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Northrop: the war years
by E.T. Wooldridge

Like the Horten brothers and Alexander Lippisch in German-, Jack Northrop found ample opportunity to apply the concept of a tailless aircraft to the practical requirements of war. Northrop's reputation as a brilliant innovator and the fact that this company was not initially overburdened with production commitments made him a logical choice to develop new aircraft designs. New mission requirements, new technologies, and Northrop's preoccupation with the concept of the flying wing led to a family of aircraft with unusual physical characteristics.

A number of aircraft propulsion systems were used in tailless aircraft, including conventional piston engines, turbojets, rockets, and pulse jets. A family of aircraft emerged with names as distinctive as their shapes, and missions: Black Bullet, Rocket Wing, Power Bomb, Bat, Jet Bomb, and Flying Ram. Northrop test pilots had more than their share of thrills and narroow escapes as they flight-tested unproven engines and airframes in the skies, over southern California. At the same time, across the Atlantic, German pilots tested the same concepts under equally hazardous circumstances, in by Lippisch, Horten, and Messerschmitt.

The first of Northrop's World War II family of tailless designs, the XP56, also called the Black Bullet. This aircraft was designed at the outset of the war in response to an Army request for new designs that would counter foreign advances in fighter aircraft technology. Northrop's competitors for a production contract were the Consolidated/Vultee XP-54 and the Curtiss XP-55 Ascender, which, like the Northrop entry, were pusher designs that incorporated rear-mounted engines driving multi-bladed propellers. All three aircraft were originally- scheduled to use the new Pratt & Whitney liquid-cooled X-1800-A3G engine, but cancellation of that project forced Northrop to use the Pratt & Whitney R-228O-29 air-cooled Double Wasp for the XP-56.

The XP-56 was a composite of a number of radical design features. The overall effect was an airplane that, by any contemporary standards, did not "look right." With the benefit of hindsight, it could be said that the failure of the program was predictable. The XP-56 was the first all-magnesium, all welded airframe in history; Northrop developed the "heliarc" welding process that assembled the strong, lightweight structure. The air-cooled engine was completely submerged in the stubby, bullet-like fuselage, driving two concentric counter-rotating pusher propellers, located a short distance aft of the cockpit. An emergency bailout by the pilot seemed guaranteed to produce disastrous results. Consequently, an explosive cord was wrapped around the engine gearbox so that in an emergency the aft portion of the aircraft, including propellers, could be blown away before the pilot left the airplane.

The XP-56 was a tailless, swept wing, with both dorsal and ventral fins mounted directly in front of the propellers. Elevons were located at the midpoint of the trailing edge, and the wing tips were deflected downward, serving the dual purpose of fin and rudder. On the second of the two XP-56 models, air-operated bellows rudders were incorporated. Each wing tip housed a horizontal duct through which air was free to travel while the aircraft was moving. When the pilot moved the rudder pedals, a valve was actuated that diverted the airflow to a bellows, which assisted in operating split-flap rudders at the wing tips.

John Myers prepares the first XP-56 (-12-1786) for a test flight in late 1943.

The first XP-56 (42-1786), which had been trucked out to Muroc Dry Lake, made its first flight on September 6, 1943, with test pilot John Myers at the controls.' The first flight was made at an altitude of four feet, at a speed of 140 mph. After the second flight that day, Myers complained of a directional control deficiency, not surprising since the dorsal fin was reminiscent of those on the infamous Granville Gee Bee racers of the 1930s. The small vertical fin on the first aircraft was capped with a larger stabilizer that improved the yaw problems. Taxi and flight tests were resumed on October 8.

After successfully taxiing across Muroc Lake twice at high speed, Myers made a straight flight at an altitude between 10 and 15 feet with no apparent difficulty. This flight was followed by a high speed taxi run on the return trip across the lake and the flight was repeated. On the return taxi run following this flight the left main tire blew out about half way across the lake while the airplane was travelling at approximately 130 mph.

