T.J.V.
Methods for accurately shaping solid wings have been around apparently forever. Probably pre-date Zaic. I expected to find the "progressive line" method in his glider handbook--but did not. In this method you sand progressive flats down to a pair of reference lines that move when each prior flat is finished. You can infer the progression from the end view.
For example, make a mark down from the top on the front of the LE that is say 25% of the thickness. Make a mark on the top surface that is ~20% of chord. Sand a flat between the lines. Then make a mark on the face of the LE that is 50% of the blank thickness and one on the top surface that is at maybe 15% of the chord. Sand a flat down to these lines. Keep going forward and down with your reference marks until the facets are just about the shape of the reference section. Then simply smooth the cusps and finally do a chordwise blocksanding motion.
The same method is used on the aft section, but it may only take one or two facets for a thin racing wing.
I would draw the airfoil and then pick dimensions aft of the LE to create a ink line. Gel pens work well since the dent the wood less and soak in much less. This improves accuracy and reduces ugly.
If you do not have good marking gauges, go get one (or better, several different types!) I have found that fake credit cards that come in the mail make great shims for marking. Stack up as many as you need. Then push the stack up against the LE of your wing blank, held down with weights on your proverbial flat work table. Poke the pen up against the top of the cards and the LE and slide the cards and pen along the full length.
On pine, spruce, or basswood wing blanks I use a full-sized hand plane. You breathe less sawdust that way, and is kind of fun when you get it tuned just right. On balsa LEs I use a Master Airscrew hobby plane for the forwardmost cuts, and then finish the facet with the sanding block.
The important thing to realize is that there is a progression that will create an accurate airfoil in distinct steps. It isn't just a freehand orgy with a large sanding block.
Divot McSlow