The Vought F4U Corsair was a carrier compatible fighter initially developed during World War 2.
Development and testingEdit
During the 1920s and 1930s two distinct schools of thought had devel- oped concerning military aero-engines. The USN reasoned that air-cooled radials offered added reliability, especially when operating over water. The US Army took the opposite view, feeling that “pursuits” (fighters) could only attain high speeds by using liquid-cooled inline engines, which permitted better streamlining. There was much to be said in favour of both types. Even though the Army had hitherto been forced to use radials (in the Boeing P-26, Seversky P-35, and Curtiss P-36), the emergence of the Allison series of engines gave them the power they needed to develop modern inline-powered fighters.
The Allison gave the USN some food for thought, as it seemed to offer more power than could be obtained from current radials. However, the engine’s complex cooling system was vulnerable to damage from enemy fire. Pratt & Whitney jumped into the engine battle with the R-2800, an 18-cylinder, two-row radial that was relatively small and compact for its displacement. When the engine was displayed in 1939 it could offer up to 2,000 h.p. from 2,800in3, a major technical feat and a figure that far outstripped other radials. Oddly, the R-2800 never went into a heavy bomber, though it would go on to develop an incredible reputation for performance, reliability and ease of maintenance.
The proposals that went before the USN review board were given close consideration, and the V-1668 came out on top — a radical design, but the Navy remained undeterred. The V-166B was the smallest airframe that could be attached to the R-2800, and to absorb all the power generated the aircratt needed a very large propeller. The three-bladed Hamilton Standard unit had a diameter of 13ft 4in, making ground clearance a major problem. Vought came up with a unique solution, using an inverted-gull-wing centre section.
On June 11, 1938, the USN issued a contract for a prototype XF4U-1 and on February 10, 1939, a full-scale engineering mock-up was made available tor USN inspection teams and windtunnel tests; an amazingly short time for such a technologically advanced aircraft. The XF4U-1 employed new construction techniques including a new spot-welding method developed by the Naval Aircraft Factory which would serve as a step in significantly advancing the pace of mass production. The method enabled a structure of heavy aluminum skin and supports to be built up, resulting in a very strong structure capable of taking the punishment of carrier operations and combat damage.
Interestingly, the outer wing panels of the XF4U-1 were fabric-covered. This was common USN practice at the time (the aft section of the Consolidated Catalina's huge wing was also covered in fabric). The wing was built in three major sections, the inverted-gull centre section an integral part of the fuselage mid-section, its stubs containing the undercarriage and gear doors in separate bays. The gear rotated 90° and folded into the bays, covered by large doors. The second portion was the leading edge of the outboard panels, which were all-metal and housed the gun ports. The ﬁnal section comprised the fabric-covered aft outer-wing panels. The ailerons were wooden, covered in plywood and fabric, another seemingly outdated feature.
Of conventional monocoque construction, the fuselage was very robust and a fine degree of finish was achieved by the use of spot-welding. Considerable attention had been paid to the cowling of the XF4U-1 to ensure that every bit of streamlining offered by the R-2800's low frontal area could be exploited for extra speed. The cowling was close-fitting but easy to remove for engine maintenance. The immense heat generated by the radial would be bled aft via a ring of cowl flaps that offered effective cooling while not disturbing the airflow to any great degree.
Because the rear cylinders could easily "cook" owing to high temperatures and limited airflow cooling, P&W engineers had to redesign the R-2800 with very thin cylinder cooling fins. Hitherto, they had been cast as part of the cylinder, but such ultra-thin units had to be milled from the solid chunk of metal that constituted the cylinder. P&W designed the necessary milling machines, the problem was solved, and radials rapidly grew in size and horsepower (culminating in the P&W R-4360, the largest production piston engine).
