Experimental, WWII

Northrop XP-56 Black Bullet – Pusher Power

The Northrop XP-56 Black Bullet was an experimental fighter built with the intention of improving aircraft design and performance by making radical alterations to existing designs.

Designed in response to a United States government specification, the Black Bullet was built by Northrop with a unique near-all-wing airframe platform and used building materials such as magnesium which were new at the time. The innovative design also prompted Northrop to adopt new welding and construction methods.

Although the design itself was ambitious, it ultimately proved to be faulty during test trials and prevented the XP-56 from reaching its intended speed and climbing abilities. The project never passed into the mass production phase, although one prototype of the Black Bullet remains and was restored.

Contents

Origins

The origins of the XP-56 Black Bullet’s development date back to July 1939.

Northrop XP-56 Black Bullet.
Northrop’s design became the prototype XP-56.

Although the United States government maintained a strict code of neutrality and non-interventionism regarding foreign conflicts, it was becoming increasingly obvious by the late 1930s with Germany’s rearmament that Europe was heading towards the brink of war and the American government wanted to be prepared in case the conflict escalated.

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The American government and the United States Army Air Corps (USAAC) began issuing requirements for new military aircraft of all types and called for the production of a new fighter and interception aircraft under the specification name “R-40C.”

The United States Government’s Assistant Secretary of War Louis K. Johnson stepped up pressure and motivation for new aircraft designs by issuing a specification for a new single-seat fighter aircraft in 1939.

He also deviated from standard government procedure and offered a six million dollar reward contract as a monetary incentive to five aerospace companies to develop a new fighter aircraft. Around this time aircraft manufacturers had generally developed designs at their own expense without state funds.

A rear shot of an XP-56 with engine running taxing.
During the Second World War many unusal designs were put forward from various companies.

Some of Johnson’s money went to aircraft builder Jack Northrop as part of the R-40C specification call and he set to work on a new concept.

Before the 1930s, Northrop had established his name as an industrialist and an aircraft designer in the 1920s. He worked as a chief design and project manager for the Douglas Aircraft Company before founding his own manufacturing business, the Northrop Corporation in 1939 which would be based in California.

Northrop had already researched the flying-wing concept idea during his designing career. The all-wing or flying-wing concept essentially features a cockpit positioned within a giant, singular wing that was often delta shaped rather than a traditional design of two wings fixed separately on either side of the cockpit and engine housing.

Northrop saw Johnson’s funds and R-40C as an opportunity to experiment with the all-wing concept further and bring it into mainstream development.

The USAAC’s specification request in the R-40C brief also provided further motivation to Northrop as it emphasised a need for designers to experiment with cutting-edge designs that departed from conventional ideas.

XP-55 in flight.
The XP-55 was another aircraft from the R-40C specification.

Crucially, the specification also called for a plane that could be ready for mass production by 1942.

Three aircraft manufacturers won the right to proceed with their designs with financial help, including Northrop’s company.

The Vultee company submitted the XP-54, a twin-boom pusher propeller concept. Curtiss offered a canard pusher designated the XP-55 Ascender. Northrop proposed a tailless and shorter aircraft design named the Northrop N2B which would go on to form the basis of the XP-56 Black Bullet.

XP-54 in flight.
The Vultee XP-54 “Swoose Goose”.

Development

In June 1940, Northrop received an official contract from the USAAC to begin model and wind tunnel tests of his concept idea.

The USAAC contract also stated that there would be an option for proceeding to orders for flying prototypes if initial data gathering on model tests was satisfactory. Encouraged by this next incentive, Northrop produced detailed information and models for the USAAC.

After a careful review, the USAAC awarded him the option for a flying prototype with a completion deadline of 26th of September, 1941. This was then amended to include a second working prototype as a backup.

To efficiently speed up the building process, Northrop borrowed similar ideas also found in the Northrop N-1M concept which also featured an all-wing delta design with pusher propellers at the rear.

A rightside view of the XP-56 parked in the desert.
The XP-56 was unconventional, to say the least.

Northrop used his own patented split-surface drag rudders were fixed in the outer wing panels and provided yawing (steering) control when opened up by the pilot. Northrop also used elevons on the inboard wing sections.

These operated together as elevators or differentially as ailerons. At the rear of the plane, a tiny dorsal fin was fitted but it was accompanied by a large ventral fin designed to protrude out into the air stream around the aircraft to increase stability.

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The armament would consist of two 20mm cannons and four .50 cal. machine guns mounted in the nose. Power was to be provided Pratt & Whitney liquid-cooled X-1800 engine in a pusher configuration at the back of the plane. Keeping true to the experimental demands of the specification, the engine would drive two contra (opposite) rotating propellers.

To mitigate the risk of the pilot or his parachute becoming caught in the rear-facing propellers in the event of having to bail out, Pratt & Whitney fitted an explosive cord to the gearbox that the pilot could trigger to blow the propellers off the plane.

