PZL P.11

Origins The history of the PZL P.11 started in 1929, when Polish aeronautical engineer Zygmunt Puławski began work on the design of an all-metal, monoplane fighter aircraft. Before this, the Polish aviation industry had concentrated on the licensed production of foreign-designed aircraft, particularly French; these typically had wooden structures, so Puławski's all-metal approach represented a considerable advance for Polish industry. The initial design produced by Puławski, designated the P.1, had many of the features of contemporary French aircraft of the era; these similarities can be attributed to Puławski himself, who had received a considerable portion of his technical education in France only a few years before. Nevertheless, the P.1 also had a number of original features, including its characteristic monoplane wing design. It demonstrated its outstanding performance compared to contemporary aircraft, such as the British Bristol Bulldog and the French Dewoitine D.27, when it achieved first place at an international air competition held in Bucharest, Romania. The design generated interest around the world; attention was such that the general layout became commonly known as the "Polish wing" or "Puławski wing". This wing had a two-spar duralumin structure, with rivetted ribs to both the spars and skin; the exterior of the wing was covered by finely corrugated duralumin sheet, while the slotted ailerons had a fabric covering. The Polish War Ministry objected to the aircraft's use of the licence-built Hispano-Suiza engine, citing insufficient practicality and poor economic grounds. The first variant of the P.11 to be ordered by the Polish Air Force was the P.11a. From the onset, this was considered to be only an interim model of the type; accordingly, a series of 50 such fighters were constructed. Otherwise similar to the P.7, the P.11a mounted the 575 hp (429 kW) Bristol Mercury IV S2 radial engine, which was produced in Poland under licence. Deliveries of Polish-built P.11bs to Romania commenced in July 1934. They were fitted with Gnome-Rhone 9Krsd Mistral engines, otherwise they were similar to the P.11a. 49 were finally made, the 50th aircraft being P.11f prototype. The Romanians then produced another Polish fighter, the PZL P.24, developed from the P.11 exclusively for export. Greece, Portugal, Yugoslavia, Turkey and Republican Spain were interested in buying the P.11, but finally Bulgaria, Greece and Turkey bought the P.24 instead. However, due to a series of rapid advances and technological development in the field of aviation, the P.11 was considered to have been rendered obsolete by 1939. It had been overtaken in terms of performance by a new generation of fighter aircraft that commonly benefitted from features such as cantilever wings and retractable landing gear; such fighters included the British Supermarine Spitfire and German Messerschmitt Bf 109. Together with the older P.7, both remained the only Polish fighters in service, however, with about 185 P.11s available, distributed within six air regiments and the aviation school in Dęblin. Being aware that the P.11 was now outdated, the Polish Air Force had pinned their hopes on the in-development PZL.50 Jastrząb, which suffered from several delays. When it became apparent that the PZL.50 would not be in widespread service in time for a major conflict that was clearly looming, consideration was given to producing an updated version of the P.11; this was to have been powered by the 840 hp (626 kW) Mercury VIII and have been furnished with an enclosed cockpit, known as the P.11g Kobuz (hobby). Only the prototype of the P.11g with a maximum speed increase to a still-slow 390 km/h (~240 mph) was flown before the war, in August 1939. In light of the unavailability of PZL.50, the only hope of replacing the obsolete P.11 lay in acquiring modern fighters from abroad. In 1939, after receiving the necessary credits, Poland ordered from France 120 Morane-Saulnier M.S.406s, and from Britain, 14 Hawker Hurricane Is (the P.11's chosen replacement), plus a single Supermarine Spitfire I for testing, in addition to 100 Fairey Battle light bombers. However, none of these aircraft were delivered to Poland before September 1939. ==Design==

The PZL P.11 was an innovative fighter aircraft for the early 1930s, with a high-mounted gull wing and an all-metal, metal-covered structure. It also had several relatively conventional features for the era, such as a fixed undercarriage. The P.11 was powered by a number of different radial engines: these included the Bristol Mercury IV S2 (normal: , maximum: 575 hp) of the P.11a, the Gnome-Rhone 9Krsd (550 hp, max: 595 hp) of the P.11b, the Bristol Mercury V S2 (565 hp, max: 600 hp) or alternatively the Mercury VI S2 (590 hp, max: 630 hp) of the P.11c: and finally the Gnome-Rhone 9Krse (560 hp, max: 610 hp) of the P.11f, the ultimate version of the aircraft. The all-metal fuselage of the P.11 was matched to the twin-spar shoulder-mounted wing via bearers mounted on the upper portion of the first and second fuselage frames. ==Operational history==

At the outbreak of the Second World War, on 1 September 1939, the Polish Air Force had 109 PZL P.11cs, 20 P.11as and 30 P.7as in combat units. A further 43 P.11c aircraft were in reserve or undergoing repairs. Only a third of P.11c were armed with four machine guns, the rest had only two, and even fewer had a radio. The P.11 were used in twelve escadrilles (eskadra), each with ten aircraft (two escadrilles constituted a squadron, in Polish: dywizjon). Two squadrons—four escadrilles—were in the Pursuit Brigade deployed around Warsaw, with the rest assigned to various armies. All of them took part in the 1939 defense of Poland. Apart from combat units, several P.11 aircraft, including a prototype P.11g, were used in improvised units at air bases. Some of the German aircraft shot down were later recovered and put back into service. This allowed German propaganda to claim smaller combat losses. The P.11c was also the first aircraft to successfully ram an enemy aircraft in the Second World War. The first large air battle of the war took place in the early morning of 1 September over the village of Nieporęt just north of Warsaw, when a German bomber group of about seventy Heinkel He 111 and Dornier Do 17 was intercepted by some twenty P.11 and ten P.7 fighters, and had to abandon their mission to Warsaw. Attacking head on, the Polish pilots managed to shoot down seven twin-engined bombers, two of them credited to Lieutenant Stanisław Skalski (future Distinguished Flying Cross & Two Bars) for no losses to themselves. Most of the P.11s were destroyed in 1939, though thirty-six were flown to Romania and taken over by the Romanian Air Force. Due to their obsolescence, these veteran aircraft were not used in combat; only a small number were used for training while the rest were dismantled for spare parts. It has been alleged that some aircraft were captured and saw limited use by the Germans. A pair of P.11s were captured by the Red Army and used for testing. One landed in Hungary (near the town of Hajdúböszörmény) and was used as a glider tow plane by the University of Technology in Budapest. ==Variants==

;P.11/I :First prototype of the P.11 fighter, powered by a Gnome-Rhône Jupiter IX ASb. The converted P.11c prototype flew for the first time on 15 August 1939, less than a month before the German invasion, forcing abandonment of the programme. ==Operators==

; • Hungarian Air Force operated one ex-Polish Air Force PZL P.11a evacuated on 23 September 1939. ; • Latvian Air Force operated one ex-Polish Air Force PZL P.11a evacuated on 17 September 1939. ; • Polish Air Force ; • Royal Romanian Air Force ; • Soviet Air Force took over the Latvian machine when they invaded Latvia 17 June 1940, and two more (see above) as war prizes. ==Surviving aircraft==

The sole surviving P.11c aircraft is on display in the Polish Aviation Museum in Kraków. ==Specifications (PZL P.11c with Mercury VI.S2 engine)==