TYPE: Lightweight fighter

ACCOMMODATION: Pilot only

POWER PLANT: One Ranger XV-770-7 air cooled engine, rated at 520 hp, driving a two-bladed propeller

PERFORMANCE: 330 mph at 4,000 ft

COMMENT:  The rapid expansion of aircraft production in the USA before WWII inevitably led to shortage in the supply of light alloy. Interest therefore began to be focused upon the substitution of non-critical materials such as wood. In October 1941discussion between USAAF personnel and engineers of the Bell Aircraft Corp began with the view of developing a lightweight “non-strategic” fighter, designated XP-77. The aircraft was a very small low wing monoplane using resin-bonded laminated wood construction with a stressed skin. The engine was a 520 hp Ranger V-770 air-cooled in-line unit that was intended to be developed in a supercharged version, the V-770-9. Six prototypes of the XP-77 were ordered in September 1942, plus two static test airframes, a mock-up and a full-scale model for wind-tunnel testing. But the lack of the supercharged engine, growth in the bare weight of the prototypes, reduced performance estimates, overrunning costs and increasing supplies of light alloys let to interest in the XP-77 programme waning during 1943. The contract was reduced to only two flying prototypes and the first of these was not ready for flight test until April 1944. Both prototypes were tested briefly by the USAAF but in December 1944 the entire development contract was terminated, the consensus of opinion being that the XP-77 was operationally unsuitable and that its performance showed no improvement over heavier fighters of conventional construction (Ref.: 8).

TYPE: Long-range fighter

ACCOMMODATION: Pilot only

POWER PLANT: One Lycoming XH-2470-1 liquid-cooled engine, rated at 2.300 hp

PERFORMANCE: 381 mph at 28,500 ft

COMMENT: The Vultee XP-54 had its origin in the US Army Air Corps Circular Proposal R-40C, which invited manufacturers to submit designs for fighters of high prospective performance, without the customary limitations on design orthodoxy. Besides Curtiss (XP-55 Ascender), Northrop (XP-56 Black Bullet), and McDonald (XP-67 Moon Bat) Vultee Field Division of Consolidated Vultee Aircraft Co submitted its design Model 78. This aircraft was powered by an Allison V-1710 (without supercharger) or Pratt & Whitney X-1800 engine driving a pusher propeller, and with a twin-boon layout. A unique feature was that the whole nose section could be varied in elevation to permit compensation for range of the guns it contained. Movement of this nose section was linked to a special compensating gun sight. A contract for the Vultee design, officially XP-54, was placed on June 1940 and the order for a prototype was given at the end of that year, followed by an order for a second prototype on March 1942.  The supercharged Lycoming H-2470 engine was chosen to replace the X-1800 when the latter was discontinued. Work on the XP-54 made slow progress during 1942 and the first prototype did not fly until January 1943. It quickly became apparent that the top speed was as much as 100 mph below estimate, partly because the Lycoming engine was not performing as planned. Although substitution of Allison V-3420 was considered as an alternative for the XP-54, this effectively brought the Vultee fighter program to an end (Ref.: 9).

TYPE: Interceptor fighter

ACCOMMODATION: Pilot only

POWER PLANT: One Allison V-1710-95 liquid-cooled engine, rated at 1,250 hp

PERFORMANCE: 390 mph at 19,300 ft

COMMENT: One of the most radical fighter designs to fly during WW II, the Curtiss XP-55 was evolved as a result of Circular Proposals R-40C which called for a fighter powered by the Pratt & Whitney X-1800-A3G engine which, by employing an conventional design, offered enhanced pilot visibility and armament installation, and a considerable reduction in overall drag by comparison with similar powered single-seaters of conventional configuration. An US Army Air Corps specification issued on November 1939 set forth performance requirements and, in addition to Curtiss-Wright, the Vultee and Northrop companies submitted design proposals, these eventually appearing as Vultee XP-54 and Northrop XP-56 and also employing unorthodox configurations. On July 1943 a contract was issued for three XP-55 fighters powered by the Allison V-1710, which engine was selected in preference to the Pratt &N Whitney X-1800 on the basis of reliability and availability. The first XP-55 was completed on July 1943, and flight testing began immediately. This aircraft was destroyed on November 1943 during stall tests. While the second prototype began flight test on January 1944 under restricted conditions, extensive modifications were incorporated in the third XP-55 that began flight test on September 1944. The results of these trials indicated that, in general, the handling characteristics of the XP-55 were satisfactory. A serious handicap was engine cooling which was critical during all phases of operation. The XP-55 attained a maximum speed of 377.5 mph at 16,900 ft. The official conclusions were that the performance did not compare favourably with standard production fighters and further development was abandoned (Ref.: 13)

