B-58 Alternate Configurations
B-58C-This model of the B-58, designated B-J/58 by Convair, but known unofficially by the Air Force as the B-58C, incorporated significant airframe modifications, including a new wing leading edge, more tail area, a 5-foot fuselage extension, and 4 Pratt & Whitney J58 engines without afterburners. In 1960 Convair estimated that its all-supersonic, Mach 2.4 B-58C would be as efficient and much cheaper than the B-70. The Air Force did not test these propositions for several reasons. Even if the proposed airplane approached the B-70's anticipated performance, it had neither the payload nor the growth potential of the latter. The B-70 was the beginning of a design, the B-58C would be the ultimate product of an old configuration. Further study of the Convair proposal practically closed the case. In April, ARDC reported that the contractor's estimate of a 5,200-nauticalmile unrefueled range was probably 25 percent too optimistic. Also, extensive use of aluminum in the B-58C could create problems since the effects of this metal's exposure to high temperatures (aerodynamic heat) was not known. Lack of funds prompted the final decision. Greatly concerned with the B-70, recently confined to development status, the Air Staff as well as SAC did not want to risk the financial interference of a new project. In early 1961, the Kennedy Administration asked the Congress to cancel production of the "unnecessary and economically unjustifiable" B-70 Valkyrie. Thereupon, the B-70 funds were reduced and the program was limited to 3 experimental planes. In late April, Convair was informed that the Air Force had no interest in the B-58C.
RB-58A-The early photo reconnaissance pod program, due to transform the B-58 into a high-altitude and speedy reconnaissance weapon system had been cancelled, reinstated, and again cancelled by December 1958. One pod, delivered in June 1958, was lost as the plane it equipped crashed in June 1960. The electromagnetic reconnaissance program followed the same pattern, being cancelled in October 1957, then reendorsed, and finally abandoned in May 1958, after delivery of two pods. In 1963, another change took place. As a result of the October 1962 Cuban Crisis, SAC decided the B-58A could be used to great advantage for low-level, highspeed photographic reconnaissance. This was based on the assumption that the extra task could be carried out without making a reconnaissance aircraft out of the few available B-58As. After rejection of several unsatisfactory proposals, a solution was found. It simply involved the incorporation of a KA-56 panoramic camera into the nose fairing of the MB-1 pod. Approved by the Air Staff in mid-1963, the modification was successfully flight tested on 30 October and 10 cameras and associated equipment were purchased. Known as Project Mainline, the modification of 44 B-58As and 10 MB-1 pods was completed on 6 December at a cost of approximately $1 million.
TB-58A-The flight characteristics peculiar to delta-wing planforms and the B-58's unmatched high speed called for a trainer version of the new bomber. The Air Force first authorized the conversion of 4 early test B-58As to the training configuration on 25 February 1959. The modification, done under production contract AF33(600)-36200, provided side-by-side seating for pilot training, with the instructor placed aft and 10 degrees right of the student. The Air Force took delivery of the first TB-58A in August 1960, and subsequently ordered the conversion of 4 additional test B-58As to a similar configuration. This last lot was modified under special contract, but the costs were lumped together for a total of almost $16 million.
Phaseout of the entire B-58 force by the end of fiscal year 1971 (June 1970) was directed in December 1965. This schedule was a change from Secretary McNamara's earlier plans and gave the aircraft an extra year of operational life. However, once underway, the B-58 retirement program moved fast, actually ending 6 months ahead of time. It was completed on 16 January 1970, when the 305th Bomb Wing's last 2 B-58s (Serial Numbers 55-662 and 61-0278) were flown to Davis-Monthan AFB, Arizona. The planes joined 82 other B-58As, including the 8 converted trainers, retired since 3 November 1969. Two B-58As, responsible for record-breaking flights in 1962 and 1963, escaped retirement at Davis-Monthan and were placed in museums.
