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I was trying to use Autocad to plot the airfoil shape for eventually
creating leading edge templates. In doing so I came up with a couple of questions. I started with the coordinates from the UIUC database. http://www.aae.uiuc.edu/m-selig/ads/coord/fx67k150.dat What I wanted to come out with was something like this: http://www.goddard.com/soaring/info/FX67K150.gif My attempts were to use the "spline" command in order to fair the shape through all of the points. The problem came with the leading edge area (doesn't it always!). My first attempt was to simply use the spline command for the top surface and then the bottom surface. But this left me with a hard point at the leading edge (0,0). Clearly, one needs to create some sort of 'fairing' around the leading edge. Intuition told me that I should start the spline at the trailing edge and continue it around the leading edge and along the other surface.\ But that approach came out with a leading edge like this: http://www.goddard.com/soaring/info/spline-full.gif This gave a very nice faired curve but it extends too far forward (into negative X territory) and puts the actual leading edge above the centerline. So then I plotted it with the top surface and bottom surface splines separately forcing each of them to a tangent with a vertical line at (0,0). That produced the following: http://www.goddard.com/soaring/info/spline-normal.gif Now that looks about like what I thought it would... but the questions occurred to me... What is the "official" method of creating accurate plots from the data? How was the coordinate system designed in order to be able to accurately recreate the shapes? How did they calculate this stuff before the advent of computers and CAD programs? I know they had an arsenal of 'french curves' but there seems like there would be a lot of "eyeball judgement" in that approach. Just wondering... Larry Goddard "01" USA |
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