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/149316
F li g h t Te s t in g Te c hn i q u e s Sawtooth Climbs VY Determination Creating your plots By Ed Kolano Last month we described the sawtooth climb test technique along with some hints and gotchas and provided a sample data grid. This month we'll show how to take the numbers you recorded during the flight test and turn them into plots that will show your airplane's best rate of climb speed, VY. the bottom-of-block altitude. We'll use this height and the elapsed time to calculate the average rate of climb through the test block. Using the terminology in Figure 1, The data presented in this article came from sawtooth climbs performed during three flights. Each climb was timed over a 500-foot altitude change, and the middle of those pressure altitudes were 3,500, 6,500, and 9,500 feet. Average airplane weight during each climb was 1,442 pounds, or 208 pounds below the maximum allowed. Our center of gravity was right in the middle of the allowable range. The next calculated column is the midpoint of the test block for each run. Determine the midpoint by adding the bottom, or start, altitude to the top, or finish, altitude, then divide by 2. Flight test data were recorded on kneeboard cards during the flights and transcribed to a worksheet for the data reduction. We created the worksheet—last month's data grid—to have a single matrix of flight test data that will be easier to work with than a bunch of test cards and separate worksheets. The worksheet in Figure 1 contains the raw test data (yellow columns) and the numbers we calculated (blue columns) as part of the data reduction for the 3,500-foot test. We'll use the 80-mph data in the first row of our worksheet in the examples during our data reduction explanation. Calculate the average rate of climb (ROC) for each run by dividing the block height by the elapsed time it took to climb through the block. Our block height is in feet, and our elapsed time is in seconds; so we multiply by 60 to make the climb rate come out in feet per minute. First, the Numbers The first calculated column is the test altitude block height, which is merely the top-of-block altitude minus 38 Vol.2 No.8 /August 201 3 As we said last month, having your airplane's climb performance charts based on density altitude will allow you to use them anytime you know the density altitude you'll be climbing through. If we make the plots based on pressure altitude, they would only be valid at those pressure