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Ed,
I thought necking-down like you have done would
cause more of a restriction and would result in less pressure.
I thought that a more direct line of travel from
the opening to the core would give less restriction and more
pressure.
From what I've been told, this particular design
seems to want to follow the trumpet ( bell) shaped opening style, whereby
1.5 times the face of the radiator, is required in the length of the duct. I
don't think 6" is enough length.
What other styles of duct have you tried which are
less successful than this design.
I must say it does look good but seems to fly in
the face of other previous recommendations.
George ( down under)
I was referring to curvature of the duct walls
which should impose on the higher pressure area in front of the core. By
pushing the duct walls into the higher pressure area in front of the core, the
higher pressure helps to keep the flow from separating as it flows along the
wall of the duct.
Here are a couple of photos.
One photo (MVC-033s) shows some templates I used and
shows the outline of my duct with the opening toward the bottom and the
core toward the top of the photo. Notice how the outer walls of the
template stay close to the centerline until diverging near the core
(top). The inlet is approx 6" long from inlet to core which is too short
for the Streamline duct coordinates I modeled it on - So I try some creative
things with the curve of the duct walls which I believe worked out. I
make the curvature more extreme than the stream line duct.
A second photo shows the current set of
ducts I am flying with which have a total combined opening of 28 sq inches for
both cores. Here I actually decrease the size of the duct after the
opening until I expand it before the core. My theory is that this
initially accelerates the air entering my inlet giving it higher energy which
helps maintain a higher pressure dome in front of the core> This in
turn permits me to curve the duct walls more without separation of
flow. Separation of course creates eddies which effectively blocks flow
through a portion of the core reducing your cooling effectiveness.
At least for the power my engine is putting out
at the current time 28 sq inches appears to be the minimum total duct opening
that I can fly with. I have tolerable temps on climbout (200F oil, 210F
coolant) and 170-180F at my nominal cruise (5600 rpm). If I go to WOT at 7500
MSL the temps will slowly climb to the 190F range and stabilize
- indicating that I am probably about as close to the minimum cooling as
advisable. To give myself a bit more margin, I will probably open the
duct area up from the current 28 sq inch to 38 sq inch - in the future - maybe
{:>)
Ed
----- Original Message -----
Sent: Monday, April 04, 2005 2:49
PM
Subject: [FlyRotary] Re: A lot to
learn
The only part that really counted was
understanding what was necessary to keep air flow from separating from the
walls in a diffuser.
er.... what was
that bit? I must have missed it. :)
John
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