[Tesla]

I only got through page 20 of thread, hope this hasn't already been dealt with, will go back and finish reading tomorrow.

I started putting together a spreadsheet so I could easily calculate the change in taper of template at each profile point for height, width & underside. these could then be plotted onto cardboard and cut out, then lined up to make a Kamm back or full boat tail, seemed easier then trying to get the angles right with a protractor.

Once I had the basic formulas down I thought I'd plot a chart to see what it looked like, then it occured to me I could reverse engineer the equation this way, with a bit of fiddling I have come up with a polynomial equation to the third order:
y = ax^3 - bx^2 + cx + d
Where
y = height from ground
x = distance from 0 point
d = height of vehicle at 0 point
and
a, b & c are constants
the width can also be determined by using vertical centreline as ground point.

Just want to check a couple of things:
I took the angles from the template i.e
10% = 3.5*
20% = 7.5* (5.5*?)
30% = 12* etc.

There was a few conflicting templates on the 20% mark, some had 5.5*, when I charted this it had a hump there and the 7.5* gave a smooth curve so I think the 7.5 is the right figure, can anyone confirm this?

While working through it, it dawned on me that the angles represent the tangent angle at that point, so at 30% the tangent of the curve is 12%, I think like myself some have taken this angle and used it to calculate the fall from the 20% to 30%, but this would have resulted in a steeper curve, the tangent at 30% represents moreso the fall between 25% to 35% points and considering the curvature is accelerating it that fall is probably representing something like the 26% to 36% points. If this was not taken into account it would result in a steeper tail and with added imperfections may contribute to loosing attached flow. If someone could also confirm this understanding of the template angles.

The third thing was the underside/diffuser, I have seen anything from 2% to 11%, read a few explanations, but still not quite sure what angle applies in what situation, there was something about using a small angle for a long diffuser and larger angle for a short diffuser, so does this mean just aiming for same elevetion change with both methods, still a bit confused on that one.

I've done some fiddling to simplify the equation, but want to get the details sorted as everytime you adjust something, the constants need to be tweaked a little.

The fundamentals I have used are the 1.78d rule for length to height ratio and the angles documented off the template,
If these are right then with the equation one should be able to calculate the change in dimension at any point along the tail length, print out data points for each section, then make all the cardboard cutouts line them up, join together and wrap a skin on them.

I'm thinking I'l probably break down the tables into 5% graduations for the first 50% as this is where the bulk of the complex curvature is.