An R-2800-2 was put on a test stand and run for the USN inspectors, while work continued on an updated version to power the prototype. This, the R-2800-4, provided 1,850 h.p. for take-off and 1,600 h.p. at 15,000ft and 2,400 r.p.m. The magical ﬁgure of 2,000 h.p. was achieved shortly after the -4 was installed, and this engine should be looked upon as a developmental engine installed in a developmental fighter. Like its part-fabric wing covering, the XF4U-1 ’s armament was rather outdated but a product of the time. Two 0.50in machine-guns were housed in the outer wing panels (one per panel), while one 0.30in and one 0.50in machine-gun were accommodated in the upper portion of the cowling and forward fuselage.
American military fighters of the time were certainly outgunned by European and Japanese aircraft, many of which carried cannon armament. Provision was also made in the mid-section of each outer wing panel for a bay that would take ten small bombs. Two windows were located beneath the pilot in the lower fuselage for aiming. Fortunately, the idea never progressed beyond the prototype.
On May 29, 1940, Lyman A. Bullard, chief test pilot for Vought-Sikorsky, made a quick inspection of the XF4U-1 on the ramp at Bridgeport Airport, Stratford, Connecticut. He was well experienced with the prototype’s systems, having watched the aeroplane grow from initial sketches. Bullard took the XF4U-1 up to 9,000ft for some standard manoeuvres - cycling the undercarriage and flaps to ensure they functioned as intended, a couple of stalling tests and an application of cruise power.
Soon the fighter could be seen entering the downwind pattern, the aircraft landing safely but, on closer inspection, not quite in one piece. Vought engineers looked on with a degree of horror as Bullard pointed out that the trim-tabs on the elevator were missing, having departed with a bang at the relatively low speed of 180kt. What would happen when the prototype went faster?
Flutter was just one of many engineering problems that plagued the F4U’s entry into carrier combat, but the type was destined to find fame first in a situation for which it was not originally intended, that of land-based fighter and attack bomber.
Testing on the XF4U-1 progressed until the fifth flight, when, during the fifth flight, disaster occurred. Shortage of fuel and bad weather resulted in Guyton making an emergency landing on a golf course, only for the prototype to end up broken among a stand of trees. The XF4U-1's rugged structure probably saved Guyton's life, and the programme. Vought employees who looked upon the crumpled aircraft in the gully saw it as scrap. However, alter the wreckage had been trucked back to the factory, closer inspection revealed that the tough centre section and its inverted-gull-wing stubs were relatively intact. Vought and the USN were anxious that the XF4U-1 be put back into the air as quickly as possible, so an overtime rebuilding programme began. The totally rebuilt machine was ready for flight in just three months.
On October 1 the XF4U-1 set a blistering pace between Stratford and Hartford (40 miles), recording a speed of 405 m.p.h. Testing continued at an accelerated pace, and modifications suggested by the USN were complied with by Vought. The Bureau of Aeronautics took its final look at the fighter during February 1941 and, in March and April, final contracts were signed, paving the way for the manufacturing contract on June 30. The Corsair, as the F4U series had been dubbed, retained the same name as the series of biplanes. Many design changes were evident in the first production Corsair, and the prototype remained unique in its configuration.
Fighting between the RAF and the Luftwaffe was making headlines daily, and the rapid advances in aerial weaponry were not lost on American designers. The British had settled on eight 0.303in machine-guns for their Hurricanes and Spitﬁres, but even this concentrated fire was often insufficient to bring down German raiders. If a vital part was not hit, an enemy bomber stood a good chance of reaching its target.
Other features besides weaponry were figuring in combat aircraft design. Armour plating was added to protect cockpits and vital systems; self-sealing fuel tanks were installed; armoured windscreens were added to help pilots survive bullet hits at low altitude. The Germans were perfecting the use of the aerial cannon and, quite often, just one shell from such a heavy-calibre weapon could destroy an aircraft.
The Corsair was modified to meet these new requirements. The nose guns were deleted and outer wing panels redesigned to take six 0-50in Browning air-cooled machine-guns. While the rate of fire was slower than that of the 0.30in weapons, the amount of lead directed at an enemy target would lead to almost certain destruction. Normally, the six 0.50ins were bore-sighted to converge 1,0OOft ahead of the Corsair, the zone covered by this fire being a circular area ranging from three to six feet in diameter. A one-second burst from all six weapons would place 80 rounds in the circle. Total ammunition capacity was 2,350 rounds, all of which could be expended in 30sec if the pilot held down the trigger.