TYPE: Interceptor fighter

ACCOMMODATION: Pilot only

POWER PLANT: One Pratt & Whitney R-2800-29 radial engine, rated at 2,000 hp

PERFORMANCE: 465 mph at 25,000 ft (estimated)

COMMENT: After the accident of the first XP-56 prototype it was decided to re-balance the second prototype and move the center of gravity forward. Other changes included a major increase in the size of the upper vertical surface, and the incorporation of a novel form of rudder control which made use of air bellows to operate wingtip split flaps for directional control. The control of the bellows was achieved by valving air to or from the bellows by means of wingtip venturis. On March 1944 the second XP-56 was flows for the first time. Nose heaviness, relative low speeds, high fuel consumption and control instability led the N.A.C.A. to test the aircraft in the wind tunnel at Moffett field. Meanwhile, some more flight test have been performed but proved not satisfactory. It was decided that further flight test were too hazardous and after the project had been inactive for more than a year the decision was taken to abandon the project (Ref.: 13).

TYPE: Interceptor fighter

ACCOMMODATION: Pilot only

POWER PLANT: One Pratt & Whitney R-2800-29 radial engine, rated at 2,000 hp

PERFORMANCE: 465 mph at 25,000 ft (estimated)

COMMENT: One of the most radical American wartime experimental fighters was Northrop’s XP-56, a unique tailless interceptor built entirely of magnesium. It was designed around the projected Pratt & Whitney X-1800 liquid cooled engine which, installed as a pusher, was to drive contra-rotating airscrews. A prototype was ordered on September 1940, but shortly after development began, Pratt & Whitney requested authority to abandon further work on the X-1800 engine. So, on July 1941, it was decided that the Pratt & Whitney R-2800-29 should be installed. In the meantime, flight trials with the Northrop N1M Flying Wing, which had an essentially similar wing of the XP-56 fighter, had confirmed the stability of the radical configuration about all three axis, and, realizing the impracticability of having only one prototype under construction, on February 1942, the U.S.A.A.F. ordered a second XP-56. Taxi trials with the first XP-56 were undertaken in April 1943 but due to many problems with the power plant the first flight was not made until September 1943. Further flights at low altitudes were completed, but during taxiing the port tire blew out and the first XP-56 was destroyed (Ref.:13).

TYPE: Long-range fighter

ACCOMMODATION: Pilot only

POWER PLANT: Two Continental XI-1430-17/19 liquid-cooled engines, rated at 1,350 hp each

PERFORMANCE: 405 mph at 25,000 ft

COMMENT: In 1939 the McDonnnell Aircraft Corporation submitted the Army Air Corps proposals for a long-range fighter with an unconventional design. The engine, an Allison V-3420-B2 or Pratt and Whitney H-3130, both with two-stage superchargers, was buried in the fuselage aft of the pilot, and driving two pusher airscrews aft of the wings by means of an extension shaft and right-angle gear drives. After further changes in the design studies in 1941 the project received the designation XP-67, and two prototypes were ordered. McDonnell design team attempted to maintain true aerofoil sections throughout the entire fighter, the centre fuselage and the rear portions of the engine nacelles merging to give the aircraft a unique appearance. Power was provided by two Continental XI-1430-1 engines fitted with General ElectricD-2 turbo-superchargers driving four-blade airscrews and using the exhaust to augment thrust. By December 1943 the first XP-67 was completed and ground trials began immediately. The aircraft eventually flew the first time on January 6, 1944, but after a few minutes the flight was terminated in an emergency landing due to difficulties with the experimental engines. Flight trials continued throughout the summer 1944 resulting in several changes in the design and on September 1944 the XP-67 was irreparably damaged by fire resulting in the termination of the development contract (Ref.: 13).