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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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