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----- Original Message -----
From: <peon@pacific.net.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, February 06, 2004 7:53 AM
Subject: [FlyRotary] FD Rads and Evap Cores
> Hi Ed, Rusty,
>
> Looks like my mate Wally has got me in trouble! So I need to
> clear up a couple of misunderstandings.
>
> I totally agree that Evap coolers do actually work, are a very
> economical solution, and fit "as a bean" in the "chipmunk cheeks"
> of most aircraft, originally designed to take an iteration of
> horizontally opposed mass folly. I also agree with all of Ed's
> points. Absolutely NO Contest.
>
> But that WASN'T the issue. All I wanted to know was why an FD
> rad wouldn't cool the same engine in an aircraft as it does in a car.
> Still don't have an answer! The plastic tanks are a side issue (well
> maybe top & bottom ...).
>
> SNIP
> So I'll go and beat Wally with your replies, and tell him to keep
> digging, instead of musing about aerodynamical cooling issues..
> Meanwhile, I'm going to fit a couple of evap cores in the race car
> and see if they will cool it better ... (}:>)
>
> Cheers guys,
>
> Leon
>
Sorry, Leon
Missed the main point of your question. Regarding why the FD Radiator
might not cool adequately for an aircraft - I think Rusty indicated it
sported approx. 340 cubic inches of core area. IF that is close to correct
then that may revealed a possible reason why the FD radiator might not be
adequate for cooling an aircraft engine.
My rather basic BTU calculations shows that to reject the BTU that an
aircraft 13B (say 160HP) puts out when you are in a climb condition (High
BTU and Low Airspeed) that you need around 640 cubic inches in radiator core
(not counting oil cooler). Once you are leveled off at altitude (less power
being produced and more airspeed) then you should be able to get adequate
cooling with around 340 cubic inches of radiator core. But of course, you
first have to climb to altitude.
While it is true cooling effectiveness is not directly proportional to
radiator thickness (doubling the thickness of the radiator does not double
cooling effectiveness), it is also true that a thicker radiator will
nevertheless still reject more heat than a thin radiator of the same frontal
area - so core volume does matter. Figures I have seen indicates doubling
the thickness of a radiator decreases airflow by approx. 10% and increases
cooling by an average of 25% over the thinner radiator of same frontal area.
So one could argue that going to a larger frontal area radiator is more
cooling effective than going to a thicker radiator (If you have the room for
the larger radiator)
So, don't really know about the FD, but that's my take on it.
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
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