The Boeing XB-56 was a proposal by Boeing for a re-engined version of the American jet-powered medium bomber aircraft, the B-47 Stratojet. The original designation for this modification was YB-47C.

Design and development

Lockheed-Marietta B-47E Stratojet 53-1830 parked at Langley Air Force Base

The B-47 was equipped with six

General Electric J47 The General Electric J47 turbojet (GE company designation TG-190) was developed by General Electric from its earlier J35. It first flew in May 1948. The J47 was the first axial-flow turbojet approved for commercial use in the United States. It ...

turbojets, each rated at thrust. The engines were mounted in four nacelles slung from the high wing, with two engines in the inboard pod and one engine in the outboard nacelle. To reduce complexity and increase commonality, it was proposed that a higher-rated engine be selected such that one engine could be mounted in each nacelle. The Allison J35 turbojet engine was being developed during the late 1940s, and it was provisionally rated at or with afterburner. Thus 4 × 8500 lb_f = using that engine, as compared to 6 × 5,200 lb_f = in the production B-47. Thus the conversion would be lighter, simpler and more powerful.Jones, Lloyd S.: ''U.S. Bombers: B1-B70'', Aero Publishers, Inc., 1969. LCCN 62-15969 A contract was signed with Boeing in January 1950, calling for rework of one aircraft. A B-47B-20-BW (s/n 50-082) was earmarked for the conversion. The date for first flight was projected as April 1951.National Museum fact sheet Boeing B-56A
A combination of delays and less-than-expected performance of the J35 led to the consideration of other engines. The

Allison J71 The Allison J71 was a single spool turbojet engine, designed and built in the United States. It began development in 1948 as a much modified J35, originally designated J35-A-23. Operational history The Allison J71 turbojet powered the Douglas B ...

was proposed, however problems with this engine meant that this was not feasible for the by-then redesignated B-56A. The Pratt & Whitney J57, eventually rated at thrust, was also considered, but that engine was still in development, and the

Boeing B-52 Stratofortress The Boeing B-52 Stratofortress is an American long-range, subsonic, jet-powered strategic bomber. The B-52 was designed and built by Boeing, which has continued to provide support and upgrades. It has been operated by the United States Air ...

, which was being concurrently developed (first flight was April 1952), had priority for this engine. The B-56 program was canceled in December 1952 before conversion of the prototype was started. The unconverted B-47 was relegated to a ground instructional airframe and in the late 1960s was in use at the Naval Air Facility El Centro as an egress trainer.

Variants

;XB-56 :Designation for a single B-47 to be re-engined with four YJ71-A-5 engines, later re-designated YB-56 and YB-47C but was not converted. ;RB-56A :Designation for production variant, cancelled and not built.

Specifications (XB-56)

Boeing B-56A Stratojet 3-view line drawing

References

Notes

Bibliography

External links

{{Boeing combat aircraft B-56 Quadjets Cancelled military aircraft projects of the United States High-wing aircraft Strategic bombers