Al,
Its been
hard to get good photos of this, because the lower cowling makes up a good
portion of the airflow path.
Basically I have a standard Cozy NACA scoop, with the oil cooler and
radiator sitting flat, end-to-end beneath the engine mount.
I have a
curved deflector on the oil cooler to help the air make the turn up and through
the oil cooler. I have another one
of those deflectors on the radiator about half way back.
The
downside to this design, is that it takes pressure to make the air turn, and go
up through the radiators. The NACA
does not work well that way.
What I’m
trying to do is augment the existing scoop, with a “bolt on” scoop ahead of it,
which will capture air outside of the boundary layer, i.e. high speed air, to
improve cooling.
I made a
scoop first, that while it worked somewhat, does not exclude the boundary layer
air. Also it’s kind of like a
funnel, with the largest are at the opening and tapering down into the existing
scoop.
I hope
that makes some sense.
Steve
Brooks
-----Original
Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net]On Behalf
Of Joseph M Berki
Sent: Wednesday, July 14, 2004
2:45 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: New Scoop
Al,
Do you have any
photos of your oil cooler install showing the airflow path?
Joe Berki
Limo EZ
At 10:57 AM 7/14/2004 -0700, Al Gietzen wrote:
Subject: [FlyRotary] New Scoop
Steve;
There are all kinds of things one could
say about trying to make the scoop ideal, effective, low drag, etc; and then
when you face the reality of fitting to your plane, you can t do it. So
it s what works for you. I ll add a few comments for whatever it s worth.
The intake area of the scoop should be
fine.
One would like to slow (expand) and
turn the air entering the scoop in a manner that maintains surface attachment
for max pressure recovery and minimum drag. This takes a much longer
scoop throat than you have. The air entering will trip to turbulent at
the abrupt corner behind the B.L dam. This will result in poor flow and
pressure distribution, with most of the air going toward the back of the
scoop. I don t know what happens in your installation downstream from the
actual scoop, but you might consider some internal baffles but get a more
uniform distribution if the rad is close to the scoop.
The boundary layer dam that you have is
high drag, and may be close enough to the entrance lip that backup of the B.L.
flow will be ingested into the scoop or it could result in some external
diffusion (pressure recovery) and allow the scoop to work just fine. The
idea in the B.L. bleed is to try to divert that flow somewhere else,
generally off to the sides. That would require a much more gradual
diverter angle.
I made a much more gradual bend in the
wall of my scoop (pic) attached. Still, in doing flow tests, I found flow
separation and turbulence which lead uneven flow distribution. I added to
baffles in the scoop get it fairly uniform. It could be that some of the
turbulence was a result of the test rig setup, although I thought I had a long
enough duct from the blower to straighten things out.
The squared off internal corners will
add frictional drag, but probably not significant in overall picture.
But, hey try it. If it gives you the
cooling you need, you ve got 90% of the battle won. If you feel you need
to reduce drag, you can consider that at your leisure.
Al
Ed, and others -
Attached are some photos of the new scoop I'm building to replace
my old new
scoop. As you can see the new one actually has less intake
area, but
extends further in order to get outside of the boundary layer.
I don't want the intake any larger than it has to be, but I want
to make
sure also that it is sufficient to allow for enough air
flow. My old new
scoop did improve cooling, but as I found out, it was only
marginal.
The new scoop, which is patterned after a P51 style scoop, not
only gets
outside of the boundary layer air, but also excludes it, with the
dam that
you see at the bottom. Well, actually it will be at the top,
once it is
mounted under the belly. It also gives me an expansion area
once inside the
scoop.
Using the program that Al sent me, the boundary area calculated
out to about
1.625-1.75 inches +/- depending on speed.
The scoop intake measures 10.75" inside at the top
(narrowest) and 14.75" at
the widest point average = 12.75"
Height of the inside of the scoop measures 4.25"
This should equal about 54.18 sq in of area.
The inside of the scoop sits exactly 2" from the bottom of
the fuselage, and
overall height to the outside of the scoop is about
6.6" again, measured
from the fuselage bottom.
I haven't glassed the scoop yet, other than on one side to help
with gluing
it together.
I am interested in any feedback concerning the size of the intake
area.
Regards,
Steve Brooks
Cozy MKIV N75CZ
Turbo Rotary
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