American National Air Races in August–September 1931.
The PZL P.6 did not enter production because the next variant, the more advanced PZL P.7, was developed. The first prototype was basically the P.6 with a more powerful Bristol Jupiter VII F engine. Due to the use of a supercharger, it had better performance at higher altitudes. The prototype P.7/I was first flown in October 1930 by Bolesław Orliński. Initially, engine cylinders had individual cylinder clearance fairings. After some changes, most noticeably adding a wide Townend ring to the engine and making the tail slimmer, the second prototype P.7/II, built in autumn 1931, was accepted for production with the designation P.7a. It also featured a redesigned wing with slightly increased span, taken from the PZL P.8, and shorter ailerons and smooth upper surfaces, instead of ribbed ones.
The first series P.7a planes were built in mid-1932. The whole series of 149 (plus two prototypes) was completed in 1933. They carried military serial numbers 6.1 to 6.150 (the first prototype P.7/I had no assigned number). The Polish Air Force received the P.7a in 1933.
After designing the P.7, Puławski started to develop his design with more powerful engines, and the result was the PZL P.11, built in a production series. Puławski was an inline engine fan, designing a new fighter, the P.8, with a slim silhouette, powered with an inline engine. It was able to reach a speed of 350 km/h. A planned variant was to be designated the P.9. Unfortunately, in March 1931, Puławski died in an air crash, and the inline engine fighter design was cancelled in favour of the radial engined P.11. The P.11 became the standard Polish fighter. In parallel with the P.11, the PZL P.24 export variant was also developed in 1932.
The all-metal, duralumin metal-covered monoplane aircraft was conventional in layout, with braced, high gull wing and fixed undercarriage with a rear skid. The two-spar wing of trapezoid shape, thinner by the fuselage, was covered with a rimmed Wibault type duralumin sheet (upper surfaces were smooth) and supported by two struts on either side. The fuselage was framed in a front section and semi-monocoque in mid- and tail sections, oval in cross-section. In keeping with the period, the pilot's cockpit was open with a windshield. The armament was two 7.92 mm machine guns mounted on the fuselage sides (initially 7.7 mm Vickers E, then re-bored to 7.92 mm). The aircraft was powered by the Bristol Jupiter VII F radial engine (normal power: 480 hp (360 kW), maximum: 520 hp (390 kW) and fitted with a Townend ring and two-blade propeller. A main 290 l fuel tank in the fuselage, behind the engine, could be dropped in case of fire emergency. The second fuel tank was 7 l.