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morid(at)northland.lib.mi
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 Posted: Fri Feb 24, 2006 6:50 am Post subject: Radiator Ideas (scoop) |
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"Bradley M Webb" wrote:
<I'm guessing what the article is really saying is that you must play around
with Bernoulli. You don't push the air through a radiator, you suck it
through. You'd ideally want a small frontal air intake, then expand that air
to slow it down, thereby increasing its pressure at the radiator surface.
Then re-squish it to lower the pressure and accelerate the air into the air
stream aft of the system. I did this on my 2, and it does work. My radiator
is mounted horizontal at the bottom of the firewall, behind the muffler can.
I built a reverse scoop with moveable flap that exits at the bottom aft
cowl. It removes the drag of being under the fuse, and shortens the coolant
lines.>
Had I the space to place my radiator up inside the engine area I would have gone this way. Prior to my first flight with my S5 Soob I was pretty sure I was going to have cooling problems. I had the radiator in the conventional area hanging in the breeze under the firewall where it acts like an air dam that adds some wonderful drag, but isn't very efficient at cooling. Air will take the easiest route, especially at higher speeds and when faced with an obstacle it will go around it. The rad fins do allow air to pass through, but higher speeds most of it doesn't.
As I wanted to ensure that radiator drag was minimum and cooling was efficient I did some extensive research into this, including Bernoulli and found that a scoop using the basic 1/3 in 2/3 out principle would be a good starting point. I fabricated a fiberglass scoop with an intake about 3X11" and the exhaust 3X33. The scoop entrance starts out well in front of the rad to allow the air to expand and terminates about 18" behind the radiator under the floorboards. The rad is sealed inside the scoop so that ALL air has to go through it, not around it.
My first flight was without the scoop and cooling was poor with cruise about 90 with 3900rpm/22"mp. I then added the scoop and cruise went up over 100 (same numbers) and cooling was perfect. Wheel pants and a couple other small speed mods have improved speed even more. Since then I've also added a cockpit controllable rear scoop flap using a Boden cable that enables me to control the amount of air exiting the scoop. The flap has a lip on it so that when wide open it increases the low pressure area behind the scoop that sucks more air through. This works great on long taxis and long climbs.
It isn't perfect, but does the job nicely.
I've added a link to the Kitfox Sportflight archives where it can be viewed if anybody is interested. Go to http://www.sportflight.com/cgi-bin/uploader.pl?action=3Dmain then "improvements" then scroll down to my radiator scoop pics, items dated 12/23/02, 12/08/00. There's also a few shots of my gas cap fairings in there too if anyone wants to get anal over drag reduction. 
Hope this helps somebody.
Regards,
Deke
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wingnut
Joined: 11 Jan 2006
Posts: 356
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| Posted: Fri Feb 24, 2006 7:29 am Post subject: Re: Radiator Ideas (scoop) |
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Beautiful work. Gorgeous Kitfox. The idea that a shrowd with a frontal area smaller than the radiator would actually improve cooling seems counter intuitive to me. Fluid dynamics is a more mysterious subject then I would have guessed. I don't suppose that you have any links to the theory that's at work here?
The radiator on my 912 powered kitfox is in the same location. I wonder if a similar contraption would yield similar results. I'm guessing that my radiator is smaller so the difference would not be so dramatic but hey.. it looks cool too.
-Luis
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morid(at)northland.lib.mi
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| Posted: Fri Feb 24, 2006 8:49 am Post subject: Radiator Ideas (scoop) |
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Thanks. This is over simplification, but you want the high pressure area at
the (smaller) inlet and low pressure at the (larger) outlet. The low
pressure creates the suction that pulls the air through which is essentially
a venturi. Fabricating a lip at the outlet end further lowers the pressure
which results in more suction. Of course, all of this can reach a point of
diminishing returns which resulted in the approximate 1/3-2/3 rule.
Consider LoPresti's cowls where he actually made the inlets smaller to
achieve better cooling and aerodynamics. Much of what I learned was from
the RV and Airsoob lists, as well as various internet sites. I'm not an
engineer or anything remotely close. I just learned what works.
Deke
---
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Lynn Matteson
Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan
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| Posted: Fri Feb 24, 2006 10:37 am Post subject: Radiator Ideas (scoop) |
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What plane are you talking about, Luis?
(Be sure to include a snippet of the previous post so somebody coming
in "a little late" will know what previous post you are referring to.)
Lynn
On Friday, February 24, 2006, at 10:29 AM, wingnut wrote:
| Quote: |
Beautiful work. Gorgeous Kitfox. The idea that a shrowd with a frontal
area smaller than the radiator would actually improve cooling seems
counter intuitive to me. Fluid dynamics is a more mysterious subject
then I would have guessed. I don't suppose that you have any links to
the theory that's at work here?
-Luis
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=14630#14630
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_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM |
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wingnut
Joined: 11 Jan 2006
Posts: 356
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| Posted: Fri Feb 24, 2006 11:02 am Post subject: Re: Radiator Ideas (scoop) |
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Sorry. I've been using the forum interface that organizes all the entries in the same thread into a single contiguous page. I'd forgotten that there are still people who would rather use email. It's too bad that not everyone can use the forum interface. It makes all the extra text unnecessary.
-Luis
| Lynn Matteson wrote: | What plane are you talking about, Luis?
(Be sure to include a snippet of the previous post so somebody coming
in "a little late" will know what previous post you are referring to.)
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nebchmp(at)wcc.net
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| Posted: Sun Mar 05, 2006 9:42 am Post subject: Radiator Ideas (scoop) |
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On my previous cowl I had a scoop that was built using Darrel Mossie's
example as a guide
http://www.sportflight.com/cgi-bin/uploader.pl?action=main&category=Improvements
<http://www.sportflight.com/cgi-bin/uploader.pl?action=main&category=Improvements>
It worked very well for my application at the time. It was my first
try at fiber glassing and has some slight imperfections. It could
however be used as a mold or with some work, used as is. I was going to
pitch it, but on second thought if someone wants it for the postage its
yours. Norm.
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