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----- Original Message -----
From: "Marvin Kaye" <marv@lancaironline.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, December 06, 2003 12:22 AM
Subject: [FlyRotary] Re: K&M and Thick Radiators
>
> Posted for "sqpilot@earthlink" <sqpilot@earthlink.net>:
>
>
> Hi, Ed.....While looking at the various evaparator cores in the catalog
at
> AutoZone, I came upon two cores that are 7 inches thick. The one I am
> interested in is 8 3/4 x 8 3/4 x 7 inches thick. If I were to use two of
> these side-by side, I would have a cooling area of around 1071 sq.
> inches.(minus end tanks, etc) Getting the air to flow through a 7" thick
> core might just work in my canard at 200 mph, but of course I'm concerned
> about take-off and climb. I can live with higher speed/lower vertical
climb
> operations, I am most interested in perfecting cruise operations, (which
> should constitute about 95% of my flying) For ground operations I might be
> able to find a small enough diameter fan. If I could make this work, it
> would be a neat, compact installation that would fit rather nicely in my
> SQ2000 without having to modify the cowling, etc. What are your thoughts
on
> an evaparator core that is 7" thick? Thanks in advance for your thoughts
> and opinions. Paul Conner
>
Hi Paul,
Wow! 7" thick. Haven't seen a core that thick - what are they made for?
Here are my thoughts. First, I only know of one individual who attempted
cooling with a radiator that was 6" thick and the results were
disappointing. The basic problem was that the builder simply could not
sufficient airflow through the thick radiator. Now, I am not certain
whether the builder ever flew with it, but I do know that despite several
different approaches, he simply could not get the air to enter the duct
feeding the radiator (used a P51 style duct) while on the ground, including
the use of a fan in an attempt to "blow" air into the radiator. I don't
have any details on fin spacing, number of rows, etc. so hard to make a
direct comparison..
Would it have cooled at cruise airspeed - hard to say, it might have - with
the more dynamic pressure, but best I know it never flew.
The NASCAR radiator's thickness, based on what I have read, range from 2-5"
thick with 3" being a nominal value. The thicker 5" radiators are used for
the tracks with long straight a-ways where they can hits speeds approaching
200MPH. So with this mind, I would probably consider 5" the upper limit in
thickness even for 200MPH. A lot would depend on fin density, less fins -
less dynamic pressure required, but then less heat dissipated.
Then you still (as you recognize) have the challenge of providing sufficient
cooling during take off and climb out. Accepting a higher climb speed and
lower rate of climb would certainly aid the cooling challenge during
climbout.
I can't recall is your 13B going to be NA or turbo? If NA then at altitude
you would probably not produce more than 75% of 160 or around 120HP. My
back of the envelop calculations indicates that at 120Hp 1 evaporator core
at 200MPH would not quite be enough for 120HP at 7500 MSL.. But, that
requires a fuel burn of 11.5 GPH so the question is do you intend to cruise
at that fuel burn rate at 7500 MSL?
If you were actually cruising at a lesser fuel burn - say 8.5 GPH (91HP) at
7500 MSL, then one evaporator core of the size I mentioned would do the job
for cruise, but take off and climbout would require some boosting (perhaps
cowl flaps) of air mass flow for adequate cooling.
So Paul, its really difficult to figure it all out - without more details,
but my gut feel is that 7" is just too thick and that a better choice would
be to limit the thickness to between 3 and 5" with 5 being the maximum.
I am still trying to see if I can dig anything of a practical/useful nature
out of the equations in the excellent K&W study - it looks promising.
FWIW
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
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