Curtiss-Wright XP-55 Ascender

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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".<ref>Jenkins 2008. p. 8.</ref> 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. Development of the Ascender was cancelled when testing revealed it to be inferior to conventional fighter aircraft, and the first jet fighters were operational.

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.<ref name=":2">Rubenstein & Goldman  (1974) p178</ref> 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.<ref name=":0">Template:Cite web</ref><ref name="NationalAirSpaceMuseum" />

Accordingly, Curtiss-Wright built at their St Louis division a flying full-scale mockup they designated CW-24B.<ref name=":3">Bowers (1984) pp 10-11</ref> The flying testbed was powered by a Template:Convert Menasco C68-5 inline engine.<ref name=":0" /><ref name=":4">Template:Cite web</ref>Template:Unreliable source? It had a fabric-covered, welded steel tube fuselage with a wooden wing.<ref name=":1">Template:Cite web</ref> The undercarriage was non-retractable.<ref name=":0" /> The canard did not carry load but only trimmed flight.<ref name=":3" /> The CW-24B model completed its maiden flight in December 1941.<ref name=":0" /> From November 1941 to May 1942, the Model 24B logged 169 flights at Muroc Dry Lake, California. The tests appeared to show potential.<ref name="NationalAirSpaceMuseum" /> The CW-24B then went to NACA at Langley Field for wind tunnel tests.<ref name=":3" />

On 10 July 1942, the United States Army Air Forces issued a contract for three prototypes under the designation XP-55.<ref name="NationalAirSpaceMuseum">Template:Cite web</ref><ref name=":4" /> 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.<ref name=":1" /> Curtiss decided to switch to the Template:Convert Allison V-1710<ref name="NationalAirSpaceMuseum" /> (F16) liquid-cooled inline engine because of its proven reliability.<ref name=":1" /> Armament was to be two Template:Convert Hispano autocannon and two Template:Convert M2 Browning heavy machine guns.<ref name=":0" /> During the mock-up phase, engineers switched to the Template:Convert V-1710-95.<ref name="NationalAirSpaceMuseum" /><ref name="AirZoo">Template:Cite web</ref> The 20 mm cannons were also replaced by 0.50 in machine guns.<ref name=":4" />

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.<ref name=":0" /><ref name=":1" />

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<ref name=":0" /><ref name="AirZoo"/> from the Army's Scott Field near the Curtiss-Wright plant in St Louis, Missouri.<ref name=":1" /> The pilot was J. Harvey Gray,<ref name=":0" /> 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.<ref name=":1" />

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"<ref name=":2" /> and it fell out of control for Template:Convert before Gray was able to parachute to safety. The aircraft was destroyed and "left a smoking hole in the ground".<ref name="NationalAirSpaceMuseum" /><ref name=":1" />

The second XP-55 (serial 42-78846) was similar to the first, but with a slightly larger nose-elevator,<ref name=":1" /> 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.<ref name="NationalAirSpaceMuseum" /><ref name=":1" /> All flight tests were restricted so the stall-zone was avoided; included no stalling below 20,000 ft.<ref name=":3" /><ref name=":1" /><ref>Bowers 1979, p. 467.</ref>

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.<ref name=":2" /> It was the only prototype to be fitted with armament - four 0.5-inch machine guns.<ref name=":3" />

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.<ref name=":1" /><ref>Balzer 2008</ref> After a low pass in formation with a Lockheed P-38 Lightning and a North American P-51 Mustang<ref name=":1" /> on each wing, its pilot, William C. Glasgow, attempted a slow roll,<ref name=":1" /> 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.<ref name=":1" /><ref>Scott, Roland B. "Air Mail", Wings, Granada Hills, California, October 1978, Volume 8, Number 5, p. 10.</ref>

In test flights the XP-55 achieved 390 mph at 19,300 feet but suffered engine cooling problems.<ref name=":2" /> In terms of overall performance, testing of the XP-55 revealed it to be inferior to conventional fighter aircraft.<ref name="NationalAirSpaceMuseum" /><ref name=":1" /><ref>Green 1969, p. 65.</ref> 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.

Aircraft disposition

XP-55 on display at the Air Zoo

Specifications (XP-55)

Curtis XP-55 Ascender side view.
Patent for the propeller jettison system used on the XP-55.

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See also

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References

Citations

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Bibliography

Further reading

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