From the Planes You’ve (Probably) Never Heard Of Department of Wingspan, we bring you the Grumman XF5F Skyrocket (and the Grumman XP-50 for good measure).
In the world of small military aircraft, there are two basic categories: fighters and interceptors. Fighters, as the name suggests, do just that. They meet enemy fighters and duke it out at altitude, or attack waves of incoming bombers, hopefully from above. Interceptors, on the other hand, are generally launched at the first sign of an attack and must be able to gain altitude quickly to meet approaching threats. Rate of climb is everything. During WWII, the US Navy had plenty of single-engine fighters, but they didn’t have a true interceptor. Seeing a need to be filled, the Grumman Corporation proposed a rather odd looking aircraft, one they hoped would become the Navy’s first twin-engine interceptor.*
Twin-engine fighters were nothing new. The Lockheed P-38 Lightning had been beating up the skies over Europe and the Pacific since 1941, and the de Havilland Mosquito practically defined the category of lightweight twin-engine fighter, putting the most powerful engines available into the lightest airframe possible. For the Skyrocket, Grumman proposed a fighter under 10,000 pounds maximum takeoff weight (by comparison, the P-38's MTOW was more than twice that) and powered by a pair of 1,200 hp Wright R-1820 Cyclone 9-cylinder radial engines. To negate the problems associated with engine torque found in single-engine fighters, the engines of the Skyrocket turned in opposite directions, greatly simplifying carrier takeoffs. But the XF5F’s most distinctive feature was its wing, placed forward of the fuselage, with its bulbous engine nacelles placed still farther forward. This arrangement provided excellent forward visibility, and made carrier landing easier, since the pilot’s view of the deck and the Landing Signal Officer was unobstructed. The Skyrocket was also the first Grumman aircraft to feature folding wings for carrier storage.
The Skyrocket took its maiden flight on April 1, 1940, and, in flight tests, it more than lived up to its name, and its light weight and powerful engines gave XF5F a climb rate of 4,000 feet per minute. When pitted against a bevy of contemporary fighters, including the Vought F4U Corsair, in a 10,000-foot climb, the Skyrocket left the Corsair in its wake. One Navy test pilot said, “I pulled away from the Corsair so fast I thought he was having engine trouble.” When the competition was completed, only the Supermarine Spitfire came in a distant second. In general, the Skyrocket performed well, though some redesigns were in order, and engine cooling issues persisted. It’s top speed of 383 mph, however, proved to be its Achilles heel. Ultimately, the Skyrocket lost out to the more traditional Grumman F4F Wildcat for mass production, in part because of a concern over the availability of spare parts and production difficulties associated with its twin-engine design.
Grumman moved on from the Skyrocket to work on the F7F Tigercat, another twin-engine shipboard fighter, but that wasn’t the end of the Skyrocket. Grumman used it as the basis for the XP-50, a redesigned variant with a more traditional fuselage that was pitted against the Lockheed XP-49, a slightly smaller variant of the P-38 Lightning. In a competition, the Lockheed design was selected over the XP-50, though neither aircraft entered production. The Skyrocket continued in a testing role until a landing gear failure in 1944 saw it struck from the list of active aircraft and the single prototype was lost to history. The sole XP-50 prototype was destroyed in a crash when a turbo-supercharger blew up during a test flight.
*The Skyrocket was not the US Navy’s first twin-engine aircraft. That distinction goes to the Douglas XT2D-1, a twin-engine biplane bomber that took its first flight in 1927 but served mostly as a land-based bomber until 1933.
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