In the B-36B, R-4360-41 engines with fluid injection supplanted the B-36A's R-4360-25s. The B-36B also offered better and more electronics equipment, including the AN/APQ-24 bombing navigation radar (substituted for the B-36A's APG-23A). The B-36B. could carry 86,000 pounds of bombs (a 14,000 pound increase). Of greater importance, it could carry atomic bombs weighing perhaps as much as 43,000 pounds. The bombs were 364 inches long and had a diameter of some 54 inches. To carry these bombs internally, bomb bays needed to be rearranged. Although approved in 1945 as the "Grand Slam Installation;' this modification did not reach the production line until all B-36As had been built. There were good reasons for the delay. When B-36 production first started, the high secrecy given to the atomic bomb kept the necessary engineering specifications from reaching the contractor. The Air Force at the time did not know how many atomic bombs were available, and lacked other data on which to base firm carrier requirements. The B-36As could have been retrofitted to carry the crucial weapons, but the modifications appeared senseless since these early bombers were highly deficient. Eighteen of the B-36Bs could handle remote controlled VB-13 "Tarzon" bombs (2 per bomber).
The plane, flown by Convair, performed well far better than expected. Several later tests by Convair and AMC pilots showed more rewarding results. On 5 December 1948, a long range mission of 4,275 miles was flown at high altitude. Save for climb and descent, an average cruising speed of 303 miles per hour was maintained during the entire 14 hour flight at 40,000 feet. This was surpassed during a similar mission on 12 December, when the average speed rose to 319 miles per hour. Then on 29 January 1949, a B-36B dropped two 43,000 pound bombs on a practice target, the first from 35,000 and the second from 40,000 feet.
The B-36B entered operational service in November 1948. The B 36Bs joined the B 36As of SAC's 7th Bomb Group at Carswell AFB in November 1948.
In contrast to the B-36As, the B-36Bs were equipped from the start with remote retraction turrets and 20 millimeter guns. Unfortunately, this was no asset. The B-36Bs in their original configuration would be long gone before either the turrets or guns worked properly. The B-36's defensive armament system, furnished by the government, was designed and built by General Electric according to Air Materiel Command specifications. At first, obvious gun and turret defects postponed the system's installation. Then, lack of ammunition, also government furnished, delayed testing until mid 1949. And, obviously, the guns had to be air fired before remaining deficiencies could be found and corrected. As the Eighth Air Force Commander bluntly put it in February 1950: "There is no use driving a B-36 around carrying a lot of guns that don't work." Also, the R-4360-41 engines of the B-36Bs demanded extra fuel tanks. Even though the new bomb bay tanks were supposedly self sealing, their leaks lasted throughout the B-36B's short life.
Many of the B-36B's initial troubles resembled those of any other new aircraft. Minor adjustments were needed and as is often the case parts shortages were acute. Although the Air Force frowned on cannibalization as never affording a lasting solution, stripping parts from one B-36 to keep another flying became fairly common. Shortages of equipment, such as empennage stands, dollies, jacks, and related items, hampered maintenance. Because there was no money for new equipment, maintenance crews utilized as well as they could some of the tools used for the old B-29s. Personnel turnover further hampered progress. All these problems persisted through 1950.
Convair actually built 73 B-36Bs, but the Air Force directed modification of 11 prior to formal acceptance. Four of the 11 appeared on USAF rolls as B-36Ds, and 7 as RB-36Ds. Convair kept on listing the planes as B-36Bs. Consequently, the Convair B/RB-36D production totals never did match the USAF B/RB-36D acceptances. These discrepancies resulted from different accounting methods and proved of no real importance.
The Air Force accepted 31 B-36Bs in fiscal year (FY)1949; 30 in FY 50, and a last one in September 1950 (FY 51).
Production ended in September 1950 with delivery of the sixty-second B-36B.
The Flyaway Cost Per Production Aircraft was $2.5 million. As in the B-36A's case, this was a prorated figure based on the estimated procurement costs of 100 B-36s. The price the Air Force paid to bring the B-36B to the B-36D configuration as well as other postproduction modification expenses were not included.
The B-36B phaseout was fast, almost as quick as that of the B-36A. Twenty five B-36Bs were already undergoing conversion during the first half of 1951.
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