At that point, as Myers so eloquently put it, "The aircraft wanted to fly upside down and backwards, and finally did!" The XP-56 began to somersault across the desert floor. After one backward flip, during which the airplane rose about 75 feet in the air, the pilot's seat supports failed, and the seat and Myers were catapulted clear. The XP-56 crashed on its upper surface and was totally destroyed. Myers, fortunately had been wearing a polo helmet for protection, and suffered only minor injuries.

The first XP-56 lies in a heap on the desert floor after John Myers's disastrous mishap. Missing from the left landing gear is the tire which blew during a high speed taxi run, causing the violent gyrations that almost took Myers's life.

A second airplane (42-238353), with a new larger dorsal fin and bellows rudders, first flew from Roach Lake on March 23, 1944, attaining an altitude of 2500 feet. The second aircraft eventually flew a total of 10 flights, during which a number of stability and control problems were experienced. Wing heaviness was attributed to a torque reaction resulting from improper propeller operation. The chief difficulty experienced was in longitudinal and directional instability.

The limited success of the flight test program did not result in great enthusiasm on the part of Army officials to continue the development program as the war ended. Limited potential and the arrival of the turbojet engine on the scene contributed to the cancellation of the program. In retrospect, Jack Northrop admitted that the application of the flying wing concepts to this particular design was not the proper solution. It was a design he was not very proud of; as he candidly admitted, "I think it was a bust."'

The second XP-56 (42-238353) was easily distinguished from its predecessors by an enlarged vertical fin and the air bellows-operated rudders at the wing tips for greater yaw control. Designed for speeds well over 400 mph, the XP-56 never measured up to performance specifications and was plagued by a variety of other problems during its abbreviated flight test program.

The second XP-56 was shipped to the Army Air Forces (AAF) storage depot at Park Ridge, Illinois, on December 20, 1946, and was later sent to the National Air and Space Museum. In 1982, it was transferred to Northrop Corporation for future restoration.

On August 13, 1941, in Germany, test pilot Heini Dittmar flew the first rocket-propelled fighter, the Messerschmitt Me 163V I Komet. Two months later, on October 2, 1941, with Dittmar again at the controls, the Komet became the first aircraft to pass a speed of 1000 km per hour by reaching 1003 km per hour (623.85 mph, Mach 0.84). The Me 163 eventually became the world's first operational rocket-powered fighter.

In September 1942, a year after Dittmar's flight, Jack Northrop produced a feasibility study for America's first rocket-powered military interceptor. An Army contract followed, calling for construction of three gliders to test the aerodynamic qualities of the configuration, and to serve as flying mock-ups for the XP-79 aircraft. In an unpowered configuration, the gliders were designated MX-334. The third aircraft, when it was eventually fitted with an Aerojet rocket engine, was then designated MX-324. The first aircraft had skids that were eventually augmented by a detachable four-wheel dolly that was jettisoned immediately after takeoff. This configuration finally gave way to a streamlined tricycle landing gear on the second and third aircraft.

Installation of a fixed nose gear on the centreline of the aircraft would have required extension of the shock strut through the pilot's cockpit, an unacceptable situation. Thus, the nose gear installation was offset to the left, a configuration that caused the pilot no problems during landing.

All three aircraft were plywood with a welded steel tubing centre section. The control system consisted of elevons operated by the pilot's control bar, and rudders and airbrakes combined, called "brudders." Air bellows were operated and controlled by foot pedals for rudder action, or a cockpit control handle for brakes. The pilot was to fly in the prone position, a concept practiced earlier by the Hortens. These accommodations permitted a wing structure thinner than the more conventional plan, and enabled the pilot to withstand considerably more gravity acceleration, reducing the strain imposed on him by violent manoeuvres.

