Military Factory logo

Boeing XB-39 (Spirit of Lincoln)

United States (1944)

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 ©

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

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.
Any available statistics for the Boeing XB-39 (Spirit of Lincoln) Heavy Strategic Bomber Prototype Aircraft are showcased in the areas immediately below. Categories include basic specifications covering country-of-origin, operational status, manufacture(s) and total quantitative production. Other qualities showcased are related to structural values (namely dimensions), installed power and standard day performance figures, installed or proposed armament and mission equipment (if any), global users (from A-to-Z) and series model variants (if any).
Boeing XB-39 Specifications
National Flag Graphic
United States
Year: 1944
Type: Heavy Strategic Bomber Prototype Aircraft
Manufacturer(s): Boeing Company / Fisher (General Motors)
Production: 1
Supported Mission Types
Ground Attack
Close-Air Support
Airborne Early Warning
Electronic Warfare
Aerial Tanker
Passenger Industry
VIP Travel
Business Travel
Special Forces
Crew: 10
Length: 99.02 ft (30.18 m)
Width: 141.24 ft (43.05 m)
Height: 27.72 ft (8.45 m)
Empty Weight: 74,516 lb (33,800 kg)
MTOW: 133,512 lb (60,560 kg)

Installed Power
4 x Allison V-3420-11 W24 liquid-cooled engines developing 2,100 horsepower each.

Standard Day Performance
Maximum Speed: 404 mph (650 kph; 351 kts)
Maximum Range: 6,251 mi (10,060 km; 5,432 nm)
Service Ceiling: 36,089 ft (11,000 m; 6.84 mi)
Rate-of-Climb: 1,000 ft/min (305 m/min)

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.

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

Operators List
United States (cancelled)

Series Model Variants
• XB-39 - Base Project Designation; single, flyable prototype completed.

Supported Weapon Systems
Graphical image of an aircraft medium machine gun
Graphical image of an aircraft heavy machine gun
Graphical image of an aircrat automatic cannon
Graphical image of an aircraft conventional drop bomb munition

Images Gallery