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Boeing XB-39 (Spirit of Lincoln)


Heavy Strategic Bomber Prototype Aircraft


United States | 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; No A.I. was used in the generation of this content.
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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Power & Performance
Those special qualities that separate one aircraft design from another. Performance specifications presented assume optimal operating conditions for the Boeing XB-39 Heavy Strategic Bomber Prototype Aircraft.
4 x Allison V-3420-11 W24 liquid-cooled engines developing 2,100 horsepower each.
Propulsion
404 mph
650 kph | 351 kts
Max Speed
36,089 ft
11,000 m | 7 miles
Service Ceiling
6,251 miles
10,060 km | 5,432 nm
Operational Range
1,000 ft/min
305 m/min
Rate-of-Climb
City-to-City Ranges
Operational range when compared to distances between major cities (in KM).
NYC
 
  LON
LON
 
  PAR
PAR
 
  BER
BER
 
  MOS
MOS
 
  TOK
TOK
 
  SYD
SYD
 
  LAX
LAX
 
  NYC
Structure
The nose-to-tail, wingtip-to-wingtip physical qualities of the Boeing XB-39 Heavy Strategic Bomber Prototype Aircraft.
10
(MANNED)
Crew
99.0 ft
30.18 m
O/A Length
141.2 ft
(43.05 m)
O/A Width
27.7 ft
(8.45 m)
O/A Height
74,516 lb
(33,800 kg)
Empty Weight
133,512 lb
(60,560 kg)
MTOW
Design Balance
The three qualities reflected below are altitude, speed, and range. The more full the box, the more balanced the design.
RANGE
ALT
SPEED
Armament
Available supported armament and special-mission equipment featured in the design of the Boeing XB-39 (Spirit of Lincoln) Heavy Strategic Bomber Prototype Aircraft .
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.
Variants
Notable series variants as part of the Boeing XB-39 (Spirit of Lincoln) family line.
XB-39 - Base Project Designation; single, flyable prototype completed.
Operators
Global customers who have evaluated and/or operated the Boeing XB-39 (Spirit of Lincoln). Nations are displayed by flag, each linked to their respective national aircraft listing.

Total Production: 1 Units

Contractor(s): Boeing Company / Fisher (General Motors)
National flag of the United States

[ United States (cancelled) ]
Relative Max Speed
Hi: 500mph
Lo: 250mph
Aircraft Max Listed Speed (404mph).

Graph Average of 375 MPH.
Era Crossover
Pie graph section
Showcasing Aircraft Era Crossover (if any)
Max Alt Visualization
Small airplane graphic
Production Comparison
1
36183
44000
Entry compared against Ilyushin IL-2 (military) and Cessna 172 (civilian) total production.
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
Aviation Timeline
EarlyYrs
WWI
Interwar
WWII
ColdWar
Postwar
Modern
Future
1 / 2
Image of the Boeing XB-39 (Spirit of Lincoln)
Image from the Public Domain.
2 / 2
Image of the Boeing XB-39 (Spirit of Lincoln)
Image from the Public Domain.

Mission Roles
Some designs are single-minded in their approach while others offer a more versatile solution to airborne requirements.
GROUND ATTACK
X-PLANE
Recognition
Some designs stand the test of time while others are doomed to never advance beyond the drawing board; let history be their judge.
Going Further...
The Boeing XB-39 (Spirit of Lincoln) Heavy Strategic Bomber Prototype Aircraft appears in the following collections:
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