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World War II: Bell P-39 Airacobra

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World War II: Bell P-39 Airacobra

P-39 Airacobra

Photograph Courtesy of the US Air Force

P-39Q Airacobra - Specifications:

General

  • Length: 30 ft. 2 in.
  • Wingspan: 34 ft.
  • Height: 12 ft. 5 in.
  • Wing Area: 213 sq. ft.
  • Empty Weight: 5,347 lbs.
  • Loaded Weight: 7,379 lbs.
  • Maximum Takeoff Weight: 8,400 lbs.
  • Crew: 1

Performance

  • Maximum Speed: 376 mph
  • Combat Radius: 525 miles
  • Rate of Climb: 3,750 ft./min.
  • Service Ceiling: 35,000 ft.
  • Power Plant: 1 × Allison V-1710-85 liquid-cooled V-12, 1,200 hp

Armament

  • 1 x 37 mm M4 cannon
  • 2 x .50 cal. machine guns
  • 4 x .30 cal machine guns
  • up to 500 lbs. of bombs

P-39 Airacobra - Design & Development:

In early 1937, Lieutenant Benjamin S. Kelsey, the US Army Air Corps' Project Officer for Fighters, began to express his frustration over the service's armament limitations for pursuit aircraft. Joining with Captain Gordon Saville, a fighter tactics instructor at the Air Corps Tactical School, the two men wrote two circular proposals for a pair of new "interceptors" which would possess a heavier armament that would allow American aircraft to dominate aerial battles. The first, X-608, called for a twin-engine fighter and would ultimately lead to the development of the Lockheed P-38 Lightning. The second, X-609, requested designs for a single-engine fighter capable of dealing with enemy aircraft at high altitude. Also included in X-609 was a requirement for a turbo-supercharged, liquid-cooled Allison engine as well as a level speed of 360 mph and an ability to reach 20,000 feet within six minutes.

Responding to X-609, Bell Aircraft began work on a new fighter that was designed around the Oldsmobile T9 37mm cannon. To accommodate this weapon system, which was intended to fire through the propeller hub, Bell employed the unorthodox approach of mounting the aircraft's engine in the fuselage behind the pilot. This turned a shaft beneath the pilot's feet which in turn powered the propeller. Due to this arrangement, the cockpit sat higher which gave the pilot an excellent field of view. It also allowed for a more streamlined design which Bell hoped would aid in achieving the required speed. In another difference from its contemporaries, pilots entered the new aircraft through side doors that were similar to those employed on automobiles rather than sliding canopy. To supplement the T9 cannon, Bell mounted twin .50 cal. machine guns in the aircraft's nose. Later models would also incorporate two to four .30 cal. machine guns mounted in the wings.

P-39 Airacobra - A Fateful Choice:

First flying on April 6, 1939, with test pilot James Taylor at the controls, the XP-39 proved disappointing as its performance at altitude failed to meet the specifications set forth in Bell's proposal. Attached to the design, Kelsey had hoped to guide the XP-39 through the development process but was thwarted when he received orders that sent him abroad. In June, Major General Henry "Hap" Arnold directed that the National Advisory Committee for Aeronautics conduct wind tunnel tests on the design in an effort to improve performance. Following this testing NACA recommended that the turbo-supercharger, which was cooled with scoop on the left side of the fuselage, be enclosed within the aircraft. Such a change would improve the XP-39's speed by 16 percent.

Examining the design, Bell's team was unable to find space within the XP-39's small fuselage for the turbo-supercharger. In August 1939, Larry Bell met with the USAAC and NACA to discuss the issue. At the meeting, Bell argued in favor of eliminating the turbo-supercharger altogether. This approach, much to Kelsey's later dismay, was adopted and subsequent prototypes of the aircraft moved forward utilizing only a single-stage, single-speed supercharger. While this alteration provided the desired performance improvements at low altitude, the elimination of the turbo effectively made the type useless as a front-line fighter at heights above 12,000 feet. Unfortunately, the drop off in performance at medium and high altitude was not immediately noticed and the USAAC ordered 80 P-39s in August 1939.

P-39 Airacobra - Early Problems:

Initially introduced as the P-45 Airacobra, the type was soon re-designated P-39C. The initial twenty aircraft were built without armor or self-sealing fuel tanks. As World War II had begun in Europe, the USAAC began to assess combat conditions and realized that these were needed to ensure survivability. As a result, the remaining 60 aircraft of the order, designated P-39D, were built with armor, self-sealing tanks, and an enhanced armament. This added weight further hampered the aircraft's performance. In September 1940, the British Direct Purchase Commission ordered 675 of the aircraft under the name Bell Model 14 Caribou. This order was placed based on the performance of the unarmored and unarmed XP-39 prototype. Receiving their first aircraft in September 1941, the Royal Air Force soon found the production P-39 to be inferior to variants of the Hawker Hurricane and Supermarine Spitfire.

P-39 Airacobra - In the Pacific:

As a result, the P-39 flew one combat mission with the British before the RAF shipped 200 aircraft to the Soviet Union for use with the Red Air Force. With the Japanese attack on Pearl Harbor on December 7, 1941, the US Army Air Forces purchased 200 P-39s from the British order for use in the Pacific. First engaging Japanese in April 1942 over New Guinea, the P-39 saw extensive use throughout the Southwest Pacific and flew with American and Australian forces. The Airacobra also served in the "Cactus Air Force" which operated from Henderson Field during the Battle of Guadalcanal. Engaging at lower altitudes, the P-39, with its heavy armament, frequently proved a tough opponent for the famed Mitsubishi A6M Zero. Also used in the Aleutians, pilots found that the P-39 had a variety of handling problems including a tendency to enter a flat spin. This often was result of the aircraft's center of gravity shifting as ammunition was expended. As distances in the Pacific war increased, the short-range P-39 was withdrawn in favor of increasing numbers of P-38s.

P-39 Airacobra - Europe:

Though found unsuitable for use in Western Europe by the RAF, the P-39 saw service in North Africa and the Mediterranean with the USAAF in 1943 and early 1944. Among those to briefly fly the type was the famed 99th Fighter Squadron (Tuskegee Airmen) who had transitioned from the Curtiss P-40 Warhawk. Flying in support of Allied forces during the Battle of Anzio and maritime patrols, P-39 units found the type to be particularly effective at strafing. By early 1944, most American units transitioned to the newer Republic P-47 Thunderbolt or North American P-51 Mustang. The P-39 was also employed with the Free French and Italian Co-Belligerent Air Forces. While the former was less than pleased with the type, the latter effectively employed the P-39 as a ground-attack aircraft in Albania.

P-39 Airacobra - Soviet Union:

Exiled by the RAF and disliked by the USAAF, the P-39 found its home flying for the Soviet Union. Employed by that nation's tactical air arm, the P-39 was able to play to its strengths as most of its combat occurred at lower altitudes. In that arena, it proved capable against German fighters such as the Messerschmitt Bf 109 and Focke-Wulf Fw 190. In addition, its heavy armament allowed it to make quick work of Junkers Ju 87 Stukas and other German bombers. A total of 4,719 P-39s were sent to the Soviet Union through the Lend-Lease Program. These were transported to the front via the Alaska-Siberia ferry route. During the course of the war, five of the top ten Soviet aces scored the majority of their kills in the P-39. Of those P-39s flown by the Soviets, 1,030 were lost in combat. The P-39 remained in use with the Soviets until 1949.>

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