The B-60 Devastator was a typical example of the results of attempting a "half generation" approach to aircraft development. While it was a significant advance over its predecessors, it was quickly outmoded by advancing technology. It played second fiddle to the B-52 for most of its career and would have languished in obscurity had it not been for its participation in Operation Jungle Hammer in 1960 which showed its capability for conventional bombing. This gave the aircraft a new lease of life and allowed it to remain in service until the early 1970s.
Despite the total (and unexpected) dominance of the piston-engined B-36 in the late 1940s, it was apparent that advancing interceptor and surface-to-air missile technology would eventually place the B-36 at risk. A faster and higher-flying successor was needed. Boeing were developing the B-52 to fill this role but that aircraft was hitting development delays and threatened to be costly. Accordingly, on August 25, 1950, Convair issued a formal proposal for an all-jet swept winged version of the B-36, initially designated XB-36G. The Air Force was sufficiently interested that on March 15, 1951 the USAF authorized Convair to convert two B-36Ps (49-2676 and 49-2684) as B-60Qs. Since the aircraft was so radically different from the existing B-36, the designation was soon changed to YB-60.
In the interest of economy, as many components as possible of the existing B-36P were used to build the YB-60. The fuselage from aft of the cabin to near the end of the tail remained essentially the same as that of the B-36P. However, the nose was lengthened to accommodate more equipment, and was tapered to a needle-like instrument probe. The conversion to a swept wing had moved the center of gravity farther aft, which necessitated the addition of a retractable tail wheel underneath the rear fuselage. The plan was to leave the tail wheel still extended during the takeoff run, retracting it just prior to rotation. During landing, the tail wheel remained retracted until both the main and nose gears were firmly on the ground. Because of the higher landings speeds that were inherent with a swept-wing design, the design team included provisions for a drag chute in the tail cone, although it is unclear if it was actually fitted to either prototype. The fuselage was a bit longer than that of the B-36P, having a length of 171 feet.
The most readily-noticeable difference between the YB-60 and the B-36P was the swept wing. A wing sweep of 37 degrees was accomplished by inserting a wedge-shaped structure at the extremity of the center portion of the center wing. A cuff was added to the leading edge of the center wing to continue to sweep line to the fuselage. The net result was an increase of wing area to 5239 square feet. The wing span was 206 feet, about 24 feet less than that of the B-36P. The aircraft was also fitted with a new swept vertical tail and a set of swept horizontal elevators. The new swept vertical tail made the YB-60 somewhat taller than the B-36P, the tip of the new swept vertical fin reaching 60 feet 6 inches from the ground. The YB-60 was to be powered by eight 8700 lb.s.t. J57-P-3 turbojets, housed in pairs on four pods that were suspended below and forward of the wing leading edge, similar to the B-52, but turboprop engines were still considered as a possible option if the jet engines did not work out.
The YB-60 also differed from the B-36P in its crew allocation and in its armament fit. The original YB-60 concept had only five crew members-pilot, copilot, navigator, bombardier/radio operator and radio operator/tail gunner. All were seated in the pressurized and heated forward compartment. At this point there was a major dispute within the Strategic Air Command hierarchy over the question of defensive armament. In common with the established practice on the B-36, all of the defensive armament was omitted, save the twin 20-mm tail cannon that were remotedly directed by the radio operator/tail gunner seated in the forward fuselage via an AN/APG-32 radar in the extreme tail. However, it was already clear that the B-60 would have onlya marginal superiority over intercepting fighters from 1955 onwards and many thought the time had come to reinstate at least some defensive armament. Accordingly, the second YB-60 and any production aircraft were to have the crew increased to nine. Early in the design process, the Air Force asked Convair to add back some of the retractable turrets that had been omitted from the initial design. The upper forward and lower aft turrets were to be identical to those of the original, pre-Featherweight B-36s, but the upper aft turrets were still to be omitted.
The K-3A bombing/navigation system, with Y-3A optical and radar bombing sight was retained. The maximum bombload capacity was the same as that of the B-36P, namely 84,000 pounds.
The conversion of 49-2676 to YB-60 configuration began in the spring of 1951. The work was completed in only 8 months, since almost 72 percent of the parts of the YB-60 were common with those of the B-36P. However, the project was delayed by the late delivery of the J57 turbojets, which did not arrive at Convair until April of 1952. The aircraft was rolled out on April 6, 1952. It was the largest jet aircraft in the world at the time. The first flight of YB-60 49-2676 took place on April 18, 1952. The top speed of the YB-60 was only 508 mph at 39,250 feet. In addition, flight tests of the YB-60 turned up a number of deficiencies—engine surge, control system buffeting, rudder flutter, and electrical engine-control system problems. The stability was rather poor because of the high aerodynamic forces acting on the control surfaces acting in concert with fairly low aileron effectiveness.
