F4U Corsair

Vought F4U Corsair

The Vought F4U Corsair was a carrier-capable fighter aircraft that saw service primarily in World War II and the Korean War. Demand for the aircraft soon overwhelmed Vought's manufacturing capability, resulting in production by Goodyear and Brewster: Goodyear-built Corsairs were designated FG and Brewster-built aircraft F3A. 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 by Vought, in 16 separate models, in the longest production run of any piston-engined fighter in U.S. history (1942–1953).

The Corsair served in the U.S. Navy, U.S. Marines, Fleet Air Arm and the Royal New Zealand Air Force, as well as the French Navy Aeronavale and other, smaller, air forces until the 1960s. It quickly became the most capable carrier-based fighter-bomber of World War II. Some Japanese pilots regarded it as the most formidable American fighter of World War II,  and the U.S. Navy counted an 11:1 kill ratio with the F4U Corsair.

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 stalling speed not higher than 70 miles per hour (110 km/h). A range of 1,000 miles (1,600 km) was specified. The fighter had to carry four guns, or three with increased ammunition. Provision had to be made for anti-aircraft bombs to be carried in the wing. These small bombs would, according to thinking in the 1930s, be dropped on enemy aircraft formations.

In June 1938, the U.S. Navy signed a contract for a prototype, the XF4U-1, BuNo 1443. The Corsair was designed by Rex Beisel and the Vought design team. After mock-up inspection in February 1939, construction of the XF4U-1 powered by an XR-2800-4 prototype of the Pratt & Whitney Double Wasp twin-row, 18-cylinder radial engine, rated at 1,805 hp (1,346 kW) went ahead quickly. When the prototype was built it had the biggest and most powerful engine, largest propeller and probably the largest wing on any fighter in history. 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, the XF4U-1 became the first single-engine U.S. fighter to fly faster than 400 mph (640 km/h) by setting an average ground speed of 405 miles per hour (652 km/h) during a flight from Stratford to Hartford. The XF4U-1 also had an excellent rate of climb but testing revealed that some requirements would have to be rewritten. In full-power dive tests, speeds of up to 550 miles per hour (890 km/h) 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 anti-spin chute. The problems clearly meant delays in getting the type into production.

Reports coming back from the war in Europe indicated that an armament of two .30 in (7.62 mm) (mounted in engine cowling) and two .50 in (12.7 mm) machine guns (one in each outer wing panel) was insufficient, so when the U.S. Navy asked for production proposals in November 1940, heavier armament was specified. 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 on 30 June of the same year. 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

The F4U incorporated the largest engine available at the time: the 2,000 hp (1,500 kW) 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 13 feet 4 inches (4.06 m) was used. To accommodate a folding wing, the designers considered retracting the main landing gear rearward, but for the chord of wing that was chosen, it was difficult to make the landing gear struts long enough to provide sufficient clearance for the large propeller. Their solution was an inverted gull wing, which considerably shortened the required length of the main gear legs. The anhedral of the wing's center-section also permitted the wing and fuselage to meet at the optimum angle for minimizing drag, without using wing root fairings. Offsetting these benefits, the bent wing was heavier and more difficult to construct.

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. In a similar manner to that of the Curtiss P-40 the landing gear oleo struts rotated through 90° during retraction, with the wheel atop the lower end of the strut; a pair of rectangular doors completely enclosed the wheel wells, leaving a completely streamlined wing. This swiveling, aft-retracting landing gear design was common to the Curtiss P-40 (and its predecessor, the Curtiss P-36), as well as the F4U Corsair and its erstwhile Pacific War rival, the Grumman F6F Hellcat. The oil coolers were mounted in the center-section of the wings, alongside of 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. In addition, the elevators were constructed from plywood. Even with its streamlining and high speed abilities, with full flap deployment of 60°, the Corsair could fly slowly enough for carrier landings.

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 would enter 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 also found that the Corsair's starboard wing could stall and drop rapidly and without warning during slow carrier landings. In addition, if the throttle were suddenly advanced (for example, during an aborted landing) the port 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, 6 in (150 mm)-long stall strip to the leading edge of the outer starboard wing, just inboard of the gun ports. This allowed the starboard wing to stall at the same time as the port

Other problems were encountered during early carrier trials. The combination of an aft cockpit and the Corsair's long nose made landings hazardous for newly-trained pilots. During landing approaches it was found that oil from the hydraulic cowl flaps could spatter onto the windscreen, badly reducing visibility, and the undercarriage oleo struts had bad rebound characteristics on landing, allowing the aircraft to bounce out of control down the carrier deck. The first problem was solved by locking the top cowl flap down permanently, then replacing it 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. In the event, because the more docile, and simpler to build F6F Hellcat had begun entering service, Corsair deployment aboard U.S. carriers was to be delayed until late 1944.

