The YB-60 originated in August 1950, when the Consolidated Vultee Aircraft (Convair) Corporation offered to develop the B-36G, a swept-wing, all-jet version of the B-36F-fourth model of the basic B-36, initiated in 1941. The design, covered by the contractor's formal proposal, could eventually be converted into a turboprop bomber. Moreover, existing B-36s could later be brought up to the new configuration's standards.
The first in a series of post-World War II military characteristics for heavy bombardment aircraft was issued on 23 November 1945. These characteristics were revised many times, but by 1950 the experimental aircraft thus far favored still fell short of satisfying the overall performance and long-range requirements expected of an atomic-capable, strategic bomber, due to be operational around 1955.
A letter, rather than a formal agreement, supplemented the basic B-36 contract and authorized Convair to convert 2 B-36Fs into prototype B-36Gs, entirely equipped with turbojets but capable of accepting turboprop engines. The first YB-36G was to be ready for flight testing in December 1951; the second, in February 1952.
The proposed B-36G had little in common with the B-36F The Air Force therefore determined that the B-60 designation would be assigned to the plane, because of the striking change in physical appearance and improvement in performance over that of the conventional B-36 airplane.
A misunderstanding concerning the configuration of the B-60 prototypes compelled Convair to recommend in August 1951 that at first only 2 stripped aircraft be developed. Accepting responsibility for the error, the contractor also proposed that the second YB-60 later be completed as a full tactical model. The Convair solution meant that separate specifications would have to be developed for each prototype. The Air Force agreed, after a 2-day conference during which the basic tactical configuration was set.
The B-60 prototype differed significantly from the B-36 by featuring swept-back wings and swept-back tail surfaces, a new needle-nose radome, a new type of auxiliary power system, and 8 Pratt & Whitney J57-P-3 jet engines, installed in pairs inside "pods" suspended below and forward of the leading edge of the wings. Another special feature of the YB-60 was its extended tail, which enabled the aircraft to remain in a level position for a considerable period of time during takeoff and to become airborne, with a gross weight of 280,000 pounds, after only 4,000 feet of ground roll.
The J57-P-3, earmarked for the YB-60, was primarily scheduled for the B-52. Thus, while Convair would be able to use the Boeing-designed nacelles and engine pods, which seemed to be a distinct advantage, engine shortages were to be expected. This was particularly true, since the J57 engine was itself the product of an intensive effort to develop a high-thrust turbojet with a low fuel consumption. By the beginning of 1951, engine prototypes had accrued only 550 hours of full-scale testing. In 1952, even though production was already started, the engines were likely to remain in very short supply for quite a while.
The YB-60 flew for the first time on 18 April 1952-only 12 days after the prototype's eighth J57-P-3 engine finally arrived at the Convair's Fort Worth plant. The 66-minute flight was hampered by bad weather, but 2 subsequent flights in the same month were entirely successful, the YB-60 actually displaying excellent handling charateristics. This encouraging trend, however, did not prevail.
Flight testing of the YB-60 officially ended on 20 January 1953, when the Air Force canceled the second phase of the test program. Convair test-flew the first YB-60 for 66 hours, accumulated in 20 flights; the Air Force, some 15 hours, in 4 flights. The second YB-60, although 93 percent complete, was not flown at all. By and large, test results were worrisome, because the stripped YB-60 displayed a number of deficiencies. Among them were engine surge, control system buffet, rudder flutter, and problems with the electrical engine-control system.
The Air Force canceled the B-60 program several months before the prototype testing was officially terminated. The decision was inevitable. From the start, the project's sole purpose had been to help the Air Force in its quest for a B-36 successor. In this capacity, the B-60 competed all along with the B-52. There was no official competition, but test results were irrefutable. The YB-52 demonstrated better performance and greater improvement potential than the YB-60. The YB-52's first flight on 15 April 1952-3 days ahead of the YB-60's-was an impressive success and generated great enthusiasm for the Boeing airplane.The latter was handicapped by the speed limitation imposed by structural considerations at low altitude and buffet at high altitudes. Also, the Convair prototype's stability was unsatisfactory because of the high aerodynamic forces acting upon the control surfaces and the low aileron effectiveness of the plane.
The B-60 program was canceled in the summer of 1952, and testing of the stripped prototype ended in January 1953. Even so, the Air Force did not accept the 2 YB-60s before 24 June 1954. There were valid reasons for the delay. Convair truly believed, and tried to convince the Air Force, that the YB-60s should be used as experimental test-beds for turbopropeller engines. Shortage of money and the YB-60's several unsafe characteristics accounted for the Air Force's decision to turn down Convair's tempting proposal.
The final cost of the 2 B-60 prototypes was set at $14,366,022. This figure, agreed upon by both the Air Force and the contractor on 13 October 1954, included Convair's fee, the contract termination cost, and the amount spent on the necessary minimum of spare parts.
The Air Force scrapped the 2 YB-60s before the end of June 1954.
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