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/142883
airplane with a 300-fpm climb rate can also be difficult. Choose block heights that make sense for your airplane. Make the block tall enough that a 1-second timing error won't make a substantial difference in the average rate of climb through the block. Make the block short enough that there isn't an appreciable difference in climb rate from the bottom to the top of the block. It's okay to have taller blocks at lower altitudes where the climb rate is better and shorter blocks at the higher altitudes, because you'll be calculating average climb rates for each block. Take a break. Relax during your descent between tests. Your only data obligation here is to record OAT and any remarks. As you descend through the bottom of the test block, begin setting up at the next test airspeed. This should expedite establishing the stabilized condition and minimize weight change due to fuel burned. Don't trust the VSI. Feel free to record the vertical speed indicator (VSI) reading within the test block, but use it for correlation with your timed data only. Most VSIs are just too inaccurate for this test. On the way back down through the test block, note the OAT at the midpoint of the block if you didn't record it during the climb. You'll need OAT to calculate density altitude later. Leaning. Lean your engine as you do for normal climbs. For the airplanes most of us fly, a single mixture setting should be fine for all your runs through the same altitude block. If you must change the mixture between tests through the same block, be as consistent as possible. The same goes for cowl flaps and any other adjustment peculiar to your airplane that can affect climb performance. Subjective assessment. Even if you've flown the test profile within the limits, you may want to make a qualitative comment about the test. You'll know whether you really nailed the point, right on airspeed, pitch attitude set in granite, perfect timing, or whether you pushed the limits with airspeed going from 1 knot fast to 1 knot slow four times during the block, constantly searching for the exact pitch attitude, etc. Making such a note on your data card can help explain a wayward data point later. You should also be alert for changes in climb rate within each altitude test block. If climb rate decreases noticeably within the block, the block height is too large. Repeat the test using a smaller, more appropriate altitude block height. Final Preparation Considerations Once you've flown all those airspeeds through all those altitude blocks, you'll have tested just one weight, center of gravity, and external configuration. You can perform these tests again for a variety of airplane loadings and configurations, if that information will be useful. You can test at the maximum and minimum anticipated weights and interpolate for intermediate weights. Or you may include an intermediate weight in your testing. Center of gravity location can affect climb performance in theory because it affects the airplane's trim drag. In reality, this influence is generally minimal enough to ignore for most homebuilt airplanes. Open canopies, cowl flaps, and cooling vent scoops affect the airplane's drag. Perhaps testing the worst-case combination of weight, center of gravity, and external configuration might be good enough, figuring you'll realize better performance for all other cases. At least this way your planning will be conservative. The final point to be emphasized is safety. The tests described require a diligent instrument scan and potentially prolonged nose-high pitch attitudes. Both affect your see-and-avoid capability. Be careful. Don't perform these tests on a gorgeous Saturday morning near a busy airport. Use your descents between test runs to look around, and why not incorporate a clearing turn into each test setup? Keep an eye on your engine. Low speed climbs at full power tax the engine and inhibit cooling. Remember to fly the airplane first; collect data second. Next month we'll explain the data reduction. Yeah, it's number crunching, but it's not difficult and will yield your airplane's best climb performance. Ed Kolano, EAA 336809, is a former Marine who's been flying since 1975 and testing airplanes since 1985. He considers himself extremely fortunate to have performed flight tests in a variety of airplanes ranging from ultralights to 787s. EAA Experimenter 41