At this point there was a strong case for scrapping the B-60 completely. The Boeing YB-52 was already flying and had exhibited a clear superiority in performance terms. It was over 100mph faster and could fly around 5,000 feet higher, re-establishing the margin of superiority held by the big bombers at altitude. The problem was that the YB-52 had development problems all of its own and the YB-60 had a clear cost advantage over the B-52 due to its 72 percent commonality with the B-36 and its use of much already-proven equipment. This was a significant advantage since the B-36 fleet had to be replaced and there were very real questions as to whether the numbers of aircraft could be maintained if the B-52 alone was to be procured. The matter was decided when the second YB-60 was flown and this demonstrated significant improvements over the original aircraft. Accordingly, the B-60 Devastator was ordered into production
Specification of Convair YB-60
Engines: Eight 8,700 lb.s.t. Pratt & Whitney J57-P-3 turbojets. Performance: Maximum speed 508 mph at 39,250 feet. Combat ceiling 44,650 feet. Maximum range 8000 miles. Combat radius 2920 miles with 10,000 pound bomb load. Initial climb rate 1570 feet per minute. An altitude of 30,000 feet could be attained in 28.3 minutes. Ground run 6710 feet, takeoff to clear a 50 feet obstacle 8131 feet. Normal cruising altitude 37,000 feet. Maximum cruising altitude 53,300 feet. Dimensions: wingspan 206 feet 0 inches, length 171 feet 0 inches, height 60 feet 6 inches, wing area 5239 square feet Weights: 153,016 pounds empty, 300,000 pounds gross Armament: Four 20mm cannon in upper nose mounts, four 20mm cannon in lower rear mounts, two 20-mm cannon in the extreme tail. Maximum bombload 84,000 pounds.
Convair B-60A Devastator
The B-60A was the first production version of the B-60, entering service with Strategic Air Command in March 1953 with the 445th Bomb Group. The B-60A was similar to the YB-60 except that the penalties of carrying a defensive armament had been clearly demonstrated and the B-60A reverted to the featherweight configuration. In addition, uprated engines were installed with a major impact on the aircraft's performance. A total of 72 B-60A production aircraft were built before the assembly lines at Forth Worth shifted to the B-60B in 1954
Specification of Convair B-60A
Engines: Eight 8,900 lb.s.t. Pratt & Whitney J57-P-5 turbojets. Performance: Maximum speed 515 mph at 43,250 feet. Combat ceiling 49,650 feet. Maximum range 9,110 miles. Combat radius 3,520 miles with 10,000 pound bomb load. Initial climb rate 1570 feet per minute. An altitude of 30,000 feet could be attained in 28.3 minutes. Ground run 6,710 feet, takeoff to clear a 50 feet obstacle 8,131 feet. Normal cruising altitude 37,000 feet. Maximum cruising altitude 53,300 feet. Dimensions: wingspan 206 feet 0 inches, length 171 feet 0 inches, height 60 feet 6 inches, wing area 5239 square feet Weights: 150,022 pounds empty, 290,000 pounds gross Armament: Two 20-mm cannon in the extreme tail. Maximum bombload 84,000 pounds.
Convair B-60B Devastator
The B-60B was the first large-scale production version of the B-60 with 600 aircraft being built during 1954 and 1956. B-60Bs were initially built at Fort Worth, Texas and Wichita, Kansas but Fort Worth dropped out of the production schedule at the end of 1954 to concentrate on the B-58 Hustler program. The B-60B had the improved electronics developed for the B-52 in place of the older B-36 derived systems on the B-60A. The nose of the B-60 was lengthened by almost 10 feet to accommodate the new equipment, this resulting in the center of balance being restored to its normal position. The tailwheel was thus deleted.
Convair RB-60C Devastator
A strategic reconnaissance version of the B-60B, the RB-60C was proposed in 1955 as an RB-36 replacement. However, the performance of the B-60 was considered inadequate and the RB-52B was procured in its place.
Convair GB-60D Devastator
The GB-60D was a version of the B-60B equipped to operate the F-85 Goblin parasite fighter as a replacement for the GB-36/F-85 combination. It was judged that the performance of the F-85 was inadequate to make further pursuit of the parasite fighter concept unprofitable and the type was abandoned.
Convair B-60E Devastator
The B-60E was the primary production version of the B-60 with 770 aircraft being built between 1956 and 1960. The only difference between the B-60E and the B-60B was that the new version had an M-61 six-barrelled 20mm gun in its tail position. Despite this enhancement, Red Sun exercises showed that the B-60 was too vulnerable to be considered a primary nuclear strike aircraft and it was scheduled to be withdrawn from service and replaced by the B-52G from 1960 onwards. However, the performance of the aircraft in Operation Jungle Hammer in 1960 showed the effectiveness of the B-60 as a conventional bomber, something that the B-52 with its smaller bomb bay could not emulate. Accordingly, the decision to eliminate the B-60 from the active force was reversed and five B-60 groups were maintained.
Convair B-60F Devastator
All surviving B-60B and B-60E aircraft were modified to B-60F standard in 1961-64. This modification included deleting the facilities for nuclear weapons. The B-60Fs continued in service into the 1970s but the aircraft retained the original light structure of the B-36 and aged quickly. By 1970 they were worn out and the accident rate was increasing. A new conventional bomber, the Convair B-74 Dominator was being developed but would not be available for some years. Fortunately, by this time, B-52s were being phased out of the frontline force and replaced by the B-70 Valkyrie. The surplus B-52s were modified to B-52J status and used as an interim conventional bomber until the B-74 was available. This allowed the last of the B-60Fs to be withdrawn in 1972.