Northrop XP-56

The first prototype of the XP-56 'Black Bullet' before it's crash in late 1943.

The 1930s were an interesting time for military aircraft, with the breakneck pace of technological development pushing the envelope farther with every year. Nations around the world were experimenting with all sorts of unconventional designs, some of which were far more successful than others.

On November 27th, 1939, the United States Army Air Force issued Circular Proposal R-40C. R-40C was for a new fighter that would be superior to all existing types, while having a low cost and easy maintenance. Specifically mentioned was the willingness to see unconventional configurations. More than 50 designs were submitted, though only a handful made it to the end. The winners of the competition all had created advanced, and highly unorthodox, pusher fighters.

The 'pusher' configuration for combat aircraft had been around since 1915, and offered several advantages over what is now seen as the conventional 'tractor' configuration, the most notable being improved visibility for the pilot and the ability to cluster weapons in the nose. Even so, this wasn't really explored in the United States until the 1930s with Bell aviation leading the way with aircraft like the deeply flawed Bell Aircuda, and other projects like their Model 16 and the XP-52/XP-59 (no relation to the jet, and one of the winners of the contest, though no prototype was ever made).

The three companies that built prototypes were Northrop with the XP-56, Curtiss with the XP-55, and Vultee with their XP-54. Preliminary contracts were issued on June 22nd, 1940, and all called for single-seat aircraft, powered by the mighty liquid-cooled Pratt & Whitney X-1800-A3G, which would produce 2,200 horsepower from its 24 cylinders. But the engine's potential was never realized, as it was canceled in October 1940, forcing the use of other powerplants for the new fighters.

A view of the second prototype from the right rear quarter, showing the counter-rotating propellers, the downturned wings, and the large vertical tail surfaces.

Among radical aircraft, Northrop's offering was the most radical of the lot, as could be expected from the company. The XP-56 (Designated in-company as the N2B) had several features in common with Northrop's flying wings such as its short length and lack of a conventional tail.

The fuselage was stubby and bullet shaped, constructed of welded magnesium to reduce weight. All armament was to be contained in the nose (though none was ever actually fitted), and consisted of a pair of 20mm cannons and four .50 caliber machine guns with 200 and 1,600 rounds for each gun respectively. The unpressurized cockpit was located very close to the nose, and like all of the other aircraft that resulted from R-40C, the XP-56 was fitted with a tricycle landing gear set with the nose wheel folding into the fuselage and the main wheels folding into the wings.

Two tail fins were mounted on the top and bottom of the fuselage, with the first prototype having a very stubby dorsal and large ventral, and the second having a larger dorsal fin than the ventral fin. The ventral fin was so large it almost dragged the ground on both prototypes.

The second prototype on supports in a hanger, showing the short nose and the wing intakes for the engine cooling system.

The wings were mounted at the midpoint of the fuselage and were steeply swept, with a noticeable downturn at the tips. On the trailing edge of the tips were split-surface drag rudders to control yaw, on the interior sections were the 'elevons', which are control surfaces for tailless aircraft that fill the role of both ailerons (when operated separately) and elevators (when operated at the same time). The leading edges featured the ducting for air to cool the rear-mounted engine.

Two tail fins were mounted on the top and bottom of the fuselage, and the most significant visual difference between the two prototypes was the difference in the size of the vertical fins. The first had a very stubby fin, while the second had one that was even larger than the ventral fin in area.

A ground run of the second prototype, notice how close the ventral fin is to the ground, and the drag-rudders on the wingtips.

The only completed X-1800-A3G engine on a stand.

The Pratt & Whitney X-1800-A3G was to be mounted behind the cockpit and was to drive a set of counter-rotating propellers. This was a powerful H-Block engine, with 24 cylinder, intended to produce between 1,800 to 2,000 horsepower with a displacement of 2,240 cubic inches. But it seems that test stand power tests fell short, and the program was canceled in October 1940 with a single prototype being constructed. Without a powerplant, Northrop turned to the R-2800 Double Wasp for power. This engine powered such icons of aviation as the F6F Hellcat, the F8F Bearcat, the B-26 Marauder, and the P-47 Thunderbolt. But there was an issue, the Double Wasp was a radial engine that was much larger in diameter than the X-1800 was, forcing the fuselage to be widened to accommodate it, and resulting in increased drag due to the greater frontal area. The engine drove a set of counter-rotating propellers.

