Originally Posted by Rktman

Need some help guys! The biggest problem is not the math involved, but the fact that every article, formula and online calculator I've come across assumes you have rectangular wings and stabs. Mine are ellipsoid. Actually they're half ellipsoid; the TE curves upward at the tip to meet a straight leading edge (imagine the wings of a British Spitfire or Apogee’s Cirrus Breeze glider except that the leading edge is straight). See sketch below.
The stab is the same shape. All my gliders use this planform and I don't want to abandon it for various reasons.

The formulas and calculators all require you to input a tip chord measurement for both the wings and stab. I have no idea what measurement to use, since the LE and TE come to a point at the tip.

I came across an article by Guppy Youngren in a 1980 issue of the MIT Rocket Society Journal that details how to determine NP and CG, and part of his formula includes how to do that for elliptical wings (where both the LE AND TE are curved). Close…but frustratingly my wings have a STRAIGHT leading edge.

So that's the problem I’ve been struggling with. I’m hoping you knowledgeable and experienced glider enthusiasts can help me out on this one.