Jack Northrop's Black Bullet was an attempt to radically improve combat aircraft performance by using an unconventional, near all-wing, airframe design. Although it ultimately failed, the XP-56 was built using a new material, magnesium, and a new construction process, Heliarc welding. Heliarc welding became a standard method for fabricating metals and Northrop patented a special welding torch for this purpose. The advanced airframe layout with a truncated fuselage and almost no empennage failed to perform as expected.
The XP-56 came about on July 17, 1939, when Assistant Secretary of War Louis K. Johnson departed from normal procedures and released $6 million as a monetary incentive to five companies to develop new single-seat fighter aircraft. Before this time, aircraft companies developed designs at their own expense. But in the summer of 1939, the clouds of war grew thick and dark and the time to develop new designs were sought with some urgency.
Some of this money went to Jack Northrop and he soon formulated a project for it. The flying wing concept had fascinated him since the late 1920s. Already, he was well along with a proof-of-concept airplane called the Northrop N-1M (see NASM collection) and he immediately seized on the federal money as the opportunity to design and build a flying wing fighter. The Army's Request for Data R-40C document also provided much impetus to the project. Within its pages, the Army described the need to try designs that departed from the conventional and could be ready for production in 1942. Three firms won the right to proceed with radical aircraft. Vultee submitted a twin-boom pusher called the XP-54. Curtiss offered a canard pusher designated the XP-55 Ascender (see NASM collection) while Northrop proposed the stubby, menacing, tailless XP-56 Black Bullet.
On June 22, 1940, Northrop received a contract from the Army to provide engineering data and wind tunnel models. The contract also mentioned the option to order flying prototypes. Northrop responded with detailed information and models, and after review, the Army exercised the option for a prototype that must be delivered by September 26, 1941. This was amended to include a second prototype. The wing of the XP-56 was very similar to that used on the N-1M. Patented split-surface drag rudders were located in the drooped outer wing panels and provided yaw control when opened (the horizontally split halves opened upward and downward simultaneously). Northrop used elevons on the inboard wing sections. These operated together as elevators or differentially as ailerons, hence the name. The design team made the fuselage "pod" the minimum size necessary to carry two 20mm cannon and four .50 cal. machine guns in the nose, a pilot behind the armament, a powerful Pratt & Whitney engine, and two 3-blade contra-rotating propellers at the rear. At the rear of the fuselage, there was only the hint of a dorsal fin but a large ventral fin protruded prominently into the air stream to increase directional stability.
Since the ejection seat did not yet exist, Pratt & Whitney wrapped explosive cord around the gearbox to blow the propellers away from the airplane, should an in-flight emergency force the pilot to take to his parachute! The most unique aspect of the XP-56, besides its flying wing configuration, was the exotic metal used to build the fighter. The design team chose lightweight magnesium to fabricate the internal airframe and the skin that covered it. Another innovative technology was devised to join the metal - the Northrop-patented Heliarc welding system.
Northrop chose Magnesium because at that time, national aluminum reserves were thought too small to meet current and future demands, particularly in light of President Franklin D.Roosevelt's call to build 50,000 airplanes a year. Aircraft companies experimented with wood, composite plastics, and stainless steel. Magnesium weighed about one third less than aluminum and promised stronger components and smoother finishes if problems with fabrication could be solved. Northrop hired a former associate, Vladimir Pavlecka, to join the company. Pavlecka developed the Heliarc welding system and tried to patent it, but General Electric had already patented the process in the 1920s. Northrop was granted a patent only on the heliarc welding torch.
Northrop originally planned to use a new engine to complement the Black Bullet's other exotic features. Pratt & Whitney was developing a liquid-cooled, 24-cylinder, 'H' engine (the designation is derived from the arrangement of the cylinder heads around the engine block) that engineers estimated could produce 2,200 horsepower. When the H engine was cancelled, Northrop substituted a Pratt & Whitney R-2800 air-cooled radial, the same basic engine that powered the Republic P-47 Thunderbolt and the Vought F4U Corsair (see NASM collection). Engineers substituted the R-2800 late in the design process and this made the experimental fighter heavier. The engine switch and other problems delayed delivery of the first prototype, AAF serial number 41-786, until March 1943. The experimental fighter did not fly until September 6 when two more flights revealed control problems. Modifications to correct them delayed testing until October 8. On that day, the left main tire failed during a high-speed taxi test. The pilot survived the ensuing crash but the aircraft did not. Further flight tests were halted until the second prototype was finished.
On March 23, 1944, the second ship flew, AAF serial number 42-38353. The first Black Bullet had exhibited yaw control problems so Northrop equipped the second airplane with a much larger dorsal fin. This had no effect and it was quickly obvious that major stability and control problems also plagued this aircraft. More tests showed a maximum speed well below the expected velocity and in August 1944, the AAF grounded the XP-56 after its tenth flight. The National Advisory Committee for Aeronautics (forerunner to today's NASA) planned to test the design inside a wind tunnel but the anticipated performance of jet-propelled aircraft then on the drawing board permanently ended the program.
The Smithsonian owns the second prototype. On December 20, 1946, the AAF shipped it to Park Ridge, Illinois. The fighter joined other World War II aircraft held there for the museum. Many of these artifacts became part of the National Air and Space Museum during 1950-51 when the Smithsonian moved this collection to Suitland, Maryland.