Hi Brian,

I'm glad you spotted this thread :)

I'm pretty certain the index numbering isn't causing any problems. Please do take a look when I post the full initial script later today.

I did think about calculating the airfoil upper surface curve in reverse order, and then adding the lower surface curve, but gave up on it as wasteful to do a moderately complex and identical airfoil thickness distribution calculation twice. It would be an interesting exercise to try out though and not difficult.

As I said, I'm glad you spotted this thread because I'd be interested to see if some of the work you've done on generating some of the more specialised (spiral) curves might be applied to describing the thickness-distribution of NACA's five-digit series airfoil odd-ball: the 43012A.

It has it's very own thickness distribution that was never formalised by any equation; certainly none that I can find. Even the seminal NACA Technical Report 610 of 1936 only talks of "filling out the concave portion of the lower surface near the nose of the NACA 43012 airfoil and thickening the upper surfaces so that the mean [chord] line is unchanged".

I've already created a 14 coefficient, almost oscillation-free, polynomial to describe the 43012A thickness distribution (using desmos.com to do some pretty cool interactive regression), and it's a pretty close fit. But I wonder if log aesthetic curve segments might fit even better. Or it may be easier still and just as good/accurate just to store ordinates of a best-fit to points, faired NURBS curve. I'd be interested to discuss it some more, after I post the script so far.

Cheers,
Hamish