Message-ID: <000401c3b3dd$8f157bc0$1702a8c0@WorkGroup>
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2772951@logan.com>
Subject: Re: [FlyRotary] Re: radiator size
Date: Wed, 26 Nov 2003 00:24:25 -0500
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
Content-Transfer-Encoding: 7bit


> >
> > At 03:27 PM 11/19/2003 -0600, you (Jim Sower) wrote:
> > >Isn't the conventional wisdom 3 cuin/hp?  Al Wick's Subaru is about 2.5
> > >but his
> > >Soob doesn't have the cooling requirements of a rotary and I believe he
> has a
> > >really nice (efficient - good recovery) plenum.  I would think 3
minimum
> > >unless
> > >you have really good ducting and plenum.
> > >Just a theory ... Jim S.
> >
> > Hi, Jim....sorry for the delay in responding.  Regarding Al Wick's
> radiator installation, he broke all the rules.  He just put the darned
> radiator in front of the NACA inlet scoop, and has NO exit plenum. After
the
> air passes thru the radiator, it just slowly finds it's way out the rear
of
> the cowling. Odd thing is that he can do extended full power climbs
without
> overheating. Go figure ! I should be so lucky.  Paul Conner
>
> >

Since Al Wick is reportedly cruising at 200 mph on 5 gph producing around
55HP, he may be able to climb out on less power as well. It  all depends on
what his fuel burn rate is on his extended climbout.  If you produce power
compariable to a rotary, then you will need cooling capacity to accommodate
it.  So depending on a particular configuration, you might get great cooling
simply because you are not producing much power - not necessarily a
desireable outcome.  Clearly if your cooling requirements are less, the
design features of your cooling system may stray further from "good"
practices without serious adverse effect.  On the other hand, if your
installation configuration (power/airspeed) place heavy demands on your
cooling system, then failure to following "best" practices could lead to
cooling problems.


Given that you are producing X amount of power, its going to take Y amount
of cooling period!.  The upper external limiting factor for cooling is going
to be bounded by the mass flow through your radiators.  Regardless of
whether you are using large thin radiator or small thick ones, if you do not
have the minimum air mass flow through them adequate to carry away the waste
heat - you will eventually over heat.

From experience it appears that 4 cubic inches per HP produced is a good
ball part figure for sizing your radiators for a rotary.  So 160 HP x4 = 640
cubic inches which happens to be two 9x10x3.6 evaporator cores (not counting
side tanks).  We know that size radiator has the capacity to cool a 160 HP
(possibly more depending on airspeed) provided you get the mass flow through
it.  Now getting the mass flow through it is not necessarily a trival
problem - especially for you pusher folks.

But,  if getting the required air mass flow through a 640 in^3 radiator is
problematic for an installation, it is doubtful (in my mind)  that going to
a larger radiator is going to buy you much.  If your configuration
constrains airflow to the point it is  inadequate for removing heat from
your 640 in^3 radiator then I don't see how going to a larger radiator will
buy you anything as you won't have the mass flow to support it either.

So, I would suggest caution about assuming that what appears to work for
someone else is also going to work for you - unless you have a near
identical configuration producing near identical power

FWIW

Ed Anderson.