The giant 18-cylinder air-cooled Wright R-3550 Duplex-Cyclon was the engine for the Boeing B-29 Superfortress and the Consolidated B-32 Dominator.
As the USAAF rushed these airplanes into combat, the R-3550 suffered from a lack of time to resolve problems inherent in developing any new engine. As a result, the R-3350 was initially unreliable and mechanically plagued.
This can be seen in a large number of versions.
Four 2000HP R-3350-5 engines powered the first XB-29 Prototype. But, they were quickly superseded by the 2,200 horsepower -13 variant. Similarly, the improved YB-29 prototypes used the upgraded R-3350-21 while early-production B-29s were fitted with -21A and -23.
With 1,366 total orders, the -23 was the first variant to be mass manufactured. Next, the -23A variant, often known as the “War engine” standard, was the most built with a total of 22,385 units made. These -23A engines were distinct from simple -23s in that their cylinder barrels were fitted with aluminum cooling fins rather than the latter’s machined steel counterparts.
Finally, R-3350-57 engines powered late-production B-29s and B-29As.
| Dash # | B-29 Model | HP | RPM | Comments |
|---|---|---|---|---|
| -5 | XB-29 | 2,000 | 2,400 | |
| -13 | XB-29 | 2,200 | 2,400 | Also used in the XB-32 |
| -21 | YB-29 | 2,200 | 2,800 | Similar to -13 except equipped with two each 2.8:1 generator and accessory drives |
| -21A | YB-29 | 2,200 | 2,800 | Similar to -21 except engineering and design changes |
| -21 | B-29 | 2,200 | 2,600 | Also used in the B-32 |
| -23 | B-29 | 2,200 | 2,800 | Similar to -21 except no torquemeter is provided. Engines also manufactured by Dodge. Also used in B-32, TB-32, XC-97, C-97, YC-97, C-121A, and YC-121B |
| -23 | B-29A &B | 2,200 | 2,600 | |
| -23 | XB-29E | 2,200 | 2,600 | |
| -23A | B-29 | 2,200 | 2,800 | Similar to -23 except engineering changes necessary to make engine suitable for combat use. Engines also manufactured by Dodge. Also used in TB-29, A, B, TRB-29A, B-32, C-97, YC-97, C-121A, and VC-121B |
| -23A | B-29A&B | 2,200 | 2,800 | |
| -23B | B-29 | 2,200 | 2,800 | Similar to -23A except incorporated a PR58Q1 or PR58K1 Bendix carburetor in lieu of a Chandler-Evans model 58CPB4. Engine performance or installation was not affected. Also used in B-32 |
| -37A | B-29 | 2,200 | 2,800 | Similar to -37 except equipped with a Bosch fuel injector |
| -39 | B-29 | 2,200 | 2,800 | Similar to -13 except cylinder head fuel injection and automatic control. Equipped with Holley fuel injector |
| -41 | B-29 | 2,200 | 2,800 | Similar to -13 except cylinder head fuel injection and automatic control. Equipped with Bosch fuel injector |
| -57 | B-29 | 2,200 | 2,800 | Similar to -13 except cylinder head fuel injection and automatic control. Equipped with a Bendix fuel injector and hightension ignition. Torquemeter eliminated. Engines also manufactured by Dodge. Also used in TB-29, A, B, TRB-29A, C-97, YC-97, C-121A, and VC-121B |
| -57 | B-29A&B | 2,200 | 2,600 | |
| -57 | XB-29E | 2,200 | 2,600 | |
| -57A | B-29 | 2,200 | 2,800 | Similar to -57 except incorporates a redesigned fuel-injection line system and redesigned airseal. Performance of engine or airplane not affected. Airplane installation was affected unless the airplane was reworked to accommodate this engine. Also used in TRB-29A, C-97, C-121A, and VC-121B |
| -57A | B-29A&B | 2,200 | 2,600 | |
| -59 | B-29 | 2,200 | 2,800 | Similar to -41 except equipped with Bosch fuel injector and high-tension ignition. Torquemeter eliminated. Also used in C-121A and VC-121B |
| -59 | B-29A&B | 2,200 | 2,600 | |
| -59 | XB-29A | 2,200 | 2,600 | |
| -59A* | B-29 | 2,200 | 2,800 | Similar to -59 except incorporates a redesigned fuel-injection line system and redesigned airseal. Engine or airplane performance is not affected but airplane installation was affected unless the airplane was reworked to accommodate this engine. Also used in B-32, C-121A and VC-121B |
| -59A | B-29A&B | 2,200 | 2,600 |
The engines were manufactured at Wright plants in Woodridge, N.J and Lockland, Ohio, and Chrisler’s Dodge Chicago Aircraft Engine plant. And it was Chrisler that supplied the majority of R-3550 built during World War II (18,413 engines vs 13,791 from Wright).
Further reading
- Boeing B-29 Superfortress Facts: 11 things to know
- Wright R-3350 Duplex Cyclone technical specification
Bibliography and source
- Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II by Graham White
- Boeing B-29 Superfortress: The Ultimate Look: From Drawing Board to VJ-Day by William Wolf
