The P.Z.L. P.11 Jedenastka

Poland
Poland

side viewfront viewunder view

The Jedenastka (= Eleventh) of P.Z.L. (Panstwowe Zaklady Lotnicze = National Aviation Establishment) was a monowing fighter based on the P.Z.L. P.7 of 1930. The design of the P.11 was a direct result of the fact that Poland had secured a license to build Bristol Mercury radial engines. The new engines offered more output/power combined with a smaller diameter, and the military wanted to take advantage of that.
Work on the P.7 prototype powered by 1 × Bristol Jupiter radial was underway, and the Polish government contacted P.Z.L. to develop a fighter based on the P.7, but powered with the Bristol Mercury. Redesign of the fighter was started by Zygmunt Pulawski as the P.11 with a structure stressed for an engine in the power range between 500 hp (373 kW) and 700 hp (522 kW), and a diameter not wider than 4 ft 3.5 inch (1,31 m). Unfortunately, Pulawski died in March 1931, but the work was continued by Wsiewolod Jakimiuk.
Early in 1931 P.Z.L. began the construction of one static test airframe and three flying prototypes. Because of delays in the delivery of the first Mercury engines from the UK, P.Z.L. completed the P.11/I first prototype with the powerplant of 1 × Gnome-Rhône (Bristol) Jupiter 9Asb radial, rated at 515 hp (384 kW) enclosed in the same type of cowling as used on the P.6 half-brother of the P.7. This aircraft made its first flight in August 1931, and by comparison with the later production standard had a wing of smaller span. The P.11/I recorded a maximum level speed of more than 186 mph (300 km/h), and soon attracted the attention of countries already considering a purchase of the P.7.
The P.11/I was therefore moved by rail to Rumania in December 1931, and evaluation in this country led to an order for 60 aircraft. A contender which failed to secure an order was the indigenously designed IAR 12 fighter with a Hispano-Suiza engine. The prototype was then moved to Turkey for evaluation by that country’s air force against American, British, Czechoslovak, French and Italian fighters. The P.11/I was declared winner, but financial problems then led the Turkish air force to postpone its order. Portugal also expressed an interest in the type as its engine was also being built under license in Portugal, and bought the P.11/I prototype while starting negotiations for the purchase of an initial five airframes and then a further 45 airframes. More proof of the success of the P.11 in 1932 are negotiations with Czechoslovakia for license-built aircraft, Greece for 24 aircraft, Japan for imported and license-built aircraft, Sweden for 20 aircraft, and Yugoslavia for an unspecified number of aircraft. Because of the world economic situation, however, Poland could not offer export credits and had to insist on payment in hard currency, so a number of these deals fell by the wayside or were postponed to the later P.24 fighter.
The P.11 was based on the same airframe as the P.7, therefore it was a gull-winged monoplane with a largely Dural structure and fixed tailskid landing gear. The circular-section fuselage was built in two sections: the forward half had a skinning of Dural sheet over a Dural and steel framework while the rear half was a Dural semi-monocoque structure. This basic unit carried the flying surfaces, which comprised a plain tail unit of Dural construction with a strut-braced horizontal surface, and the gulled wing of Dural construction: the wing extended from the upper fuselage at a sharp dihedral angle and with increasing thickness and chord, and then flattened into outer panels that were tapered in thickness and chord, carried trailing-edge ailerons, and were braced on each side to the lower fuselage by parallel struts. The airframe was completed by the fixed tailskid landing gear, which included a main unit of the divided type with each half based on a Vee strut and a P.Z.L. oleo-pneumatic shock absorber located inside the fuselage.

