The Wright-powered B-29 had always been somewhat underpowered for its weight, and it became clear that the airframe could take substantially more engine power if it were available. In pursuit of this objective, one B-29A (42-93845) was handed over to Pratt & Whitney for conversion as a testbed for the new four-row 28-cylinder Pratt & Whitney R-4360 Wasp Major air-cooled radial engine, which was rated at 3500 hp. The aircraft was later redesignated XB-44, and was readily recognizable by the new engine installation, with the oil cooler intake pulled further back on the lower part of the nacelle.
An order for 200 production examples under the designation B-29D was placed in July of 1945, but was reduced to only 50 after V-J Day. In December of 1945, the designation of the B-29D was changed to B-50A. This was a ruse to win appropriations for the procurement of an airplane that appeared by its designation to be merely a later version of an existing model that was already being cancelled wholesale, with many existing models being put into storage. Officially, the justification for the new B-50 designation was made on the basis that the changes introduced by the B-29D were so major that it was essentially a completely new aircraft. The ruse worked, and the B-50 survived the cutbacks to become an important component of the postwar Air Force.
The decision to produce the B-50 was confirmed on May 24, 1947. From the start, the B-50 was earmarked for the atomic bombing role. This decision was prompted by the uncertain future of the Convair B-36, the first long-range heavy bomber produced as an atomic carrier. A few B-29s that had been modified to carry the atomic bomb were still available, but they were nearly obsolete and would have to be replaced by a more efficient, atomic-capable bomber pending the availability of the B-36 or another bomber truly suitable for the delivery of atomic bombs.
The B-50 was externally quite similar to the B-29, but a momentary glance was sufficient to tell the difference between the two aircraft. The traditional 24 ST aluminum structure of the B-29 was replaced by the newer 75 ST, which resulted in a wing that was 16 percent stronger than the wing of the B-29 and 600 pounds lighter. The 3500-hp R-4360 Wasp Major engines gave a power increase of 59 percent. The new engine installation was the primary external feature distinguishing the B-50 from the B-29, with the oil cooler being pulled further back on the lower part of the nacelle. Increased weight resulted in a requirement for larger flaps and a higher vertical tail. The new higher tail was first tested on B-29-35-BW serial number 42-24528, which had been assigned to Seattle Experimental Flight Test. The tall vertical tail could be folded down to permit storage in standard USAF hangars. Other features included hydraulic rudder boost and nose wheel steering, faster acting undercarriage retracting mechanism, and electrical de-icing of the pilots' window through the use of conductive NESA glass. The wings and empennage were de-iced thermally by having the exhaust from three combustion heaters flow through hollow double-wall structures in the leading edges of the aerodynamic surfaces. The propellers had a reversible pitch, which allowed the use of engine power as an aid to braking on short or wet runways. There was also some rearrangement of the crew. Despite the overall similarity of the two aircraft, only about 25 percent of the B-50 parts were interchangeable with B-29 parts.
The crew complement of the B-50A was typically eleven--pilot, copilot, engineer, navigator/radar operator/bombardier, bomdardier/navigator/radar operator, radio/electronic countermeasures operator, left side gunner, right side gunner, top gunner, tail gunner, plus one extra crew member.
The B-50 was assigned the Boeing factory designation of Model 345-2. The first B-50 to be built was a production article rather than a prototype. The first production version was designated B-50A, reflecting the new Air Force policy of assigning the A series suffix to the first production model of a new series. The B-50 was originally to have been built at Renton, but a change in plans resulted in a shift of manufacture to Seattle Plant 2.
The first B-50A (46-002) flew on June 25, 1947. 59 B-50As were built as standard bombers, with block numbers from -1 to -35. Although there was officially no prototype B-50, seven of the B-50As built were allocated to testing. The 60th and last example was held at the factory for modification as the YB-50C, which was intended as a prototype for the B-54A series, a further-improved version of the B-50.
