They also show what happens when a 20% chord flap is deflected 40 degrees. These graphs show test results for several different Reynolds numbers and for “standard roughness” on the surface. Note that for the symmetrical shape the lift coefficient is zero at zero angle of attack. The airfoils presented represent a cross section of airfoil shapes selected to illustrate why one would select one airfoil over another for any given aircraft design or performance requirement.įigure A-1 shows data for the NACA 0012 airfoil, a classic symmetrical shape that is used for everything from airplane stabilizers and canards to helicopter rotors to submarine “sails”. In the following appendix material a selection of airfoil graphical data is presented which can be found in the Theory of Wing Sections and in the non-copyrighted NACA publications which are the source of the Dover publication’s data. While the date of original publication might lead one to think this material must be out of date, that is simply not true and the Theory of Wing Sections is one of the most valuable references in any aerospace engineer’s personal library. Many of the more important airfoil shapes have their test results summarized in the Theory of Wing Sections, a Dover paperback publication authored by Ira Abbott and Albert Von Doenhoff and first published in 1949. This data is most conveniently presented in plots of lift coefficient versus angle of attack, pitching moment coefficient versus angle of attack, drag coefficient versus lift coefficient, and pitching moment coefficient versus lift coefficient and is found in literally hundreds of NACA and NASA Reports, Notes, and Memoranda published since the 1920s. Lift, drag, and pitching moment data for hundreds of such airfoil shapes was determined in wind tunnel tests by the National Advisory Committee for Aeronautics (NACA) and later by NASA, the National Aeronautics and Space Administration.
#Cambered airfoil vs symmetrical airfoil series
Many of us have demonstrated this when we were children, by putting our arms out the window of a moving car, and pivoting (pronating and supinating) our hands in the wind to produce up and down lift.In Chapter 3 of this text we discussed many of the aspects of airfoil design as well as the NACA designations for several series of airfoils. On a symmetric wing, this will probably be near the center point, and equal on both the top and the bottom. The aerodynamic center of any airfoil will be immediately aft of the point of maximum thickness on a cambered wing, this will be on the top side, usually well forward of the center point. This means they will produce exactly zero lift at zero AOA, and require some angle to produce lift.įinally, to respond to the true-or-false questions about your two statements, it would depend on each airfoil's curvature. On the other hand, symmetrical wings (airfoils) have no aerodynamic camber, but rather have equal distances for the air to travel over both the top and bottom surfaces.
If you inverted the airfoil, so the curved surface was on the bottom, there would be negative lift (downward pressure) at zero degrees angle of attack. The result of all this head-spinning aerodynamics is that the pressure directly on the bottom (at right angles to) surface of the airfoil is higher than that on the top surface, resulting in aerodynamic lift on that wing (airfoil), even at zero degrees angle of attack.
#Cambered airfoil vs symmetrical airfoil plus
Since Total air pressure = Static (directly onto the airfoil) Pressure plus Dynamic Pressure (speed of the air), and the Dynamic pressure (speed) on the top is higher, that means to balance the total pressure, the static pressure on the top must be lower.
This means air on the top surface flows at a higher relative speed.
The result of this is that air passing over the top surface of the airfoil has a longer distance to travel than air passing over the bottom surface. A cambered, or "airfoil-shaped" wing cross section will have a significant curve (bulge) on the top surface, usually with the thickest part nearer the leading edge, while the bottom surface will have no or minimum curve.