enginehistory.org

[hfriedman]

NACA Report 135 on this engine cites Report 1350 of the US Army Air Service Engineering Division. Does anyone know whther that is a different report and, if so, how to get acces to it? I am also interste in any other material on this enigne.

[jkinney]

Herb,
It is a different report. If it survives, two places it could be are the Sarah Clark Files at the National Archives (take a look at the AEHS online finding aid) or the Air Force's Historical Research Agency (AFHRA) at Maxwell AFB, Montgomery, AL. I've seen dozens of the same types of reports on airframe construction and propellers at AFHRA, but never looked at engine-related material there.
All the best,
Jeremy
_________________
Dr. Jeremy R. Kinney
Curator, Aeronautics Division
National Air and Space Museum
Smithsonian Institution

[hfriedman]

Thanks for the information. I will give it a try.

[hfriedman]

Here are the particulars of the BMW IIIa six cylinder in line water cooled engine: Figures are in American units unless otherwise indicted.:


PARTICULARS OF THE B.M.W. ENGINES.

TYPE OF MOTOR BMW IIIA
HORSEPOWER 185
NUMBER OF CYLINDERS 6
BORE (INCHES) 5.9
STROKE (INCHES). 7.1
CONTINUOUS NORMAL OUTPUT AT GROUND LEVEL AT 1,400 REVS. PER MIN (H.P.) 185
NORMAL NUMBER OF REVOLUTIONS OF PROPELLER PER MINUTE 1,400
OUTPUT REMAINS CONSTANT TO A HEIGHT OF (FEET) 11,700
OUTPUT CAN BE TEMPORARILY INCREASED AT GROUND LEVEL TO (H.P.) 240
FUEL CONSUMPTION PER I.E. (OZ) 7
<FUEL CONSUMPTION PER I.E. (POUNDS)> .438
LUBRICATING OIL PER H.P. (OZ) 0.35
SERVICE WEIGHT OF ENGINE, EXCLUDING WATER, OIL AND PROPELLER HUB (*INCLUDING REDUCING GEAR (LB) *630
WEIGHT OF COOLING WATER (LB) 27.5
WRIGHT OF OIL IN CRANK CASING (LB) 8.8
WEIGHT OF PROPELLER HUB 14.4



REPORT No. 135, PERFORMANCE OF B. M. W. 185-HORSEPOWER AIRPLANE ENGINE By S. W. SPARROW Bureau of Standards states:

"The engine has six vertical water-cooled cylinders with a bore of 5.90 inches, a stroke of 7.09 inches, and a compression ratio of 6.7. Report No. 1350 of the Engineering Division describes the engine. Descriptions have appeared also in some of the automotive journals.' The engine is not designed for full-throttle operation at ground-level densities. In fact, because of the high-compression ratio, such operation with ordinary aviation gasoline is likely to result in preignition.”

Apparently the compression ration of this engine was 6.37:1 compared with 4.64 for the Mercedes and it was known as an “overcompressed engine.”

Herschel Smith wrote in Aircraft Piston engines. “Such engines would destroy themselves if operated at full throttle a low altitudes . . .”

The engines were designed to optimize performance at the increasingly high altitudes were combat was occurring during the last year of the Great War. However, they were used to some extent in civilian aircraft in 1919-21 when most of the flying was done at low altitude. It would have made a considerable difference if it was possible to run the engine at full bore for a minuet or two at sea level for take-off. And my question is does it seem possible that this couldhave been done without a severe risk of destructive detonation.