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Boeing Model 294 / B-15 / XBLR-1

Although the Boeing B-17 was to gain greater fame, Boeing also designed and built an even larger four-engine bomber in the mid-1930s, the XB-15. Its design was actually begun before the B-17, but it did not make its first flight until 1937, more than two years after that of the B-17. The mammoth Boeing XB-15 began in 1934 as a design study for the Army to see if it was possible to build a heavy bomber with a 5,000-mile range. When it made its first flight, it was the largest and heaviest plane ever built in the United States. It was so large that the crew could go through passages in the wing to make minor repairs while the airplane was flying.

In the summer of 1934, Boeing began to manufacture new production tools, and the main structural components of the Model 294 were also completed. The manufacturing work was initially carried out at Boeing's No. 1 workshop, but later a barge was used to transport the fuselage to the larger space of the second workshop. A few years later, the plant took on the assembly work of another important model, the B-29 "Super Fortress."

In July 1933, the Air Corps Materiel Division reported that an airplane capable of carrying a one-ton bomb load 5000 miles at a speed of 200 miles per hour was feasible. On the basis of that report, the Air Corps asked the General Staff in December for a plane of those specifications. Taking this advice, the air staff justified the request by pointing out that the bomber could reinforce Hawaii and Panama. Their argument worked. On May 16, 1934, the General Staff authorized the Air Corps to negotiate contracts for an experimental aircraft, named "Project A." The General Staff required the experimental plane to be able to destroy "distant land or naval targets" and "reinforce Hawaii, Panama, and Alaska without the use of intermediate servicing facilities."

While the Air Corps was working out the proposal for Project A, the Geneva Disarmament Conference collapsed without reaching an agreement on arms reduction. In October 1933, Germany withdrew from the Conference and the League of Nations. The other delegates stayed on in Geneva until the spring of 1934, but the conference was effectively over. France announced a return to its traditional methods of security: armaments and alliances.

Boeing won the contract and the airplane it produced was designated the XB-15. In May 1936, Air Corps leaders asked the General Staff for fifty more B-17s and eleven more Project "A" long-range bombers. The General Staff concluded that the international situation did not indicate a need for more long-range bombers.

Completed in 1937, the XB-15 proved to be underpowered. The Boeing XB-15 was conceived as a four-engine aircraft using the most powerful advanced engines of the Allison V-3420, which were a pair of V-1710 engines with a capacity of 1100 hp, working on a single screw. (At that time these engines were not available, and so in fact the XB-15 flew with Twin Wasp, whose power was much less than half the power of the V-3420).

Coincidentally, some participants in the 294 project had some understanding of Tupolev's large aircraft design. Five years ago, when the TB-1 was flying around the world, it flew over Siberia from Alaska in the state of a seaplane. When it arrived in Seattle in mid-October 1929, it needed to change the floats to wheels to adapt to the North American continent. Requirements. At that time, Boeing was the largest manufacturer of seaplanes in the northwestern United States, and it was logical to undertake this work. When retrofitting the TB-1, Boeing engineers made a study of its structure and learned about the manufacturing process that Tupolev applied when designing TB-1.

Because a long-range flight, powered by the engines of the time, took several days, the crew had bunks to sleep on between shifts. The XB-15 had been designed for four 1,000-horsepower liquid-cooled engines, but because those engines were not available in time, it was powered by 850-horsepower engines. Nonetheless, it set several load-to-altitude records, including taking a 31,205-pound payload to 8,200 feet on July 30, 1939.

An important B-15 mission was the Mercy Flight of nearly 10,000 miles from Langley Field to Chile and B-15, "big brother" of the B-17, made Mercy Flight to Chile in 1939. Passageway in wing permits access to each of four engines. return. Made between February 4 and 14, 1939, its purpose was to deliver 3,250 pounds of medical supplies after an earthquake had devastated sections of Chile.

The trip out was made in 29 hours and 53 minutes of flying, with stops only at Colon, in the Canal Zone, and Lima. Major Haynes, again in command, subsequently received the Distinguished Flying Cross. The B-15 he used is still flown by the Air Transport Command as long cargo and transport missions. Delivered in December 1937, it then had insufficient power for its advanced design. With plans for still better heavy. bombers under consideration, the idea of putting the B-15 in production was abandoned.

With a wingspan of 149 feet, almost half again as large as the B-17, the XB-15 was the victim of lag in engine development -- there were simply no engines available which were powerful enough to give it the performance it deserved. Numerous test projects were made with the XB-15, but in 1943 it was relegated to the role of a cargo airplane and redesignated the XC-105. At the end of World War II, it was dismantled in Panama.

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Page last modified: 07-09-2018 07:20:52 ZULU