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      Boeing XB-39 (Spirit of Lincoln) Heavy Strategic Bomber Prototype Aircraft  

    Boeing XB-39 (Spirit of Lincoln) Heavy Strategic Bomber Prototype Aircraft


    Intended to test the feasibility of an alternative powerplant, the Allison-powered Boeing XB-39 Superfortress ended its days as a single prototype.



     Updated: 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.

    Boeing XB-39 Technical Specifications


    Service Year: 1944
    Type: Heavy Strategic Bomber Prototype Aircraft
    National Origin: United States
    Manufacturer(s): Boeing Company / Fisher (General Motors)
    Production Total: 1



    Structural (Crew Space, Dimensions and Weights)


    Operating Crew: 10
    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 lb (33,800 kg)
    Weight (MTOW): 133,512 lb (60,560 kg)

    Installed Power and Standard Day Performance


    Engine(s): 4 x Allison V-3420-11 W24 liquid-cooled engines developing 2,100 horsepower each.

    Maximum Speed: 404 mph (650 kph; 351 knots)
    Maximum Range: 6,251 miles (10,060 km)
    Service Ceiling: 36,089 feet (11,000 meters; 6.84 miles)
    Rate-of-Climb: 1,000 feet-per-minute (305 m/min)

    Armament / Mission Payload


    STANDARD:
    10 x 0.50 cal Browning M2 heavy machine guns in four remote-controlled turrets.
    2 x 0.50 cal Browning M2 heavy machine guns and 1 x 20mm M2 cannon in tail unit.

    OPTIONAL:
    Up to 20,000lb of conventional drop stores held internally.

    Global Operators / Customers


    United States (cancelled)

    Model Variants (Including Prototypes)


    XB-39 - Base Project Designation; single, flyable prototype completed.

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