Disclaimer: I'm a long way from even
running the engine.
I tried to copy (at least in spirit) Tracy's install, as well.
Renesis in RV-7. For fit (& financial) reasons, I used a Civic
racing rad that has a more or less square face & is a downflow
design instead of a crossflow 2 pass like the Scirocco style that
Tracy used. It's around 400 cu in volume. One thing I intend to
try is to use an exit duct. Because of this, my duct is on the
engine side of the rad (Tracy dumps his exit air toward the
engine). The layout in my cowl (I wanted as straight a shot as
possible into the wedge) & the desire for an exit duct forced
that change for my installation.
I tried to use the formulas & guidance from the K&W book
as a starting point, but discovered that some of the stuff about
wedges doesn't seem to match 'real world' application. Tracy saw
my 1st draft & warned that it wasn't thin enough at the back
of the wedge, & he was right. I used canned foam to re-shape
the wedge to thin it out at the back. Once I determine that the
internal shape actually works, I'll glass over the canned foam. I
also used a turning vane in the duct to get more even air
distribution through the core (thanks to Al Gietzen for that tip).
The vane was needed because the inlet height is well above the
center-line of the rad. I did try to use the K&W streamline
diffuser concept to transition from the round inlet to the
somewhat larger area of the entrance to the 'wedge'.
I used clear packing tape as a release on the flatter areas, and
cheap electrical tape on the highly curved areas. Tape works fine
as a release, but any texture on the form will get reproduced in
your part. I had to do a lot of work to smooth the interior of the
duct because of the ridges formed by wrapping the tape around the
form. It's a lot like painting; if you do a lot of prep work,
there will be a lot less finish (repair) work on the duct.
Shots showing the core I made, & the resulting duct with
turning vane are on Photobucket at
http://s1155.beta.photobucket.com/user/rv7charlie/library/radiator%20duct
Video of the airflow is at
http://www.youtube.com/watch?v=D0mUJdzzrG0
Charlie
On 12/15/2012 08:20 AM, Tracy wrote:
I used a male mold made of foam. Use the good stuff, not the closed cell styrene or the canned foam which is hard to work with. After shaped, I 'paint' it with drywall compound sand it smooth then cover with vinyl tape or coat with molten paraffin as mold release.
The rad duct was shaped based on my imagined airflow within the duct. It is compound curves everywhere, not a simple wedge. Much thinner at the edges than in center for example. Is it better than a wedge? Don't know, but the leaf blower flow test method showed pretty good distribution with higher flow near the back (should have been even thinner there). Fixed that with a bit of ridge vent material (porous coarse fiber stuff) stuffed in the back section. Not the best solution there but I've not had water cooling problems so good enough.
Tracy
Sent from my iPad
On Dec 14, 2012, at 7:33 PM, Stephen Izett <steveizett@me.com> wrote:
Hi Guys
I am about to reinstall the Renesis engine in the Glasair SII and create the ducts to the exchangers.
I plan to copy as closely as possible Tracy's 20B setup.
Questions:
1. What is a good process? Shaping foam, sounds good. So how do you then seal it before applying glass/epoxy?
2. Tracy, why is your diffuser not a simple wedge? Do you believe you are getting a more even pressure to the top and bottom? Have you ever measured your pressure distribution?
Thanks
Steve Izett
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