Production F4U-1s featured several major modifications compared with the XF4U-1. A change of armament to six wing mounted .50 in (12.7 mm) M2 Browning machine guns (three in each outer wing panel) and their ammunition (400 rpg for the inner pair, 375 rpg for the outer) meant that the location of the wing fuel tanks had to be changed. In order to keep the fuel tank close to the center of gravity, the only available position was in the forward fuselage, ahead of the cockpit. Accordingly a 237 gal (897 l) self-sealing fuel tank replaced the fuselage mounted armament, the cockpit had to be moved back by 32 in (810 mm) and the fuselage lengthened. In addition, 150 lb of armor plate was installed, along with an 1.5 in (38 mm) bullet-proof windscreen which was set internally, behind the curved Plexiglas windscreen. The canopy could be jettisoned in an emergency and curved transparent panels, providing the pilot with a limited rear view over his shoulders, were inset into the fuselage, behind the pilot's headrest. A rectangular Plexiglas panel was inset into the lower center-section to allow the pilot to see directly beneath the aircraft and assist with deck landings. The engine used was the more powerful R-2800-8 (B series) Double Wasp which produced 2,000 hp (1,491 kW). On the wings the flaps were changed to a NACA slotted type and the ailerons were increased in span to increase the roll rate, with a consequent reduction in flap span. IFF transponder equipment was fitted in the rear fuselage. All in all these changes increased the Corsair's weight by several hundred pounds.

Operational history

United States Navy and Marine Corps

The performance of the Corsair was impressive. The F4U-1 was considerably faster than the F6F Hellcat and only 13 mph (21 km/h) slower than the P-47 Thunderbolt, all three were powered by the R-2800. But while the P-47 achieved its highest speed at 30,020 feet (9,150 m) with the help of an intercooled turbosupercharger, the F4U-1 reached its maximum speed at 19,900 ft (6,100 m), and used a mechanically supercharged engine.

Carrier qualification trials on the escort carrier USS Sangamon, on 25 September 1942, caused the U.S. Navy to release the type to the United States Marine Corps.  Early Navy pilots spoke disparagingly of the F4U as the "hog", "hosenose" or "bent wing widow-maker". After all, the U.S. Navy still had the Grumman F6F Hellcat, which did not have the performance of the F4U but was a far better deck landing aircraft. The Marines needed a better fighter than the F4F Wildcat. For them it was not as important that the F4U could be recovered aboard a carrier, as they usually flew from land bases. Growing pains aside, Marine Corps squadrons readily took to the radical new fighter.

Despite the decision to issue the F4U to Marine Corps units, two Navy units, VF-12 (October 1942) and later VF-17 (April 1943) were equipped with the F4U. By April 1943, VF-12 had successfully completed deck landing qualification. However, VF-12 soon abandoned its aircraft to the Marines. VF-17 kept its Corsairs, but was removed from its carrier, USS Bunker Hill, due to perceived difficulties in supplying parts at sea. In November 1943, while operating as a shore-based unit in the Solomon Islands, VF-17 reinstalled the tail hooks so its F4Us could land and refuel while providing top cover over the task force participating in the carrier raid on Rabaul. The squadron's pilots landed, refueled, and took off from their former home, Bunker Hill and the USS Essex on 11 November 1943.

The U.S. Navy did not get into combat with the type until September 1943 and the Royal Navy's FAA would qualify the type for carrier operations first. The U.S. Navy finally accepted the F4U for shipboard operations in April 1944, after the longer oleo strut was fitted, which finally eliminated the tendency to bounce. The first Corsair unit to be based effectively on a carrier was the pioneer USMC squadron, VMF-124, which joined Essex. They were accompanied by VMF-213. The increasing need for fighter protection against kamikaze attacks resulted in more Corsair units being moved to carriers.

From February 1943 onward, the F4U operated from Guadalcanal and ultimately other bases in the Solomon Islands. A dozen USMC F4U-1s of VMF-124, commanded by Major William E. Gise, arrived at Henderson Field (code name "Cactus") on 12 February. The first recorded combat engagement was on 14 February 1943, when Corsairs of VMF-124 under Major Gise assisted P-40s and P-38s in escorting a formation of B-24 Liberators on a raid against a Japanese aerodrome at Kahili. Japanese fighters contested the raid and the Americans got the worst of it, with four P-38s, two P-40s, two Corsairs and two Liberators lost. No more than four Japanese Zeros were destroyed. A Corsair was responsible for one of the kills, although this was due to a midair collision. The fiasco was referred to as the "Saint Valentine's Day Massacre". Although the Corsair's combat debut was not impressive, the Marines quickly learned how to make better use of the aircraft and started demonstrating its superiority over Japanese fighters. By May the Corsair units were getting the upper hand, and VMF-124 had produced the first Corsair ace, Second Lieutenant Kenneth A. Walsh, who would rack up a total of 21 kills during the war.

