The XB-46 is a relatively obscure American jet bomber from the 1940s. It combined traditional features of WWII bombers with new advancements, like jet engines, resulting in an elegant, streamlined aircraft that, in the end, wouldn’t see service.
The XB-46 bridged the gap between WWII understanding and the jet age, but this ultimately left it incapable of competing with aircraft that entirely embraced the future later in the decade.
Stripped of its military equipment, the XB-46 had already been cancelled before it completed its handful of test flights. Today it is a forgotten, overshadowed, yet amazing-looking bomber.
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Development of the XB-46
In 1944, the US issued a requirement to develop a new advanced bomber that would take advantage of all the latest technological developments in aviation, such as pressurisation and jet-power.
One manufacturer to respond to this was Convair. The company was technically “new”, having been created the previous year by the merging of Consolidated Aircraft and Vultee Aircraft, but its experience was vast.
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Consolidated in particular arguably had the most experience out of any American aircraft builder, having created the B-24, which would go on to become the most-produced bomber in history. Following this came the B-32 Dominator, a lesser known, but pressurised “successor” to the B-24.
This put Convair in a good position, as they had plenty of experience with bombers and pressurisation. What they lacked though was work with jet engines.
Convair responded to the government’s request for an advanced bomber by incorporating new technology into tried and proven designs – this would reduce the chances of the project being bogged down with technical issues.
In May 1944 the company started work on this new bomber, naming it the Model 109.
It had a fairly conventional layout, with a shoulder-mounted Davis wing, as used on the B-24, underslung engines, a single rear tail fin and tricycle landing gear.
It was to carry a small crew of three, and a single remotely-controlled gun turret in the tail.
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A clear emphasis was placed on minimizing drag, and as a result the Model 109 was a visually sleek and well-contoured aircraft.
The plans for this futuristic-looking machine had already been submitted in November 1944. By mid-January 1945, a contract had been signed for further development, and following this came a contract for the production of three prototypes under the name XB-46.
The military was impressed with the XB-46, but Convair was up against stiff competition. This came in the form of the XB-45 from North American, and the XB-48 from Martin. But the most daunting opponent was Boeing’s submission, the XB-47.
Convair continued to work on their design, but in August 1945, just days after the atomic bombs were dropped on Japan, the US suddenly ordered Convair to stop all work on aircraft in development.
After some negotiations they were permitted to continue work on a single XB-46 that wouldn’t contain any military equipment.
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As a result of this reduced budget, work progressed very slowly on the XB-46, and the project fell behind by almost a year. The single example was finally completed in 1946, and it wasn’t until 1947 that it would take to the air.
XB-46 Design
The XB-46, as mentioned, was a rather conventional design.
Its 106 ft (32.2 meter) long fuselage was streamlined and tapered towards the rear. The nose was dominated by a large plexiglass cone, used by the the radar-operator/bombardier and navigator.
Above and behind the nose was the cockpit, which was home to a pilot and co-pilot that sat in a tandem arrangement. As with the XB-45, XB-47 and XB-48, the XB-46 had a large, fighter-style bubble canopy that offered excellent views around the aircraft.
Unlike fighter canopies though, the XB-46’s canopy was fixed in place. Access was instead granted via a pneumatically operated door on the left side below the cockpit. This door, which also doubled as a set of steps, was 30 inches wide, enough for crews wearing bulky flight suits and parachutes.
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In emergencies the cockpit canopy could be jettisoned as an alternative means of escape.
Mid-way along the fuselage was the high aspect ratio, shoulder mounted Davis wing that had a span of 113 ft (34.4 meters).
By 1947 standards this wing type was rather outdated, but it was exceptionally efficient. Reportedly, the XB-46 was capable of gliding a distance of 200 miles from 40,000 ft.
Under the wings were two bulbous engine nacelles, each of which contained two Allison J35 turbojets. These jets provided around 4,000 lbf of thrust each, and were deemed rather underpowered.
They received air through an oval opening at the front of the nacelle. Also contained in the nacelles were the main landing gear. The third gear was located in the nose.
As the engines lacked a power take-off for landing gear hydraulics, the XB-46’s landing gear were pneumatically powered.
Pressure was generated by electric compressors, which was then stored in bottles inside the fuselage. This resulted in a wheels-up time of just two seconds.
The XB-46 also had a very unconventional means of control. To adjust the electric trimmers, the pilot and co-pilot were provided with a scale model of the XB-46, positioned atop a post on the right-side of the cockpit.
To apply the desired trim, they had to simply move the model in the desired motion. Need nose-up trim? Simply tilt the model up. Nose down? Tilt it down.
The controls were kept light with balanced surfaces and spring tabs.
Cancellation
The XB-46 first flew on April 2, 1947, and was found to handle well.
The version used in these tests was not fully equipped, as it was known that the aircraft would never enter production. As such the cockpit was simplified, the fuselage was mostly empty and the gun position in the tail was faired over.
While crews praised the aircraft’s smooth handling, they noted some resonance issues relating to the wing spoilers, and the cabin air system was finnicky.
They also noted that they weren’t comfortable with the exit door, as it relied on the pneumatic system functioning properly to open against the wind in an emergency situation.
However by this point the aircraft was mostly obsolete, and the aircraft’s program was cancelled in August 1947.
Like many other aircraft, it had been completely overshadowed by Boeing’s B-47. Once a competitor to the XB-46, Boeing had updated the B-47’s design to incorporate swept wings during its development.
It was also fitted with six engines, rather than four like the XB-46. As a result it was faster, could carry a heavier payload and reach higher altitudes. The B-47 was a solid, adaptable design, that would serve as the basic blueprint for the legendary B-52 Stratofortress.
In the early 1950s the single retired XB-46 was moved to Florida, where its pneumatic system was tested in simulated cold-weather conditions. In 1952, the sole example was scrapped.
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Only the nose cone was saved, and today resides at the U.S. Air Force Museum in Ohio.