Northrop and his chief aerodynamicist, Dr. William R. Sears, designed the aircraft as a pure flying wing with no vertical fin. Controversy developed when calculations showed that a vertical tail would be required for stability at the high speeds contemplated. Sears reluctantly agreed to add a wire-braced vertical fin made of plywood, on the condition that he be allowed to saw off part of it if flight tests showed that the aircraft did not need a tail. Following the tests, however, the tail remained in place.

John Myers conducted the first unpowered glider flight of the MX-334 on October 2, 1943. The intervening months between this first gliding flight and the first powered flight the following July were occupied by numerous test flights in which the stability and control characteristics of the three gliders were investigated by John Myers, and fellow Northrop pilots Harry Crosby and Alex Papana. AAF test pilots also participated in the flights conducted at the Flight Test Base at Muroc, Dry Lake, Harper's Lake, California, and Roach Dry Lake, Nevada. In the rather bland prose of official Army flight test reports, there is little evidence of the moments of stark terror experienced by company pilots Alex Papana and Harry Crosby at the controls of the tiny gliders.

Harry Crosby stands 111 the MX-334 during a lull in unpowered gliding tests in early 1944. Access hatches on the top and bottom gave Crosby a unique opportunity to add scale to the glider as it rested on the parched, cracked surface of Muroc Dry Lake.

Army pilots concluded that the glider was indeed flyable and controllable about all three axes. Aileron effectiveness was good, but fell short of current requirements for fighter aircraft. With regard to directional control, the time lag between operation of the rudder pedals and movement of the air-operated control surfaces was so great that the arrangement was considered impractical for that type of aircraft. Despite these limitations, the overall handling characteristics of the MX-334 were considered as good as or better than those of any other flying wing aircraft tested by the Army pilots to that date.

Test pilots sometimes described the tragedies and misfortunes that mark their daily lives in language entirely different from the engineering jargon of formal reports. Alex Papana and Harry Crosby flew many flights in the MX334 gliders that deserved a few extra superlatives in their description.

Two harrowing experiences occurred during this program. The first involved Alex Papana as pilot. Upon reaching the test altitude, Alex reached for the tow-line release, but inadvertently pulled the lever which jettisoned both the upper and lower escape hatch covers. The absence of the stream-lining effect of the hatch enclosures resulted in a dramatic increase in airplane drag and brought on very severe aircraft buffeting. Through a combination of pilot skill and good luck, Alex successfully landed on the lake bed after what must have been a hair-raising descent.

The other harrowing experience occurred a few days later with Harry Crosby as the pilot. Immediately following towline release, Harry flew into the propwash of the P-38 tow plane ... his glider pitched up, stalled and rolled off into a spin from which it recovered in a stable, shallow glide. The problem, however, was that it was flying inverted, and there was Crosby on his back in a prone position aircraft and unable to reach the controls. The escape hatch, which normally was on the bottom of the airplane, was now overhead. Somehow Harry managed to jettison the hatch and crawl through the opening to the top of the wing, which really was the bottom of the wing. He sat there for a moment contemplating his predicament. After deciding there was nothing he could do, he released his grasp, slid off the wing, and deployed his parachute. When he looked around he was amazed to see his still up-sidedown glider flying in circles around him and descending at about the same rate he was. Although both the glider and the pilot landed at about the same time and in about the same place, they did not collide and Harry escaped without injury. The glider was damaged beyond repair.

Despite the loss of the second MX-334 glider at Muroc, the test program proceeded in an orderly fashion through late 1943 and early 1944, until it was time for Northrop technicians to install the 427-pound Aerojet rocket motor in the squat, tailless aircraft. The motor nozzle, protruding through the trailing edge of the thin wing, was the only outward evidence of the engine's presence, although the actual motor, four pressure tanks, two propellant tanks, and hydraulic and electric control equipment were carefully fitted into the wing. One of the considerations in the design of this airplane was protection of the pilot from the mono-ethylaniline fuel and red fuming nitric acid oxidizer. The fuel tank was installed on one side of the pilot and the oxidizer tank on the other side. A heavy neoprene curtain was installed on each side of the pilot to protect him from any rupture of tanks or lines.

