PZL P.11 – Polish fighter aircraft constructed by engineer Zygmunt Puławski from the period before World War II. Manufactured in Poland at the PZL plant in 1934–1936, as well as under license at the IAR plant in Romania. It was a single-seater high-wing metal structure, with an open cab and an external chassis, driven by a star engine. At the time the service was handed over in 1935, it belonged to the world leaders in terms of modernity, but in 1939 the new German aircraft significantly gave way. Despite this, in the most numerous version P.11c was a popular Polish fighter during the defensive wars in 1939. Colloquially called the “eleven”, it is considered the symbol of Polish military aviation in the September reference period [1]. P.11a and P.11c fighter planes used 12 fighter squadrons out of 15 owned, being part of the Pursuit Brigade and army aviation. Used additionally in combat on the Eastern Front of World War II by Romanian aviation, which also took over some Polish aircraft. In total 350 aircraft were produced, including 200 serial for Polish aviation and 145 for Romanian.
At the turn of the 1920s and 1930s, in the newly established Państwowe Zakłady Lotnicze in Warsaw, Eng. Zygmunt Puławski constructed a series of large, all-metal fighter aircraft, starting with PZL P.1 from 1929 with an in-line engine [2]. Their characteristic feature was the arrangement of the high-wing strut with the wing patented by Puławski, known as Puławski’s wing. The wings were bent down at the fuselage, connecting to it, and at the junction were narrowed and thinned, accessible completely visible to the pilot [3]. The durable scissor chassis with shock absorbers hidden in the hull was also patented [3]. P.1 aroused interest in the world, Connect like another PZL P.6 model with a 1930 star engine, but both remained prototypes [4]. In the 1930 component, the PZL P.7 model was flown with a 520 HP Bristol Jupiter VIIF star engine, selected for Polish aviation equipment and produced in 1932–1933 [5]. It should be mentioned equally that the use of star engines deteriorated visibility to the front, eliminating the advantages of Puławski flakes [4]. The successful presentation of P.6 at the Paris salon in December 1930 was the endeavor of leading machine manufacturers to use them on a Polish aircraft, so in January 1931 the management of PZL decided to develop two new models in parallel, initially for export: P. 11 with a more powerful Bristol Mercury star engine and PZL P.8 with an in-line engine [6].
PZL P.11 was a strengthened and improved development of the P.7 model, with a stronger engine and other changes. After the death of Puławski in an air accident on March 21, 1931, his colleague, Eng. Vsevolod Jakimiuk [7]. Aerodynamic and related calculations for PZL P.11 calculations were performed by Eng. Piotr Bielkowicz [7]. In the course of development, five prototypes were created with different engines, reworked several times. The first prototype (P.11 / I) was flown in August 1931 by Bolesław Orliński [7]. He received the French Gnome-Rhône Jupiter VII 9Asb engine with a power of 480 hp, for users of French engines [8]. I was similar to P.6, from which it differed primarily improved wing, devoid of protruding combs on the surface of the surface due to changes in riveting technology, and then the hull and tail were the same [a]. This prototype was presented at the end of the year in Romania and Turkey [9]. In November 1931, an attempt was also made on a statistical payer, with the participation of the Romanian delegation, with very good destructive activities [6]. In publications reported that the first prototype was delivered to Portugal in August 1932, but is not covered by this newer literature [b].
Construction
All-metal stringer wing. The hull with a circular cross-section in the front part, elliptical to the rear, covered with a smooth dural sheet [51]. In P.11a and b, the front truss section, and the middle and rear half-shell; in P.11c and f the front and middle part behind the pilot’s cabin in the form of a multi-span truss, and the rear half-shell [52]. Hull covering in the truss area from removable sheet metal panels [51]. In P.11c behind the cabin on the left side of the radio hatch, and above the trunk in the fairing [51]. One-seat pilot cabin, open, with a seat adapted to the parachute seat. The arm suspended on a cross arm, it could be lifted within 110 mm [53]. The edge of the cab cutout is protected by a leather roller, behind the pilot’s head a leather headrest [53]. Windbreak composed of four organic glass panes [53].
The wing is “Puławski’s patch” or “Polish patch.” Contour of the double trapezoidal lobe, with rounded tips. Double-girder lobe, with 16 ° hull rise and 1 ° in the outer parts [51]. Bartel 37IIa panel profile modified, with varying thickness over the span [51]. Split flap, halves attached to the hull truss, supported by two drop-shaped braces. Finishing with sheet metal according to the improved Wibault patent [51]. The wings had Frize type shuttles [51]. Classical formation, covered with sheet metal; horizontal stabilizer supported by jacks [53]. In P.11c and f balancing flaps at height controls [53].
