Thanks for the links Ed.
It looks like I have some reading to do!
From: Rotary motors in
aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Monday, December 21, 2009 7:19 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Mereidth effect: [FlyRotary] Re: Air Flow Question
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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