An excellent discussion on this so far. If the forumulas can be fine tuned to provide a more accurate tool we'll all benifit.

A little trick I read of years ago for calculating the neutral point for model rockets was to cut out a side view from cardstock and then balance the profile cutout over a pivot to determine the NP for the rocket. For stability the CG then needed to be so far in front of that. It was suggested in those magazine writeups that this trick could be used for model airplanes as well. Could anyone comment on this?

JohnG, how critical are the numbers from the chart? Would it be pratical to use a small list of "constants" that are picked to work over a range of designs? This would introduce a small (hopefully) error but if the NP could be figured that way to within a few % error it would be good enough for our purposes.