Jarrett,
What sort of CNC is that ?
George ( down under)
Dave,
I'd vote for the smiley, I would still wonder if having the
opening out off the bottom face of the cowl wouldn't be better. Mind you,
two other things come into play. There probably isn't to much [more] turbulent
air or thicker boundry layer that close behind the prop at that location. No
more than the turbulance farther out. Secondly, the rotational vector up close
to the cowl very well could be less than farther out.[ to exagerate the issue,
imagine the rotational vector out near the prop tip's.]
I've designed a few cowls over the last couple years.
Attached are a couple pictures to illustrate. Since you plan to use
a lower and upper ducting, I've attached drawings/pic's showing how I've done
both designs. It would be a simple matter to combine the two, to arrive at
your desired design.
Also I've not said much in the past, but my CNC mill has been
installed and is just awaiting final wire-up and commisioning. I plan to start
offering its use to the Rotary crowd in producing components like cowls,
proper diffusion ducting, spinners [which properly fair into the cowls] etc.
Theres many other components I'd like to get into building but plan to start
out with these few and expand from there. The mill is currently capable of milling parts up to 8 x 18 x 3 [feet] and will
be upgraded in the spring to have a 4ft [instead of 3] Z axis. Later, we plan
to expand its abilities to 5 axis, however this is more in the neighbourhood
of a year or so.
I'll have a website up in the next month or so. However the
meantime, if I can be of help, please let me know.
Jarrett Johnson
----- Original Message -----
From: David Leonard <wdleonard@gmail.com>
Date: Tuesday, January 30, 2007 2:22 pm
Subject: [FlyRotary] Re: New Cowl Contest
> Todd, if it aint broke dont fix it!!!!
>
> You are
right about the boundry layer. But you can make up for
> that
with a
> little extra size or maybe moving closer to the prop (eg
P-40).
>
> Also, Doug dempsy has been telling me how Chuck
Dunlap had a real
> problemwith a duct that was away from the boundry
layer, but fixed
> his issue when
> he make it bigger and more
like the smile.
>
> The smile votes seem to have it so far...
>
> Dave Leonard
>
>
> On 1/30/07, Todd
Bartrim <bartrim@gmail.com> wrote:
> >
> > I was
thinking that the "oh cowl" would be better at excluding the
> >
boundary layer, which would be better for cooling. This is just
> based
on
> > comments I've read on the list during previous ducting
> discussions. Based on
> > this info, I felt my oil cooler
duct was less than optimal (even
> though> temps are good), so I
figured I could reduce the size of
> my inlet if I
> >
eliminated the boundary air layer. As your "smile" duct is
> similar
(see
> > attached pic) I figured this would be applicable. I hope
I'm
> wrong and you
> > prove it before I change my cowl.
> >
> > Todd (building Electric Bob's
Audio Isolator Amplifier today)
> >
> > On 1/30/07, Ernest
Christley <echristley@nc.rr.com > wrote:
> > >
>
> > David Leonard wrote:
> > >
> > > > I
call them the "Oh Cowl" and the "Smiley Cowl..."his
> > >
> > > Go with the smile, but put a raised ledge on the cowl side
> just behind
> > > the spinner to accelerate the air and
thin the boundary layer.
> Reduces
> > > the ingestion of
turbulent air. Check the CAFE Foundation's drag
> > >
reduction report. They have a picture of what it looks like
> on
a
> > > production aircraft. I have a link to it at home,
but not here.
> > >
> > > --
> >
>
,|"|"|,
Ernest Christley |
> > >
----===<{{(oQo)}}>===---- Dyke Delta
Builder |
> >
> o| d
|o http://ernest.isa-geek.org
|
> > >
> > > --
> > > Homepage:
http://www.flyrotary.com/
> > > Archive and UnSub:
> http://mail.lancaironline.net/lists/flyrotary/> >
> >
> >
> > --
> > Homepage:
http://www.flyrotary.com/
> > Archive and UnSub:
http://mail.lancaironline.net/lists/flyrotary/
> >
> >
> >
> >
>
>
> --
> David
Leonard
>
> Turbo Rotary RV-6 N4VY
> My websites at:
> http://members.aol.com/_ht_a/rotaryroster/index.html
>
http://members.aol.com/_ht_a/vp4skydoc/index.html
>
http://leonardiniraq.blogspot.com
>
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