Twitter
Facebook
***image1***In the beginning of World War II, the U.S. Army Air Corps, seeing the rapid advances in fighter designs in Europe, issued requirement R-40C for a fighter that would be superior to any fighter in world.
The service specifically said they would consider aircraft with unconventional configurations; one of the aircraft presented was the Northrop XP-56, which bears the distinction of being one of the most radical aircraft built during WWII.
The XP-56 was part of Jack Northrop’s fascination with flying wings. It was a swept-wing, tailless single seat fighter with no forward-mounted canards and had a small, 27-foot-long fuselage and a huge 42-foot-long wing that dominated the design. It was made entirely of magnesium – developing techniques for welding the material was a separate feat in itself – and the XP-56 was built around a Pratt & Whitney liquid-cooled X-1800 engine that drove contra-rotating propellers located at the tail of the aircraft, a “pusher” design. To protect the pilot there was an explosive “rope” around the prop that, in the event of a bail out, would be pulled and blow the propeller off the aircraft.
The XP-59’s stubby, rounded fuselage had a small dorsal fin and a very large ventral fin, which protected the propellers but was very close to the ground. The mid-mounted wing had “elevons” – a combination of elevators, ailerons and wing flaps – mounted on the trailing edge of the drooping wing tip, a feature that was expected to add stability. Air ducts for cooling of the engine were located on the wing leading edge, and the proposed armament was two 20-mm cannon and four 0.50-inch machine guns mounted in the nose.
Unfortunately for the XP-56, Pratt & Whitney stopped development of the liquid-cooled X-1800 and Northrop was forced to substitute the air-cooled Pratt & Whitney R-2800 engine, which provided more horsepower but was much wider. This necessi-tated a new fuselage as well as the addition of a considerable number of drag-producing intakes for cooling air, causing significant delays in the program.
Once the XP-56 prototype was com-pleted, taxi tests began in April 1943.
Before the aircraft flew, high speed taxi events showed the aircraft yawed sharply and dangerously – not a good omen for flight. The first flight – to an altitude of five feet – was delayed until the end of September 1943 but additional flights showed that the aircraft was very nose-heavy and the unusual elevons did not provide sufficient lateral control in any flight regime. However, before any of these aerodynamic problems could be addressed, during another high speed taxi test the left main wheel tire blew out and the XP-56 flipped over and was destroyed.
Fortunately, the test pilot was wearing a polo helmet instead of a leather helmet and survived.
A number of changes were made in the second prototype, including moving the
center-of-gravity forward and increasing the size of the upper vertical tail, and the XP-59 flew again March 23, 1944. The pilot had difficulty rotating the aircraft for takeoff below 160 mph, but when the landing gear was retracted the nose heaviness disappeared. The bad news was that the XP-59 was now extremely tail heavy and further flights showed it was underpowered, had excessive fuel consumption and was generally unstable.
After a few flight tests, the Army Air Force concluded that the XP-56 was not airworthy and it was too dangerous to continue flight tests, especially since jet propulsion was bringing the era of even zvery promising propeller-driven fighters to a close.
In May 1944, NACA began to use their wind tunnel at Moffett Field, Calif., to look into the causes of the XP-56s’ low performance, but higher priority projects delayed the XP-56 wind tunnel tests until late October 1944. The wind tunnel tests of the XP-56 provided valuable data on flying wing designs, some of which was ultimately used in the design of the Northrop B-2 Spirit stealth bomber of the 1990s.
Questions or comments, contact Dr. Michel at marshall.michel@ramstein.af.mil.
