Al,
What kind and
size of radiator(s) are you using.
I assume that there are 2 of them, but maybe not. I like the set up, and I can see where
the flow would be very even. That
type of set up would be a major change from what I have now.
Steve
-----Original
Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net]On Behalf
Of Al Gietzen
Sent: Wednesday, July 14, 2004
1:57 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: New Scoop
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