Much consideration was given to the fuel system, and tanks in the prototype were redesigned to provide safer fuel storage. The four integral wing tanks were eliminated, and one huge self-sealing tank mounted behind the engine firewall was added. While the fuel tank modification made the Corsair safer from the fire standpoint, it created one of its biggest problems. The cockpit had to be moved aft 32in to make room for the tank. This gave the pilot a better view of the ground, but made the already poor forward view even worse. The new cockpit location changed the Corsair’s lines, but the fuel-hungry P&W would have its thirst somewhat slaked by the 237 US gal fuselage tank and by two small wing-leading-edge tanks, giving the fighter an impressive range that would soon be needed for what would become the Corsair’s hour of glory — the Pacific War.
Why the inverted gull wing?Edit
The design of the Corsair was optimised for high performance. The aircraft was aerodynamically clean and employed spot-welding and flush-riveting to achieve as smooth a surface as possible. However, a major consideration of the design team was to give the 13ft 4in-diameter propeller the necessary ground clearance without having very long undercarriage legs. Rex Beisel decided to use a centre section in the form of an inverted gull wing.
The go-ahead to use this unusual concept came about only after the idea was studied by a number of outside concerns. Vought was a conservative company, and there were numerous questions regarding the aerodynamic properties of the inverted-gull section, including stalling characteristics, slow-speed handling and high-speed compressibility. In the end, it was concluded that the advantages of the new design outweighed any possible problems.
The undercarriage attachment was positioned at the lowest point of the inverted-gull section, which gave adequate ground clearance for the propeller, and also meant that a shorter and lighter undercarriage leg could be used than on a straight-winged aircraft. Since the leg had a shorter strut, it could fold aft and retract within the chord of the wing. The centre section also improved the pilot's view, since the “dip" in the wing enabled him to look down and out with more ease.
The optimum 90° attachment of the inverted-gull section to the fuselage also produced the least possible drag. Moreover, when the wings were folded, they would be of lower overall height, which was important on crowded hangar decks. Thus, Rex Beisel’s solution to a complex problem had many benefits, while also creating one of the most distinctive aircraft of the Second World War.
The US Navy quickly realised that, even with all-out production, Vought would not be able to deliver as many Corsairs as the Navy and American Allies needed, so licence contracts were drawn up with Brewster Aeronautical Corporation in Long Island, New York and Goodyear in Ohio. The two companies were to produce widely different products. Goodyear became a model of aircraft production efficiency and churned out thousands of high-quality copies, while Brewster built a shoddy product that was eventually terminated with a Congressional investigation.
Brewster built just over 700 F3A-1 Corsairs, delivered behind schedule and of inferior quality. In the ensuing investigation, the fact was brought up that German agents may well have been at work on the Brewster production lines — this may be true, but no hard facts were ever revealed. One Marine pilot remembers that if he and his squadron mates saw the F3A designation on a Corsair, it would be avoided. Rumours had circulated through the squadron of wings coming off Brewster-built machines and many of the F3As were red-lined for top speed and prohibited from performing the more violent aerobatic manoeuvres.
In a fit of international co-operation, the US Government shipped many of the Brewster Corsairs to Britain, while the ones remaining in America were assigned to training squadrons.
World War 2Edit
- ↑ Wikimedia
- ↑ Template:Aeroplane Monthly Database: October 2002 (F4U Corsair) Page 40
- ↑ Aeroplane Monthly Database: October 2002 (F4U Corsair) Pages 40 and 42
- ↑ 4.0 4.1 Aeroplane Monthly Database: October 2002 (F4U Corsair) Page 42
- ↑ Aeroplane Monthly Database: October 2002 (F4U Corsair) Pages 42 and 42
- ↑ 6.0 6.1 Aeroplane Monthly Database: October 2002 (F4U Corsair) Page 44