Version list:

Further pictures:

P.Z.L. P.11c on the ground
P.Z.L. P.11c on the ground

P.Z.L. P.11c on an airfield, in a line-up
P.Z.L. P.11c on an airfield, in a line-up

Polish P.Z.L. P.11's while on a courtesy visit to Sweden before the War
Polish P.Z.L. P.11's while on a courtesy visit to Sweden before the War

 

Technical data on the P.Z.L. P.11c
Powerplant 1 × Skoda (Bristol) Mercury VIS.2 radial, rated at 645 hp (480.84 kW) Role during war
  • Fighter
Length 24 ft 9.5 inch Height 9 ft 4.5 inch
Empty weight 2529 lb Operational weight 3593 lb typical,
3968 lb max
Wing Span 35 ft 2.5 inch Wing Aspect ratio 6.42
Wing Area 192.68 sq ft Service ceiling 26245 ft
Maximum speed 242 mph at 18045 ft Cruising speed unknown
Initial climb rate Climb to 16,405 ft in 6 min 0 sec Range 435 miles typical
Fuel capacity internal 72 Imp gal (86 US gal) Fuel capacity external -
Machine guns
  • 2 × 0.303 inch KM Wz.33 fixed forward-firing in the sides of the nose, 500 rounds each
  • 2 × 0.303 inch KM Wz.33 fixed forward-firing in the wing leading edge, 300 rounds each (in about one-fifth of all aircraft)
Cannons -
Bomb load Up to 110 lb of disposable stores carried on four underwing hardpoints, rated at 27.5 lb each. General disposables load consisted of:
  • 4 × 27.5 lb bombs
Torpedoes/rockets -
Crew 1Naval or ground based Ground
First flight (prototype) August 1931 Operational Service Fall 1934 - 1942
Manufacturer Panstwowe Zaklady Lotnicze Number produced About 338 total, 175 this version
Metric system
Length 7.56 m Height 2.86 m
Empty weight 1147 kg Operational weight 1630 kg typical,
1800 kg max
Wing Span 10.73 m Wing Aspect ratio 6.42
Wing Area 17.9 m² Service ceiling 7999 m
Maximum speed 389 km/h at 5500 m Cruising speed unknown
Initial climb rate Climb to 5.000 m in 6 min 0 sec Range 700 km typical
Fuel capacity internal 326 liters Fuel capacity external -
Machine guns
  • 2 × 7,7 mm KM Wz.33 fixed forward-firing in the sides of the nose, 500 rounds each
  • 2 × 7,7 mm KM Wz.33 fixed forward-firing in the wing leading edge, 300 rounds each (in about one-fifth of all aircraft)
Cannons -
Bomb load Up to 50 kg of disposable stores carried on four underwing hardpoints, rated at 12,5 kg each. General disposables load consisted of:
  • 4 × 12,5 kg bombs
Torpedoes/rockets -

Here is a quick overview of all different versions, without the full technical specifications:

