P-39 Airacobra
The P-39 Airacobra was one of America's first-line pursuit planes at the time of the Pearl Harbor attack. It made its initial flight in April 1939 at Wright Field and by December 1941 nearly 600 had been built. The P-39 was one of the first military airplanes with tricycle landing gear. The pilot of the cobra sat on the front end of the gearbox with the engine behind him and the propeller shaft passing underneath his legs. Its unique engine location behind the cockpit caused some pilot concern, but this proved to be no more of a hazard in a crash landing than with an engine located forward of the cockpit. The P-39's spin characteristics, however, could be quite a problem if recovery techniques were ignored.
Bell's chief engineer Robert J. Woods had designed the unconventional plane-its power plant amidships, at the center of gravity, and its cannon in the nose-as a 400-MPH fighter. At Wright Field in the spring of 1939, the unarmed XP-39 prototype (with a turbosupercharged Allison engine, rating 1150 horsepower) flew to a maximum speed of 390 MPH at 20,000 feet. The aircraft reached this speed, however, with a gross weight of only 5550 pounds, thought to be about a ton less than a heavily armored production P-39.
That meant that the existing aircraft, when normally loaded, would have a hard time exceeding 340 MPH. Still, the test performance impressed the Air Corps enough for it to issue a contract, three weeks later, for 13 production model YP-39s. Gen. Henry H. "Hap" Arnold, desperate for a new fighter, hoped that the speed of the airplane could be increased to over 400 MPH by cleaning up the drag. On 9 June 1939 he formally requested NACA approval for immediate testing of the XP-39 in the Full-Scale Tunnel.
The most important work done by the National Advisory Committee for Aeronautics [NACA] during the war was "drag cleanup." Drag is the resistance to airflow. Every engineer or experimentalist since the beginnings of heavier-than-air flight has struggled to minimize it. Between 1938 and 1940, researchers at Langley pioneered a method using its cavernous Full-Scale Wind Tunnel to measure drag and make recommendations to the manufacturer as to how best to correct the problems. The military was so enthusiastic about the results of the "drag cleanup" process -- which helped solve technical problems and was quick and inexpensive -- that it had the NACA test virtually every new prototype.
A good example of the impressive results produced by drag cleanup was the Bell P-39 Airacobra. The aircraft originally had a top speed of 340 mph. After undergoing two months of drag cleanup work, the plane emerged with a new maximum speed of 392 mph. Instead of an expensive and time-consuming complete redesign of the aircraft, the NACA's drag cleanup research showed that minor modifications would enable the P-39 to meet the Army's specifications.
Bell was shown preliminary data indicating that the prototype in a completely faired condition had a drag value of only 0.0150 compared to 0.0316 in the original form. This meant a maximum increase in speed, if all the NACA's suggestions for drag improvement were met, of 26 percent. The NACA realized, of course, that not all of the changes to the configuration studied in the FST were feasible for the production aircraft.
By cuffing the propeller at the point where it met the hub, streamlining the internal cooling ducts of the wings, lowering the cabin six inches, decreasing the size of the wheels so that they could be completely housed within the wing, and removing the turbosupercharger and certain air intakes, the speed of the XP-39 airplane for a given altitude and engine power could be increased significantly. Extrapolating from the same weight airframe to a more powerful (1350-horsepower) engine with a geared supercharger, the NACA estimated that the top speed attainable with the aircraft might be as high as 429 MPH at 20,000 feet.
Bell incorporated enough changes recommended by the NACA to improve the speed of the airplane by about 16 percent. These changes included installation of an engine that could be equipped with a gear-driven supercharger but had only 1090 horsepower - 60 horsepower less than the engine which had driven the unarmed XP-39 to 390 MPH at Wright Field in the spring of 1939 (and 260 horsepower less than that used hypothetically in the NACA paper study).
The Air Corps then resumed flight trials. The less powerful aircraft, redesignated XP-39B, weighed some 300 pounds more than the original, and without the turbosupercharger flew to a maximum speed of 375 MPH at 15,000 feet in the first trials. Both the Air Corps and Bell expressed satisfaction with the NACA results. In January 1940 the Air Corps told Bell to finish the production of the first series of YP-39s without turbosuperchargers. The Bureau of Aeronautics called the NACA report on the XP-39B the "worst condemnation of turbo supercharging to date."
