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