America's first rocket-powered aircraft, the Northrop MX-324/33, was designed at the Army Air Forces Materiel Centre, Wright Field, Dayton, Ohio, and subsequently built by Northrop using non-critical materials.

A close-up of the MX-334 cockpit reveals the V-shaped support upon which the prone pilot rested his chin during flight.

Beginning on June 20, 1944, exhaustive ground tests of the rocket motor were conducted at Harper Dry Lake, culminating in taxi tests on the desert floor by Harry Crosby. By the evening of July 4, the craft and Crosby were ready for their momentous flight.

Harry Crosby flies the MX-324 under rocket power. The vertical fin was in place, despite appearance to the contrary in this poor photograph.

Finally, almost three years after the successful maiden flight of the German Me 163, Harry Crosby eased himself into the prone position in the cramped cockpit of the MX 324. With his head resting in a special sling behind the large glass windshield, Crosby had a clear view of the long tow line and the P-38 Lightning that was to tow him up to release altitude off the cracked, dry surface of Harper Dry Lake near Barstow, California. Early in the morning of July 5, 1944, P-38 pilot Martin Smith' towed Crosby and his strange-looking craft over the dry lake at about 8000 feet. Crosby tripped the towline release, braced himself in the narrow confines of the cockpit, and pressed the propulsion trigger on the control stick. Ignition of the 200-pound thrust Aerojet XCAL-200 rocket motor produced acceleration that, though hardly comparable to that of an afterburner in a modern jet.

America's belated entry into the era of rocket-powered flight. A short flight of over four minutes ended with a gentle landing on the dry lake bed.

Following Crosby's July 5th flight, other powered flights of the Rocket Wing were conducted. Some of these featured the early use of telemetry to transmit flight test data by radio to ground-based recorders. Despite the progress in the test program, however, the lack of more powerful rocket engines and a redirection of priorities resulted in termination of the project. Attention shifted to more unconventional approach to adapting the principles of the flying wing to aerial combat - the XP-79B.

The XP-79 was to have been an all-magnesium, rocket-powered, prone pilot fighter-interceptor capable of speeds over 500 mph, with an exceptional rate of climb, and outstanding operational ceiling. It was to have been powered by an Aerojet 2000-pound thrust rocket using red fuming nitric acid and monoethvlaniline (aniline) as propellants. Northrop engineers understood the corrosive effect of red fuming nitric acid on the magnesium fuel tanks in the aircraft. Thus, the protection of the fuel tanks from battle damage was of overriding importance. Allowing the acid and aniline to mix any where other than in the combustion chamber would have been catastrophic. To protect the propellants from battle damage, the fighter was a welded magnesium alloy monocoque structure with skin varying in thickness from three-quarters of an inch at the leading edge to one-eighth at the trailing edge. As in the MX-324 design, the pilot was to fly in the prone position.

Continuous delays in the development of a suitable rocket motor ultimately led to a decision to abandon that phase of the project and proceed with a turbojet-powered modification. In March 1943, plans were made to add two Westinghouse 19-B (J30) axial flow turbojets to the craft and its designation became XP-79B.

At this juncture the XP-79B acquired a new mission and a new nickname, the Flying Ram. Original specifications for the XP-79 do not mention ramming enemy aircraft as a mission requirement, but pilots associated with the MX-324 program recall that ramming was indeed the primary mission of the XP-79B. In Jack Northrop's words, "It was designed as a projectile, with the thought that it could be used to intercept and knock wings or tails off other airplanes. Rather than shooting at them, this airplane was going to slice sections off the other airplanes to destroy them."

