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Posted 6/25/2009 Printable Fact Sheet
Boeing Y1B-9
Boeing Y1B-9. (U.S. Air Force photo)
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The Y1B-9 was the second prototype (S/N 32-302) B-9 modified for Curtiss V-1570-29 Conqueror liquid-cooled engines. These powerplants each produced 25 more horsepower than the R-1860s of the YB-9. The increased power combined with more streamlined engine nacelles gave the Y1B-9 a top speed of 173 mph -- 10 mph faster than the first prototype.

The liquid-cooled inline engine was tested on various U.S. Army bombers until the advent of jet bombers, but was never used on a production aircraft (with the exception of the Curtiss B-2). The radial engine was favored, in part, because it was air cooled and thus simpler and more reliable than liquid-cooled engines which were more vulnerable in battle if the cooling system was hit.

Type Number built/
Y1B-9 1 1 YB-9 with V-1570-29 engines

Armament: Two .30-cal. machine guns and 2,200 lbs. of bombs
Engines: Two Curtiss V-1570-29 Conqueror liquid-cooled engines of 600 hp each
Top speed: 173 mph at sea level
Cruising speed: 151 mph
Service ceiling: 19,200 ft.
Range: Approx. 500 miles with a full normal bomb load
Span: 76 ft. 9 in.
Length: 51 ft. 6 in.
Height: 12 ft. 8 in.
Weight: 15,590 lbs. gross
Crew: Four
Serial number: 32-302

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