The P.Z.L. P.7 was the first domestically designed fighter to enter Polish service and allowed the Polish air force to be the first to convert to an all metal monoplane fighter.
The P.7 was an improved version of the earlier P.Z.L. P.1, the first full aircraft to be designed by Zygmunt Pulawski. This was a high wing monoplane, with a gull wing central section that reduced drag and improve the pilot’s view forward by eliminating the central section of the wing.
By the time the first prototype of the P.1 made its maiden flight, work had already moved onto the P.Z.L. P.6 and P.7, two very similar aircraft, both powered by versions of the Bristol Jupiter radial engine. The P.1 had been powered by an inline engine, but the Polish Air Service preferred radial engined aircraft, and the negotiations were underway to produce the Jupiter in Poland.
Work on two P.6 and two P.7 prototypes began in the middle of 1929. The P.6 used a low-altitude Jupiter VI engine, while the P.7 used a high altitude Jupiter VII.F with supercharger, capable of producing 520hp at 10,000ft.
Although these aircraft looked quite similar to the P.1, most of the aircraft was redesigned. The P.7 kept the scissor type undercarriage of the P.1, which had shock absorbers carried inside the fuselage, began with the same tail, and kept the basic shape of the wing, although with a smaller wing. However the fuselage was totally redesigned to fit the radial engine, replacing the flat sided fuselage of the P.1 with one with a circular cross section. The P.6 and P.7 had very similar fuselages, although the P.7 had some steel elements in the forward part to cope with the high altitude engine. The larger fuselage meant that the fuel tanks could be moved from the wings to the fuselage, but the airframe was still 441lb lighter.
The two P.6 prototypes and the first P.7 prototype used the same fuselage structure, which turned out to be rather difficult to build. As a result the second P.7 used a new design that was easier to manufacture.
The first P.7 prototype, P.7/I, made its maiden flight in October 1929, two months after the P.6/I. The P.7/I used an very effective close-fitting helmeted cowling in which each cylinder head was surrounded by its own individual cover. This was aerodynamically efficient and also worked well for the engine cooling, but was too difficult and expense to produce to be used on the production aircraft.
P.7/II followed early in 1931. It had the improved rear fuselage framework, and a narrow Townend ring similar to the design used on the P.6 prototypes. While the P.6 prototypes were sent to International shows or used to try and drum up export sales, the P.7/II was chosen for airworthiness trials, then went to the Experimental Squadron for Service evaluation.
In the spring of 1931 an order was placed for ten pre-production aircraft. This was followed by a large order for 110 aircraft, and another 29 were ordered in the 1932-33 aviation budget. A total of 150 aircraft were thus delivered to the Polish Air Force. At the same time the Polish Skoda Works in Warsaw received an order to produce 250 of the licence built Jupiter engines.
Production of the pre-production batch of aircraft, with the designation P.7a, began in June 1931. The P.7a had a new Polish developed ring cowling, a revised cockpit, shorter ailerons and a modified tail. It was to be armed with two Vickers ‘E’ machine guns, modified to fire a 7.92mm round.
Production of the first ten aircraft didn’t go well. By October work was quite far advanced, but the fuselages were discovered to be twisted by 30mm, and had to be rejected. A new way of assembling the aircraft had to be developed, and the existing fuselages rejected. The ten pre-production aircraft were finally completed in the Autumn of 1932, but by the end of the year the Air Force had only received them and five aircraft from the main order.
The P.7a finally entered service in the winter of 1932-33 when the first few unarmed fighters were delivered to No.11 Eskadra Kosciuszkowska Squadron of the 1st Air Regiment at Warsaw, to allow for conversion training. The 1st Air Regiment had fully converted to the type by the summer of 1933 and by September 1933 the Polish front line fighter regiments had all converted to the type, making the Polish air force the first in the world to be fully equipped with all-metal monoplane fighters.
The P.7 was soon superseded by the improved P.11, which began to enter service in 1934-35. By the end of 1938 40 were at the training centre at Deblin, but three squadrons (Nos.123, 151 and 162) were still equipped with the P.7 when the Germans invaded.
By this point the P.7 was basically obsolete. The Vickers E guns were increasingly prone to jam in combat. No.123 Squadron used its aircraft in some air battles, but Nos.151 and 162 were used as reconnaissance units.
The P.7 was popular with its pilots, with good handling characteristics and robust construction. However the unreliable Vickers guns turned out to be rather badly placed low down the side of the fuselage, apparently making it more difficult to judge where the fire was going.
About fifty surviving aircraft were evacuated to Romania late in September, and the Germans captured a similar number of aircraft. Those in German hands may well have been prepared for use as a night harassment aircraft on the Eastern Front.
Engine: Polish Skoda licence built Jupiter VII.F supercharged nine-cylinder radial engine
Power: 485hp normal, 527hp max
Span: 33ft 9.75in
Length: 23ft 5.75in
Height: 9ft 0.25in
Empty Weight: 2,226lb
Loaded weight: 3,106lb
Maximum Speed: 197mph at 13,123ft; 190.4mph at 6,561ft; 171.4mph at sea level
Climb rate: 1min 38sec to 3,280ft; 5min 3sec to 9,842ft
Ceiling: 27,147ft (service ceiling)
Range: 348 miles
Guns: Two Vickers ‘E’ Guns, sources disagree on calibre – 7.7mm or 7.92mm both given