I learned quickly that altitude was paramount. Whoever had altitude dictated the terms of the battle, and there was nothing a Zero pilot could do to change that — we had him. The F4U could out-perform a Zero in every aspect except slow speed manoeuvrability and slow speed rate of climb. Therefore you avoided getting slow when combating a Zero. It took time but eventually we developed tactics and deployed them very effectively... There were times, however, that I tangled with a Zero at slow speed, one on one. In these instances I considered myself fortunate to survive a battle. Of my 21 victories, 17 were against Zeros, and I lost five aircraft in combat. I was shot down three times and I crashed one that ploughed into the line back at base and wiped out another F4U.

VMF-113 was activated on 1 January 1943 at Marine Corps Air Station El Toro as part of Marine Base Defense Air Group 41. They were shortly given their full complement of 24 F4U Corsairs. On 26 March 1944, while escorting 4 B-25 bombers on a raid over Ponape, they recorded their first enemy kills when they downed eight Japanese aircraft. In April of that year, VMF-113 was tasked with providing air support for the landings at Ujelang. Since the assault was unopposed the squadron quickly returned to striking Japanese targets in the Marshall Islands for the remainder of 1944.

Corsairs were flown by the famous "Black Sheep" Squadron (VMF-214, led by Marine Major Gregory "Pappy" Boyington) in an area of the Solomon Islands called "The Slot". Boyington was credited with 22 kills in F4Us (of 28 total, including six in an AVG P-40, though his score with the AVG has been disputed). Other noted Corsair pilots of the period included VMF-124's Kenneth Walsh, James E. Swett, and Archie Donohue, VMF-215's Robert M. Hanson and Don Aldrich, and VF-17's Tommy Blackburn, Roger Hedrick, and Ira Kepford. Nightfighter versions equipped Navy and Marine units afloat and ashore.

At war's end, Corsairs were ashore on Okinawa, combating the kamikaze, and also were flying from fleet and escort carriers. VMF-312, VMF-323, VMF-224, and a handful of others met with success in the Battle of Okinawa.

Corsairs also served well as fighter bombers in the Central Pacific and the Philippines. By spring 1944, Marine pilots were beginning to exploit the type's considerable capabilities in the close-support role during amphibious landings. Charles Lindbergh flew Corsairs with the Marines as a civilian technical advisor for United Aircraft Corporation in order to determine how best to increase the Corsair's payload and range in the attack role and to help evaluate future viability of single- versus twin-engine fighter design for Vought. Lindbergh managed to get the F4U into the air with 4,000 pounds (1,800 kg) of bombs, with a 2,000 pounds (910 kg) bomb on the centerline and a 1,000 pounds (450 kg) bomb under each wing. In the course of such experiments, he performed strikes on Japanese positions during the battle for the Marshall Islands.

By the beginning of 1945, the Corsair was a full-blown "mudfighter", performing strikes with high-explosive bombs, napalm tanks, and HVARs. She proved surprisingly versatile, able to operate everything from Bat glide bombs (without sacrificing a load of 2.75 in/70 mm rockets) to 11.75 in (300 mm) Tiny Tim rockets. The aircraft was a prominent participant in the fighting for the Palaus, Iwo Jima and Okinawa.

Statistics compiled at the end of the war indicate that the F4U and FG flew 64,051 operational sorties for the U.S. Marines and U.S. Navy through the conflict (44% of total fighter sorties), with only 9,581 sorties (15%) flown from carrier decks.  F4U and FG pilots claimed 2,140 air combat victories against 189 losses to enemy aircraft, for an overall kill ratio of over 11:1. The aircraft performed well against the best Japanese opponents with a 12:1 kill ratio against Mitsubishi A6M and 6:1 against the Nakajima Ki-84, Kawanishi N1K-J and Mitsubishi J2M combined during the last year of the war. The Corsair bore the brunt of fighter-bomber missions, delivering 15,621 tons (14,171 tonnes) of bombs during the war (70% of total bombs dropped by fighters during the war).

Corsair losses in World War II were as follows:

• By combat: 189
• By enemy anti-aircraft artillery: 349
• Accidents during combat missions: 230
• Accidents during non-combat flights: 692
• Destroyed aboard ships or on the ground: 164

One particularly interesting kill was scored by a Marine Lieutenant R. R. Klingman of VMF-312 Checkerboards, over Okinawa. Klingman was in pursuit of a Kawasaki Ki-45 Toryu ("Nick") twin engine fighter at extremely high altitude when his guns jammed due to the gun lubrication thickening from the extreme cold. He simply flew up and chopped off the Ki-45's tail with the big propeller of the Corsair. Despite missing five inches (127 mm) off the end of his propeller blades, he managed to land safely after this ramming attack. He was awarded the Navy Cross.

The Japanese Navy captured two Corsairs from an unknown Allied unit for evaluations fairly late in the war; one of examples originally marked YoD-150 was remarked with Yokosuka Ku air testing signs ED-150, but they never flew them.