The P-39 story was a disappointment for the NASA Full-Scale wind tunnel. Although some recommendations from Langley were taken which helped to reduce drag, the engine’s turbo supercharger was removed after the test and the airplane weight significantly increased. The original airplane had a top speed of 390 mph, but the production models had top speeds of only 350 mph. The army added a new and bigger power plant and heavier armor plate to the production model. The XP-39E would weigh nearly 9000 pounds. It was referred to as “The Iron Dog”.
The aircraft's deceptively streamlined shape belied a mediocre performance, especially above 15,000 feet. Because its engine was not equipped with a supercharger, the P-39 performed best below 17,000 feet altitude, and it often was used at lower altitudes for such missions as ground strafing. The plane showed reasonable stability and roll rates and maneuverability at low altitudes, which meant it would be useful in ground support as a strafer and fighter-bomber.
Deliveries of the first production model P-39s, which were very similar to the service-test YP-39, began at the end of 1940. In 1941 the United States sent nearly 700 Airacobras to Great Britain and the Soviet Union under Lend-Lease. After the Japanese attack at Pearl Harbor, the Air Corps rushed P-39 units into action in the South Pacific.
The Airacobra saw combat throughout the world, particularly in the Southwest Pacific, Mediterranean and Russian theaters. After initially seeing duty in the Pacific and European theaters of operation, P-39s were supplanted, then replaced by the P-38, P-47 and P-51. The Army P-39 Airacobra type was used against the Japanese attacks in the Aleutian Islands. From September to November 1942 pilots of the 57th Fighter Squadron flew P-39s and P-38s from an airfield built on land bulldozed into Kuluk Bay on the barren island of Adak in Alaska's Aleutian Islands. They attacked the Japanese forces which had invaded Attu and Kiska islands in the Aleutians in June 1942. The number one foe that claimed the most lives, however, was not the Japanese but the weather. The low clouds, mist, fog, driving rain, snow and high winds made flying dangerous and lives miserable. The 57th remained in Alaska until November 1942 and then returned to the United States.
Lieutenant General H.H. Arnold, commanding general, U.S. Army Air Forces, has telegraphed Bell Aircraft Corporation of Buffalo, New York of their success against a squadron of Japanese invaders without a single loss. "Only a truly fine airplane, skillfully and carefully constructed could surmount such obstacles intact. With your forces producing such planes and our forces flying them, we cannot fail."
Bell was rescued by the largest military contract, involving supply of "Airacobra" for the Red Army Air Force. The P-39 “Airacobra” was the favorite American aircraft received by the USSR during the Lend Lease program of American aid. Along with “Studebaker” trucks, “Dodge three-quarter ton” automobiles and cans of stewed meat called “Spam,” the P-39 became the symbol of America’s unselfish aid to the Soviet Union in the years of WWII. American schoolchildren raised money for “Airacobras” for the Red Army. German pilots tried to avoid fighting with “Airacobras” as they knew perfectly well that the “Red Falcons” would win. Three out of the five best Soviet pilots fought on “Airacobras”: Aleksandr Pokryshkin, Grigoriy Rechkalov and Nikolay Gylayev. The record holder was Rechkalov, a native of Irbit, who gained 50 victories in the air.
By the end of World War II aircraft P-39N and P-39Q were the main fighters supplied allies in the Soviet Union under the Lend-Lease. The first truly mass modification became P-39N (manufactured 2095 aircraft). Almost all of them were sent to the Soviet Union where were popular because of structural reliability and the ability to return after receiving multiple combat damage. Most of the aircraft had four wing fuel tanks. Rear armored plate was replaced bent bulletproof glass, and in general take-off weight was reduced from 4128 to 3969kg.
The main production version was P-39Q (4095 were built). At the sub-embodiment (Q-1) instead of four wing machine guns were installed two 12.7-mm machine guns in underwing gondolas. Fuel capacity and weight reservation remained in former range, but some sub-options had four screws. Beginning with sub-option Q-20, the wing machine guns are often not set: Soviet experts believed the presence of one 37-mm cannon and two 12.7mm machine guns was sufficient and more appreciated some increase flight performance and maneuverability.
Many of the Bell Fighters made their way to the Soviet Union, while others were used in the Unites States. When P-39 production ended in August 1944, Bell had built 9,584 Airacobras, of which 4,773 were allotted to the Soviet Union. Russian pilots particularly liked the cannon-armed P-39 for its ground attack capability. Other P-39s served French and British forces.
The P-63 saw action with the Soviets primarily in the Pacific Theater, where Kingcobras flew escort, provided close air support, and engaged in ground attack. Despite a 1943 agreement stating that the Soviets would not use the P-63 against Germany, unconfirmed reports by Soviets and Germans claim it was.
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