A Pratt & Whitney R-2800 Double Wasp engine on a stand.

Like the others from the R-40C program, a solution had to be found for the issue of bailing out of the aircraft. With the propellers located right in the path of the escaping pilot, something needed to be done to prevent the aircraft from shredding its own pilot in the event of an emergency. This issue is present with most pusher-prop aircraft, and saw many solutions implemented by various nations and companies. Northrop's solution was to wrap the gearbox with explosive cord to blow the propellers away.

Of note is the welded magnesium construction, which used the new method of Heliarc Welding. Magnesium was lighter than aluminum, and with the concerns of shortages of that metal as the US prepared for war, many companies tried to figure out how to use the material. Northrop set his chief of research, Vladimir Pavlecka to solve the issue, and Pavlecka developed the heliarc torch. Today, this is known as TIG welding and uses an inert gas to shield the weld from the regular atmosphere. The patent only applied to the torch, as General Electric had already patented the process in the 1920s.

Jack Knudson Northrop was an interesting figure in aviation history, born in 1895 he entered the world of aviation in 1916 by joining the Loughead Aircraft Manufacturing Company (not Lockheed yet, but the same people) to work on their F-1 flying boat. The company, founded by the brothers Allan and Malcolm Loughead tried and failed to sell their aircraft to the navy. Their next major aircraft, the S-1 sport plane was a commercial failure in 1919, selling for $2,500 in a market filled with $300 surplus army aircraft. As a result, the Loughead company closed in 1920, and it's assets were liquidated the next year.

But that wasn't enough to keep Northrop out of aviation, he joined Douglas aircraft and worked on their World Cruiser aircraft all while making his own calculations on a high-efficiency aircraft that was just a wing. 1927 saw a revival of Lockheed, and Northrop became the lead engineer for aircraft like the Lockheed Vega. In the next ten years he started, joined, and left five different companies all while developing aircraft like the Northrop Alpha, Beta, and Gamma. But this Northrop company dissolved in 1937, and was acquired by Douglas. In this time he also developed the technique of stressed skin construction, which became standard for aircraft construction.

1939 saw Jack Northrop start the third company that bore his name, and this was the company that would continue to this day. This company allowed him to develop his radical concepts for flying wings, such as the N-1M which first flew on July 3rd, 1940.

The first prototype on a ground run in September or early October 1943.

The XP-56 was the first fighter designed by the Northrop company, with a contract for a powered wind tunnel model and preliminary data being issued on June 22nd, 1940. On the 26th of September a prototype was ordered with the serial number 41-786 to be delivered on September 26th, 1941. But the next month saw the cancellation of the X-1800, the substitution of the R-2800, and the resulting changes to the fuselage. The engine change and other issues delayed the first prototype until 1943, even so the Army Air Force ordered a second prototype on February 13th, 1942. The second prototype was given the number 42-38353.

In April 1943 the first prototype was ready, but suffered serious issues during tests at Muroc Dry Lake (now Edwards AFB). While at high speeds in ground handing tests, it yawed dangerously which was solved by replacing the wheel brakes with manual hydraulic ones. At last, the XP-56 took flight on September 30th, 1943 with John Myers at the controls. This first flight was at an altitude of five feet, but seemed to be fairly normal. But further flights showed issues, the aircraft was nose heavy, and lateral control was hard to manage at all times. There were modifications attempted which delayed testing until the 8th of October. But on that day the port main wheel tire blew out during a high-speed taxi. Resulting in the XP-56 flipping over and being totally written off, fortunately the pilot survived the crash.

The aftermath of the crash, the missing tire that caused the crash is easy to see, as are the detached propellors.

