The XP-55 Ascender – July 1, 2013

Less than two years before America declared war on the Japanese in 1941, the U. S. Army Air Corps sponsored three radical and unorthodox fighter aircraft designs. Pusher power plants propelled these three flying experiments but the similarities between the aircraft ended there. Vultee proposed a twin-boom pusher called the XP-54 and Northrop championed a bobbed-tail flying wing dubbed the XP-56 Black Bullet (see NASM collection). Curtiss-Wright designers stuck the main wing behind the engine and the pilot, at the tail end of the fuselage, and they mounted a short wing, or canard, near the nose. The Air Corps designated this entry the XP-55 Ascender. After considerable testing, Air Corps test pilots and engineers judged the Ascender’s performance and handling too poor for an effective combat fighter; however, it demonstrated exactly where future trends in fighter design should not go.

All three designs grew from a document the Air Corps released late in 1939 titled “Request for Data R-40C.” With this paper, Air Corps planners sought to ‘jump-start’ fighter designers and spur them to depart from accepted, low-risk, aircraft design practices and embrace radical new technology. In the beginning, Pratt & Whitney proposed a unique liquid-cooled, 28-cylinder ‘H’engine to power all three aircraft. They claimed the motor could be in production by 1942. Development problems arose, and the engine fell short of projected power ratings. The Air Corps thus turned to less powerful but more conventional power plants.

On June 22, 1940, Curtiss received a contract for engineering data and a powered, wind tunnel model of the XP-55 plus an option for a prototype. By November 2, Curtiss had completed a 1/4 scale powered model and designed two different sweptback wings, one with a conventional airfoil and the other with a new, low-drag, laminar flow airfoil. To control yaw, Curtiss mounted a small vertical fin and rudder on each wingtip. Exhaustive wind-tunnel tests that ran from November 1940 through January 1941 left the Air Corps yawning over mediocre performance estimates but still interested enough in the design to order further study of the laminar flow wing.

To prove the design was sound, Curtiss decided to spend its own money to build a manned flying test bed, the Model 24-B. From November 1941 to May 1942, the Curtiss 24-B logged 169 flights at Muroc Dry Lake, California. The tests appeared to show potential. On July 10, 1942, the Army Air Corps issued a contract for three prototypes equipped with the Allison V-1710 engine. They had already cancelled the Pratt & Whitney H power plant.

The Curtiss factory in St. Louis, Missouri, completed the first prototype XP-55 in July 1943 and quickly moved to the flight test phase. The test schedule progressed satisfactorily until November 15. During a stall test, the aircraft suddenly pitched forward in an outside loop until it stopped inverted, falling straight down. The engine quit in such a way that righting the stricken fighter using engine power was impossible. The Ascender and its pilot fell 4,900 m (16,000 ft) before he bailed out. The XP-55 dug a smoking hole in the ground. More wind tunnel tests followed and the results led to design corrections that Curtiss incorporated into the third prototype. The second prototype was already too far along in construction to incorporate any of these improvements.

Ascender number 2 flew for the first time on January 9, 1944, with major restrictions on in-flight maneuvering. The third prototype flew late in April. After much testing, it looked as though Curtiss engineers had cured the deadly stall situation that doomed the first XP-55. Curtiss retrofitted the stall fixes into prototype number 2, and resumed testing in September 1944. The Army Air Forces (AAF) carried out some armament testing with Ascender number 3 but the end was near for the whole project. Pilots feared the Ascender’s vicious stall characteristics, and it was just plain slow compared to most fighters already in production. The program ended after the third prototype crashed at Wright Field during an air show.

NASM owns the second and last remaining prototype, serial number 42-78846. The flight test career of this airplane ended on April 21, 1945. In May, the Army flew it to Warner Robins Field, Georgia, and it remained stored there until the service transferred it to Freeman Field, Indiana. Along with other aircraft destined for the National Air Museum (now NASM) the XP-55 arrived at Park Ridge, Illinois, in July 1946. The Smithsonian stored the XP-55 at the Paul Garber Facility in Suitland, Maryland, until it was loaned to the Kalamazoo Air Zoo in 2001 for restoration. The Air Zoo finished the project in 2006 and the aircraft is now on display in the Kalamazoo Air Zoo.

Source Document

Have a good week, fly safe, and remember the future of those who follow in your footsteps is based on the professional decisions that you, and others, make today when dealing with the the management teams who control the main line, and regional, carriers.

Robert Novell

July 1, 2013