The B-29 Superfortress went through fewer variants than just about any other major aircraft of the Second World War. The original B-29 model made up nearly two thirds of the total production. The very similar B-29A accounted for most of the remaining aircraft, and only 311 of the significantly different B-29B were built. This is partly a tribute to the basic design and party due to the late appearance of the B-29, at a time when most Japanese aircraft were approaching obsolescence.
The standard B-29 was built by three companies – Boeing at Wichita (1,620 aircraft), Martin at Omaha (538 aircraft) and Bell at Atlanta (357 aircraft). Two main changes were made from the YB-29 service test aircraft. A new version of supercharger was used, as some of the over heating problems on the earlier aircraft had been traced to the previous model.
The number and location of guns remained the same, but the Sperry turrets used on the earlier aircraft were replaced by General Electric remote turrets, with lead computing guns sites, while the teardrop sighting blisters were replaced with large circular bubbles on the middle of the aft fuselage. The B-29 also used four bladed Hamilton Standard propellers in place of the three bladed propellers used during development.
One of the few major changes made during the production of the B-29 was the replacement of the two gun forward-upper turret with a four gun model. This was introduced on the Wichita B-29-40 (40th production block), the Bell B-29-10 block, the Renton B-29-20 block and was used on the majority of Martin aircraft.
The B-29A was the version of the aircraft produced at Boeing’s Renton plant. It differed from the standard B-29 in two ways. The main visual difference was the use of a four-gun forward upper turret in place of the two gun version carried on the B-29. Structurally the B-29A wing was built in a different, more efficient way. On the standard B-29 the wing was built in two sections, which were joined in the middle of the aircraft. The engines were then attached to the wings. On the B-29A the wing was made of three sections. A short central section was attached to the fuselage. The outboard wing panels, complete with the engines, were attached to this central wing section. The resulting wings were easier to build, stronger, and one foot wider.
The B-29B was a stripped down version of the basic aircraft built by Bell at Atlanta. It reflected a change in the tactics being used by the USAAC in the Pacific, where high altitude bombing raids had been replaced by low level high speed night attacks on Japanese cities. Weight was saved by removing the four remote controlled turrets and the central fire control system. Only the rear guns were retained, in the belief that the high speed aircraft would only be vulnerable to attacks from the rear. To aid the rear gunner the aircraft was given an AN/APG-15B radar set, which had a distinctive ball-shaped antenna located below the guns. The B-29B was the faster version of the aircraft, with a top speed of 367mph. A total of 311 were produced.
Wingspan: 141ft 2 in
Empty Weight: 70,140lb
Loaded Weight: 135,000lb
Engines: Four Wright R-3350-23 Cyclone engines
Horsepower: 2,200hp each
Armament: Ten 0.5in machine guns in five turrets plus one 20mm cannon in tail
Bomb load: Up to 20,000lb
Max speed: 358mph at 25,000ft
Cruising Speed: 230mph
Range: 3,250 miles*
Operational Radius: 1,600 miles with 15,000lb bomb load
* Longest round trip on a bombing mission was 3,900 miles