Boeing XB-55

The Boeing XB-55, company designation Model 474, was a strategic bomber proposed to replace the Boeing B-47 Stratojet in United States Air Force service. It grew out of a request for proposals issued in October 1947, and Boeing received a contract for further engineering studies on 1 July 1948. The first concept hung four Allison T40 turboprop engines, each driving contra-rotating propellers, from a wing with less sweepback than the B-47, and was projected to reach 490 miles per hour. A dispute between the engine and propeller makers over the T40 driveshaft, and the prospect that the jet-powered XB-52 could fly a year sooner, ended the programme, and the Air Materiel Command was directed to cancel the contract on 29 January 1949. No prototype was built, but the studies proved valuable in the development of the B-52 Stratofortress.