The so-called Flying Ram was distinguished by twin vertical fins, two turbojet engines, and wing tip inlets for bellows type rudders like those on the second XP-56. The XP-79B was the fourth turbojet-powered aircraft to fly in the United States.

It is possible that the unusually high impact strength resulting from the magnesium construction might have provided Air Force planners with a rare opportunity to explore a concept of aerial warfare seldom practiced except in extremis. In retrospect, a tactic of such a desperate nature would seem unwarranted in view of the fact that in 1945 the U.S. Air Force had total command of the skies in every theatre of war and mid-air collisions as a tactic would seem highly unrealistic. It is doubtful that many U.S. pilots had the skill or motivation to manoeuvre their aircraft in such a precise manner to collide with their opponents and return home intact.

Despite its debatable wisdom, the concept was approaching reality by mid-1945. In June 1945, the test aircraft, with its two 1 150-pound thrust J30

turbojets installed and sporting two vertical fins had been delivered to Muroc dry Lake for taxi tests. In September, the ill-fated XP-79B was ready for flight. On September 12, 1945, just 10 days after the end of World War II, the XP79B (43-52437) flew for the first and last time. The pilot was Harry Crosby, who had narrowly escaped death in the MX-334 glider, and was by then contemplating a more placid life on his ranch in California. Now, he again found himself in a situation beyond his control. Jack Northrop described the flight:

"The takeoff for this flight was normal, and for 15 minutes the airplane was flown in a beautiful demonstration. The pilot indicated mounting confidence by executing more and more manoeuvres of a type that would not be expected unless he were thoroughly satisfied with the behaviour of the airplane. After about 15 minutes of flying, the airplane entered what appeared to be a normal slow roll, from which it did not recover. As the rotation about the longitudinal axis continued the nose gradually dropped, and at the time of impact the air plane appeared to be in a steep vertical spin. The pilot endeavoured to leave the ship but the speed was so high that he was unable to clear it successfully. Unfortunately, there was insufficient evidence to fully determine the cause of the disaster. However, in view of his prone position, a powerful electrical controlled trim tab had been installed in the lateral controls to relieve the pilot of excessive loads. It is believed that a deliberate slow roll may have been attempted (as the pilot had previously slow rolled and looped other flying wing aircraft developed by the company) and that doing this manoeuvre, something failed in the lateral controls in such a way that the pilot was overpowered by the electrical trim mechanism.'

With the loss of the sole XP-79B, the program was cancelled. Coincident with the MX-334, project, Northrop attempted to design an unmanned flying wing. Influenced by the British experiences with the German "buzz bombs," the AAF contracted with Northrop for development of the flying wing JB-1 Power Bomb.

Equipped with a pre-programmed guidance system, and powered by two turbojet engines, the Power Bomb was to be a ground-launched craft capable of 'striking a target some 200 miles away.

Under Project MX-543,13 JB-1s were ordered but only two were built; the others were redesigned and redesignated JB-10. The first of the JB-1s was a manned glider to test the flying qualities of the basic design. The bat-like configuration consisted of a magnesium and aluminium alloy wing with a magnesium alloy centre section containing a pilot's compartment and two bomb containers, one on either side of the pilot.

TheJB-1 manned glider (above) was built to flight test the design of the turbojet-equipped Power Bomb that followed. Two hitches were attached to the tips of the two bomb containers, one of which is visible in the right foreground. The jet-powered JB-1 (below), designed with wing containers for two 2000-pounds bombs, is poised for a ground launch from a 400-foot track.

The first series of test flights of the glider began in 1944 with Harry Crosbv at the controls, a year before his death in the XP-79B. Using aircraft tows to get airborne and ascend to release altitude, Crosby put the revolutionary aircraft through a successful test program. Following this unpowered phase, the second JB-1 was equipped with two 400-pound thrust General Electric B 1 turbojet engines, which were modified turbo-superchargers. The unmanned craft was launched by means of a rocket-assisted sled that carried the Power Bomb down a 400-foot track to attain a take off speed of160 mph.

