Jerry Hey wrote:
Consider making the bottom of the oil pan from a sheet of aluminum
folded to make up the sides of the plenum. It could be extended
down
to hold (first) the radiator (tabs with nut plates welded to rad)
and
(second) the louvers. This would completely eliminate the VERY
LARGE
problem of how to hang the rad and louvers. Jerry
That is a great idea Jerry. I was just about to say the new Kis
layout
box Schertz could use the stock oil pan:) This might improve the oil
cooling
a bit as well.
Paul Lamar
Paul,
Forgive the novice question but it seems you describe a layout much
like in a car. Oil cooler in front of the radiator, correct? Are
the louvers you describe there to straighten the airflow into the
radiator? Also, has anybody investigated the heat exchangers used
by race cars to cool the oil? Would they handle the pressure I
wonder?
Charlie Smith
KIS Cruiser 4021
The drawback to that scheme is the hot air from the oil cooler is now
trying
to cool the water rad.
It is along side the rad Charlie. Both cores can be 19 inches long.
those louvers are the exit air louvers on the bottom of the cowl.
Anything within ten inches of the back side of the rad will reduce
the air flow. iI is necessary to dump the used rad air directly
to the out side of the cowl.
the Kis has that fat bulge on the bottom of the cowl so that might
work alone.
Paul Lamar
I understand now Paul. My suggestion is do not have the air exit the
underside of the cowl. This is a high pressure zone, and especially
so when the aircraft's nose is pointed up. The exit has to be very
long and shaped properly. Usually what you end up with is a
condition that when you need cooling most (ascent) you have the
lowest amount of delta P available. My idea is to exit the bad air
via louvres on the sides of the cowl. I further intend to seal off
the bottom as much as is possible to prevent air from coming in from
the bottom. The sides are always in the slip stream with the sole
exception of when you slip the aircraft. Usually under those
conditions you are not applying max power. Why do you need louvers
anyway? Don't these engines have thermostated cooling systems?
As for radiator size, I have a friend near here that runs a Ford 3.8
liter V-6 in a BD4 that uses a 12X20 (I can verify these eimension
later) two row core radiator and it is adequate. One row of core was
nearly adequate. Since rotary burns richer, less radiator may be
required. He also had information available on what size openings
worked well. He also has a belly mounted radiator but again, the
exit is quite long to promote air flow in the diffuser. I'll check
into his data later tonight and make it available if there is
interest.
Charlie Smith
KIS Cruiser 4021
I think the high pressure on the bottom is over rated. Lots of people
have been
using bottom exits for years. Including Mike Hersfield who's airplane
is
shown in the picture. Cessna, Piper, etc., etc..
Side exits are good on the cool side of the engine. The big problem
with anything else is the pressure build up in the exit duct unless
it is quite large. That kind of rules out almost all other
configurations
of under the cowl rads. According to my full scale test rig mounted
on top of my dodge Caravan the air velocity through a 2.25" core is 40%
of the forward velocity. Higher for a thinner core. What that means is
you will build dynamic pressure behind the rad unless all objects
are more than ten inches away. When you start to mock this up using
3D software and or actual hardware you will soon find out how hard
that is
to fit inside a cowl. You could go the P51 route but that adds frontal
area and long coolant hoses.
Paul Lamar
Charlie, there is some evidence that we can get by with smaller rads
if we can get the air to pass through them efficiently. My favorite
example is Ian, who was using two 200 cu in evap cores in Australia!
Not to say his cooling system was fully adequate but it was pretty
good. I think on hot days he had to limit climb outs. Based on this,
I will guess that if and when we get the perfect system, the rad core
volume will be less than 500 cu in. My Schirrocco race rad is only
468 cu in.
You have a good point about the bottom of the cowl being a high
pressure area, but there will be low pressure in the shadow of the
louvers. Paul's experiments about two years ago showed this to be the
case. We need to bring together a properly sized inlet, good ducting,
a wedge shaped plenum and generous low pressure area on the back side
of the rad. It is a real challenge. So far, the best solution "in
theory" has been the belly rad exhausting through louvers. But it is
an unproven concept. BTW, engine temp will be controlled by
adjusting the louvers--no thermostat in the system. Jerry
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