Vought F4U Corsair
The Vought F4U Corsair is an American fighter aircraft that saw service primarily in World War II and the Korean War. Designed and initially manufactured by Chance Vought, the Corsair was soon in great demand; additional production contracts were given to Goodyear, whose Corsairs were designated FG, and Brewster, designated F3A.
The Corsair was designed and principally operated as a carrier-based aircraft, and entered service in large numbers with the U.S. Navy and Marines in World War II. It quickly became one of the most capable carrier-based fighter-bombers of the war. Some Japanese pilots regarded it as the most formidable American fighter and U.S. naval aviators achieved an 11:1 kill ratio. Early problems with carrier landings and logistics led to it being eclipsed as the dominant carrier-based fighter by the Grumman F6F Hellcat, powered by the same Double Wasp engine first flown on the Corsair's initial prototype in 1940. The Corsair's early deployment was to land-based squadrons of the U.S. Marine Corps and U.S. Navy.
The Corsair served almost exclusively as a fighter-bomber throughout the Korean War and during the French colonial wars in Indochina and Algeria. In addition to its use by the U.S. and British, the Corsair was also used by the Royal New Zealand Air Force, French Naval Aviation, and other air forces until the 1960s.
From the first prototype delivery to the U.S. Navy in 1940, to final delivery in 1953 to the French, 12,571 F4U Corsairs were manufactured in 16 separate models. Its 1942–1953 production run was the longest of any U.S. piston-engined fighter.
Development
In February 1938, the U.S. Navy Bureau of Aeronautics published two requests for proposal for twin-engined and single-engined fighters. For the single-engined fighter, the Navy requested the maximum obtainable speed, and a minimum stalling speed not higher than. A range of was specified. The fighter had to carry four guns, or three with increased ammunition. Provision had to be made for antiaircraft bombs to be carried in the wing. These small bombs would, according to thinking in the 1930s, be dropped on enemy aircraft formations.Image:XF4U-1 NACA 1940.jpeg|thumb|The XF4U-1 prototype in 1940/41, showing its more forward cockpit location
In June 1938, the U.S. Navy signed a contract with Vought for a prototype bearing the factory designation V-166B, the XF4U-1, BuNo 1443. The Corsair design team was led by Rex Beisel. After mock-up inspection in February 1939, construction of the XF4U-1 powered by an XR-2800-4 prototype of the Pratt & Whitney R-2800 Double Wasp twin-row, 18-cylinder radial engine, rated at went ahead quickly, as the first airframe ever designed from the start to have a Double Wasp engine fitted for flight. When the prototype was completed, it had the biggest and most powerful engine, largest propeller, and probably the largest wing on any naval fighter to date. The first flight of the XF4U-1 was made on 29 May 1940, with Lyman A. Bullard, Jr. at the controls. The maiden flight proceeded normally until a hurried landing was made when the elevator trim tabs failed because of flutter.
On 1 October 1940, the XF4U-1 became the first single-engined U.S. fighter to fly faster than by flying at an average ground speed of from Stratford to Hartford. The USAAC's twin engine Lockheed P-38 Lightning had flown over 400 mph in January–February 1939. The XF4U-1 also had an excellent rate of climb, although testing revealed some requirements would have to be rewritten. In full-power dive tests, speeds up to were achieved, but not without damage to the control surfaces and access panels, and in one case, an engine failure. The spin recovery standards also had to be relaxed, as recovery from the required two-turn spin proved impossible without resorting to an antispin chute. The problems clearly meant delays in getting the design into production.
Reports coming back from the war in Europe indicated an armament of two synchronized engine cowling-mount machine guns, and two machine guns was insufficient. The U.S. Navy's November 1940 production proposals specified heavier armament. The increased armament comprised three.50 caliber machine guns mounted in each wing panel. This improvement greatly increased the ability of the Corsair to shoot down enemy aircraft.
Formal U.S. Navy acceptance trials for the XF4U-1 began in February 1941. The Navy entered into a letter of intent on 3 March 1941, received Vought's production proposal on 2 April, and awarded Vought a contract for 584 F4U-1 fighters, which were given the name "Corsair" – inherited from the firm's late-1920s Vought O2U naval biplane scout, which first bore the name – on 30 June of the same year. The first production F4U-1 performed its initial flight a year later, on 24 June 1942. It was a remarkable achievement for Vought; compared to land-based counterparts, carrier aircraft are "overbuilt" and heavier, to withstand the extreme stress of deck landings.
