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.

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Page 39 of 44

40 Vol.3 No.12 / December 2014 UNDER THE COWL the intake stroke, the intake valve will open, and the suc- tion caused by the downward movement of the piston will draw the air/fuel mixture into the cylinder and cylinder head. The intake air/fuel mixture flow path is not smooth. The flat surfaces and internal corners are not conducive to good airflow. Usually there are too many obstructions that cause turbulence and airflow eddies that impede ef- ficient air movement. The same thing happens during the exhaust stroke. When I asked the D -motor designers about this subop- timal side-valve engine characteristic, I got the following answer: "That is true and we can't deny these facts. We have tested countless cylinder heads solutions with dif- ferent combustion-chamber shapes until we reached the present optimal shape. Because our engine is directly driv- ing a propeller (low rpm engine), those nonoptimal engine characteristics don't affect our engines." That is pretty correct because this airflow inefficiency is not a problem for low revolving engines, and the LF26/39 engines turn at 3,000 rpm. At D -motor they are particularly proud of the safety aspect of their engines. They said, "When a valve of a conventional overhead engine does not close, the en- gine stops and is likely to be ruined. When a valve of a side- valve engine does not close, the engine develops less power but it will not stop running and there won't be expensive repair cost." The engine block is divided in two halves vertically. The crankshaft protrudes out of the front part of the engine block with a prop-flange attachment (different length prop flanges can be ordered); on the rear, the crankshaft ends with a toothed gear that drives the single camshaft. The camshaft ends on the engine front with an oil pump. Neither of the four-stroke engines has cooling liquid or oil thermostats, but they can be fitted if required. ENGINE PRODUCTION The D -motor factory has its own molds for the engines, and most of its aluminum engine parts are machined in- house, making them less dependent on outside suppliers. Another interesting engine detail is that the cylinders and cylinder heads are not screwed to the engine block by long steel studs, such as with the Rotax 912 engines. Instead the cylinders are bolted to the engine block with short screws, as with Lycoming engines. The cylinder heads are screwed by even shorter screws to the cylinder bodies. Nonmoving engine parts are aluminum, while the crankshaft, camshaft, and connecting rods are steel, of course. The cylinder walls are Nikasil coated. Because of these material choices and because the engines have a relatively low number of parts, they don't weigh much. The 92-hp, four-cylinder engine weighs only 126 pounds (58 kilograms). The 135-hp six- cylinder engine weighs 170 pounds (78 kilograms). Those numbers are for dry weight and include the exhaust, intake, fluid coolant, and the oil tank. Wet weight with Photography by Marino Boric This image of the upside-down engine shows the fl at cylinder head cover... ...and below it the extraordinary fl at cylinder head. For a better explanation, two cylinder-heads are pictured--one from inside (above) and the other from outside (below). Close-up of the "real" cylinder head; because of the engine's fl athead design, the valves are not located in the cylinder head. Instead, they are located below it parallel to the cylinder barrel.

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