The only telling difference between the B-36F and the preceding B-36D lay in the substitution of more powerful engines; R-4360-53s in lieu of R-4360-41 engines.
The prototype B-36F and B-36F production models were equipped from the start with six 3,800 horsepower R-4360-53 engines. Each generated 300 more horsepower than a B-36D engine, but still failed to bring the B-36F's performance up to par.
The Air Force accepted a first B-36F in March 1951 and a few more in the months that followed. No B-36Fs reached SAC until August.
The B-36F's R-4360-53 piston engines were not wholly satisfactory because of excessive torque pressure as well as ground air cooling and combustion problems. Pratt & Whitney, Convair, and the Air Materiel Command joined forces to solve these deficiencies quickly.
As in the case of other B-36 model series, a number of the new B-36Fs were brought up to the configuration introduced by the Featherweight B-36J 111. Approval of the Convair modification contract in February 1954 was followed by delivery of the first B-36F 111 in May. The B-36F featherweight modifications were completed in December, on schedule.
Among the 34 B-36Fs bought by the Air Force was the B-36F prototype, later completed as a true production model.
The Air Force took delivery of the first 4 B-36Fs toward the end of fiscal year 1951-1 in March 1951, 1 in May, and 2 in June. The other 30 B-36Fs were accepted in FY 52-2 in July 1951, 5 in August, 4 in September, 8 in October, 6 in November, 4 in December, and 1 in January 1952.
The Air Force did not get its last B-36Fs until several months after production was over.
The B-36F carried the price tag of the B-36D. Airframe, engines, electronics, all cost the same.
The Air Force ordered and took delivery of 24 long range reconnaissance versions of the B-36F. The first 4 RB-36Fs were accepted in fiscal year 1951 (all in May); the 20 others in FY 52 (between August and December 1951). Cost records listed both the B-36F and the RB-36F at $4.1 million each.
The YB-60 was a B-36 configuration that never went past testing. First known as the YB-36G, this apparent successor to the B-36F, was redesignated YB-60 in mid 1951 because it so obviously differed from the B-36. At the same time, Convair's plans to bring existing B-36s to the G configuration were given up. The swept wing, pure jet YB-60, with its new needle nose radome and new type of auxiliary power system, soon found itself competing with the future B-52. Both used the same jet engines (Pratt & Whitney J57 P 3s), but in comparison the YB-60's performance test results proved disappointing, and the program was canceled in January 1953. The cost of building and testing the 2 B-60 prototypes (accepted in the fall of 1951) ran around $15 million.
In mid 1958, 46 RB-36s remained in the active inventory. SAC identified 19 of them as RB-36Fs. No B-36Fs were listed, although USAF rolls still reflected 32 B-36s. Total phaseout was imminent in any case.
On 16 June 1954, SAC's 4 RB-36 equipped heavy strategic reconnaissance wings were given a primary mission of bombing. They did limited reconnaissance as a secondary mission. Then on 1 October 1955, the RB-36 reconnaissance wings were redesignated heavy bombardment wings, while retaining a latent reconnaissance capability.
A total of 34 B-36Fs were accepted from 1951 to 1952. Phaseout was largely complete by 1958.
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