For recreational purposes, we can probably neglect any change in performance with Reynolds number, thus ignoring this setting altogether. Experiments have shown that a wing’s coefficients of lift, drag and moment vary somewhat with Reynolds number. The Reynolds number is simply the air density times the speed of the airplane times the chord of the wing divided by the viscosity of air (wow!). In the upper left of the screen is a number labeled Re, for Reynolds number, as highlighted in Figure 3. We’ll look at the behavior of each of these lines below. The yellow line is the coefficient of moment, called cm in the coefficient display box. The red line is the coefficient of drag, called cd in the coefficient display box. The green line in the graph is the coefficient of lift, called cl in the coefficient display box in the bottom left. It is the angle at which the wing hits- attacks-the air). (Remember that the angle of attack is the angle of the wing to the air. The center of the chart represents an angle of attack of zero degrees. Select the AOA-180 tab to see the coefficients from -180° to +180°. The same goes for the right edge with its +20° angle of attack. Therefore, moving the mouse to the left edge of the chart will cause the alpha reading in the black box to go to –20, corresponding to the –20° angle of attack. On the AOA-20 tab, the left edge of the graph corresponds to an angle of attack of –20°, and the right edge corresponds to an angle of attack of +20°. Just point the mouse at the part of the curve you are interested in, and look at the exact coefficients in the coefficient display box. This is the coefficient display box which displays, for whatever spot on the graph the mouse it pointing at, the coefficients of the airfoil at that angle of attack. Moving the mouse around in the graph will cause the numbers displayed in the black box in the bottom left of the screen (seen in Figure 2) to change in real time. The graph of the airfoil’s coefficientsįigure 1: The graph of the airfoil’s coefficients
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