Different versions of the P.Z.L. P.11  Jedenastka
P.Z.L. P.11 prototypes The story of the first prototype is already covered more or less in the introduction of this page. This aircraft was designated P.Z.L. P.11/I. The P.11/II second prototype was completed in the fall of 1931, powered by 1 × Skoda (Bristol) Mercury IVA engine, rated at 530 hp (395 kW), which was enclosed in a long-chord wing cowling carrying flush exhausts. Engine cooling problems delayed its first flight to December of the same year, when the type’s two-blade metal propeller was fitted with a P.Z.L.-developed propeller spinner with cooling louvers. Another incorporated change before the first flight was the incorporation of a pilot’s headrest with a long fairing along the upper part of the rear fuselage. In 1932 this fairing was shortened to the length used in the first two production models of the P.11.
The P.11/II was put through a rigorous evaluation by the Polish authorities, for a time was re-engined with the Gnome-Rhône (Bristol) Mercury IVS radial, and was used for tests with Bristol, Chauvière, Letov, Ratier and Szomanski propellers among others. The P.11/II also secured notable successes in the course of international air meetings and in the summer of 1932: while in Paris to arrange the appearance of the prototype in the forthcoming Salon International de l'Aéronautique, the managing director of P.Z.L. received the free offer of a French engine. This was the Gnome-Rhône 9K Mistral radial, rated at 500 hp (373 kW), and the offer was made by Gnome-Rhône in an effort to give the fighter a more Gallic ‘feel’ and therefore make it more attractive to the French air ministry, which was considering the negotiation of a license for French manufacture of the P.11 fighter.
The P.11/II was accordingly revised with the Mistral engine enclosed in a cowling similar to that of the P.7a and driving a three-blade Gnome-Rhône metal propeller, spatted wheels and a number of other small refinements. The revised prototype was exhibited at the 1932 Salon, and in this form was essentially the precursor of the P.11b series being planned for Rumania.
By this time the P.11 had been provisionally selected for the Polish air force, and the prototype for this service’s aircraft was the P.11/III that first flew in June 1932 and was subsequently revised with a cowling that incorporated an exhaust collector ring in its leading edge. The P.11/III was comprehensively evaluated in the spring of 1933, and was then ordered into production for the Polish air force, which agreed to defer its receipt of production aircraft so that a pressing order for the Rumanian air force could be completed first.
Number built: 3
P.Z.L. P.11a Only 30 aircraft were built and delivered of this version. It was armed with 2 × 0.303 inch (7,7 mm) KM Wz.33 fixed forward-firing guns, 700 rounds each. Powerplant consisted of 1 7t Skoda Mercury IVS.2 radial, rated at 497/517 hp (370/385 kW), and driving a wooden two-bladed Szomanski fixed-pitch propeller. Internal fuel capacity was 67 Imp gal (81 US gal, 307 liters). Of this amount 65 Imp gal (78 US gal, 294 liters) was contained in the main fuselage tank, which could be jetisoned in an emergency. Dimesnions were: 35 ft 2.5 inch (10,72 m) wing span, 23 ft 9.5 inch (7,25 m) length, 8 ft 10.25 inch (2,69 m) height, 2,461 lb (1.116 kg) empty weight and 3,483 lb (1.580 kg) max ake-off weight
Number built: 30
P.Z.L. P.11b This was the initial export version destined for Rumania. The order was for 50 aircraft, including the P.11/II prototype adapted to full production standard. It was powered by 1 × Gnome-Rhône or IAR (Gnome-Rhône) 9K Mistral radial, rated at 525 hp (391 kW) at optimum altitude. The last 30 aircraft to be delivered received a revised cowling incorporating an exhaust collector ring in its leading edge
Number built: 49
P.Z.L. P.11c The P.11 was designed and developed in parallel with the P.24 which was intended for export. The P.11c benefited of this, showing a number of changes to previous models that were similar to the P.24, like: the engine was lowered, the pilot's seat was placed further back and set higher, and the wing which had thinner inner sections incorporating a larger cut-out on the trailing edge, a different angle of incidence, and slightly increased dihedral. These latter changes were meant to improve the pilot's view from the cockpit. Other changes consisted of the addition of 2 × 0.303 inch (7,7 mm) KM Wz.33 fixed forward-firing guns in the wing leading edges. the relocation of the two existing guns to a higher position, the addition of provisions to carry four light bimbs under the wings, a longer fairing for the pilot's head rest, and a revised tail unit with a fixed in stead of a variable-incidence horizontal surface and a vertical surface of a different shape and greater aspect ratio.
Number built: 175 + 28 by Rumania (IAR)
IAR P.11f Rumania had already secured a license to build the P.11b by IAR, but the improvements on the P.11c were substantial. The license was changed to enable IAR to build an indeginous version of the P.11c, powered by 1 × Gnome-Rhône 9Krse Mistral.
Number built: about 80
P.Z.L. P.11g Right before the War production of the P.11 was to be reinstated to allow Poland an improved version of the fighter that could be built quickly. Powerplant would have been 1 × Bristol Mercury VIII, rated at 840 hp (626 kW). However, less than three weeks later the invasion of Poland by Germany was a fact, and the new version was never built.
Number built: 0

Operational remarks:

By all means the P.11 was obsolescent when the War broke out. 12 Polish fighter squadrons were equipped with the fighter, and were used galantly, with courage, when the German Molog unleashed it's power in September 1939. It was no use, the enemy forces were too strong and well-equipped, and the P.11 fighters suffered heavy losses. Nevertheless, the P.11 scored 125 Kills against the Luftwaffe, and lost 114 in the process.
Later, when the Soviet Union also invaded Poland some fighters were evacuated to Rumania, where they were impressed for service.
When Germany launched it's offensive against the Soviet Union in July 1941, Rumanian forces fought on the Axis side. 5 Squadrons of Rumania were still equipped with the P.11, but they never entered the offensive. In stead, they were used for home defense and fighter training up until 1942.

Strengths:

Weaknesses:

 

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© by Frans Bonné, 2000
Last revision: 9/23/01