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GERMAN AIRPLANE MOTORS
In a paper on “Aviation Motors,” presented by E. H. Sherbondy before the Cleveland section of the S. A. E. in June, 1917, the Mercedes and Benz airplane motor is discussed in some detail and portions of the description follow.
Fig. 244.—Side and End Sectional Views of Four-Cylinder Argus Engine, a German 100 Horse-Power Design Having Bore and Stroke of 140 mm., or 5.60 inches, and Developing Its Power at 1,368 R.P.M. Weight, 350 Pounds.
MERCEDES MOTOR
The 150 horse-power six-cylinder Mercedes motor is 140 millimeters bore and 160 millimeters stroke. The Mercedes company started with smaller-sized cylinders, namely 100 millimeters bore and 140 millimeters stroke, six-cylinders. The principal features of the design are forged steel cylinders with forged steel elbows for gas passages, pressed steel water jackets, which when welded together forms the cylinder assembly, the use of inclined overhead valves operated by means of an overhead cam-shaft through rocker arms which multiply with the motion of the cam. By the use of steel cylinders, not only is the weight greatly reduced, but certain freedom from distortion through unequal sections, leaks and cracks are entirely avoided. The construction is necessarily very expensive. It is certainly a sound job. In the details of this construction there are a number of important things, such as finished gas passages, water-cooled valve guides and a very small mass of metal, which is water-cooled, surrounding the spark-plug. Of course, it is necessary to use very high compression in aviation motors in order to secure high power and economy and owing to the fact that aviation motors are worked at nearly their maximum, the heat flow through the cylinder, piston, and valves is many times higher than that encountered in automobile motors. It has been found necessary to develop special types of pistons to carry the heat from the center of the head in order to prevent pre-ignition. In the Mercedes motor the pistons have a drop forged steel head which includes the piston boss and this head is screwed into a cast iron skirt which has been machined inside to secure uniform wall thickness.
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