MANUFACTURER(S): Boeing Company / Fisher (General Motors)
OPERATORS: United States (cancelled)
LENGTH: 99.02 feet (30.18 meters)
WIDTH: 141.24 feet (43.05 meters)
HEIGHT: 27.72 feet (8.45 meters)
WEIGHT (EMPTY): 74,516 pounds (33,800 kilograms)
WEIGHT (MTOW): 133,512 pounds (60,560 kilograms)
ENGINE: 4 x Allison V-3420-11 W24 liquid-cooled engines developing 2,100 horsepower each.
SPEED (MAX): 404 miles-per-hour (650 kilometers-per-hour; 351 knots)
RANGE: 6,251 miles (10,060 kilometers; 5,432 nautical miles)
CEILING: 36,089 feet (11,000 meters; 6.84 miles)
RATE-OF-CLIMB: 1,000 feet-per-minute (305 meters-per-minute)
Detailing the development and operational history of the Boeing XB-39 (Spirit of Lincoln) Heavy Strategic Bomber Prototype Aircraft.
Entry last updated on 9/19/2016.
Authored by Staff Writer. Content ©www.MilitaryFactory.com.
Such was the importance of the Boeing B-29 Superfortress to the United States Army Air Forces during the latter stages of World War 2 (1939-1945) that the program was given several fail safes to keep it a viable heavy bomber product moving forwards. This led to a YB-29 developmental machine being set aside by the USAAF for alternative powerplant implementation - assuming that the required stock of problematic Wright R-3350 radial engines would not be available for one reason or another. A modification process was undertaken by Fisher Body (General Motors) in 1944 on the YB-29 aircraft and this went on to produce the XB-39 "Spirit of Lincoln" bomber prototype.
Its basic form and function remained faithful to the original Boeing design but the powerplants in play were now focused on 4 x Allison V-3420-17 series liquid-cooled engine (the original B-29 relied on the aforementioned Wright air-cooled units). Fisher was also using these engines in its (ultimately failed) P-75 "Eagle" long-range escort fighter. Delays in the intended turbosuperchargers dogged the XB-39 project so the first-flight on December 9th, 1944 was had without these installed - though the aircraft provided a successful demonstration nonetheless.
Despite the promising nature of the large aircraft, the Wright air-cooled radials, warts and all, remained the primary focus of the B-29 production campaign, leaving the XB-39 without a battlefield role or notable buyer. Additionally, Fisher was pushed to commit more and more of its resources to the XP-75 fighter prototype which held higher priority for the USAAF at this point in the war. Decisions led to the ultimately abandonment of the XB-39 project with the single prototype being completed and flown (if only for a short time).
As built, the XB-39 held 4 x Allison V-3420-11 liquid-cooled engines of 2,100 horsepower each able to propel the aircraft to speeds of 405 miles per hour out to ranges reaching 6,300 miles and a service ceiling of 35,000 feet. Its crew numbered ten and the armament suite was similar to that of the original B-29 (including remote-controlled turrets and tail cannon). 20,000lb of drop stores could be carried internally.
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Relative Maximum Speed Rating
This entry's maximum listed speed (404mph).
Graph average of 375 miles-per-hour.
Graph showcases the Boeing XB-39's operational range (on internal fuel) when compared to distances between major cities.
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Unit Production Comparison
Comm. Market HI*: 44,000 units
Military Market HI**: 36,183 units