Classic aircraft landing gear, fixed with tail skid. Shaving of the V-shaped main chassis, in scissor system, with cushioning inside the hull, stiffened with single rods from the ends of the lever inside the hull to the wheel hubs [54]. Drum brake wheels, Stomil tires, 750 × 150 mm [54]. The main fuel tank with a capacity of 320 l (P.11c) was located in the fuselage behind the engine, supported from below by a belt, it could be thrown out in case of fire hazard [54]. In P.11a, the tank had a capacity of 294 l [55]. In the left wing near the fuselage there was a drop-down fuel output tank with a capacity of 11 l [54]. The 27-liter oil tank was mounted inside the hull in front of the fire wall, on the starboard side there was an oil cooler [54].
Drive
9-cylinder radial engines, air-cooled, with compressor and reducer (nominal / start power) were used:
P.11a: Bristol Mercury IV S2 (Skoda Merkury IV S2) with 525/575 HP (386/423 kW) [12]
P.11b: Gnome-Rhône 9Krsd with 500/515 HP (368/374 kW) [12]
P.11c: Bristol Mercury VS2 (PZL Mercury VS2) with 565/600 HP (416/442 kW) [12]
P.11c (demonstrator): Bristol Mercury VIS2 with 605/645 HP (416/442 kW) [12]
P.11f: Gnome-Rhône (IAR) 9Krse with 560/610 HP (412/449 kW) [12]
The serial aircraft used a two-blade, fixed pitch wooden propeller made by Szomański, with a diameter of 2.8 m in P.11a and b, 3 m in P.11c and 2.9 m in P.11f [54]. Mercury Viet 200 pneumatic motor starter, powered from the cylinder [54].
P.11c – visible hull machine gun and oil cooler
12.5 kg bomb under the wing
Armaments and equipment
The armament consisted of two machine guns mounted in the hull wz. 33 cal. 7.92 mm from the State Armaments Factory (PWU), with a theoretical rate of fire of 1,100 rpm, synchronized with the propeller using the JS-2 synchronizer from Motolux [56]. Initially used were Vickers km km. 7.92mm E with a rate of fire of 650 rpm./56]. The barrels were placed in recesses on the sides of the fuselage, bullets flew through a pipe passing through the fire wall, between engine cylinders [56]. The pilot could manually reload machine guns from the cockpit [56]. Few P.11c had two additional machine guns wz. 33 placed in the wings [56]. Ammunition: P.11a 700 cartridges per km (total 1,400), P.11c 500 cartridges per hull km and 600 cartridges per wing km (1000 or 2,200 in total) [12]. Sighting sights were a circular sight with a cross and a sight in the form of a stand-up collar with a hole with a hole [56]. For practice purposes, it was possible to mount a photo carabiner on the rear strut of the left lobe [56]. P.11c could carry up to four PuW bombs weighing 12.5 kg on four, less often two winged ejectors Świątecki SW [56].
The P.11c aircraft used the N2L / M shortwave transceiver radio structure of the National Telecommunication and Radio Engineering Plant (PZTiR) in Warsaw, enabling communication between airplanes over a distance of 2 km and with the ground at a distance of 10 km [57]. Just before the war, most radio stations were modified, which led to an increase in communication range (up to 100 km with the ground) [57]. According to other publications, the radio range was 10 km between aircraft and 50 km with soil [18]. Antennas extended from the fuselage to the top of the vertical stabilizer and from the stabilizer to the wing tips [57]. Airplanes equipped with a radio had a generator driven by a shaft from the engine gear [54].
Preserved copies
Currently, the only preserved copy of P.11c is in the collection of the Polish Aviation Museum in Krakow. This aircraft, number 8.63, was produced in 1935 and belonged to the 121st Fighter Squadron (side No. 2 and winged 39-K) [58]. Literature is credited with using this aircraft during the September campaign, see pil. To Wenceslaus King [58]. Conquered by the Germans, he was sent to the Aviation Museum in Berlin, and at the end of the war, along with the collection of this museum, he found himself in Poland [58]. From 1964, he was first shown at the exhibition and then at the museum in Krakow [58]. In 1996, after renovation, the engine was started [58].
Small fragments of another PZL P.11c from the 121st Hunting Squadron, piloted by Wacław Król and shot down on September 3, 1939, were found in April 2012 near Kłaj. The found remains of the aircraft are currently displayed in the Municipal Regional Chamber in Kłaj [59].
