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.

Issue link: http://experimenter.epubxp.com/i/118927

Contents of this Issue

Navigation

Page 46 of 49

hour of 13.6. Next we multiply by the fuel system factor of 125 percent or 150 percent and get 17 or 20 gallons/hour, depending on the type of fuel system we have. Continuing on, we divide gallons per hour by 60 to get gallons per minute and then multiply by 128 to get ounces per minute. We then get results of 43 or 36 ounces per minute, depending on the fuel system we have. All of this can be simplified with either of these formulas: Gravity system: Hp x BSFC x 1.5 x .36 = Ounces/minute, or Pressure system: Hp x BSFC x 1.25 x .36 = Ounces/minute The Tests With the level-flight test complete, we move on to a more difficult test, the climbing-flight test. For this test we will need to put the aircraft in a nose-up position to simulate a maximum climb. We first need to determine the required angle. Here are some possible ways to do that: Consult with the kit or plans designer or measure the angle in a similar aircraft using a Smart level. You will then need to add 5 degrees to that number for your test. If you can't determine the number, you can use 25 degrees for your test and later verify that angle in Phase I flight testing. You don't need to add 5 degrees to the 25-degree number. With the angle established, position the aircraft at that angle by some combination of raising the nose and/or lowering the tail. You definitely need some help to do this To perform these tests we need a few things: 1. a gas can in which the fuel quantity is visible 2. a level, preferably a Smart level (easier to measure angles) 3. blocks or other supports and wheel chocks 4. a two-quart measuring cup 5. a timer or watch with a second hand 6. some willing helpers to position the plane for the measurements. The first test is the maximum-power-in-level-flight test. For this we first level the aircraft both side-to-side and front-to-back. Then place one gallon of fuel in each tank. Be sure to shut the fuel valve off. Next, disconnect the fuel line where it goes into the carburetor or fuel injection servo. If you need to extend the fuel line a bit to make it so you can easily drain into the cup measure, be sure to keep the exit end at the same level as the point where you disconnected it. A kinked or partially collapsed fuel line, such as the one shown here, will drastically reduce fuel fow. Open the fuel valve to verify you have fuel flow. Turn on the auxiliary fuel pump if you have a pressure system. Be sure to catch the fuel flowing out of the line, and have a fire extinguisher handy in case of an accident. If no fuel flows when you open the valve and/or turn on the pump, then you will need to add another gallon to each tank and try again until fuel begins to flow. With fuel flow established, open the valve for one minute and see how much fuel you collect. Then let fuel flow out of the line until no more comes out. Measure this fuel and subtract it from what you put in the tanks to determine your unusable fuel. Compare the fuel drained in one minute to the number you calculated previously. As long as it is equal to this number or more, you are in good shape. Do not run the engine during this test! Record the results of this test in your builder's log. To do the fuel fow tests you will need a gas can, a 2-quart measuring cup, a Smart level, and some cinder blocks or other blocking material. EAA Experimenter 47

Articles in this issue

Archives of this issue

view archives of Experimenter - April 2013