Twitter
Facebook
Just before World War II began, the U.S. Army Air Corps realized its fighters were woeful compared to the German Bf109 and the British Spitfire. While advanced fighters like the Lockheed P-38 Lightning and Republic P-47 Thunderbolt were in sight, in February 1940, the Air Corps issued Proposal R-40C for a fighter superior to anything previously considered.
It asked for a top speed of more than 500 knots (more than 100 knots faster than anything coming into service) and the very heavy armament of two 20mm cannons and four 50-caliber machine guns. It also allowed for “unconventional configurations.”
Since Lockheed and Republic were occupied and North American was not on the fighter design horizon yet, only second string fighter designers Curtiss, Vultee and Northrop responded. The results — the Northrop XP-56 “Black Bullet,” Vultee XP-54 “Swoose Goose” and the Curtiss XP-55 “Ascender” — were a collection of some of the most bizarre fighters ever designed.
To get the desired performance, all three used the 1915 “pusher” design with the engine in the rear. This allowed good pilot visibility, heavy armament in the front of the fuselage where the engine was on conventional fighters and the promise of less aerodynamic drag than a conventional airplane.
The XP-56 of the Northrop Aircraft Inc. was, perhaps not surprisingly, a type of flying wing with an anhedral kink at the outer edge for stability. For control, the wing had elevons that functioned as both ailerons and wing flaps.
The fighter had a stubby, round central fuselage to house the engine, pilot and armament.
It had no horizontal tail and a small vertical tail above the fuselage and a very large ventral fin that nearly scraped on the ground. The Pratt & Whitney liquid-cooled X-1800 engine drove contra-rotating propellers that had an explosive severing cord to jettison the prop in case the pilot had to bail out.
Because aluminum was expected to be in short supply during wartime, the XP-56 was mainly built of magnesium alloy, and this required the development of the new technique heliarc welding and a special welding torch for this purpose developed by Northrop.
Early in the project the X-1800 engine proved to be a failure and a more powerful — but larger and heavier — Pratt & Whitney R-2800 engine used in the P-47 Thunderbolt was substituted. The new engine required a redesigned fuselage, delaying the project.
The first engine runs were conducted in late March 1943, but the first XP-56 taxi tests in early April 1943 showed a serious yaw problem, at first thought to be caused by uneven wheel brakes. Manual hydraulic brakes were installed and the first prototype flew on Sept. 30, 1943, but was wrecked a week later when a tire blew on a high speed taxi test and the aircraft flipped over.
The second prototype — now called the “Black Bullet” — was not completed until January 1944 and had a number of changes, notably increasing the size of the upper vertical tail.
However, these changes were largely made “in the blind” since higher priority projects kept the XP-56 from being tested in the National Advisory Committee for Aeronautics wind tunnel.
The second prototype first flew on March 23, 1944, but required a very high speed for takeoff —160 mph. The flight lasted less than eight minutes. The next nine flights were longer, but the “Black Bullet” proved very un-bullet like — it was very slow and handled badly because the center of gravity was too far aft. When the wind tunnel was finally available in May 1944, the Army Air Force decided not to waste wind tunnel time on what was clearly a lost cause, and the project was abandoned.
(For questions or comments, contact Dr. Michel at marshall.michel@spangdahlem.af.mil.)
