Alan Tolle wrote:

Paul, here are two more data points for your chart on water radiator size:

The single radiator in the Powersport RV-4 measured (in inches) 21 wide by
24 tall by 2 deep for a whooping total of 1008 cubic inches.  Talk about
overkill, but then theirs was the first in the air, and too big was better
than too small.   A very effective cowl flap kept the temperatures where
they belonged without the use of a thermostat.   The radiator was an all
aluminum Griffin unit.   As you know the unit was mounted transversely
behind the engine with the top tilted back toward the firewall.  Air flow
from the pressure plenum went straight into the radiator and made a 75
degree bend down the firewall to the cowl flap.  There was a turning baffle
at the top and the bottom of the firewall.  The bottom one was very much
like what you observed on Tracy Saylor's  RV-6

The dual radiators in my RV-3 were each 14 long by 12 tall by 2 deep for a
total of 672 cubic inches.  They were again mounted between the engine and
the firewall but were oriented vertically with long dimension fore to aft,
and located towards the sides of the cowl.   Airflow from the pressure
plenum had to make a 90 degree bend into and out of each radiator.  As I
think you noted, the air flow  through the radiators is so slow (about 20
mph by actual measurement) that the bends don't cause any problem.  There
was an exit baffle at the bottom of the firewall as described above.

I explained in an earlier post that the double radiator installation in the
RV-3 was necessitated by a long induction system which projected behind the
engine in the Powersport 180 superlite.  For what is is worth, if I were
installing a radiator for a 13B in the RV-3 today I would use a single unit,
custom made by Giffin, with dimensions of 21 wide by 14 tall by 2 deep,
mounted transversely like the RV-4.  The dual radiators were plumbed in
parallel and designing a system to divide the water flow out of the engine
equally to each of the two radiators was a challenge in itself.  You don't
just Y a pipe.  The mounting, plumbing, and baffling are all much simpler
with a single radiator.

Paul, you must have missed the post some time ago by David Carter that Ross
Aero can provide a gear box 11 inches long.  The Powersport gear box was
just under 10 inches.  Close enough.  So it would be nice if you (and it
sounds like Jeff helped) would run the analysis of the behind-the-engine
arrangement, so that future builders can know that options are available.

After all, the behind-the engine arrangement has been test flown for the
same total number of hours (800+) as the total number of hours flown by the
two-radiators-up-front arrangement in the three aircraft which you did
consider.  There are some concrete data on the cooling effectiveness of
installations in the aircraft which have already been flown.  We should all
at least try to make use of all the data available.

Thanks Allan. I feel we are slowly getting a handle on this. I see
no real reason why the engine and prop can not be moved forward as 
long as the weight and balance can be worked out. A little extra
work on the cowl perhaps. I will have to check with Chris Ross on 
the current availabilty of the 11 inch PSRU. I recall that but I just 
forgot to follow up on it.

BTW I just found out that the Allison engine used in the P40 had
a similar PSRU to the PowerSport unit. I will scan a drawing of it
and upload it soon.
 
Paul Lamar
 
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