Boeing XB-39 Superfortress
Boeing · United States · first flew 1944 · bomber
The Boeing XB-39 Superfortress was a single engine-testbed conversion of a production B-29 airframe, fitted with Allison V-3420 24-cylinder liquid-cooled engines in place of the standard Wright R-3350 radials, intended to provide an alternative powerplant in case R-3350 production proved insufficient.
Recognition (WEFT)
| W — Wings | High-mounted, straight |
|---|---|
| E — Engines | 4 × piston, wing-mounted |
| F — Fuselage | 30.18 m fuselage |
| T — Tail | Conventional |
WEFT is AircraftIQ's four-point recognition method — how it works.
Spot it by:
- Engine testbed variant of the B-29 Superfortress with Allison V-3420 engines
- Standard B-29 airframe identifiable by the different engine nacelles
- Single prototype used to evaluate alternative powerplant — never produced
Externally almost identical to the standard B-29 Superfortress; identifiable only by the different engine nacelles housing the liquid-cooled V-3420 engines, which have a different cross-section and cooling arrangements compared to the radial-engined standard.
Specifications
- The Boeing XB-39 Superfortress has a length of 30.18 m (99 ft).
- It has a wingspan of 43.05 m (141 ft).
- Its maximum speed is 648 km/h (403 mph).
- Typical crew: 11.
Figures are for the representative variant described above; marks differ. See how AircraftIQ sources figures.
History
The War Department ordered the XB-39 conversion in 1942 as an insurance policy against potential shortfalls in Wright R-3350 engine availability. A standard B-29-1-BW airframe was modified with four Allison V-3420-11 engines, each driving contra-rotating propellers. Test flights in 1944 showed the Allison installation offered no performance advantage over the standard R-3350 fit.
Variants
Only one XB-39 was converted; the concept was not pursued further as R-3350 production proved adequate and the performance advantage did not materialise.
Where you'll see it
The XB-39 never entered service, serving only as a test aircraft. The programme confirmed the standard B-29 powerplant as satisfactory and the single aircraft was eventually scrapped.
Related aircraft
- Boeing C-97 Stratofreighter
- Boeing B-17G Flying Fortress
- Boeing C-108 Flying Fortress
- B-29 Superfortress
- Avro Lincoln
- Beechcraft XA-38 Grizzly
- Bristol Brigand
- Canadian Car and Foundry Helldiver Mk.I
AircraftIQ — the aircraft field guide: 5,024 recognition guides, live overhead identification, works offline.