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Home > Fact Sheets > Boeing XB-39 "Spirit of Lincoln"


Posted 10/23/2009 Printable Fact Sheet
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Boeing XB-39
Boeing XB-39 pilot station. (U.S. Air Force photo)
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The XB-39 "Spirit of Lincoln" was a modification of the first YB-29 (S/N 41-36954). The XB-39 project was similar to the XB-38 project -- the standard air-cooled radial engines of the production aircraft were replaced by liquid cooled 'Vee' engines. On the XB-39, the original Wright R-3350-21 Cyclone radials were replaced by Allison V-3420-11 engines. The V-3420 was essentially two V-1710 engine spliced together (one crankcase and two crankshafts geared together).

The XB-39 project was basically a proof-of-concept project to demonstrate performance with liquid-cooled "Vee" engines. It was also insurance against shortages of the production engine. Only one XB-39 was built; it was delivered the U.S. Army Air Force in early 1944 for testing. Most of the problems with the standard B-29 production version were fixed by mid-1944, and no orders for the XB-39 were placed.

Click here to view the General Description of the XB-39.

Type Number built/
XB-39 1 (cv) YB-29 with V-3420-17 engines

Armament: 10 .50-cal. machine guns plus 20,000 lbs. of bombs (maximum overload).
Engines: Four Allison V-3420-11 engines of 2,100 hp each (3,000 hp each, takeoff power)
Maximum speed: 405 mph at 25,000 ft.
Cruising speed: 282 mph
Range: 2,850 with 4,000 lbs. of bombs; 6,290 miles maximum ferry range
Service ceiling: 35,000 ft.
Span: 141 ft. 3 in.
Length: 99 ft. 0 in.
Height: 29 ft. 7 in.
Weight: 135,000 lbs. (maximum gross weight)
Crew: Six normal (10 with gunners; 12 with relief crew)
Serial number: 41-36954 (YB-29-BO)

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