The Curtiss-Wright XP-55 Ascender (company designation CW-24) is a 1940s United States prototype fighter aircraft built by Curtiss-Wright. Along with the Vultee XP-54 and Northrop XP-56, it resulted from United States Army Air Corps proposal R-40C issued on 27 November 1939 for aircraft with improved performance, armament, and pilot visibility over existing fighters; it specifically allowed for unconventional aircraft designs. An unusual design for its time, it had a canard configuration with a rear-mounted engine, and two vertical tails at end of swept wings. Because of its pusher design, it was satirically referred to as the "Ass-ender".[1] Like the XP-54, the Ascender was designed for the 1,800 hp Pratt & Whitney X-1800 24-Cylinder H-engine, but was redesigned after that engine project was canceled. It was also the first Curtiss fighter aircraft to use tricycle landing gear.
Design and development
Curtiss CW-24B at Langley wind tunnel.
In June 1940, the Curtiss-Wright company received an Army contract for preliminary engineering data and a powered wind tunnel model.[2] The designation 'P-55' was reserved for the project. The exhaustive wind-tunnel tests that from November 1940 through January 1941 left the USAAC dissatisfied with the results of these tests.[3][4]
Accordingly, Curtiss-Wright built at their St Louis division a flying full-scale mockup they designated CW-24B.[5] The flying testbed was powered by a 275 hp (205 kW) Menasco C68-5 inline engine.[3][6][unreliable source?] It had a fabric-covered, welded steel tube fuselage with a wooden wing.[7] The undercarriage was non-retractable.[3] The canard did not carry load but only trimmed flight.[5] The CW-24B model completed its maiden flight in December 1941.[3] From November 1941 to May 1942, the Model 24B logged 169 flights at Muroc Dry Lake, California. The tests appeared to show potential.[4] The CW-24B then went to NACA at Langley Field for wind tunnel tests.[5]
On 10 July 1942, the United States Army Air Forces issued a contract for three prototypes under the designation XP-55.[4][6] Serial numbers 42-78845 through 42-78847 were assigned to the aircraft. During this time, the Pratt & Whitney X-1800 H-block sleeve valve engine was delayed, and was eventually canceled.[7] Curtiss decided to switch to the 1,000 hp (750 kW) Allison V-1710[4] (F16) liquid-cooled inline engine because of its proven reliability.[7] Armament was to be two 20 mm (0.79 in) Hispano autocannon and two 0.50 in (12.7 mm) M2 Bowning heavy machine guns.[3] During the mock-up phase, engineers switched to the 1,275 hp (951 kW) V-1710-95.[4][8] The 20mm cannons were also replaced by 0.50-in machine guns.[6]
One feature of the XP-55 was a propeller jettison lever inside the cockpit to prevent the pilot from hitting the propeller during bailout. The jettison device was invented by W. Jerome Peterson while working as a design engineer for Curtiss-Wright.[3][7]
Operational history
The first XP-55 following a testing crash.
Three XP-55 prototypes were built. Two were destroyed during flight testing, as a result of their propensity for sudden wing stalls.
The first XP-55 (42-78845) was completed and delivered on 13 July 1943, with the same configuration as the final prototype CW-24B. The aircraft made its first flight on 19 July 1943[3][8] from the Army's Scott Field near the Curtiss-Wright plant in St Louis, Missouri.[7] The pilot was J. Harvey Gray,[3] Curtiss' test pilot. Testing revealed the takeoff run was excessively long. To solve this problem, the nose elevator size was increased and the aileron up-trim was interconnected with the flaps so it operated after the flaps were lowered.[7]
In 15 November 1943, test pilot Harvey Gray, flying the first XP-55 (S/N 42-78845), was testing the aircraft's stall performance at altitude. Suddenly, the XP-55 inverted into an uncontrolled descent. The engine failed "making recovery impossible"[2] and it fell out of control for 16,000 ft (4,900 m) before Gray was able to parachute to safety. The aircraft was destroyed and "left a smoking hole in the ground".[4][7]
The second XP-55 (serial 42-78846) was similar to the first, but with a slightly larger nose-elevator,[7] modified elevator-tab systems, and a change from balance tabs to spring tabs on the ailerons. It flew for the first time on 9 January 1944.[4][7] All flight tests were restricted so the stall-zone was avoided; included no stalling below 20,000 ft.[5][7][9]
The third XP-55 (serial 42-78847) flew for the first time on 25 April 1944. Modifications resulting from the investigation of the crash of the first prototype were introduced during construction; the addition of four-foot wingtip extensions to improve the stall characteristics and increasing the limits of the nose elevator travel to improve recovery if a stall did occur.[2] It was the only prototype to be fitted with armament - four 0.5-inch machine guns.[5]
After the second XP-55 (42-78846) was given the same modifications as the third prototype, it underwent official USAAF flight trials between 16 September and 2 October 1944.
The third prototype XP-55 (s/n 42-78847) was lost on 27 May 1945, during the closing day of the Seventh War Bond Air Show at the Army Air Forces Fair at Wright Field in Dayton, Ohio.[7][10] After a low pass in formation with a Lockheed P-38 Lightning and a North American P-51 Mustang[7] on each wing, its pilot, William C. Glasgow, attempted a slow roll,[7] but lost altitude and crashed, sending flaming debris into occupied civilian ground vehicles on a highway near the airfield. The crash killed Glasgow and four civilians on the ground.[7][11]
In test flights the XP-55 achieved 390 mph at 19,300 feet but there were engine cooling problems.[2] In terms of overall performance, testing of the XP-55 revealed it to be inferior to conventional fighter aircraft.[4][7][12] In addition, by the end of 1944, German and British jet-powered fighters were fully operational, and the Lockheed XP-80 was about to commence operational trials with USAAF units in Italy. Development of completely new piston-engine fighter designs was regarded as redundant; further development of such aircraft was terminated, including the XP-55.
Balzer, Gerald H. (2008). American Secret Pusher Fighters of World War II: XP-54, XP-55, and XP-56. North Branch, MN: Specialty Press. ISBN978-1-58007-125-3.
Bowers, Peter M (1979). Curtiss Aircraft, 1907–1947. London: Putnam. ISBN0-370-10029-8.
Bowers, Peter M (1984). Unconventional Aircraft. Blue Ridge Summit, PA: Tab Books.
Green, William (1969). War Planes of the Second World War, Volume Four: Fighters (Sixth ed.). London: MacDonald & Co. (Publishers) Ltd. ISBN0-356-01448-7.
Green, William; Swanborough, Gordon (1977). WW2 Aircraft Fact Files: US Army Air Force Fighters, Part 1. London: Macdonald and Jane's Publishers Ltd. ISBN0-356-08218-0.
Jenkins, Dennis R.; Landis, Tony R. (2008). Experimental & Prototype U.S. Air Force Jet Fighters. North Branch, MN: Specialty Press. ISBN978-1-58007-111-6.
McIntyre, Violet. Niagara Gazette, Niagara Falls, NY, 11 November 2004[full citation needed]
Rubenstein, Murray; Goldman, Richard M. (1974). To Join With The Eagles : Curtiss-Wright aircraft, 1903-1965. Garden City, NY: Doubleday.
Further reading
Balzer, Gerald H. (2014). Curtiss XP-55 Ascender. Air Force Legends. Vol. 217. Simi Valley, CA: Ginter Books. ISBN978-0-9892-5833-3.
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