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Aviation / Aerospace

Boeing XB-39 (Spirit of Lincoln)


Heavy Strategic Bomber Prototype Aircraft [ 1944 ]



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



Authored By: Staff Writer | Last Edited: 07/29/2020 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site.

VIEW SPECIFICATIONS [+]
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.©MilitaryFactory.com
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Specifications



Boeing Company / Fisher (General Motors)
Manufacturer(s)
United States (cancelled)
Operators National flag of the United States
1944
Service Year
United States
National Origin
Cancelled
Project Status
10
Crew
1
Units


GROUND ATTACK
Ability to conduct aerial bombing of ground targets by way of (but not limited to) guns, bombs, missiles, rockets, and the like.
X-PLANE
Aircraft developed for the role of prototyping, technology demonstration, or research / data collection.


99.0 ft
(30.18 meters)
Length
141.2 ft
(43.05 meters)
Width/Span
27.7 ft
(8.45 meters)
Height
74,516 lb
(33,800 kilograms)
Empty Weight
133,512 lb
(60,560 kilograms)
Maximum Take-Off Weight
+58,996 lb
(+26,760 kg)
Weight Difference


4 x Allison V-3420-11 W24 liquid-cooled engines developing 2,100 horsepower each.
Propulsion
404 mph
(650 kph | 351 knots)
Max Speed
36,089 ft
(11,000 m | 7 miles)
Ceiling
6,251 miles
(10,060 km | 5,432 nm)
Range
1,000 ft/min
(305 m/min)
Rate-of-Climb


MACH Regime (Sonic)
Sub
Trans
Super
Hyper
HiHyper
ReEntry
RANGES (MPH) Subsonic: <614mph | Transonic: 614-921 | Supersonic: 921-3836 | Hypersonic: 3836-7673 | Hi-Hypersonic: 7673-19180 | Reentry: >19030


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.


0
Hardpoints


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


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Images



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Image of the Boeing XB-39 (Spirit of Lincoln)
Image from the Public Domain.
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Image of the Boeing XB-39 (Spirit of Lincoln)
Image from the Public Domain.

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