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The Boeing XB-15 (Boeing 294) was a United States bomber aircraft designed in 1934 as a test for the United States Army Air Corps (USAAC) to see if it would be possible to build a heavy bomber with a range. For a year beginning in mid-1935 it was designated the XBLR-1. When it first flew in 1937, it was the most massive and voluminous airplane ever built in the US. It set a number of load-to-altitude records for land-based aircraft, including carrying a payload to on 30 July 1939.

The aircraft's immense size allowed flight engineers to enter the wing through a crawlway and make minor repairs in flight. A flight took 33 hours at its cruising speed; the crew was made up of several shifts, and bunks allowed them to sleep when off duty.

Design and development

thumb|The XB-15's front gun turret

The specification that produced the XB-15 began in mid-1933 as "Project A", USAAC discussions regarding the possibility of flying a very large bomber with a range of . Boeing gave the project the internal name of Model 294, while the USAAC called it the XB-15. Martin's design, the XB-16, was judged inferior by the USAAC before a prototype was built, and was canceled.

Starting in August 1934, Boeing began designing the Model 299 in answer to a proposal by the USAAC to replace the Martin B-10 bomber. The Model 299 design team incorporated elements of the Boeing 247 and the Model 294, especially its use of four engines. The Model 299 design team worked alongside Klystra's team, but difficulties in fabricating such a large aircraft slowed progress on the 294.

In mid-1935, the USAAC combined Project A with Project D; a proposal asking for "the maximum feasible range into the future." The combined program was designated BLR for "Bomber, Long Range". The XB-15 was renamed the XBLR-1; it was joined under the BLR program by two other projects: one from Douglas Aircraft, the XBLR-2 which later became the XB-19; and one from Sikorsky Aircraft called the XBLR-3, later canceled. The next year, the XBLR designation was dropped and the Boeing prototype was once again the XB-15. However, Boeing engineers projected that the prototype would be capable of carrying the heaviest air cargo to date: a load of . Haynes was awarded certificates issued by the National Aeronautics Association (NAA) for an international record for "the greatest payload carried to an altitude of 2,000 meters". The XB-15 was not fast for a bomber but it was the fastest aircraft that could carry so much weight, and for such distances. In July 1939, Haynes received certificates from the NAA for an international speed record with a payload. The latter performance also established a national closed circuit distance record of . It displayed nose art depicting an elephant carrying a large crate on its back labeled "supplies".

thumb|The XB-15 parked on an airstrip.

Operators

;

  • United States Army Air Corps

: 2d Bombardment Group

  • United States Army Air Forces

: 20th Troop Carrier Squadron

Specifications (XB-15)

See also

References

Notes

Bibliography

  • Boniface, Patrick. "Boeing's Forgotten Monster: XB-15 a Giant in Search of a Cause." Air Enthusiast, No. 79, January–February 1999. pp.&nbsp;64–67.
  • Bowers, Peter M. Boeing Aircraft since 1916. London: Putnam, Third edition, 1989. .
  • Kohn, Leo. "Boeing XB-15 Super Flying Fortress: U.S. Heavy Bomber". In Ray Merriam. "U. S. Warplanes of World War II." World War II Journal, 69. Bennington, Vermont: Merriam Press, 2002. .
  • Maurer, Maurer. Aviation in the U.S. Army, 1919–1939. Washington, D.C.: United States Air Force Historical Research Center, Office of Air Force History, 1987. .
  • Moy, Timothy. War Machines: Transforming Technologies in the U.S. Military, 1920–1940 (Texas A&M University Military History Series, 71)."] College Station, Texas: Texas A&M University Press, 2001. .
  • Swanborough, F. Gordon and Peter M. Bowers. United States Military aircraft since 1909. London: Putnam, 1963.
  • Yenne, Bill. The Story of the Boeing Company. Minneapolis, Minnesota: Zenith Imprint, 2005. .
  • Boeing's description of the XB-15
  • Encyclopedia of American aircraft
  • USAF Museum description of XB-15