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 ...).

Additionally,  an important thing to remember is that a rad that is
twice as thick won't cool twice as good.  Especially at slow
speeds.  Which is a REAL issue here in Oz in summer.  

It can be 50 Deg C out on the tarmac during taxi and run-up.  
Nothing good has ever come of boiling a rotary,  and they don't
really like running much higher than about 115 Deg C. They WILL
run at those temps,  but they definitely don't like it,  especially
turbo engines.  

Turbo rotary engines tend to be prone to detonation at high coolant
temps (for some obscure reason)  ... (}:>).  Nothing ever good
came of detonating a rotary either ...  So we need to keep the
sucker cool on the ramp before take-off.

As for drag,  and frontal area,  I'm from the "P51s R US" school of
cooling.    I like the idea of belly scoop,  a nice diffuser,  a big rad,  
and big (adjustable) dump door.  Most efficent way of cooling a
watercooled aero engine ever.  

The fastest piston engine aircraft at the time (502 MPH),  was a
CAC CA -15 (looked like a Mustang on steroids),  and it had a
belly scoop,  and a dump door.

http://www.dropbears.com/av/KFXart/articles/CA15pic.htm
http://users.chariot.net.au/~theburfs/ca15MAIN.html
http://dropbears.com/av/KFXart/articles/ca15.htm

The Martin Baker MB-5 was no slouch either,  and it was
configured exactly the same - design convergance??.  

http://www.martin-baker.co.uk/history_mb5.html
http://www.samoloty.ow.pl/str210.htm

No where near as pretty and graceful as a Spit,  but the
quintessance of aerodynamic pulchritude nevertheless.  
Unfortunately,  jets outclassed them and they were both  
unceremoniously scrapped.  What a shame.

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