Thomas, Here is probably the best, most
understandable (without a lot of math) on the cooling challenge that I have come
across. You might want to check it out. Here is one of
the statements you will find in this short article
It has been shown that the diffuser
efficiency is key in the reduction of the overall radiator drag. It is the most
critical part, and unfortunately the most frequently botched by homebuilders.
http://contrails.free.fr/engine_aerodyn_radia_en.php
Also note his comment about how to control
airflow once your intake is 30-50% of your core area – may surprise you.
http://contrails.free.fr/tunnel_en.php
Here is a summary by Meredith on the
effect. There is still some debate about whether the P-51 cooling system
actually resulted in a net thrust – but, most agree whether it did
produce significant thrust or not the cooling drag was probably close to an
optimum minimum.
http://contrails.free.fr/refroid_meredith_en.php
You are right, there is always trade offs. You can
certainly put an oil cooler in front of your radiator – in effect you are
just making a thick radiator as far as airflow is concerned. Obviously
you will have hotter air flow through the part of your radiator behind the oil
cooler so its cooling effectiveness will be reduced. Also, you may find
that a lot of the air in their common duct may want to go through the other
part of the radiator core – due to its less air resistance.
Placing them side by side (or top bottom) is another approach.
However, it is my opinion that unless your oil cooler and radiator core have
similar air flow characteristics or great care is taken in designing your ducts
to each, that air will take the route of least resistance. So one core
could end up “bleeding’” cooling air from the other. Similarly,
the exit pressure of one (generally the one with the least air resistance) will
be higher than the one with less resistance. So this can cause airflow problems
under the cowl as well.
Its my opinion that keeping your oil and coolant cores
separate (if possible and there are always space constraints in our vehicles)
and also keeping their air flow separate is generally the best course of action
to get the best cooling. But, compromises are frequently necessary, in
which case you simply have to try and figure out the possible interaction and
effects.
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://www.dmack.net/mazda/index.html
http://www.flyrotary.com/
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.rotaryaviation.com/Rotorhead%20Truth.htm
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Thomas Mann
Sent: Monday, December 21, 2009
6:17 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Air Flow
Question
“Stick with this group, we’ve all been there and have
conquered the cooling beast – well, at least tamed it a bit.
Ed”
That is the plan Ed.
I’m trying to figure out how much
radiator I can fit into my configuration. I’m running the numbers and
drafting it out in AutoCAD.
I’m hoping that I can cash in on
the Meredith Effect in my design. I’m planning on an adjustable exhaust
opening much like the P-51s had. I’m not sure if I need it or not but
it’s easier to not use it vs. add it later.
Question: If I use a separate oil
cooler, can I place it in front of the radiator?
I’ve seen some installations like
this but it seems to me that there is a cost involved.
T Mann
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