You got me there Brian.

     Is X2 really X^2  or X times 2?
     Is X max = L?

     Variable are usually expressed in lower case.

     Got a sketch with the axis labeled?

     Other than use a spread sheet sheet to plot the curve coordinates the loft feature in Rhino
     can't do that as far as I know. If you can enter that equation in Excel and plot
     the curve with Y coordinates as a function of X I can then loft it. Anybody else on here
     know how to do this? Any other suggestions on an approach to this problem?
    Paul Lamar

Ahh- I see the problem-- X2 is X squared. I put the 2 in an uppercase in  Microsoft Word (spit, spit), but it was put into lower case when I transferred it.
The diameter of the spinner is 16 inches, so the radius is 8. 8 squared is 64.  L is the length of the spinner from the backing plate to the forward tip. I'm
thinking that a 19 inch length would be just about right. I'd like to have pretty much a continuous curve from the front of the cowl up to the curve of the
spinner. Follow me? No? That's why I'm not a teacher.


Y is the vertical axis,  X is the horizontal axis, L is the apex of the parabola. If it's a real  pain in the ass to build on rhino and put on the cowl, then
don't sweat it. When you get me the coordinates for the cowl, I can find the parabola that matches by the rate of change of the slope of the curve. Got It? :
)


Thanks,
Brian

I follow you.  A spinner is symmetrical about an axis but the cowl is un-symmetrical
in the region of the spinner so only part of the spinner is a continuation
of the cowl curves. The main determination of the shape of the cowl is
fitting all the parts inside. That leads to a non simple mathematical shape.
It is a trial an error process. I loft a cowl and see if any part or parts poke
through and then I make adjustments if they do. Rhino smoothes the curve automatically.
It is called Non-Uniform Rational B-Splines or NURBS for short. 

Check out http://cs.wpi.edu/~matt/courses/cs563/talks/NURBS.htm

For a simple mathematically determined spinner it is not a pain if I have the coordinate 
for the spinner curves. It is just the script language in Rhino does not do math 
as far as I can tell. It will read a text file consisting of coordinates and plot 
curves through those points. 

The other thing that can be done is select the side
view and continue the top curve out to a point located x distance from
the front of the cowl and on the thrust center line. Here is a dwg of that.
The lower line is a straight line or a cone. The middle is a NURBS continuation 
of the side view and the upper line was a first guess cone. Take your pick :)


"When you get me the coordinates for the cowl"?  I thought I was off the hook and
you were going to use strips of wood instead ? :)
 
Paul Lamar
 
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