Curtiss P-55 Ascender
The XP-55 (Curtiss Model 249C), along with the XP-54 and XP-56, resulted from Army Air Corps proposal R-40C calling for unconventional aircraft designs. Like the XP-54, the Ascender was initially designed for the Pratt & Whitney X-1800 engine and had to be redesigned when the engine project was canceled. The XP-55 first flew on 13 July 1943 with an Allison V-1710 engine. It was to be one of the last projects supervised by Donovan Berlin before he left Curtiss to work on the P-75 project for Fisher.
The XP-55 had a pusher engine mounted at rear, swept-back wings and forward canard mountings. The foreplane was not a canard in the true sense, but a free-floating surface with no fixed stabilizer. Its limits were 68 degrees up and down, although the down angle was restricted to 17 degrees for take-offs. Entry to the cockpit was said by test pilots ro be rather awkward, requiring a telescoping ladder that was stored behind the pilot's seat. The XP-55 was essentially a flying wing, having only vestigial vertical surfaces which were distributed on the rear fuselage and outer wings.
The XP-55 was a single-seat single-engine design. The pusher-type engine was mounted to the extreme rear and the wings were highly swept. First drawings and scale models were completed and assessed as early as 1940 to which the Army Air Corps needed more convincing. As a result, Curtiss took it upon itself to produce a flyable full scale model - this one to be designated in-house as the CW-24B. The test aircraft differed some from the final three prototypes developed from the granted contract of 1942. The test bed flew with a Menasco C68-5 powerplant, whereas the final prototype models were fitted each with the Allison V-1710 engine.
Curtiss built a full-scale flying testbed, the company Model CW-24B, powered by a Menasco C65-5 engine. The fabric-covered CW-24B went to a new US Army test site, the airfield at Muroc Dry Lake, California, for 1942 tests. These revealed serious stability problems which were only partly resolved by moving its vertical fins farther out from their initial mid-way position on the swept-back wing. The Curtiss 24-B was not a true canard, in that it had no fixed forward 'tail' surface. Essentially it was a flying wing with a nose-mounted elevator. The 24-B made 169 flights from California's Muroc Dry Lake, but after Curtiss-Wright had validated its concept with the CW-24B flying mock-up the USAAC ordered three XP-55 prototypes, on July 10, 1942. Armament for the XP-55 was originally drawn up to include a pair of 20mm cannon to go along with twin 12.7mm (.50 caliber) machine guns. This arrangement was revisited and revised to a quad .50 caliber array during the testing phase and this standard armament stayed with the life of the program.
For Curtiss, it would be its first design to feature a powered tricycle landing gear assembly (though fixed on the initial test models). The absence of a true rudder resulted in smaller vertical surfaces mounted far off onto the wings. The use of forward canards was also revolutionary as was the ejection system - the propeller had to be jettisoned before the pilot could eject himself. The XP-55 used a single rotation, three-bladed propeller instead of the co-axial, contra-rotating type which had been planned.
The first XP-55 (42-78845) was completed on July 13, 1943. It made its first test flight on July 19, 1943 from the Army's Scott Field near the Curtiss-Wright St Louis plant. The aircraft experienced stability problems and underwent several modifications to increase the canard elevator surface, vertical stabilizer area, and eventually received four-foot wing tip extensions to improve stall characteristics. It was found that excessive speed was required in the take-off run before the nose-mounted elevator could become effective. Before this problem could be addressed, the first machine was lost during spin tests at St Louis on 15 November 1943. The first prototype underwent stall testing and on the third attempt the aircraft pitched forward 180 degrees onto its back and fell into the same inverted descent predicted in original Air Corps wind tunnel tests. The engine quit and nothing the pilot did could break the stall. After a perfectly stable fall of 16,000 feet, the pilot, J. Harvey Gray, bailed out safely. The aircraft continued straight down and dug a large smoking hole in the desert floor. After modifications, stall tests were performed satisfactorily, although the complete lack of any warning prior to the stall and the excessive loss of altitude necessary to return to level flight after the stall were undesirable characteristics.
The second XP-55 was flown in St Louis on 9 January 1944. The third followed on 25 April 1944 and, soon after, went to Eglin Field, Florida, for tests of its nose-mounted 12.7mm machine-guns.
The XP-55 had the advantage of being constructed largely from non-strategic materials and for a time a jet version, the company Model CW-24C, was contemplated. But lingering problems, including generally poor stability, remained unsolved when the third XP-55 was returned to Wright Field, Ohio, for further tests continuing into 1945.
An artificial stall warning device was introduced to try and correct some of these problems, and between September 16 and October 2, 1944, the second Ascender underwent official USAAF trials. The trials indicated that the XP-55 had satisfactory handling characteristics during level and climbing flight, but at low speeds and during landings there was a tendency on the part of the pilot to over-control on the elevators because of a lack of any useful "feel". Pilot, Russ Schleeh, commented that it was terribly unstable, and that if you took your eyes off the horizon for a moment, even in the landing pattern, the plane would drift wildly off course.
The performance of the XP-55 prototype aircraft built (S/N 42-39347, 42-78845-7) was not very impressive and was in fact inferior to that of the more conventional fighters already in service. Performance was mediocre with the Allison V-1710 engine attaining only 377 mph instead of the hoped-for 500 mph. Engine cooling was also a problem. In addition, by 1944, jet-powered fighter aircraft were clearly the wave of the future. Consequently, no production was undertaken, and further development was abandoned. The third prototype survived the testing program, but was destroyed in an accident on May 27, 1945, at Wright Field, Ohio. The pilot, Captain William C. Glascow, came in low over the field during an air show, attempted a barrel roll at low altitude, and crashed. Not only was the aircraft destroyed but the pilot was killed as well as a passing motorist. The sole surviving XP-55 (42-78846) was flow to Warner Robins Field in Georgia in May of 1945. It was later taken to Freeman Field to await transfer to the National Air Museum at the Smithsonian Institution in Washington. Currently the aircraft is in the Kalamazoo Aviation History Museum undergoing a complete restoration.
The second XP-55 has survived and is among numerous historically valuable airframes held by the Smithsonian Institue's National Air and Space Museum in Washington D.C.
The name Ascender had originated as a joke on the part of a Curtiss engineer, a reference to the aircrafts rather odd design which was not appreciated by the congressional oversight committee. The name stuck, and eventually became official.
Curtiss-Wright XP-55 Ascender
Engine: 1 x Allison V-1710-95 liquid-cooled V12, 1,275hp, 951kW
Length: 29 ft 7 in (9.02 m)
Wingspan: 40 ft 7 in (later 44 ft 6 ft)
Wing area: 209.0 sq ft / 19.41 sq.m later 21.83 sq.m / 234.98 sq ft
Height: 9.84ft (3.00m)
Empty Weight: 6,354lbs (2,882kg)
Maximum Take-Off Weight: 7,710lbs (3,497kg)
Maximum Speed: 390mph (628kmh; 339kts) at 19,300 ft (5,885 m)
Service Ceiling: 34,600ft (10,500m)
Climb to 20,000 ft (6,095 m): 7 minutes 6 seconds
Range: 635 miles (1,022 km)
Armament: 4 x 12.7mm (0.5-in) Colt Browning M2 machine guns in nose
Engine: Menasco C68-5, 275-hp, 633kW