The rear of the XP-56 in a hangar.
Bailing out of any aircraft is hazardous, but especially so with a pusher propeller design.

Perhaps the most interesting design feature of the plane was not its appearance, but its building materials. In the early 1940s, national aluminium reserves were becoming too depleted to meet current manufacturing demands, particularly as President Franklin D. Roosevelt had set a target for the United States to build 50,000 warplanes a year.

Aircraft manufacturers experimented with different solutions such as wood, composite plastics or stainless steel. Northrop chose to build the XP-56 from magnesium as it weighed about one-third less than aluminium and was considered a strong metal.

As the aluminium fabrication could prove difficult, Northrop hired expert welder Vladimir Pavlecka who had tried to patent his Heliarc welding system. Although the Heliarc method was disputed as to who first created it, Pavlecka was able to bring his expertise to the project and used the new Heliarc welding torch to fuse the plane together.

The design process hit an interruption when Pratt & Whitney cancelled their engine concept which Northrop had sought to use. Instead, Northrop substituted the engine for a Pratt & Whitney R-2800 air-cooled radial unit, the same engine unit that powered the Republic P-47 Thunderbolt and the Vought F4U Corsair.

The XP-56 from the lefthand side.
To achieve a high top speed, the XP-56 needed to use a powerful engine.

Although a reliable and powerful engine, the R-2800 added additional weight to the Black Bullet and the design had to be slightly altered to accommodate the new engine which pushed the project back behind the USAAC’s original deadline.

Testing

The XP-56 attempted its first maiden flight in September 1943 at Muroc Air Base in California.

The first two test runs were stymied by a faulty control column and the aircraft was sent out for another test flight once the problem was fixed in October of that year. However, the prototype was severely damaged by a tyre blowout during a taxi run and slid off the runway. The test pilot survived the crash but the prototype XP-56 was written off.

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Further testing was halted until the arrival of the second completed prototype in March 1944. As the first Black Bullet had control and steering issues, Northrop redesigned the second prototype with a bigger dorsal fin to rectify the problem.

The wing design is easily identifiable from the front.
The XP-56’s wing design is easily identifiable from the front.

However, tests found the larger fin to be a cosmetic change that had no effect. Test pilots and military engineers found that major stability and control problems continued to plague the aircraft’s performance as a whole and that a major redesign of the aircraft from scratch would be needed to address the problem.

Subsequent test flights also recorded the maximum speed as being well below the expected velocity Northrop had intended for the plane. Although the Pratt & Whitney engine was capable of producing a top speed of 465 miles per hour and could enable the plane to climb to around 33,000 feet, the Black Bullet’s design was accused of preventing the plane from reaching its optimal performance expectations.

In August 1944, the United States Army Air Force (USAAF), who had succeeded the USAAC during the XP-56’s development, pulled the plug on the project. The XP-56 was grounded after its tenth flight.

There was some talk of the National Advisory Committee for Aeronautics (the precursor of NASA) using Northrop’s design for wind tunnel tests as part of aerodynamic experiments, but the idea ultimately came to nothing.

The XP-56 on stands in a hangar.
The XP-56 on stands in a hangar.

By the latter stages and end of the war, both the British and Germans had experimented with and developed their own jet fighter designs, pointing to the future direction of high-performance fighter aircraft. The National Advisory Committee for Aeronautics had also brainstormed their own ideas for jet-propelled aircraft and decided the Black Bullet’s use would be superfluous to any future developments.

Aftermath

Although the first prototype was destroyed and the project was not deemed a success, Northrop and the USAAF had the second prototype model preserved.

After the end of the war, the airframe was placed into storage until the USAAF shipped it to Park Ridge, Illinois in December 1946 and later to Freemen Field in Indiana for restoration work. It was joined by other Second World War era aircraft held there until readied for public display.

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The Smithsonian Institute subsequently took ownership of the XP-56. It was displayed as part of the Smithsonian’s National Air and Space Museum’s collection from 1950 to 1951 after which it was moved to Maryland for further restoration work.

Specifications

  • Crew: one, pilot
  • Length: 27 ft 6 in (8.38 m)
  • Wingspan: 42 ft 6 in (12.96 m)
  • Height: 11 ft 0 in (3.35 m)
  • Empty weight: 8,700 lb (3,955 kg)
  • Gross weight: 11,350 lb (5,159 kg)
  • Max takeoff weight: 12,145 lb (5,520 kg)
  • Powerplant: 1 × Pratt & Whitney R-2800-29 radial, 2,000 hp (1,492 kW)
  • Maximum speed: 465 mph (749 km/h, 404 kn) at 25,000 ft (7600 m)
  • Range: 660 mi (1,063 km, 570 nmi)
  • Service ceiling: 33,000 ft (10,061 m)
  • Rate of climb: 3,125 ft/min (15.88 m/s) at 15,000 ft (4600 m)

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