Before a complete development program could be conducted for the JB-1 Power Bomb, official interest switched to the use of the pulse jet engine. Consequently, the JB-1 program was modified in late 1944, and Northrop was asked by the Army to design the JB-10 Jet Bomb (a modified JB-1) using a Ford Motor Company version of the German V-1 buzz bomb engine. The engine, designated PJ-31-1, was located in a cooling shroud in the wing centre section. One 1825-pound warhead was positioned on each side of the engine.

Theoretically capable of striking targets at a range of up to 185 miles, the JB-10 was ground launched from a Northrop-developed rocket-sled arrangement. Four Tiny Tim rockets propelled the flying wing on its launch down the track to a speed of 220 mph required for pulse jet engine operation. Cruising speed was to have been about 425 mph.

Test launchings of the JB-10 were conducted in 1945 at Muroc and at Eglin Field, Florida. Only 1 JB-10s were constructed by the end of World War. However, over 1000 Northrop-designed sleds were built for launching other guided missiles, such as the JB-2. The program was terminated at the end of the war.

Constructed of aluminium and magnesium using Northrop's patented "Heliarc" welding process, the JB-10 was launched from a track-mounted sled by electrically-fired Tiny Din rockets.

AJB-10 is shown undergoing tests at Eglin Field, Florida, near the end of World War 2

One concept that had its genesis in late 1945 deserves consideration, although it does not fit conveniently into the categories of flying wings designed for tactical purposes during World War II, nor does it belong to the post-war family of flying wings. The Northrop X-4, nicknamed the Bantam, or Skylancer, was a swept wing, tailless research aircraft designed to investigate stability and control problems at transonic velocities of about Mach 0.87. By the spring of 1946, Jack Northrop was by far the leading proponent and most experienced designer of tailless aircraft in the United States, and the obvious choice to develop the tiny X-4 for the AAF and NACA.

Drawing on previous experience with the ill-fated XP-79 program, the Northrop design team, under the leadership of Arthur I. Luck, produced a rather rakish-looking aircraft that bore a decided resemblance to the British de Havilland D.H. 108 Swallow, which preceded the X-4 by more than two years. Two X-4s were built; the first (46-676) flew on December 16, 1948, with Northrop pilot Charles Tucker at the controls. Various mechanical problems limited test flights to three in six months, a disappointing performance record that the plagued X-4 No. I never overcame during its brief 10 flight history. It remained for X-4 No. 2 (46-677) to carry the brunt of the Flight test program, one that stretched interminably from first flight on June 7, 1949, through late 1953.

In the 102 flights of the second X-4, Northrop, NACA, and U.S. Air Force test pilots explored the transonic regime to determine the effectiveness of the tailless design at high subsonic Mach numbers. Flight tests vividly demonstrated that above Mach 0.76, yawing and rolling motions persisted, elevon effectiveness decreased markedly, and at Mach 0.88, the pilots encountered an uncontrollable oscillation about three axes, with an un-damped porpoising motion above Mach 0.9.

Small and highly manoeuvrable the X-4 (above) was powered by two 1600 pound thrust Westinghouse J30 turbojets fitted in the wing roots. Wing control surfaces consisted of outboard elevons and split flaps designed to serve as speed brakes and landing flaps. The speed brakes, shown in the extended position on the second X-4 (below) were extremely effective for speed control during flights at high subsonic speeds.

Viewed purely from the standpoint of contributions to the war effort, the record of success of the wartime flying wings was hardly impressive. Harry Crosby lost his life; Alex Papana and John Myers very nearly lost theirs; none of the projects really came close to operational service, with the possible exception of the JB-10; it experienced two partially successful test flights in 10 attempts. Notwithstanding the negative aspects of the programs, however, there was probably some transfer of technical data and expertise from these programs to the N-9M and XB-35 aircraft which were then undergoing concurrent development.