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

Paul,

You can make a parabola by either focus or vertex in the curves menu. I
don't think you need to go through the generate import and curve fit
routine.

Monty

Thanks Monty I'll take a look. Learn something new about Rhino every day.

Paul Lamar
 
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