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Ross does the SDS EFI system and did 2 videos on
cooling his Subaru engine.
https://www.youtube.com/watch?v=GGXXEgqhmmc&ab_channel=rv6ejguy
It seems him and Tracy agree that we need a thicker core,
then the 1" Paul L kept on suggesting. My coolant rad is
almost as wide as the plane with the 1" truck core.
I'm definitely not happy with my cooling setup, but needed to
get moving and finish the plane. Can sit around all day
talking about it, or start with something and get better in
time. I'm done the flyoff hours in FL and hoping to bring the
plane back to Canada in the spring where I can tinker with it
then. 3D draw things out and get suggestions from people then.
What do you guys think of a belly mount coolant rad? How would
we plum the exhaust out of the way? Keep oil coolant in the
cowl? Or Below the engine?
I think that a good starting point for engineering issues is to look
at what's already been demonstrated as successful. 1" thick rads (or
even thinner) work great in cars, where there's plenty of room and
they spend most of their time barely moving (minimum air pressure
delta across the core). On the other hand, a typical a/c oil cooler
is 3"-4" thick. And if what I read is correct, most NASCAR and other
racers run radiators that are in the same thickness range. Racers
and a/c both operate in the same speed range, with roughly the same
delta-p available (assuming proper diffusers).
My takeaway is that something like a Pietenpol or Cub-type a/c would
benefit from a large area, thin rad, while faster planes can use
thicker cores, which have the benefit of letting the airframe be
more aerodynamically efficient. The compromise is poorer cooling
performance while idling or taxiing.
Location is what you can make work. Ross' system is orders of
magnitude better than his original system. But have you looked at
his original system??... There are things that still could be
improved by quite a bit on his system, like not letting the cowl
exit air feed into the rad cooling inlet. Also note that he still
needed turning vanes in his diffuser. I'm not knocking turning
vanes; I'm using them in both my diffusers. But I've got everything
inside the cowl (very short, curved diffusers), without the
advantage of a really long, straight diffuser. Another thing to
remember is that he's flying a relatively heavy engine, compared to
the stock Lyc in that airframe. Moving his cooling aft likely helped
his CG. IIRC, when Tracy did his 1st rotary install in the -4, he
considered a ventral rad system but because the 13B was *lighter*
than a Lyc, he needed to keep the weight forward. My experience
matches Tracy's; my FWF weight (less fluids) is ~332 lbs, which is
lighter than a Lyc FWF.
FWIW,
Charlie
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