April 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/287214

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Page 36 of 38

EAA Webinars What would you like to learn? Interactive. Educational. Mobile. EAA offers a series of free live webinars moderated and presented by aviation experts on a variety of topics. Register today! EAA.org/webinars EAA Webinars are supported by Sheet Metal for Kit Aircraf $ 29 .95 $29.95 is the EAA Member price. Non-member price is $36.95. EAA SportAir Workshop instructor Mark Forss walks you through the terms, tools, and skills required to build the aircraf of your dreams. Visit ShopEAA.com or call 1-800-564-6322 to order or for more information. ShopEAA.com | Copyright © 2014 EAA EAA Experimenter 37 faster than the fast-end speed of the trim-speed band. Apply forward-stick to accelerate, but don't retrim or adjust the engine or propeller controls. For our example airplane, you'd probably stabilize at 130 knots. Note how much push force it takes to maintain a steady 130 knots. Add a little more forward-stick, and stabilize at 140 knots. Repeat this until you map the airspeeds faster than the trim speed. Remember, you're not expanding your airplane's fl ight envelope during this test, so do not exceed VNE or any airspeed for which you have not already cleared the fl ight en- velope. In the landing condition test, your fastest test airspeed should not exceed any speed limitation of extended landing gear or fl aps. Naturally, your altitude will change during this test, and that's okay within reason. If you fi nd you're approaching 1,000 feet above or below the altitude where you initially trimmed for hands-of fl ight, simply climb or descend toward the original altitude and resume your testing. It's important not to retrim or adjust the engine and propeller controls during this reposition- ing maneuver. Our example used 10-knot increments for target airspeeds, but stabilizing a couple of knots faster or slower than the target speed is okay. The idea is to get a feel for how the required stick-force changes when you fl y of -trim airspeeds. Predict- ability is always a good thing, so the stick force should increase smoothly as the airspeed deviations increase. There should be enough stick-force change to be obvious to you that an airspeed deviation occurred, but not so much force that intentional of - speed fl ight is dif cult. Figure 1 shows a simplifi ed static stability curve. Remember, the stick force corresponding to a particular airspeed is the force required to maintain that speed; it is not the force needed to change from another speed to that speed. Admittedly, Figure 1 is admittedly overly simplistic, because it does not show the control system breakout forces, trim-speed band, or the ef ects of control system friction. Next time we'll explain how to check for control system friction and show how friction af ects the static stability plot. We'll also bring the trim- speed band back into the discussion and discuss how all these ingredients in this long-stab stew feed into your overall impres- sion of your airplane's handling qualities. Ed Kolano, EAA 336809, is a former Marine who's been fl ying since 1975 and testing airplanes since 1985. He considers himself extreme- ly fortunate to have performed fl ight tests in a variety of airplanes ranging from ultralights to 787s. E A A E X P _ A p r 1 4 . i n d d 3 7 EAAEXP_Apr14.indd 37 3 / 3 1 / 1 4 9 : 4 6 A M 3/31/14 9:46 AM

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