ORIGINAL: Popriv
Now to get a flat bottom is it just a matter of how you line up the material at the TE? Even like I did gives a symmetrical wing. for a flat bottom I need more material on the top when I line up the TE? Seems harder that way? ( But not much)
I think that's why the top is wider than the bottom on all the STTB plans and you fold it over after your spar is glued in place, then mark it and cut it off flush. That's a lot easier than trying to calculate the distance with the spar height and the curve and all. To get the flat bottom, I have a piece of 1x4 that I cut a 45 deg bevel on one side. I fold over my wing and get the TE even with the edge of my wooden bench. I jam the 1x4 up tight against the LE and screw it down to my bench. Then I glue her up, jam the LE up under the 1x4, put a 2x2 over the TE of the wing and clamp it down tight. When I pull it out it's pretty flat except for a little bit of reflex on the bottom near the TE where the pressure of the top is pulling up on it. Seems to work pretty good. An angled 2x4 might be even better because then you've got more height so you can not jam the wing under all the way and let the LE come up a bit and you can get a symmetrical wing or a semi-symmetrical if you'd like. <br type="_moz" />