Before the unique, twin-engined Grumman XP-50 popped up on U.S. Army radars prior to World War 2 (1939-1945) it existed as a similar form for potential sale to the United States Navy (USN) as the XF5F "Skyrocket" lightweight fighter prototype. It was originally envisioned as a fast shipborne interceptor with the handling and performance capabilities to match enemy fighters of the period head-to-head. After Grumman presented the USN with its radical design, it was ordered for prototyping on June 30th, 1939 - nearly a two-years-and-a-half before America's entry into World War 2 (December 1941). Its model designation became "G-34".
The XF5F was unique by any measure of the period. It sat the sole crewmember in a truncated fuselage that was capped at its front by the straight-edged wing mainplanes. These mainplanes mounted the two engine nacelles at their leading edges, giving the fighter a wholly unique appearance. The tail unit was set in its usual place but carried a twin-rudder configuration set about a pair of upward-cranked horizontal planes. A "tail-dragger" undercarriage rounded out the aircraft's physical qualities.
Dimensions included a running length of 28.8 feet, a wingspan of 42 feet, and a height of 11.3 feet. Empty weight was 8,110 lb against a Maximum Take-Off Weight (MTOW) of 10,900 lb.
Power was served through 2 x Wright XR-1820-40/42 "Cyclone" 9-cylinder air-cooled radial piston engines outputting 1,200 horsepower each. The engines drove the three-bladed propellers in opposite directions, effectively cancelling the natural torque effect generated by each engine's spinning blades and making for a more steady flying and gunnery platform. Performance was promising to say the least.
The entry of the XF5F during this period of American naval aviation history was of particular note as it was a twin-engined performer during a time when the first monoplanes in USN service were just beginning to take hold in inventory. Twin engines offered better range and power at the expense of complexity, maintenance requirements, and overall size on space-strapped carriers. Regardless, any advantage that could be gained against an enemy fighter was certainly entertained and Grumman had already established itself as the premiere aircraft supplier to the USN so the partnership between the two was not unwarranted.
First flight of the XF5F prototype occurred on April 1st, 1940 and this early period of testing revealed issues that forced revisions including a lengthening of both nose and engine nacelles and a reworking of the engine cooling system. Aerodynamics were further addressed by spinners added to each propeller unit and the cockpit canopy being lowered. The armament fit was changed from 2 x cannons to 2 x 0.50 caliber heavy machine guns with 2 x 0.30 caliber medium machine guns. This combination armament approach was common to many interwar American fighter planes - particularly before it was realized that a full battery of 0.50 machine guns offered the best firepower against more modern enemy fighters. On the whole, the fighter proved to have exceptional straight line speed for its time, good maneuverability, and a stellar rate-of-climb.
When tested against its contemporaries, the Grumman aircraft outshined the competition - including such war-winning classics like the British Supermarine "Spitfire" and the in-development Vought XF4U (to become the F4U "Corsair"). Due to logistical matters, however, the complex twin-engine aircraft was not pursued by the USN -instead it favored more conventional, easier-to-produce and maintain monoplanes like Grumman's other product - the F4F "Wildcat" and its successor, the F6F "Hellcat".
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