The Italian "Profili" program can export dxf files that is usefull in
autocad, maybe it have to many coordinates!? but..

Jan Carlsson
www.jcpropellerdesign.com

"Larry Goddard" skrev i meddelandet
...
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