History
Background
On November 27, 1939, the US Army Air Corps issued a Request for Proposal R-40C that sought a high-speed, long-range, high-altitude interceptor with improved performance, armament, and pilot visibility over existing fighters. The interceptor was to be specialized to exterminate enemy bombers. The specifications already outlined that the interceptor must be capable of reaching 20,000 feet in 7 minutes and attaining 425 mph at 15,000 to 20,000 feet. The armament would be either at least four guns or cannons. The specifications were very ambitious, and they intended to encourage manufacturers to produce innovative interceptors that would outperform any existing fighter in the era. In addition, they allowed the manufacturers to come up with unconventional radical aircraft designs.
Just 22 other manufacturers had issued proposals to meet the Army’s request; the XP-54, XP-55, and XP-56 designs were among the accepted proposals.
Design and Development
Vultee submitted a proposal for XP-54 design in response to the US Army Air Corps’ R-40C. Subsequently, the Vultee design received the most points in the evaluation in May 1940. On June 22, 1940, a contract for the XP-54 was placed, with a prototype being ordered at the end of the year.
The XP-54 was designed as an inverted gull-wing monoplane with a pusher engine in the rear of the fuselage, and its tail was mounted rearward between two mid-wing booms. Span was projected to be 40.0 feet, 37.5 feet long, and 9,055 pounds gross. Armament was planned to be two .30- and two .50-cal. machine guns and a pair of 20-mm cannons, all in the nose. The aircraft was estimated to attain 525 mph at 15,000 feet to 20,000 feet with military power. The Pratt & Whitney X-1800 engine was proposed as the powerplant, rated at 1,850 horsepower.
During 1941, after the preliminary design and wind-tunnel testing with the mockup, the original design had to be extensively redesigned, as the XP-54 was required to have a turbo-supercharger system, pressurized cockpit, beefier armament, and heavier armor added. Consequently, the aircraft’s weight was estimated to have increased to 18,000 pounds with these features, and its armament was changed to 37-mm cannons and .50-cal. machine guns. Due to development issues, the liquid-cooled Lycoming XH-2470 engine, rated at 2,300 horsepower, was substituted for the planned X-1800 engine. The new engine was heavier than Vultee had intended for the airframe, so the redesign had to be pursued. The plan to install contra-rotating propellers was considered but later dropped. The estimated peak speed was downgraded to 476 mph at 30,000 feet and eventually revised to 403 mph.
The redesigned XP-54 featured unique designs. The pressurized cockpit required an entry from the ground for the cockpit access. The pilot’s seat acted as an electrical elevator, and it could be lowered, sat in, and raised into the cockpit. In events of bailout and emergency, the pilot would have to bail out via a downward ejection to clear the propeller arc. The nose section had mounts that could also hydraulically pivot in elevation, from 3 degrees up to 6 degrees down, to compensate for the range of the guns. a special compensating gun sight was used to control the movement of these nose mounts. The gun sight functions included controls via the yoke and throttle, values, and symbology projected onto the combiner glass. This large nose section of the XP-54 earned its nickname, the Swoose Goose.
Flight Testings
By September 1941, a second prototype was ordered and scheduled to be delivered on March 17, 1942. The prototype was built and delivered on July 1, 1942, but it did not fly until January 15, 1943, as Vultee was working on an additional project of the A-35 Vengeance development. Flight tests of the prototype (41-1210) with an Olive Drab camouflage began on January 15, 1943, out of Muroc Army Airfield Base, California. However, this aircraft was temporarily equipped with a Curtiss propeller that reduced performance. The aircraft completed a 31-minute flight, and it was uneventful until it began to experience the malfunction of the Curtiss propeller. The faulty propeller was immediately replaced by a Hamilton-Standard propeller.
By March 11, 1943, the aircraft had completed its tenth flight, and it revealed that its performance did not meet expectations. Although the XP-54’s unique wing features and turbo-superchargers allowed it to reach impressive altitudes, the experimental engine proved volatile due to overheating issues. The Vultee engineers introduced changes to the aircraft by enlarging vertical tails to remedy fin stall and extending the top leading edge forward, revising an exhaust behind the cockpit, and installing steel cowls aft of the turbo exhausts to prevent overheating of the structure. After the engine change, the aircraft was ferried to Ontario Army Airfield Base, California, and testing continued there and at Vultee Field. The aircraft was then flown to Wright Field on October 28, 1943. At arrival, this aircraft had completed 63.2 hours in 86 flights. However, the Lycoming engine developed serious problems after it broke down on takeoff, and the engine had to be returned to the manufacturer for repairs. The repair costs were found to be very costly. The Allison V-2420 engine was proposed to replace the Lycoming engine, but it required substantial airframe changes, which would set the project back further. Consequently, the aircraft was out of action and would never fly again after scraping away.
The second prototype (42-108994) with a natural-metal finish was built but delayed by the need to change from the Wright Type B turbo-supercharger system to an experimental General Electric XCM turbo-supercharger system. However, on May 25, 1943, the US Army Air Forces decided there would be no production order for the P-54s. Nevertheless, the aircraft was delivered by May 24, 1944, and began flying that day. This aircraft had the armament installation and continued for testing. The aircraft made a 20-minute flight from Downey to Ontario, California. The overall performance of the loaded aircraft fell below the expectation, as the top speed was only 381 mph. This aircraft would go through a thorough cleanup of the design. The aircraft flew nine more times, and it was able to reach 404 mph at 28,000 feet. Its last flight was on April 2, 1945, without firing any guns. The combination of the engine and experimental turbo-superchargers was unsatisfactory, as the aircraft experienced catastrophic engine failure and broke down. The aircraft was returned to the manufacturer before being stripped of essential parts. The aircraft only flew ten flights for 10.7 hours.
Epilogue
The XP-54 was the last project that the Vultee Aircraft Company attempted to deliver for the US Army Air Force under its name. In June 1943, Vultee was merged with Consolidated to form Consolidated Vultee Aircraft Corporation. This name was later officially renamed and registered as Convair in 1954 when it was purchased and became a division of General Dynamics.
Although the XP-54 had the most innovative features in its design, it would never enter production, as the engine issues and inadequate performance were attributed to the failure. However, development complexes, delays, and cost overruns were so prohibitive that they already had doomed the entire project. Also, the effectiveness of conventional aircraft designs during World War II, such as the P-38 Lightning, P-47 Thunderbolt, and P-51 Mustang, made the XP-54’s specialized mission redundant. Despite its doomed failure, the XP-54 remained one of the important aircraft in US aviation history since it became an existing pioneer of innovative aircraft designs during the pre-war era.