The second prototype was changed to try and mitigate the failings of the first, with an enlarged dorsal fin, a different type of rudder control that used bellows at the wingtips to control a set of split flaps for directional control, airflow was controlled with venturis mounted on the wingtips. Changes were also made to the center of gravity.

The second prototype, showing the enlarged dorsal fin.

March 23rd, 1944 saw Harry Crosby in the cockpit of the second prototype. He found that it was impossible to raise the nosewheel below 160 miles per hour, forcing a quick end to the first test flight. But the issue was swiftly remedied and the shortcoming of nose-heaviness vanished when the landing gear were stowed. But the changes to the engine in 1940 and the changes to the second prototype resulted in the aircraft being very underpowered, falling far short of its projected 465 mph at 25,000 feet.

The second prototype in the air.

The National Advisory Committee for Aeronautics (NACA, precursor to NASA) was told to use their Moffett Field wind tunnel to try and resolve the issues of the XP-56. But other projects forced delays until October, 1944. In the meantime, more test flights were performed, after the tenth flight, the pilot spoke of tail-heaviness, excessive fuel consumption, and low power. After further consultations, the XP-56 was declared to be essentially un-airworthy and dangerous to fly. After this, the XP-56, the 'Black Bullet' was canceled.

Despite the failure of the XP-56, Northrop managed to learn a great deal about flying wing designs. This knowledge was put to use with their XB-35 flying wing and the subsequent YB-49.

A view of the second prototype from the front, showing the cooling air intakes and the wingtip venturis.

Jack Northrop's designs didn't enter service in the years just after the end of WWII, the rise of jets, the abundance of more conventional aircraft, and the issues of controlling flying wings all made his designs unappealing to the Air Force. This refusal took a toll on him, and he retired from the Northrop company in 1952 at the age of 57. His activities in the real estate market over the next several years drained his personal wealth and degraded his health, to the point he was unable to speak or walk by the late 1970s.
In 1980, he was shown the preliminary models and drawings for the B-2 Spirit, designed and built by the company that bore his name. He is said to have grabbed a pen and written, “I know why God has kept me alive for the past 25 years!”. He passed away ten months later at the age of 85, his radical concepts having finally come to fruition.

Jack Northrop standing in front of an XB-35 around 1948.

Specifications:

NOTE: There were few flight tests, so most of these stats differ from source to source, and prototype to prototype.

A three-view of the second prototype.

Pratt & Whitney R-2800-29 2000 hp

First Prototype

Dimensions:

Wingspan: 42' 7''

Length: 23' 6''

Height: 9' 8''

Wing Area: 306 ft^2

Weight:

Empty: 8,700 lb

Gross: 11,350 lb

Maximum: 12,145 lb

Gallons of fuel: 320 Gallons

Performance:

Top Speed: 465 mph @ 19,500 feet OR 25,000 feet (estimated/projected)

At Sea Level: 417 mph

Cruising Speed: mph

Landing Speed: mph

Service Ceiling: 33,000 Feet

Normal Range: 445 Miles @ 396 mph

Maximum Range: 660 Miles

Second Prototype

Dimensions:

Wingspan: 42' 6''

Length: 27' 6''

Height: 11'

Wing Area: 306 ft^2

Weight:

Empty: 8,700 lb

Gross: 11,350 lb

Maximum: 12,145 lb

Gallons of fuel: 320 Gallons

Performance:

Top Speed: 465 mph @ 19,500 feet OR 25,000 feet (estimated/projected)

At Sea Level: 417 mph

Cruising Speed: mph

Landing Speed: mph

Service Ceiling: 33,000 Feet

Normal Range: 445 Miles @ 396 mph

Maximum Range: 660 Miles

What is Left?

The second prototype was sent to the Smithsonian on December 20th, 1946. The AAF sent it to Park Ridge, Illinois and then was moved to Suitland, Maryland sometime in 1950-51. It's not on display, but it is part of the collection of the National Air and Space Museum. We can hope that one day they'll be able to put it on display somewhere.

The website Northrop Nurflügels has three photos from the author's collection of the stored XP-56. Shown below, these include the fuselage and cockpit, but doesn't show the wings even though they are probably still in the collection somewhere.