Design
Engine considerations
The F4U incorporated the largest engine available at the time, the 18-cylinder Pratt & Whitney R-2800 Double Wasp radial. To extract as much power as possible, a relatively large Hamilton Standard Hydromatic three-blade propeller of was used.Landing gear and wings
To accommodate a folding wing, the designers considered retracting the main landing gear rearward, but for the chord of wing that was chosen, making the landing gear struts long enough to provide ground clearance for the large propeller was difficult. Their solution was an inverted gull wing, which considerably shortened the required length of the struts. The anhedral of the wing's inboard section also permitted the wing and fuselage to meet at the optimum angle for minimizing drag, without using wing-root fairings. The bent wing was heavier and more difficult to construct, however, offsetting these benefits.The Corsair's aerodynamics were an advance over those of contemporary naval fighters. The F4U was the first U.S. Navy aircraft to feature landing gear that retracted into a fully enclosed wheel well. The landing gear oleo struts—each with its own strut door enclosing it when retracted—rotated through 90° during retraction, with the wheel atop the lower end of the strut when retracted. A pair of rectangular doors enclosed each wheel well, leaving a streamlined wing. This swiveling, aft-retracting landing gear design was common to the Curtiss P-40, as adopted for the F4U Corsair's main gear and its Pacific War counterpart, the Grumman F6F Hellcat. The oil coolers were mounted in the heavily anhedraled inboard section of the wings, alongside the supercharger air intakes, and used openings in the leading edges of the wings, rather than protruding scoops. The large fuselage panels were made of aluminum and were attached to the frames with the newly developed technique of spot welding, thus mostly eliminating the use of rivets. While employing this new technology, the Corsair was also the last American-produced fighter aircraft to feature fabric as the skinning for the top and bottom of each outer wing, aft of the main spar and armament bays, and for the ailerons, elevators, and rudder. The elevators were also constructed from plywood. The Corsair, even with its streamlining and high-speed abilities, could fly slowly enough for carrier landings with full flap deployment of 50°.
Technical issues
In part because of its advances in technology and a top speed greater than existing Navy aircraft, numerous technical problems had to be solved before the Corsair entered service. Carrier suitability was a major development issue, prompting changes to the main landing gear, tail wheel, and tailhook. Early F4U-1s had difficulty recovering from developed spins, since the inverted gull wing's shape interfered with elevator authority. It was also found that the Corsair's left wing could stall and drop rapidly and without warning during slow carrier landings. In addition, if the throttle were suddenly advanced the left wing could stall and drop so quickly that the fighter could flip over with the rapid increase in power. These potentially lethal characteristics were later solved through the addition of a small, -long stall strip to the leading edge of the outer right wing, just outboard of the gun ports. This allowed the right wing to stall at the same time as the left.Image:F4U-1 NACA 1943.jpeg|thumb|left|An early F4U-1 showing the "birdcage" canopy with rearwards production cockpit location.
Other problems were encountered during early carrier trials. Visibility problems caused by the Corsair's combination of an aft-mounted cockpit and long nose made landings hazardous for newly trained pilots. During landing approaches, it was found that oil from the opened hydraulically powered cowl flaps could spatter onto the windscreen, severely reducing visibility, and the undercarriage oleo struts had bad rebound characteristics on landing, allowing the aircraft to bounce down the carrier deck. The first problem was solved by locking the top cowl flaps in front of the windscreen down permanently, then replacing them with a fixed panel. The undercarriage bounce took more time to solve, but eventually a "bleed valve" incorporated in the legs allowed the hydraulic pressure to be released gradually as the aircraft landed. The Corsair was not considered fit for carrier use until the wing stall problems and the deck bounce could be solved.
Meanwhile, the more docile and easier-to-build F6F Hellcat had begun entering service for its intended carrier-based role. The Navy aimed to standardize on a single type of carrier fighter, and although the Hellcat was slower than the Corsair, it was deemed simpler for inexperienced pilots to land on a carrier. The Hellcat proved to be successful almost immediately after its introduction. The Navy's decision to select the Hellcat allowed the Corsair to be assigned to the U.S. Marine Corps. With no initial requirement for carrier landings, the Marine Corps deployed the Corsair to devastating effect from land bases. Deployment of the Corsair aboard U.S. carriers was delayed until late 1944, by which time the last of the carrier landing issues related to the Corsair's long nose had been addressed by the British.