Notes on the History of the XF5F-1
Development of the XF5F-1 twin-engine Navy fighter was undertaken on contract 61586 issued to Grumman Aircraft Engineering Corporation, June 30, 1938. At the time the development was begun, no twin-engine aircraft had operated from a carrier. This was so even though some thought had been given to operating the twin-engine Martin Bomber MT/MBT, from the Navy's first carrier, the Langley, which was commissioned in 1922. In the late twenties a second twin-engine model, the T2D/P2D, was developed for possible carrier use. Various hazards such as the difficulty of retaining precise control during carrier landings appeared insurmountable and in consequence neither aircraft was assigned to carrier for operation although both were used from shore bases, the Mt/MBT from 1920 to 1928 and the T2D/P2D from 1927 to 1937. The first landing of a twin-engine aircraft aboard a carrier was not made until August 30, 1939 when LCDR Thurston B. Clark made 11 landings and take-offs from the Lexington, flying the XJO-3. During the early 1930's, the Navy expressed some interest in a twin-engine fighter, but no development was undertaken until the F5F of 1938. Despite LCDR Clark's basic demonstration of feasibility, the F5F was never operated from carrier and the follow-on twin-engine F7F was operated only experimentally. Routine operation of twin-engine, propeller driven aircraft from carrier was not to begin until the AJ went into service in 1949.
In the mid-1930's the Navy was committed to biplanes for carrier operation. Its in-service fighters were small, compact aircraft with gross weights from under 3,000 to slightly over 4,000 pounds and maximum speeds of less than 200 miles an hour. The August 1935 flight of the prototype Boeing B-17 from Seattle to Dayton, Ohio, at an average speed of 232 miles-per-hour, strongly underlined the need for improved fighters. In the next few years, reports of destruction wrought by aerial bombardment during the Spanish Civil War and a general worsening of international relationships emphasized the need for developing high performance fighters.
In that atmosphere, the Wavy took a number of steps in an effort to obtain fighters that would provide it with an adequate aerial defense. New modifications of in-service biplane fighters were developed which used the 950 and 1050 horsepower R-1820 and R-1830 engines in lieu of the 550 to 700 horsepower R-1350 and R-1535 engines in the operational models. Fighters under development were similarly modified to incorporate the larger engines and the Grumman XF4F-1 biplane was converted into the monoplane XF4F-2. (To look ahead, this model was the initial prototype of the Navy's first line fighter, the F4F-3/-4 of 1942-1943 and a direct ancestor of the F6F which superceded the F4F for fighter-to-fighter combat in the last two years of World War II.)
Increasing engine size meant greater power and higher speeds. It also meant that the aircraft would be larger and heavier than their predecessors and burn more fuel. Insofar as fighter-to-fighter tactics were concerned, this indicated a shift from maneuverability towards high speed as the prime characteristic. Larger and heavier aircraft also indicated that accepted practices of launching, recovering and stowing aircraft aboard carrier would require revision.
In the midst of such conflicts in requirements, the Bureau of Aeronautics in 1937, held a design competition for a small twin-engine fighter. A basic assumption which led to that competition was that installation of engines larger than the R-1830 would not appreciably improve fighter performance. Hence, multi-engine designs warranted consideration. None of the designs submitted showed sufficient improvement in performance over existing developmental aircraft to warrant development. In consequence, the Bureau of Aeronautics engineers conducted an extensive study of the potential of various airframe-engine combinations and in February, 1938 announced another design competition. The analysis had indicated that a twin-engine aircraft incorporating radial air-cooled engines, or a single engine aircraft incorporating liquid-cooled engines were the most promising means of improving fighter requirements. In specifying its requirements, however, the Navy also left the door open to single-engine aircraft with air-cooled engines. Equally important, allowable stalling speed was to be increased to 70 miles-per-hour compared to 60 to 66 mph for in-service models and folding wings would be allowed, thereby facilitating stowage aboard carrier.
Three designs were selected for development from this competition, the Bell XFL-1 incorporating a 1150 horsepower Allison VX-1T10 in a buried installation behind the pilot (a Navy version of the P-39), Chance Vought's Gull winged XF4U-1 incorporating an 1850 horsepower air-cooled XR-2800-4 engine, and Grumman's XF5F-1. (it may be appropriate to observe at this point that while neither the XF5F-1 nor XFL-1 was developed into a service model, the XF4U-l was the prototype for the F4U Corsair which entered combat in late 1943 and remained in naval service through 1955.)
As previously noted, the contract for development of the XF5F-1 was issued June 30, 1938. At the end of September, the aircraft was described in the following terms:
The wings are arranged as a low wing cantilever monoplane consisting of two outer panels and a center section. The outer panels are designed to fold. The wing panels are of metal beam and rib construction with covering of metal. Split trailing edge flaps are provided for reducing landing speeds. The fuselage from the windshield aft is of semi-monocoque aluminum alloy construction. Forward of the windshield the fuselage is of welded steel tube construction. The two engine nacelles extend forward and slightly below the leading edge of the center section and are of welded tube construction. The landing gear retracts into the engine nacelles. The airplane is equipped with two Pratt & Whitney Model R-1535-2 (2 stage) geared engines and a 3-blade constant speed hydromatic propellers. The airplane is designed for catapulting and arresting operations.
