DEC 2014

Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.

Issue link: https://experimenter.epubxp.com/i/434207

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Page 38 of 44

EAA Experimenter 39 The actual engine production facility is located within a stone's-throw distance of the car company. When we got there, I found a completely different world; a modern fac- tory with computer-aided lathes and an engine assembly line with an engine test bench. SIDE-VALVE, 'FL ATHEAD' ENGINE Both engines—the four-cylinder LF26 and the six-cylinder LF39—look similar, although the new LF39 six-cylinder looks much more "intimidating " with its longer engine block. All D -motor engines are liquid-cooled, fuel-injected, four-stroke, flat-opposite engines with direct drive to the propeller. On each cylinder head, pairs of spark plugs protrude, sitting halfway between the pistons and the laterally lo- cated valves. Typically, spark plugs are not located here, but these cylinder heads and the "flathead" location of the intake and exhaust valves beside the cylinders is the unique feature of D -motor engines. Currently, D -motor is the only aviation engine manufacturer using the side-valve, "flat- head" design. The pistons and cylinders are conventionally built with a bore/stroke of 103.6/80 mm. The side valves dictate the unusual design of the combustion chambers and the position of the intake and exhaust valves. The valves of the LF26/39 engines are not located above the pistons in the cylinder head; rather they are beside and below the cylinder. The stems of the valves are parallel to the cylinder walls, and the valve tops are facing toward the engine center and toward the single camshaft. The camshaft that actuates the intake and exhaust valves is located below the crankshaft so short pushrods are used. In normal engines where the valves are located above the pistons, we can find pushrods that are more than 10 inches long. If you take off the cylinder head of a conventional engine, you will see a round, hemispheric combustion chamber directly above the piston. Because the valves of the side-valve D -motor engine are located beside the cylinder, the combustion chamber is unusually laterally developed. A part of the combustion chamber, about two- thirds of it, is above the piston and the rest of it is alongside the cylinder—above the valves. Thus instead of the usual circular-shaped combustion chamber, we find a kidney- shaped combustion chamber protruding alongside of the cylinder perimeter. The result of this flathead design is a very slender and narrow engine. This combustion chamber/valve design was in regular street use almost 50 years ago. In the United States, the most common and most famous side-valve engine was the Ford side-valve V-8 or flathead used in automobiles from 1932 to 1953. A similar design was used in Moto Guzzi mo- torcycles in Europe in the pre- and postwar period. The disadvantage of the side-valve engine is that the air- flow characteristics of the design are far from optimal. On The D-motor assembly line in Belgium. The cylinders of the four-cylinder engine LF26 (top) and the six-cylinder engine LF39 (bottom). Alain Dejager showcased the six-cylinder engine, the LF39, at the French Blois Fly-In this fall. The scale was indicating 175 pounds.

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