Tips, Tricks, Common Errors

• Coordinates start at the trailing edge, continue along the upper surface to the leading edge and follow the lower side back to the trailing edge.
• The trailing edge must be at x=1.0, the leading edge at x=0.0.
• Specify each coordinate point only once (check for duplicate points at the leading edge - only the trailing edge point will occur twice).
• Coordinates should be as smooth as possible. If the velocity distribution shows waves and oscillations, especially close to leading and trailing edge, you should smooth these regions or omit points which don't fit smoothly into the airfoil shape (provided that you have still enough points).
• Use enough points! For the panel method you should use at least 50 to 100 points. If you use less points, the polars may become jagged and unrealistic. You can imagine, that the flow solver makes the flow jump from corner to corner of your airfoil. If you define a flat plate by four points, you will get absolute nonsense, but if you supply a smoothly rounded, elliptical leading edge and enough points along the flat sides, you might get something realistic (as long as the flow does not separate from the surface, which will happen quite early on a flat plate).
• Separate x- and y-values by one or more spaces (blanks).
• Do not include blank lines in the data.
• Before entering new points, make sure, that you have cleared the coordinates text field - there may be some lines outside of the visible scroll range.
• Instead of entering values directly into the coordinates field, you could enter the data into a text editor and save them to disk. Then use the copy and paste method available of your system (in Microsoft Windows™ you can use the notepad.exe program). This is highly recommended as the coordinates could be lost otherwise and you would have to retype them.
• The trailing edge should be closed smoothly (no thick trailing edge); the code will collapse the first and the last coordinate points to close the trailing edge anyway, which might result in a too abrupt closure.
• If you want to deflect a flap, it is usually the best to start from the initial un-flapped airfoil for each flap deflection and not to accumulate flap deflections.
• Generally, natural (free) transition is assumed, and the program calculates the transition location. To force early transition, you can select a higher roughness level or specify transition locations for both sides of the airfoil.

Conversion Hints

I will leave the conversion factors for those, who are measuring the propeller diameter in townships or teaspoons, mass in scruples and force in kips as an example for the interested reader.

Last modification of this page: 21.05.18

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