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 cars were reminiscent of the shape of horse-drawn carriages, early steamships combined steam engines with sails, the first turbojet fighters that had a straight wing, etc. In this line is the "mastodon" B-36 - the world's first bomber with an intercontinental range of flight, which has also become the last bomber with piston engines. Created on the eve of the era of jet aircraft and nuclear weapons, in appearance, it belongs to the generation of its piston predecessors Boeing B-29 and Lancaster, but in terms of global goals, nuclear armament, equipment with additional jet engines, he claimed an important role in the new world, formed after the Second World War. These claims were not fully implemented. The B-36 was in service with the US Air Force for less than ten years and in the second half of the 1950s it was replaced by a B-52 aircraft, which brought the "form in line with the content."
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.
The installation of four additional turbojets on the B-36D and subsequent modifications allowed several incraeases in speed and ceilings of the aircraft. There were projects for the installation of eight additional turbojets under the wing, in the same standard gondolas from the B-47. Some improvement in the characteristics of the aircraft was achieved for the modifications of the B-36F, B-36H and B-36J due to the installation of more powerful R-4360-53 combined engines. But further increase in the available capacity for the B-36 was not very promising. According to the compressibility conditions, the speed of 700 km/h at high altitudes for the B-36 aerodynamic scheme was the limit. The "aerodynamic resource" for speed for the B-36 was almost exhausted.
Since 1950, Convair had been working on modernization projects for the B-36 by installing a new swept wing on the aircraft and new more powerful types of power plant. Variants were considered with reciprocating combined engines and with turbojets, with supersonic propellers. The estimated maximum speed of such an aircraft was to reach 885 km/h without reducing the range of the aircraft. The practical ceiling of the aircraft was to reach 16,800 m. As a powerplant, it was intended to use either the Allison T-40-1 TVD turbojet with a take-off power of 5500 kg, or the piston combined R-4360-55C engines with the same take-off power, but with a specific fuel consumption of 25% less than for the trubojets. The project with the theater of operations, according to the proposed project, was to be equipped with six engines. Later the project was reworked under eight turbojet engines J57, with a thrust of 4000 kg, similar to those used in the project of another American strategic jet bomber B-52, on which Boeing worked during this period. Later, during the work on the project, engineers went to a more powerful modification with a draft of 5218 kg. The engines were installed two on pylons, under the wing (similarly B-52). It was assumed that with these engines the aircraft will provide a top speed of 880 km / h and a ceiling of 16,700 m.
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. On March 5, 1951, the Air Force ordered two experimental B-36 airplanes with a turbojet engine from Convair. Serial aircraft B-36F-1 and B-36F-5 (49-2676 and 49-2684) were to be altered for the installation of the turbojet engine and the new swept wing.
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. The initial designation of these B-36F vehicles was changed to YB-36G, and the first two aircraft received the YB-60 cipher later(YB-60-1 and YB-60 -5). The new aircraft had 72% of the common with the serial B-36 airframe and equipment assemblies. The first YB-36G was to be ready for flight testing in December 1951; the second, in February 1952.
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 rear of the fuselage was taken unchanged from the B-36F, the central and front ones were redesigned, with the total length of the aircraft increased by 2.4 m, due to a new arrow-shaped keel and a new pointed front fuselage with an air pressure receiver. The center-wing part of the wing was taken almost unchanged from the B-36. The area of ??the new swept wing (the sweep of the quarter of the chords - 35%) was increased to 475 m2, with a swing to 62.8 m. The new was a swept tail unit, with increased areas of the stabilizer and keel. The crew of the aircraft was reduced to 5 people, all of them were now in the front airtight cockpit. Defensive weapons were reduced to one two-gun remote fodder with a sighting AN / APG-32 radar. The three-wheeled chassis was similar to the B-36. To protect the tail of the fuselage, during take-offs and landings, an additional retractable rear wheel was installed.
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.
The tests of the first aircraft continued until June 25, 1954. During the flight tests the aircraft flew for more than 40 hours and showed the following flight data: the mass of the empty aircraft was about 69,000 kg; takeoff weight - 187000 kg; with a flight mass of 118,000 kg, the maximum speed of the aircraft at an altitude of 11,800 m was 816 km / h; ceiling in the target area - 13,700 m; The combat range of action with 4540 kg of bombs is 4700 km.
Flight testing of the YB-60 officially ended on 20 January 1953, when the Air Force cancelled 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. 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 B-60 program was cancelled in the summer of 1952, and testing of the stripped prototype ended in January 1953. The Air Force cancelled 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.
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 second YB-60, although 93 percent complete, was not flown at all. The second machine YB-60-5 (49-2684) was completely finished by construction on July 8, 1954. The second aircraft was fully equipped with the target equipment: the new K-ZA bomber system, guns and the REB system. But by this time the Air Force made the final choice in favor of the B-52, which had the best flight data (for example, the YB-52 showed a maximum speed advantage over the B-60 of 160 km/h on tests) and, most importantly, as a completely new machine with a reserve for further development and subsequent upgrades. In connection with the curtailment of the entire program for the B-60, the work on the second aircraft was stopped even without the first flight.
A year later, the first B-52s, which became a symbol of American air power, began to supply the SAC.
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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