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/126719
9. Repeat Steps 4 through 7. 10. Continue this alternating slower/faster process until all planned airspeed test points are accomplished. 11. Reset your altimeter to the local setting. The Fine Print How am I supposed to maintain an off-trim airspeed within one knot for 30 seconds! Calm air is essential. The slightest turbulence can upset your airplane enough to cause bad data. Even if the airspeed indication doesn't change, the fact that your plane was just shoved up or down can ruin the test point. If you catch a rogue gust, just restart the test after you re-establish the steady flight condition. Wiggling control surfaces also contaminate data. It's possible to maintain a constant airspeed while rapidly moving the stick fore and aft, but the resultant tail wagging creates drag that can affect your results. Don't chase the airspeed needle with your airplane's nose, because the airplane will never really stabilize at the desired speed. Similarly, using an artificial horizon to maintain your pitch attitude will likely lead to frustration. An analog attitude indicator is too coarse, and you might end up chasing that last pixel on an electronic display on your quest for steady, constant-airspeed flight. Use the real horizon to hold the required pitch attitude. The relative position of the airplane's nose and the horizon will show tiny pitch changes before any instrument will indicate a change. There are a couple of gotchas, however. If you move your head, you'll change the visual relationship be- tween your plane's nose and the horizon. One way to avoid this is to put your head against the headrest and move just your eyes to look in different directions. If you don't have a headrest, you can put a grease pencil mark on the windscreen so it lines up with the top of the cowling. As long as the mark and the cowling top line up, your eyes will remain in the same spot. This test presents some challenging flying. Any pilot can do it, but not indefinitely. As soon as you're sure the airplane has stabilized on the test point flight condition, begin timing. While you're waiting for that 30 seconds to pass, note the airspeed, OAT, and anything else—such as VSI—you want to record. Note the OAT in the middle of the altitude change. So how do you write down all this stuff while concentrating on flying with your head glued to the headrest? Don't. Make a mental note of airspeed, OAT, start altitude, and end altitude during each test, and then write them down when you finish testing that speed. Or you can use a small video or audio recorder or a co-pilot to record the numbers as you call them out. (No co-pilot unless you've completed the FAA-mandated fly-off time! And make sure any audio/video setup does not interfere with the flight controls or airplane systems.) Flying with a co-pilot can be a good idea because he might detect an airspeed variation or excessive stick activity you might not notice when concentrating on flying the test point. Your scribe can also keep a rough plot of airspeed versus descent rate as a quality check on the data. Any data point that appears to fall far from the emerging curve is suspect. With this nearreal-time analysis, you could re-fly the suspect points EAA Experimenter 43