----- Original Message -----
From: <peon@pacific.net.au>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, February 05, 2004 5:14 PM
Subject: [FlyRotary] FD Rad Cooling Capacity was Re: [FlyRotary] Re: Engine.


> Hi Guys,
>
> On 4 Feb 2004, at 1:39, Finn Lassen wrote:
>
> > Russell Duffy wrote:
> >
> SNIP>>
>
> .  The radiator in the car would be too small for aircraft use.
> > > Some people are using a large aftermarket radiator, though
> most are
> > > using air conditioner evaporator cores.
> > >
>
> Hmmmmmm, ... I was discussing this the other day with "Wally
> the muddle headed wombat"  and we were just pondering why on
> earth an FD radiator wouldn't cool a 13B turbo in an aircraft?
>
> It goes without saying that providing of course, you fed it sufficient
> air in a properly designed dukt - that man at that "other place"
> knows how to do it - he's been preaching it for years - nice big thin
> rads).
>
> Wally reasoned that as they seem to work OK on 300 + neddie
> ekranoplans (aka porsche beating FD RX7's) down Conrod straight
> at Bathurst (130 - 140 + MPH,  albeit in ground effect),  they
> should work in an "ordinary" aircraft as well.
>
> They also seem to work OK at idle and heavy traffic, even on our
> hottest Sydney daze.  Only downside is that the plastic header
> tanks are known to split,  which can be interesting!  So can you
> please enlighten us??
>
> Cheers,
>
> Leon
> (aka The Rotary Duck - ordinary ducks just go "quack,  quack" -
> this one's a bit "daffy").
>

Hi Leon,

    Don't know if it  would cool an aircraft application or not, but I
strongly suspect that if it can cool a racer full out then it probably can.
Given sufficient surface area and air mass flow through it almost anything
will cool.  I suspect that the reasons a lot of evaporator cores are used
include 1:  They do cool the 13B NA just fine,  2.  Their small size
provides flexibility in placement compared to one large radiator
(particularly for tractor installations). 3 They are designed for much more
pressure than would ever see in a radiator application  4 They are very
cheap relative to a custom radiator  5 There are plenty of them around in
the junk yards 6 They have no plastic or epoxy

A somewhat more debatable view  is - that since drag is proportional to
frontal area -  that a larger radiator may incur more drag.  However, that
view is offset by the fact that a smaller radiator must have higher air
velocity through it to get the same mass flow and therefore cooling effect
and drag is proportinal to the square of the air velocity.  So with perfect
ducting/diffusion  in both cases the larger radiator supposedly wins with
less cooling drag, since the same cooling effect can be had with lower flow
velocity through a larger radiator.   However, if you ducting is less than
optimum and your velocity through your larger radiator is higher than
optimum then the larger radiator can indeed be a higher source of drag than
a smaller radiator.  Also a smaller radiator might enable packaging with
reduced external (airframe) drag.  In fact, they are just the right size to
stick under the cowl behind the traditional twin ducts each side of the
propeller.


If cooling drag is a large part of total drag (as it frequently is in higher
performance aircraft) then ducting diffuser and core size all become very
important - on the other hand if cooling drag is a small part  (like perhaps
on a liquid cooling bi plane) of the overall drag, then I would think
cooling drag is less of an consideration - just cool it.

FWIW

Ed Anderson



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