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GRUMMAN F6F HELLCAT
Design & Development

XF6F
The unpainted XF6F-1 prior to its first flight. Grumman had been working on a successor to the F4F Wildcat since 1938 and the contract for the prototype XF6F-1 was signed on 30 June 1941. The aircraft was designed to use the Wright R-2600 Twin Cyclone two-row, 14-cylinder radial engine of 1,700 hp driving a three-bladed Curtiss Electric propeller. Instead of the Wildcat's narrow-track, hand-cranked landing gear retracting into the fuselage, the Hellcat had wide-set, hydraulically actuated landing gear struts which rotated through 90° while retracting backwards into the wings, much like that of the earlier Chance Vought F4U Corsair. The wing was mounted lower on the fuselage and was able to be hydraulically or manually folded, with each panel outboard of the undercarriage bay folding backwards from pivoting on a specially oriented, Grumman-patented diagonal axis pivoting system much like the earlier F4F, with a folded stowage position parallel to the fuselage with the leading edges pointing down.


The unpainted Grumman XF6F-1 Hellcat fighter in 1942, prior to it's first flight.
[Source: U.S. Navy]

Throughout early 1942 Roy Grumman, along with his chief designers Jake Swirbul and Bill Schwendler, worked closely with the U.S. Navy's Bureau of Aeronautics (BuAer) and experienced F4F pilots, to develop the new fighter in such a way that it could counter the Zero's strengths and help gain air command in the Pacific Theater of Operations. On 22 April 1942, Lieutenant Commander Butch O'Hare toured the Grumman Aircraft company and spoke with Grumman engineers, analyzing the performance of the F4F Wildcat against the Mitsubishi A6M Zero in aerial combat. BuAer's LT CDR A. M. Jackson directed Grumman's designers to mount the cockpit higher in the fuselage. In addition, the forward fuselage sloped down slightly to the engine cowling, affording the Hellcat's pilot good visibility.

Based on combat accounts of encounters between the F4F Wildcat and A6M Zero, on 26 April 1942, BuAer directed Grumman to install the more powerful 18-cylinder Pratt & Whitney R-2800 Double Wasp radial engine in the second XF6F-1 prototype. Grumman complied by redesigning and strengthening the F6F airframe to incorporate the 2,000 hp (1,500 kW) R-2800-10, driving a three-bladed Hamilton Standard propeller. With this combination Grumman estimated the XF6F-3s performance would increase by 25% over that of the XF6F-1. The Cyclone-powered XF6F-1 (Bu. 02981) first flew on 26 June 1942, followed by the first Double Wasp-equipped aircraft, the XF6F-3 (Bu. 02982), which first flew on 30 July 1942. The first production F6F-3, powered by an R-2800-10, flew on October 3, 1942, with the type reaching operational readiness with VF-9 on USS Essex in February 1943.

Further Development
The F6F series were designed to take damage and get the pilot safely back to base. A bullet-resistant windshield and a total of 212 lb (96 kg) of cockpit armor was fitted, along with armor around the oil tank and oil cooler. A 250 gallon self-sealing fuel tank was fitted in the fuselage. Standard armament on the F6F-3 consisted of six .50 in. M2/AN Browning air-cooled machine guns with 400 rounds per gun. A center-section hardpoint under the fuselage could carry a single 150 gal disposable drop tank, while later aircraft had single bomb racks installed under each wing, inboard of the undercarriage bays; with these and the center-section hard point late model F6F-3s could carry a total bomb-load in excess of 2,000 lb. Six 5 in. HVARs (High Velocity Aircraft Rocket) could be carried; three under each wing on "zero-length" launchers.


A U.S. Navy Grumman F6F-3 Hellcat of fighter of VF-1 over California, in early 1943.
[Source: U.S. Navy]

Two night fighter sub-variants of the F6F-3 were developed: the 18 F6F-3E's were converted from standard-3s and featured the AN/APS-4 radar in a pod mounted on a rack beneath the right wing, with a small radar-scope fitted in the middle of the main instrument panel and radar operating controls installed on the port side of the cockpit. The later F6F-3N, first flown in July 1943, was fitted with the AN/APS-6 radar in the fuselage, with the antenna dish in a bulbous fairing mounted on the leading-edge of the outer right wing; approximately 200 F6F-3Ns were built. Hellcat night fighters claimed their first victories in November 1943. A total of 4,402 F6F-3s were built through until April 1944, when production was changed to the F6F-5.

The F6F-5 featured several improvements including a more powerful R-2800-10W engine, embodying a water-injection system and housed in a slightly more streamlined engine cowling, spring-loaded control tabs on the ailerons, and an improved, clear view windscreen, with a flat armored-glass front panel replacing the F6F-3's curved plexiglass panel and internal armor glass screen. In addition, the rear fuselage and tail units were strengthened, and, apart from some early production aircraft, the majority of the F6F-5's built were painted in an overall gloss sea blue finish. After the first few F6F-5s were built, the small windows behind the main canopy were deleted. The F6F-5N night fighter variant was fitted with an AN/APS-6 radar in a fairing on the outer-starboard wing. A small number of standard F6F-5s were also fitted with camera equipment for reconnaissance duties as the F6F-5P. While all F6F-5s were capable of carrying an armament mix of one 20 mm M2 cannon in each of the inboard gun bays (220 rounds per gun), along with two pairs of .50 in. machine guns (each with 400 rounds per gun), this configuration was only used on later F6F-5N night fighters. The F6F-5 was the most common F6F variant, with 7,870 being built.


A Grumman F6F-5 Hellcat fighter armed with HVAR rockets at the
Naval Ordnance Test Station at Inyokern, California, in 1944/45.
[Source: U.S. Navy]

Other prototypes in the F6F series included the XF6F-4 (Bu. 02981, a conversion of the XF6F-1 powered by an R-2800-27 and armed with four 20mm M2 cannon) which first flew on October 3, 1942 as the prototype for the projected F6F-4. This version never entered production and 02981 was converted to an F6F-3 production aircraft. Another experimental prototype was the XF6F-2 (Bu. 66244), an F6F-3 converted to use a Wright R-2600-15, fitted with a Birman manufactured mixed-flow turbocharger, which was later replaced by a Pratt & Whitney R-2800-21, also fitted with a Birman turbocharger. The turbochargers proved to be unreliable on both engines, while performance improvements were marginal. As with the XF6F-4, 66244 was soon converted back to a standard F6F-3. Two XF6F-6s (Bu. 70188 and Bu. 70913) were converted from F6F-5s and used the 18-cylinder 2,100 hp Pratt and Whitney R-2800-18W two-stage supercharged radial engine with water injection and driving a Hamilton-Standard four-bladed propeller. The XF6F-6s were the fastest version of the Hellcat series with a top speed of 417 mph (671 kph), but the war ended before this variant could be mass-produced.

The last Hellcat rolled out in November 1945, the total production being 12,275, of which 11,000 had been built in just two years. This high production rate was credited to the sound original design, which required little modification once production was underway.

Source:
Wikipedia

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