The first B-50As were delivered in June of 1948 to the Strategic Air Command's 43rd Bombardment Wing, based at Davis-Monthan AFB in Arizona. This wing was assigned the mission of being the primary carrier of the atomic bomb. The Strategic Air Command had come into existence in 1946 with about 250 B-17s and B-29s as initial equipment. It had always been intended that the B-50 would be only an interim strategic bomber, pending the availability of the B-47 Stratojet. However, delays in the Stratojet program forced the B-50 to soldier on until well into the 1950s.
Production of the B-50A ended in January of 1949, with delivery of the last 3 aircraft. The B-50A remained in front-line service with SAC alongside the B-36 for several years. There were some problems with cold-weather performance of the B-50A. After one B-50A had crashed in Alaska, it was found that the congealing of oil in the small-sized tubing of the aircraft's manifold pressure regulator was to blame, and the regulators were modified. There were numerous engine malfunctions, and the constant speed drive alternators were faulty. A deficient turbosupercharger resulted in a short period during which the aircraft was restricted from flying above 20,000 feet. Cracking of the metal skin on the trailing edge of the wings and flaps required additional modifications. Later, failure of the rudder hinge bearing caused the temporary grounding of all B-50As. Progress in fixing these problems was made, and the B-50A's performance steadily improved throughout 1949.
After a short time in service, 57 B-50As were sent to the newly-opened Wichita plant to be modified as receiver aircraft using the British-developed hose tanker inflight refuelling system. Using this system B-50A 46-010 "Lucky Lady II" of the 43rd Bombardment Group made the first nonstop flight around the world between February 26 and March 2, 1949, being refuelled enroute by four pairs of KB-29M tankers of the 43rd Air Refuelling Squadron. It took 94 hours to complete the 23,452-mile journey.
Some B-50As were employed in special temporary test programs under the designation JB-50A. The armament was generally removed to make space for internal modifications and test equipment.
Eleven B-50As on the first contract were later modified as TB-50A bombing-navigation trainers. They were primarily intended for use as training of the crews of the B-36.
The B-50As began phasing out of SAC in mid-1954, when the 93rd Bombardment Wing finally began receiving its long-awaited B-47s. As obsolescence approached, all surviving B-50As (including the TB-50A conversions) were converted to KB-50J three-hose tankers.
Engines: Four Pratt & Whitney R-4360-35 Wasp Major 28-cylinder, four-row air
cooled radials with General Electric CH-7-B1 turbosuperchargers.
Performance: Maximum speed 385 mph at 25,000 feet, 391 mph at 30,000
feet. Cruising speed 235 mph. Stalling speed 136 mph. Service
ceiling 37,000 feet. Initial climb rate 2225 feet per minute. Combat
radius 2193 miles with 10,000 pounds of bombs. Maximum range 5230
miles. Takeoff ground run 5940 feet at sea level. Takeoff over
50-feet obstacle 7425 feet at sea level.
Dimensions: Wingspan 141 feet 3 inches, length 99 feet 0 inches,
height 32 feet 8 inches, wing area 1720 square feet.
Weights: 81,050 pounds empty, 120,500 pounds combat, 168,708 pounds
Armament: Four 0.50-inch machine guns in forward dorsal turret, two
0.50-inch machine guns in rear dorsal turret, two 0.50-inch machine
guns in forward ventral turret, two 0.50-inch machine guns in rear
ventral turret, two 0.50-inch machine guns and one 20-mm cannon in
tail turret. Maximum internal bombload 20,000 pounds.
46-002/005 Boeing B-50A-1-BO Superfortress c/n 15722/15725 46-006/015 Boeing B-50A-5-BO Superfortress c/n 15726/15735 010 was *Lucky Lady II*, which made first nonstop flight around the world Feb 26-March 2, 1949. 46-016/025 Boeing B-50A-10-BO Superfortress c/n 15736/15745 46-026/035 Boeing B-50A-15-BO Superfortress c/n 15746/15755 46-036/045 Boeing B-50A-20-BO Superfortress c/n 15756/15765 46-046/060 Boeing B-50A-25-BO Superfortress c/n 15766/15780 46-061 Boeing YB-50C Superfortress - Project cancelled 47-098/112 Boeing B-50A-30-BO Superfortress c/n 15782/15796 47-113/117 Boeing B-50A-35-BO Superfortress c/n 15797/15801