Sorry it took so long to post this - I really need to check this Forum more often!

Here is a link to the model:
https://grabcad.com/library/elliptical-wing-1

A couple of comments:

Again, converting the Spline to a "Proportional Spline" in the Spline Property Manager will fix the shape of the spline, but allow it to grow/shrink as it sweeps along the Guide Curves.

Also, I try to avoid sharp corners (i.e, sharp trailing edges) whenever possible. Singularities like that lead to real problems in sweeps and lofts...

SF