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116 APPENDIX A. AIRFOIL MAKER SUPPLEMENT Figure A.5: A NACA 2412 airfoil [Full size →] An oldie but goodie! This book has the lift, drag, and moment plots of many airfoils in it, so the reader can choose their favorite airfoil for a design and then enter it into the computer using the technique described below. A.2.4.3 Types of Airfoils In the following discussion, thin and symmetrical, thick and highly cambered, and “normal general aviation” airfoils will be discussed. These types of airfoils serve as a good introduction because they are so different from one another. Thin, symmetrical airfoils are thin and have the same shape on both the top and bottom surfaces. They do not produce very much lift or drag. They typically are used for vertical stabilizers and often horizontal stabilizers as well because they are not called upon to produce a lot of lift, and are not expected to produce much drag, either. Use thick, high-cambered airfoils in the foreplanes of canards, or other applications where you want a large amount of lift from a small wing area. These foils are known for providing a large amount of drag as the penalty for providing a large amount of lift. So-called “normal general aviation airfoils,” like the NACA 2412 (seen in Figure A.5), are compromises between the two, and are good candidates for the wing of a general aviation aircraft. Supercritical, laminar-flow, and other possible groupings of airfoils exist, but for the purposes of our discussion we will concentrate on the thin and symmetrical, thick and highly cambered, and “normal general aviation” airfoils just outlined. A.2.5 Generating Airfoils A.2.5.1 Coefficient of Lift Intercept Now let’s actually generate an airfoil. The control to modify first is the coefficient of lift intercept control, found in the upper left, as highlighted in Figure A.6. To increase this number, just click right above the digits that you want to increase, and below the ones that you want to decrease. For example, if the lift intercept on the screen is 0.25 (as in Figure A.6), and you want to change it to 0.33 to model your airfoil, just click above the “2” in “0.2500” and twice below the “5” in “0.2500.” This is how all of the data for the entire design and simulation system is changed. The coefficient of lift intercept is the coefficient of lift at an angle of attack of 0 degrees. For a symmetrical airfoil, this will always be zero, since, in such an airfoil, the air is doing exactly the same thing on the top and bottom of the wing at zero degrees angle of attack. Symmetrical airfoils are sometimes used for horizontal stabilizers, and are almost always used for vertical stabilizers. Sleek, skinny wings with low camber might have a lift intercept of 0.1. Fat, highly cambered foils
A.2. DESIGNING AN AIRFOIL 117 Figure A.6: The parameters used in generating an airfoil [Full size →] have a value around 0.6. A typical airfoil like the NACA 2412 (commonly used in general aviation) has a value of about 0.2. A.2.5.2 Coefficient of Lift Slope This is the increase in coefficient of lift per degree increase in angle of attack. A thin airfoil has a value of about 0.1. A really fat airfoil has a value of about 0.08. Fatter airfoils have slightly lower lift slopes. (You will find, however, that lift slopes are almost always very close to 0.1). The coefficient of lift slope is modified using the slope control, seen in Figure A.6. A.2.5.3 Coefficient of Lift Curvature Near the Stall As the angle of attack gets close to stall, the lift slope is no longer linear. Instead, it gradually levels off as it approaches the maximum, or stalling, coefficient of lift. This value is modified by the first power control, seen in Figure A.6. Just play with this control until you find a power curve that connects the linear and stalling regions smoothly. Chances are a power of around 1.5 will work pretty well. Just play with it until the lift comes up smoothly, then gradually levels off to the stall, since that is what happens with a real airfoil. A.2.5.4 Coefficient of Lift Maximum This is the maximum coefficient of lift, or the coefficient of lift right before the stall. A very thin, symmetrical airfoil has a value of around 1.0. A thick, highly cambered airfoil has a value of around 1.8. A typical general aviation foil might have a value of around 1.6. This value is modified using the maximum control, seen in Figure A.6. A.2.5.5 Coefficient of Lift Immediate Drop at Stall This is the drop in lift that immediately follows the stall. For thin airfoils, which tend to stall sharply, this value might be 0.2. For many airfoils, however, there is no immediate drop, but instead a more
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U L T R A -R E A L IS T IC F L IG H
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iv ABOUT THIS MANUAL
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vi CONTENTS 3.3.2.1 Special Conside
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viii CONTENTS 7.1.2.2 VOR Navigatio
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x CONTENTS B Troubleshooting X-Plan
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2 CHAPTER 1. ABOUT X-PLANE instrume
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4 CHAPTER 1. ABOUT X-PLANE software
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6 CHAPTER 1. ABOUT X-PLANE Aerospac
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8 CHAPTER 1. ABOUT X-PLANE
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10 CHAPTER 2. QUICK START GUIDE 2.
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18 CHAPTER 3. PREPARATION AND INSTA
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28 CHAPTER 4. CONFIGURING AND TUNIN
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62 CHAPTER 5. FLIGHT IN X-PLANE
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64 CHAPTER 6. ADVANCED SIMULATION I
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166 INDEX OF MENU ITEMS Location Re
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168 INDEX OF MENU ITEMS
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170 GLOSSARY Figure G.1: The flight
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172 GLOSSARY Distance Measuring Equ
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174 GLOSSARY Speed: The change in t
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