Message-ID: <000c01c3c706$61368500$1702a8c0@WorkGroup>
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2897924@logan.com>
Subject: Re: [FlyRotary] Re: evap core versus radiator
Date: Sat, 20 Dec 2003 09:34:30 -0500
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> >
> > Hi Paul,
> >
> >     No - sorry if I misled you.  Unless the pass several weeks of
studying
> > K&W are for naught, its fairly clear that for 160HP at 120MPH you need
two
> > GM cores.
>
> Thanks, Ed.....I was relatively certain that it would take two cores....I
> was just fishing for that last ray of hope, that there might be a small
> frontal radiator or evap. core that could magically do what others have
not
> been able to do. Proves the old saying....If it sounds too good to be
> true....
>       After putting my bottom cowling in place (several times), and making
> cardboard radiator core "dummies", the most practical radiator I came up
> with measures 16 x 10 x 3.5 inches overall. C&R Racing said they can make
it
> for me with only 1 inch tanks, leaving more area for cooling fins. That
> would leave a total core area of 14 x 10 x 3.5 inches. That size would fit
> in my cowling without modifications, and very minimal effort to build the
> plenum.  They quoted a cost of $500.00, including mounting two -16 male AN
> fittings, one 1/4"npt female drain hole, and mounting brackets as needed
for
> my installation. It is all aluminum, and no epoxy. The radiator might be a
> little small for takeoff and climb?, but might have a chance of cooling
130
> or so HP at cruise?  A bit pricey, but maybe I can finally put this time
> consuming part of the equation behind me and continue getting this thing
> ready for flight. The other alternative I have is to have the radiator
made
> 16" x 13" x 3.5", (core area of 14 x 13 x 3.5)  but that will take more
> effort in trying to get the plenum stuffed in the cowling. Take care.
Paul
> Conner
>


Ok, Paul

    Using the K&W formulas, I calculate that the 14x10 core area would
handle 120HP at 120MPH TAS, you would need to get to 160 MPH to get the mass
flow to handle 160HP.  On the other hand, the 14x13 core could handle 160 HP
at 120 MPH. So that additional 42 in^2 would appear to make a difference.
However, are you really going to be climbing out producing 160HP?.  While my
13B will apparently produce around 180HP on take off, I am throttled back
after about 1500 ft of altitude gain to approx 130HP for initial cruise
climb and power continues to decrease as altitude is gained.  So I would
think your decision needs to look at the difficulity of cramining in the
larger core vs a careful examination of the power you will be
needing/generating.

I calculated a power climb profile assuming you took off a 160 HP and never
pulled back on the throttle until 4000 MSL.  The decreasing density would
have reduced your power to approx 140HP at 4000 MSL.  It averaged out to
156HP to 1500 MSL, and averaged 150HP to 4000 MSL.  However the average from
1500 MSL to 4000 MSL was 144HP.  So your heat rejection needs decreased
automatically as you increased altitude..  To maintain cooling with your
larger core, you would still need 120MPH up to 1500 MSL - which would likely
mean you would be running some cooling capacity deficit up to that point.
From 1500MSL the cooling picture gets better with only 113 MPH required for
cooling and by the time you get to 4000 MSL you could get adequated cooling
with only 110 MPH air speed.

Since, of course, you would normally be increasing airspeed which means >>
120MPH you should find adequate cooling for the flight regime - the
exception being up to 1500 MSL and 120 MPH. So you could expect your coolant
and oil temps to be elevated by the time you get to 1500 MSL and 120 MPH,
but should start to fall after that.

Having said this, it is clear that you would need good airflow ducting to
get the optimum cooling.  Although my calculations does assume a "realistic"
ducting system (meaning losses are encountered), so you could possible do
better than these calculations.  If you built a near perfect ducting system,
your core frontal area could be reduced by appox 33%.  Or another way of
looking at it is you cooling system could reject 33% more heat than my
calculations show.  But perfection is hard to come by {:>)

Ed Anderson


Ed Anderson