The initial engine selection was approved somewhat reluctantly. The major problem being that the engine was experimental and the Navy believed that the market for it was so small that Pratt & Whitney would not complete the development. Accordingly, in November 1938, that contract was modified to provide for installation of Wright Aeronautical Corporation R-1820 engines that were in commercial use.
[The R-1820 engine had substantially greater power than the R-1535 but this was just offset by its greater drag owing to its larger frontal area. Thus performance calculations showed a top speed of 350 miles-per-hour with either engine. The Navy was concerned that the R-1820 engine might have even greater drag than was allowed for in the above prediction of top speed. In an effort to obtain more solid data, a full scale wind tunnel model of the aircraft was constructed and provided with alternate nacelles for R-1535 and R-1820 engines. This model was sent to the National Advisory Committee for Aeronautics full scale wind tunnel at Langley Field for test. Before these wind tunnel tests were completed, the Navy approved use of the larger engine to avoid delay in development of the aircraft.]
Other factors weighed in the decision were that because of a more open arrangement, the larger engine was simpler to overhaul and maintain.
The aircraft was originally expected to be completed and delivered to the Navy about 1 July 1939. The stimulus of overseas orders for aircraft was causing a vast expansion of the American aviation industry. Exports totalled $39,000,000 in 1937, $68,000,000 in 1938 and $117,000,000 in 1939. This in conjunction with modest annual increases in government appropriations for aviation in the United States taxed the capacity of the aviation industry and set it on the stage of conversion from a handicraft industry to the high volume mass production industry that it became during World War II.
The resulting congestion, however, was a major contributor to slippage in delivery of many developmental aircraft during that time period. In addition, some of the delay in completing the XF5F-1 can be attributed to the shift in engines (discussed above). For whatever reasons, the XF5F-1 did not make its first flight until 1 April 1940 with Grumman test pilot B. Gillies at the controls.
Preliminary flight tests showed that the aircraft possessed unexpectedly high drag. In consequence its high speed was much less than anticipated. Accordingly, the F5F was placed in the National Advisory Committee for Aeronautics' Langley Memorial Aeronautical Laboratory and tested in the full scale wind tunnel. (The use of that wind tunnel to effect aerodynamic clean-up of an airplane had begun in 1938 with the XF2A-1 and XF4F-2. The tests had indicated a number of relatively simple changes whereby the drag of the aircraft could be decreased and the maximum speed increased by approximately 10 percent.) Changes to the XF5F-1 resulting from these tests included redesign of the exhaust ejection system, and lengthening both the engine nacelles and the nose section of the fuselage. These changes, it was estimated, would increase the aircraft's top speed by 24 to 27 miles-per-hour. It was not until early 1941, however, that flight tests could be resumed.
By that time, basic requirements for fighter aircraft had been modified to include installation of pilot armor and self-sealing fuel tanks, and other gear whose essentiality had been demonstrated during aerial combat over Europe and the British Isles. Such gear could not have been installed in the existing XF5F-1 airframe, therefore that aircraft could not have served as a true prototype for a production aircraft. Moreover, the single engine XF4U-1, which made its first flight in mid-1940, had exhibited outstanding performance and a contract for 584 aircraft had been issued on 30 June 1941. At the same time design of a new twin-engine fighter, the XF7F-1, had been initiated through contract with Grumman also dated 30 June 1941. Simultaneously, complete redesign of the F4F into the F6F was undertaken.
One other aspect of the F5F which had been significant at the time of its first flights was that the Army Corps was sponsoring development of the Grumman XP-50 which was generally similar to the F5F but was equipped with tricycle landing gear. That aircraft made its first flight in February 1941. In consequence, the F5F had been considered of some value in determining the flight characteristics of the XP-50. An engine explosion caused the XP-50 to crash into Smithtown Bay in May 1941, and the Army chose to drop the design.
With the Army's abandonment of the XP-50 and the Navy's initiation of the twin-engine XF7F-1 fighter, the XF5F-1 lost its military significance. It was still viewed as having technical significance and the Navy planned to use it to develop carrier landing techniques for twin-engine fighters. Even these trials were given low priority.
In mid-1941 the aircraft was at NAS Anacostia, D. C. for combat trials. These were completed and in September it was sent to the Naval Aircraft Factory, Philadelphia, for simulated carrier trials by the Ships Experimental Unit. Upon the aircraft's arrival at Philadelphia, its wheels were damaged during brake repairs; replacement wheels were not obtained until January 1942. At the resumption of tests it experienced a landing gear failure while making an arrested landing with damage to its engine, propeller and cowling. Repairs were made and the flights were resumed in mid-June. Then, during landing trials, the arresting gear on the landing platform failed, causing further damage to the aircraft. These were repaired in mid-August and the aircraft was returned to the contractor for a general check-over prior to tests by the Fleet. Soon after its arrival, the XF5F-1 experienced a taxiing accident. Repair was scheduled, but the XF5F-1 was a low priority project and available records do not indicate that it was flown again. It was finally stricken from the Navy list in 1944. No official reports of its tests have been found.