The next production version was the B-50B (Model 345-2). It was externally identical to the B-50A, with all the differences being internal. The aircraft had an increase in the gross weight from 168,480 pounds to 170,400 pounds and was equipped with a strengthened wing containing a new type of lightweight fuel cell.
The B-50B introduced a new wrinkle into the production block number system. Instead of starting the block numbers over at -1 for the new series, the B-50B block numbers simply continued on from where the B-50A blocks had ended. Consequently, the first B-50B was B-50B-40 and continued on to -60. Subsequent B-50s continued this practice.
The first B-50B (47-118) took off on its maiden flight on January 14, 1949. The first example (47-118) was retained at the factory for test work under the designation EB-50B, and was at one time fitted with a track-tread undercarriage in place of the conventional wheels. This was designed to reduce the overall pressure exerted on the ground by spreading the aircraft weight over a larger ground contact area. However, the caterpillar type tracked landing gear proved to be inefficient and difficult to maintain and was never used on any production aircraft. The EB-50B was later converted back to a conventional landing gear system and used for other test projects.
All of the other B-50Bs were sent to Wichita for conversion to the reconnaissance role under the designation RB-50B. The RB-50B featured four camera stations (supporting a total of 9 cameras), weather reconnaissance instruments, and extra crew members housed inside a capsule that was installed in the aircraft's rear bomb bay. The RB-50B was capable of being refuelled by the British-developed hose refuelling system, and could carry a 700-gallon auxiliary fuel tank under each wing.
In 1951, the RB-50Bs were again modified. There were three different configurations produced, which were later redesignated RB-50E, RB-50F, and RG-50G respectively.
There were 14 RB-50E conversions carried out. The RB-50E was earmarked for photographic reconnaissance and observation missions. The crew was normally ten. According to the type of mission being flown, the left-side gunner could serve as a weather observer or as an inflight refuelling operator. The defensive armament consisted of 13 0.50-inch machine guns, housed in five electrically-operated turrets.
The RB-50F resembled the RB-50E but carried the SHORAN radar navigation system designed to conduct mapping, charting, and geodetic surveys. However, the SHORAN system interfered with the RB-50F's defensive armament, so the SHORAN radar and its associated equipment were housed in removable kits. The first RB-50F aircraft entered service with SAC in January of 1951. A total of 14 RB-50F conversions were carried out.
Electronic reconnaissance was the primary mission of the RB-50G. It entered SAC service between June and October 1951. A total of 15 RB-50B-->RB-50G conversions were made. The RB-50G differed significantly from the RB-50E and F, so much so in fact that it was assigned a different manufacturer's number of Model 345-30-025. The RB-50G featured six electronic countermeasures stations, which required a number of internal structural changes. Some external modification had to be made to accommodate the radomes and antennae of the aircraft's new radar equipment. During the reconfiguration process, the 16-crew RB-50G was fitted with the improved nose of the B-50D, which had a large molded plastic cone and an optically-flat bomb-aiming window in the lower portion instead of the seven-piece B-29 unit that was used throughout the B-50B series. In contrast to the RB-50F, the RG-50G could use its defensive armament while operating its new electronic equipment.
Leaks from the new light-weight fuel cells were an unexpected problem.
Very early in the production run of the B-50B, these leaky cells had
to be replaced by a new type of fuel cell. Pending the availability
of new cells, deliveries of new B-50Ds were actually stopped. The new
aircraft experienced fuel tank overflows, leaks in fuel check valves,
failures of the engine turbosuperchargers, warped turbos and warped
turbo bucket wheels. The B/RB-50Bs shared the B-50A's trailing wing
cracking problem. The permanent solution to this problem was to use
heavier metal in the fabrication of future wing flaps, but was not
quick to be implemented.
47-118/127 Boeing B-50B-40-BO Superfortress c/n 15802/15811 118 retained by the factory for test work under designation EB-50B. All later modified to RB-50B configuration. 119,120,122/127 modified as RB-50E for special photographic missions. 121 modified as RB-50F with navigational radar. 47-128/137 Boeing B-50B-45-BO Superfortress c/n 15812/15821 All later modified to RB-50B configuration. 128/132, 135 modified as RB-50E for special photographic missions. 134, 137 modified as RB-50F with navigational radar. 133, 136 modified as RB-50G with additional radar and B-50D type nose. 47-138/147 Boeing B-50B-50-BO Superfortress c/n 15822/15831 All later modified to RB-50B configuration. 138/142, 144, 146 modified as RB-50F with navigational radar. 143, 145, 147 modified as RB-50G with additional radar and B-50D type nose. 47-148/157 Boeing B-50B-55-BO Superfortress c/n 15832/15841 All later modified to RB-50B configuration. 148/154, 156,157 modified as RB-50G with additional radar and B-50D type nose. 47-158/162 Boeing B-50B-60-BO Superfortress c/n 15842/15846 All later modified to RB-50B configuration. 158/160, 162 modified as RB-50F with navigational radar. 161 modified as RB-50G with additional radar and B-50D type nose.