The Grumman Aircraft Engineering Corporation of Bethpage, Long Island is best known for its line of superb carrier-based fighters such as the F4F Wildcat and the F6F Hellcat. One of its less well-known products was the XP-50, which was an Army-financed development of the Navy's Grumman XF5F-1 Skyrocket experimental twin-engined shipboard fighter.
The XF5F-1 traces its origin back to 1935, when the US Navy's Bureau of Aeronautics (BuAer) first contemplated the development of a single-seat, twin-engined carrier-based fighter. In early 1937, the BuAer sent out to the aircraft industry a request for proposals for twin-engined, carrier-based fighter designs capable of exceeding 300 mph.
Brewster, Curtiss, Lockheed, Seversky, and Vought all submitted proposals in response to the request. Grumman's submission was known by the company as Design 25--a high-altitude fighter powered by a pair of turbosupercharged Allison V-1710 liquid- cooled engines. However, the Navy deemed that none of these proposals promised sufficient performance improvements over new single-engined fighters to justify issuing a development contract.
The Bureau of Aeronautics revised its fighter requirements in early 1938. They concluded that the best performance could be obtained by using either a pair of turbosupercharged R-1535 or R-1830 radials, or a single turbosupercharged V-1710 liquid-cooled engine. On February 1, 1938, the BuAer issued a new request for proposals, calling for either a single-engined fighter powered by a mechanically-supercharged Allison engine or for a twin-engined fighter powered by a pair of radial engines. Armament was to be 2 20-mm cannon and two 0.30-in machine guns. The top speed was not specified, but it was to be the highest possible that could be attained.
Bell, Brewster, Curtiss, Grumman, and Vought all submitted designs in response to the request for proposals. Vought also took a chance and submitted a design powered by the Pratt and Whitney R-2800 radial engine, although this particular engine was not specified in the RFP. On April 11, 1938, the Navy issued contracts to Vought for the XF4U-1 with an 1850 hp Pratt and Whitney XR-2800-4 radial (this was to evolve into the famous Corsair), and to Grumman for the XF5F-1 powered by a pair of 750 hp. Pratt and Whitney R-1535-96 radials driven by two-speed superchargers. On November 8, 1938, a third contract was issued to Bell for the XFL-1 (a navalized version of the P-39 Airacobra) powered by the 1150 hp Allison V-1710-6 liquid-cooled engine.
Grumman's XF5F-1 design was given the company designation of Design 34. Very early on, Grumman was forced to substitute Wright R-1820 radials for the much smaller R-1535 engines, since Pratt and Whitney was no longer offering the two-speed supercharger as an option. Although the greater diameter of the Wright engines offered the gloomy prospects of considerably poorer forward and downward visibility (particularly serious defects for a carrier-based aircraft), the Navy reluctantly agreed to the change. Since Grumman was at that time forced to give priority to the development of the F4F-3 Wildcat, work on the XF5F-1 proceeded very slowly.
The prototype XF5F-1 (BuNo 1442) finally took to the air for the first time on April 1, 1940. An unusual feature of the aircraft was an extremely short nose--the forward extremity of the nose did not go past the leading edge of the wing. A large and high cockpit canopy was fitted. Like Navy carrier-based planes of the period, the XF5F-1 was a taildragger. The wings folded just outboard of the engine nacelles, and the main undercarriage members retracted into the engine nacelles. The XF5F-1 was powered by two 1200 hp Wright XR-1820-40 and -42 engines driving 3-bladed propellers rotating in opposite directions. Provision was made for four 23-mm Madsen cannon to be mounted in the abbreviated nose, but no armament was ever actually fitted.
There were problems with the XF5F-1 almost from the very beginning-- engine oil cooling was inadequate, aerodynamic drag was excessive, and there were problems with the closing of the undercarriage doors. Sideward and downward visibility were both atrocious, owing to the forward location of the wings and the position and large diameter of the radial engines.
The XF5F-1 was delivered to the Navy at NAS Anacostia on February 22, 1941. By that time, it was painfully obvious to just about everyone that the Skyrocket would never make a useful carrier-based fighter. The XF4U-1 Corsair was already exceeding 400 mph in its test flights, and the Navy had requested that Vought adapt its design for production.
Nevertheless, the Navy was not entirely ready to give up on the XF5F-1, and returned the aircraft to Grumman for some major modifications in an attempt to alleviate some of its more obvious shortcomings. The engine nacelles were lengthened and extended further aft, spinners were fitted to the propellers, the height of the canopy was reduced, wing fillets were added, and the fuselage nose was extended forward of the wing leading edge. However, when the plane was returned to Anacostia on July 24, 1941, it was found that the changes had not provided any significant improvements in the aerodynamic drag or in the engine cooling problems.
The strongest point of the XF5F-1 was its rate of climb--4000 feet per minute as compared to 2660 ft/min for the XF4U-1 and 2630 ft/min for the XFL-1. However, maximum speed was only 383 mph at sea level. Empty weight was 8107 lbs and normal loaded weight was 10,138 lbs. Service ceiling was 33,000 feet and maximum range was 1170 miles. The XF5F-1 was used off and on for tests in support of the XF7F-1 project for the next couple of years, until it was finally stricken off record on December 11, 1944 after suffering an undercarriage failure.
As detailed in the article on the XP-49, in early 1939, the Army had issued a Circular Proposal calling for a new generation of fighters which would match existing airframes with new and more powerful engines. Four companies submitted designs in response to the proposal. Lockheed submitted its Model 522, which was an adaptation of the P-38 powered by either Pratt and Whitney XH-2600 or Wright R-2160 turbosupercharged engines. Grumman submitted a proposal known under the company designation of Design 41. Design 41 was an aircraft quite similar to Design 34 (XF5F-1) but was powered by a pair of Wright R-1820 radials fitted with turbosuperchargers.
The Lockheed design came in first in the competition, and was ordered by the Army as the XP-49. However, the Army saw sufficient merit in Grumman's Design 41 that they encouraged the company to submit a revised design, just for insurance in case the XP-49 ran into problems. The revised proposal, known by the company as Design 45, incorporated a nosewheel tricycle undercarriage and a longer nose. Provision was to be made for self-sealing fuel tanks and for armor protection for the pilot. On November 25, 1939, the Army issued a contract for one prototype of Grumman's Design 45 under the designation XP-50. The XP-50 was to be powered by two 1200 hp Wright R-1820-67/69 radials fitted with turbosuperchargers. Armament was to be two 20-mm cannon and two 0.50-in machine guns, all mounted in the nose.
The XP-50 (Ser No. 40-3057) flew for the first time on February 18, 1941, with Grumman test pilot Robert L. Hall at the controls. Early tests were encouraging, and the XP-50 handled much better than did the XF5F-1. Furthermore, the supercharged engines of the XP-50 gave it a much better performance at medium and high altitudes. However, on May 14, 1941 the XP-50 experienced an inflight turbosupercharger explosion while on a flight over Long Island Sound, and pilot Robert Hall was forced to parachute to safety. The loss of the aircraft brought an abrupt end to the XP-50 program.
Estimated maximum speed of the XP-50 (never achieved in tests) was 424 mph at 25,000 feet. Estimated service ceiling was 40,000 feet. An altitude of 20,000 feet could supposedly be reached in 5 minutes. Maximum range was estimated to be 1250 miles. Empty weight was 8307 lbs, and loaded weight was 10,558 lbs. Maximum weight was 13,060 lbs. Wingspan was 42 feet, length was 21 feet 11 inches, height was 12 feet, and wing area was 304 square feet.