Experimenter

July 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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the lower altitude tests for later when you'll feel more comfortable with the test technique. Fly your airplane a couple of hundred feet below the bottom of the test altitude block. Use good judgment here; your lowest block should be at least 1,000 feet AGL over reasonably flat and obstruction-free terrain. Establish the climb airspeed in level flight. Choose an airspeed close to the predicted VY airspeed for your first test. You'll eventually fly a range of airspeeds, but prudent flight testing generally starts in the middle of the flight envelope—the climb speed envelope in this case. After you've stabilized your airplane in this level-flight condition, advance the throttle while raising the nose to maintain the test airspeed until you are stabilized in a climb at full power (or climb power or maximum continuous power, if appropriate) at the test airspeed. Trim. The reason for this careful setup is for you to be established in a stabilized climb before recording any data. Your engine should be stabilized at the selected setting. Your pitch attitude should be stabilized to hold the test airspeed. Trimming is usually not an essential requirement for our data accuracy purposes, but starting with the airplane trimmed for a hands-off climb generally makes the profile easier to fly. If you are not stabilized as you climb through the bottom of the first altitude block, reduce power, descend, and set up again. You may want to begin your setup lower to give yourself more time to stabilize the airplane on the test condition before reaching the bottom of the test block. With the plane stabilized, note the time or start a stopwatch as you pass the bottom of the test block. Hold Te technique is called sawtooth because of the vertical sawtooth pattern you'll fy throughout the test. the airspeed constant through the test block, and note the time or stop the stopwatch as you pass the top of the block. Record the time, start and finish altitudes, and any other data you think useful. A sample data grid is shown in Figure 1. Note: The blue fields will be filled in during data reduction. Your test cards should also include other information you'll need for thorough documentation, such as airplane weight or fuel remaining, center of gravity, configuration, etc. Customize your data cards so they'll be most useful to you in flight. When you've completed your first test climb, select idle power, perform a 180-degree turn, and descend to your setup altitude to get ready for the next climb at a different airspeed. The reason for descending with idle power is to minimize the weight change between test runs due to fuel burned. If you really want to be efficient, you can perform a sawtooth descent through the same altitude block for your descent performance charts. If you are uncomfortable with this full-power/ idle suggestion because of engine wear and tear considerations, use whatever descent power you are comfortable with, and accept the weight change inaccuracies for now. When you're finished with the entire process, you can check your climb performance charts and make adjustments then if necessary. You may find the weight change does not create a significant change anyway. Figure 1 EAA Experimenter 39

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