My next step was to tranfer the airfoil to the jig. There are several ways to do this. My plans come with a full size template of the wing ribs. I could just tape/glue/varnish the template to the jig like some people do. However i had heard of problems of it not being the correct size due to shrinkage. I checked mine and it was off. The spar spacing is supposed to be 30" on center and the length of the rib 60". Both were off by about 1/2". So i could have went to a printing or blueprint shop and had them blown up alittle, but getting them perfect would have been difficult. So i decided to redraw the airfoil and use the full size template as a guide for all the capstrips, plywood and gussets.
The first step was to find the actual coordinates. I searched the web and found several sets of coordinates for the NACA 4412 airfoil. Both in 18 point and 60 point. I decided to use the 18 pt coordinates as it would be alot easier to plot. I would just have the points a bit farther apart than with a 60 pt. The coordinates usually come in a decimal form ranging from 0.0 to 1.0. I had to multiply those by wing cord length which is 60"s. That in turn gave me my final coordinates to plot onto my jig. You can draw this onto paper and then glue the paper to the jig but i decided to omit the gluing step and just draw it directly onto the jig. My piece of MDF has a white melamine surface on it. Perfect for drawing on.
The first step was to draw a base line about two inches above the bottom of the jig. That would allow enough space for the lower airfoil shape and allow more room on top for the upper more curved airfoil. Then i place the starting point of the airfoil 1" form the end of the jig. From there i drew all of my "X" coordinates along the line all the way ending about 1" from the end of the jig. Next was to draw the "Y" coordinates. I used a metal "L" ruler and marked a vertical line thru the X coordinates perpendicular to the base line.
