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

Paul,
Another easy way is to use an elipse. In side view set the center of the elipse at the prop flange intersection of the propshaft center line. set minor axis
endpoint to desired spinner radius and major axis endpoint to desired spinner length.
      Draw a few other elipses with different axis dimensions till you get one you like.
next trim off the rear half and front bottom quarter of the elipse, revolve what is left around the propshaft axis and you will have a 3D spinner. This is how
I did it in AUTOCAD.

Ed. Sadler

Thanks Ed.

Paul Lamar
 
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