For the first time, the prototype of the future Aerocobra XP-39 took to the air on April 6, 1939 (test pilot Jimmy Taylor). An experienced, still unarmed aircraft reached a speed of 628 km / h.

The unusual layout scheme - the placement of the engine behind the cockpit near the center of mass gave the aircraft obvious advantages over the traditional layout:

• Such a scheme made it possible to obtain a very maneuverable aircraft, since the moments of inertia were significantly reduced during the evolution of the aircraft.
• The empty nose compartment made it possible to place a powerful 37mm automatic cannon in it.
• The three-post landing gear with a nose wheel made it possible to taxi on the ground at much higher speeds, take off and land even on muddy ground, without fear of nose-over, which was inherent in almost all fighters of the classical scheme. However, it is obviously impossible to apply this scheme with the front engine, due to the lack of space for cleaning the nose strut.
• Provide good visibility for dogfighting. The absence of an engine in the nose of the aircraft made it possible to push the cockpit forward somewhat and at the same time improve the aerodynamics of the forward fuselage.

The new fighter was also distinguished by very good aerodynamics. The water and oil coolers were installed inside the wing rather than in the protruding fairings. Cooling air was supplied to them through holes located in the toe of the wing.

The first P-39S (40-2971) took off in January 1941. Earlier (April 13, 1940), according to the results of prototype tests, the British ordered no less than 675 aircraft. Aircraft began to arrive in Britain in July 1941. The British fighter was similar to the P-39D, but the American 37 mm gun had an extremely low rate of fire, the British replaced it on their models with the 20 mm British Hispano gun. The results of the overflight in England showed that the fighter was useless for the RAF. The first assault strike revealed 19 deficiencies, including high levels of carbon in the cockpit when firing a machine gun, compass errors after firing a cannon (reducing metal after firing changed its setting), an unacceptably long takeoff run (686 meters), a maximum speed of 53 km /hour is lower than stated. Immediately after their commissioning, it became clear that the decision to remove the turbocharger from the engine was wrong, since the aircraft had insufficient rate of climb and unacceptable high-altitude flight characteristics. Only about 80 machines from the entire order were adopted by the Royal Air Force, which already in March 1942 re-equipped their fighter squadrons with Supermarine Spitfire aircraft. On the other hand, more than 250 aircraft, in accordance with the military assistance program, were delivered by Britain to the USSR Air Force (212 aircraft were transferred, 54 were lost at sea), about 200 aircraft at the end of 1942 were used in British aviation and almost 200 aircraft were re-acquired US Air Force after the country entered World War II in December 1941.

Armament of the aircraft was quite diverse, depending not only on the modification, but also on the series of the aircraft. As a rule, it consisted of a 20 mm caliber gun (60 rounds) or 37 mm caliber (30 rounds), two synchronous 12.7 mm caliber machine guns (200-270 rounds each) and four 7.62 mm wing machine guns (500 rounds each). -1000 rounds). On the P-39Q modification, instead of four wing machine guns, two were installed, but of 12.7 mm caliber, placed in fairings under the wing. On some series of Airacobras, there were no wing-mounted machine guns. Bow large-caliber machine guns were installed in such a way that their breech went into the cockpit, which allowed him, if necessary, to carry out manual reloading. The holes in the front wall of the cockpit, through which the breech of the machine guns passed, were closed with a leather partition with a zipper to prevent cold air from entering during the flight. This design did not effectively protect the pilot from powder gases when firing from cannons and machine guns. To prevent the alignment of the aircraft from changing too much during firing, the links of the machine-gun belt, together with the spent cartridge cases from the cannon and nose machine guns, were accumulated in special compartments in the lower part of the fuselage, and were removed from there already on the ground.

Wing machine guns of 7.62 mm caliber were shifted relative to each other for the convenience of placing supply hoses and links. In front, the machine-gun compartment was sometimes closed with a cloth partition, put on the barrel casings and fastened with buttons to the spar. On aircraft of modification N, the wing machine guns were covered with steel welded casings. To prevent freezing in flight, hot air from radiators was supplied to the machine guns through flexible hoses. The power of the wing machine guns was carried out using a crumbling link belt. Cartridges and links were ejected into the air through the sleeve and link outlets. On the machines of the first series, the holes for ejection of cartridge cases and links were closed with spring-loaded hatches, which were opened by cables only at the moment the machine gun was reloaded when fired. In subsequent series, these hatches on the R-39 aircraft were abolished. On some series, a film machine gun was placed in the right wing.

Before the end of mass production, 9558 Airacobra fighters were assembled.

Read more

• Pilot`s Flight Operating Instructions for Army Model P-39Q-1 Airplane
• Disadvantages of the P-39 "Airacobra"
• P-39 "Airacobra" in the USSR
• P-39 Airacobra on the Soviet - German Front

P-39 modifications

• In 1941-1942. production focused on the P-39D-1, D-2, D-3, and D-4 variants. All of them could carry an outboard gas tank with a capacity of 284 liters or a bomb of 227 kg caliber under the fuselage. They were equipped respectively with a fork and a 20-mm M-1 cannon, a V-1710-63 engine (with a power of 1325 hp), armored water and oil coolers (as on the first D-series aircraft), two cameras in the tail section fuselage. There were such shortcomings as the lack of heating of machine guns at high altitude and the release of oil from the propeller gearbox onto the cockpit canopy.
• The P-39E tested a laminar flow wing, which was then used on the P-63 Kingcobra.
• The P-39F variant, built in 229 copies, had an Aeroproducts propeller; (replacing the Curtiss) and a 12-pipe exhaust device, first introduced on the P-400.
• G/H/I variants were not built, but there were 25 examples of the P-39J modification, basically similar to the F variant, but with automatic control of engine boost pressure.
• 210 P-39Ks and 250 P-39-Ls were delivered, ordered as variant G but with minor differences and powered by a 1325 hp Dash-63 engine. (988 kW).
• The next 240 of the ordered G-series were built as the R-39M with the engine; providing the best high-altitude performance, but with worse performance at low altitudes.
• The first truly massive modification was the R-39N (2095 machines were produced). Almost all of them were sent to the Soviet Union, where they were popular due to the reliability of the design and the ability to return after receiving multiple battle damage. Most of the machines had four wing-mounted fuel tanks supplied as an additional set. If a longer range was not required, low-altitude performance could be improved accordingly. The rear armor plate was replaced with curved bulletproof glass, and in general the takeoff weight of the aircraft was reduced from 4128 to 3969kg.
• The main production variant was the P-39Q (4095 produced). At the same time, the total release of "Airacobra" reached 9558 aircraft. On the sub-option (Q-1), instead of four wing machine guns, two 12.7 mm machine guns were installed in underwing gondolas. Fuel capacity and booking weight remained the same, but some sub-options had four-bladed propellers. Starting with the Q-20 sub-variant, wing machine guns were often not installed: Soviet specialists considered the presence of one 37-mm cannon and two 12.7-mm machine guns to be sufficient and appreciated some increase in flight performance and maneuverability more.

Photo	Description
	Drawing P-39N-1
	Drawing P-39 modification
	Bell P-39 Airacobra, 601 Sqn AuxAF-RAF, Duxford 1941

Bibliography

• "Encyclopedia of military engineering" /Aerospace Publising/
• "American Warplanes of World War II" /under cor. David Donald/