PZL P.24 A-G

The PZL P.7 was first flown by Orlinski in October 1931, at Mokotow airfield in Warsaw. It was fitted with a 520 hp engine providing 70 hp more than the P.6 and was capable of a maximum speed of 317 kph (197 mph) at 4,000 m (13,123 ft.). After intensive testing of two P.7 prototypes some modifications were made and the design was sent to production. The wings and control surfaces were fitted with a new type of corrugated skin. Out of 150 P.7a planes ordered by the Polish army the first were ready in the fall of 1932 and the last were delivered in November 1933. With the P.7 the Polish air force became the first in the world to be equipped with an all-metal fighter plane.
It was assumed at the beginning of the Thirties that the average speed for fighter planes would increase by 10 kph /year and the Department of Aeronautics was aware of the fact that as soon as a fighter was introduced its successor would have to be on the drawing board. When Bristol designed the new Mercury engine developing 600 hp in 1930, which Poland had the rights to build, the Department of Aeronautics ordered the P.6 to be adapted to this engine. During production of its prototype, designated P.11, in March 1931, Pulawski was killed in an accident while flying the PZL.12 amphibious plane, also one of his designs. Further work on the PZL P.7 and P.11 was directed by Wsiewolod Jan Jakimiuk, Pulawski's deputy. Jakimiuk emigrated to Canada after the war and designed the DHC-1 Chipmunk training plane in 1946 (1,292 built), the DHC-3 Beaver transport plane in 1947 (1,718 built). In 1948 he designed the DH.112 Venom sea fighter plane for England (381 built) and in France the SE 5000 Baroudeur fighter plane.


P24  z7

The first PZL P.11 prototype was similar to the P.6 and was flown for the first time by Orlinski in August 1931. The P.11 was modified to reflect advances made on the P.7 and newer prototypes were tested for the next two years (since the P.7a had just entered service, there was apparently no need to speed up development). When Romania showed interest in buying a fighter from PZL a fourth prototype, the PZL P.11/IV, was fitted with a 550 hp Gnôme Rhôme K9 and sent to the Paris Salon in December 1932. At the beginning of 1933 the Polish Ministry of Army Affairs ordered 50 P.11a fighters, while in April Romania ordered fifty P.11 fighters with the Gnôme-Rhône K9 engine. The decision was made to give the Romanian order for fifty PZL P.11b fighters priority over the order from the Polish government. The first forty-nine P.11b fighters and plans for the P.11f (to be built under license) were delivered in the first quarter of 1934. An improved version, the P.11c was built in a series of 150 fighters between the fall of 1934 and the summer of 1936. Romania built ninety-five P.11f fighters between 1937-38. The last stage of development for the P.11 was the P.11g Kobuz prototype with a 800 hp Mercury VIII engine, and production was scheduled to begin in the fall of 1939.

P24  z8

The PZL P.24 fighter plane
Foreign interest in Pulawski's fighter planes led to the development of special versions for export. Obviously the Bristol engines couldn't be used, since the British didn't want their newest technologies to be sold abroad, and declined to allow Poland to sell licensed engines. France, on the other hand, was very willing to sell its newest engines, and so the Gnôme-Rhône was chosen as the export engine for PZL fighter planes. For Gnôme-Rhône it was a chance not only for export. They hoped that the PZL fighter would be chosen for the French army air force and their orders would grow. In the spring of 1932 the director of PZL, Witold Rumbowicz, while in Paris, received a formal proposal from Gnôme-Rhône to use their engines in Pulawski's fighters. Gnôme-Rhône gave Rumbowicz an engine for fitting in a prototype which Wsiewolod Jakimiuk, head of design since Pulawski's death, would adapt for the P.7 and P.11. The new plane was assigned the number P.24 and was fitted with the 14 cylinder 760 hp Gnôme-Rhône 14Kds. Construction of the first prototype began in July 1932.
Much of the P.24 prototype came from the P.7a already in production. Unchanged were the wings, rear fuselage, horizontal stabilizers and elevators, rudder and vertical stabilizer. The undercarriage was slightly raised to accommodate the changes made to the forward end of the fuselage and the increased weight and speed of the plane. To correctly locate the center of gravity with the heavier engine, a 45 cm section was added between the wing mounts and the cockpit. The cockpit was redesigned and the pilot's seat was raised 50 mm. The wings were not strengthened, as static trials showed that the wing could withstand an ultimate load factor much greater than the required 12.8. With a total weight of 1,420 kg the wing's limit load factor was 19 and at a factor of 12.8 would have been acceptable for a plane weighing 2,100 kg. A slight modification was made to the wing by thinning it at the fuselage to fit a machine gun mount and the P.7 flaperons were eliminated. Because a 14 cylinder engine doesn't have gaps between the cylinders it was impossible to mount machine guns on the fuselage, as on the P.7 which had barrels fitted between the cylinders. With the mounting of two Swiss-made 20mm Oerlikon canon the P.24 was one of the most advanced fighter designs of its day. Flaperons were adapted from the P.1 (which were shorter than those on the P.7) and could be used as flaps to reduce the take-off and landing speed. A larger stabilizer was developed to compensate for the more powerful engine and longer fuselage and the oil shock absorber on the tail skid was changed to a rubber one.

P24  z9

Boleslaw Orlinski first test-piloted the P.24/I prototype in May, 1933, at Mokotow airfield in Warsaw. An interesting note is that although the plane belonged to PZL it was painted in the khaki color of the Polish air force, and carried the red and white checkerboard military insignia. This resulted in the "myth" that the Polish air force actually put the PZL P.24 into service, which is untrue, and the national insignia were later removed. During the first flight Orlinski achieved a climb rate of 12 m/s (2,340 ft/min) but flew too long at full throttle with the supercharger running and as a result of the vibrations the wooden propeller cracked and broke off. When Orlinski landed the mechanics found that only one of the engine mounts was still holding. Both the engine and airframe needed over­hauling. During subsequent trials fairings were mounted on the wheels, a pitot tube was mounted under the wing and ventilation openings were introduced to the front of the fuselage underneath the exhaust manifold. Flight testing on that prototype ended in February, 1934.
The PZL P.24/II was fitted with a Gnôme-Rhône 14 Kfs engine which output a nominal 900 hp and maximum 930 hp. At first a two blade wooden propeller designed by Szomanski was mounted, later to be replaced by a Gnôme-Rhône metal three blade propeller. It was test flown in June, 1934, by Orlinski and named the "P.24. Super" On June 28, 1934, Orlinski set a new world speed record for radial engine fighter planes overseen by the FAI. At first a speed of 404 km/h (251 mph) was announced but when adjustments for atmospheric conditions were made a speed of 414 km/h (257 mph) was officially given. Orlinski later reached 416 km/h (258.5 mph). During flight testing it turned out that the oil was overheating and a cooler was added to the fuselage under the starboard wing and in the summer of 1934 the armament was installed. Two Vickers 7.9 mm machine guns were mounted forward of the cockpit and two 20 mm Oerlikon cannon were mounted in fairings under the wings.


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