Experimenter

April 2013

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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Hangar Debrief Afer making up a fuel line, pull a clean patch of cloth through the line to make sure there is no debris lef inside. A gun-cleaning patch works well for this. flow when the aircraft is in its maximum nose-up attitude. This would be on the edge of a power-on stall in the takeoff configuration—what is often called a departure stall. 3. We need to be sure that even when fuel levels are low that we can maintain fuel flow in the maximum normal nose-down attitude. This would be in a fullflap, power-off descent at the top of the white arc, or in a plane with no flaps, a power-off descent at the top of the green arc. 4. We need to be sure fuel flow remains steady in a slip with low fuel. All of these are normal flight attitudes. We do not address aerobatic maneuvers in this testing. Fuel Flow Standards There are two basic standards that may apply to any particular aircraft. If your aircraft has a gravity fuel system, then that fuel system needs to provide 150 percent of maximum fuel flow in these tests. Gravity systems use either no fuel pump or a fuel pump that must rely on gravity as the backup if that pump fails. Typically these are high-wing aircraft, but some low-wing airplanes, such as the Sonex, also have gravity systems. These aircraft have carburetors rather than fuel injection systems. If your airplane is fuel injected, and/or if it is a typical low-wing design such as the popular RV models, you need 46 Vol.2 No.4 / April 2013 an engine-driven fuel pump and a backup or auxiliary fuel pump, even if you don't have fuel injection. These are called pressure systems, and they must flow at least 125 percent of maximum fuel flow in these tests. If we need to see 125 or 150 percent of maximum fuel flow, we must first determine what maximum fuel flow is for your aircraft. The manufacturer of your engine may give you maximum fuel flow at full power, or it may give you horsepower and specific fuel consumption (also called brakespecific fuel consumption or simply BSFC). Lycoming, for example, lists BSFC for each engine in a series of publications it calls "Detailed Engine Specifications," which is available from its publications department for each major engine type. If you can't easily find the BSFC for your engine, you can simply use the conservative figure of 0.55. For you engineering types, the units on this number are pounds per horsepower-hour. The fuel flow for any particular engine is simply horsepower x BSFC. This gives you pounds (not gallons) per hour. This needs to be converted to ounces per minute so we can easily measure it. Here is a sample calculation: The Lycoming O-320-D1A engine produces 160 hp. It has a BSFC of 0.51 pounds/hp-hour. We simply multiply 160 by 0.51 to get 81.6 pounds per hour, our maximum fuel flow at full power. We then divide pounds by 6 to get gallons per

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