On 25 August 1950, Convair issued a formal proposal for a swept-winged version of the B-36 with all-jet propulsion. The United States Air Force was sufficiently interested that on 15 March 1951, it authorized Convair to convert two B-36Fs as B-36Gs. Since the aircraft was so radically different from the existing B-36, the designation was soon changed to YB-60. The YB-60 had 72% parts commonality with its piston-engined predecessor. The fuselages of the two aircraft were largely identical, although the YB-60 had a longer, pointed nose with a needle-like instrument probe instead of the B-36's rounded nose; its tail surfaces were swept to match the wings and a wedge-shaped insert added at the wing root. The swept wings also used many B-36 parts. The YB-60's unofficial competitor for an Air Force contract was Boeing's B-52 Stratofortress. Convair's proposal was substantially cheaper than Boeing's, since it involved modifying an existing design rather than starting from scratch. Like the B-52, it was powered by eightPratt & Whitney J57-P-3 turbojets mounted in pairs in four pods suspended below the wing. Instead of the B-36's crew of 15, the YB-60's crew numbered 10. Production B-60s were to have defensive armament similar to those of the B-36. Convair YB-60 serial number49-2676 made its maiden flight on 18 April 1952, piloted by Beryl Erickson. The Boeing YB-52 beat the Convair aircraft into the air by three days. The YB-60 was approximately slower than the YB-52 and also had severe handling problems. It did carry a heavier bomb load — against for the YB-52 — but the Air Force did not see the need for the extra capacity, given the YB-60's other drawbacks. Later, "big belly" modifications increased the B-52's bomb load to. The flight test programs were canceled on 20 January 1953, with 66 flying hours accumulated. A second prototype was never completed: the airframe was built, but it was not fitted with engines or much equipment. Since Convair completed their prototype contract satisfactorily, both YB-60s were formally accepted by the Air Force in 1954. The operational aircraft never flew again, and both airframes were scrapped by July.
