Subject: Brian's Cowl
From: ACRE
Date: 7/6/2004, 6:48 AM



     > >      This is how I would do it. Make the water rad out of a

stock 19 inch long core

     > >      16 inches wide. Mount it along side the oil cooler.

They

will then both be the

     > >      same over all length.
     > >
     > >      I got bad news. No way can I squeeze a 4 by 4 air

intake

plenum in there. Perhaps

     > >      you can find 3 by 3 by 1/8 wall aluminum extrusion for

a

plenum.

     > >
     > >      Are you sure about that exhaust tubing bend radii?

Three

inch center

     > >      line two inch tube goes right through the motor mount

tube

with

     > >      rubber bushings at 8.5 inches from center line. If you

made a new

     > >      schertz beam and moved the rubber bushing outboard

about

an 1-1/2 inches

     > >      you would have more room for the exhaust.
     > >
     > >      We are nearing the end here.
     >
     > > That looks really nice. The alternator is a 40 amp unit, 4"

dia.,  the top of it sticks up 12 inches above the centerline of the

e-

shaft. I'm

     not sure about
     > > the radius of the exhaust pipes, but they obviously are

inside

of the motor mount with about 3/4" to spare. Thanks for the work on

the

cowl. I'm

     sure that I
     > > can make an air box that resides alonside the redrive. What

are

your thoughts about air filtration?

     > >
     > > Thanks again,
     > > 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
     >

     > "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
     >
     > OK here is a new 16 inch spinner and matching cowl. I think

you

can just get the

     > four inch intake plenum in there. You can just see it peeking

out

on the right side.

     > Do you like a point on the spinner or a rounded end?

     > That looks really nice. There is another inch or so above the

alternator due to a different mount setup. The alternator is mounted

on a

bracket

     welded to the water pump where it was modified. Not that it

makes a

difference in the cowl design. That is exactly what I had envisioned.
Thanks. I

     prefer a parabolic shaped spinner.
     >
     > Brian Trubee

     Pointed or rounded?

     It won't be impossible to get the exhaust in there just

difficult.

This problem happens

     over and over again. People put the rubber bushings too close

to

the engine.

     You want to get those rubber motor mount bushings as far

outboard

as you

     can. Probably the last thing you want to design is the motor

mount.


     Paul Lamar











     You guys are doing great here.  I had decided that it couldn't

be

done with a RV-4 cowl!  The engine mount seemed to be in the way of

the

exhaust no

     matter what I tried - this is why I went with a cantelevered

mount

design (I originally was working on a scheme similar to the Schertz

beam

where

     the bean went thru the oil pan right under the forward exhaust

port) .  I am really glad to have those mount tubes out of the way!


     Ken Powell



With all due respect Ken this P51 beam system would be much easier to
build than
the cantilever mount. It is just that Brian is too far along to change

to

a
P51 beam type RV4 mount.

Paul Lamar




Yes, I agree that the P51 system is better.  Like Brian, I am too far
along to start over.  I was finished with my mount by the time you had
presented the P51 type mount.

Ken Powell


I am sorry it did not come to light earlier but I don't think I 
thought of it. I think somebody else came up with the idea.
It will certainly work for any rubber bushing spacing.

Paul Lamar
 
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