Bill Freeman wrote:
Jerry,
Long EZs are cooling O320s (one I know has been souped and dynoed to
176 hp) with a belly mounted NACA duct. Mine is about 4" deep and about
12" wide (from memory, I can measure it if you want) at the outlet. These
belly
NACA ducts work pretty well because they are in a positive
pressure field when
climbing. I have a moveable floor in mine, set to about 3" deep since I only
need to
cool 108 hp. Seems like a 12-14" wide and 4-5" deep NACA duct with
a good diffuser would be a good starting point for a rear fuselage radiator
system. An upright radiator with a bell type diffuser dumping out
into the rear
fuselage with a pair of exits under the horizontal stab seems worth a
> try. Make the ducts out of two plies of BID glass over a simple
styrene foam
mold covered with duct tape and melt out the foam with gasoline when done.
Mount the rad to the fuselage tubes, sealed to the diffuser, which is sealed
to the
NACA duct.
Might be good to check out what the pressure inside the rear fuselage is at
cruise
in a std Tailwind. If you have a friend with one flying, ask him to put a
tube into
the aft fuselage, run it up to the cabin and connect to either a water
manometer
connected to a static port. This is a critical piece of info. If the
pressure is high, you'll need to make an outlet duct and run it to a lower
pressure location on the aft fuselage. This would be best done with a
pressure survey on a flying Tailwind, looking at the
exterior pressures at various locations. I would expect the top surface to
be low
pressure, but that is a pure guess. You need an outlet location that is low
at both cruise and climb.
What do you think, Paul??
Bill Freeman
Sounds like a good program to me Bill. I wholeheartedly agree.
Nothing like real world, full scale data.
Paul Lamar
Thanks, Bill, Amazing, only one day ago I had exhausted every
possibility I could think of. Now I have some very promising paths
to study. How long is the ramp on your NACA duct? The formula in
Sport Plane Builder calls for a 7º ramp. A five inch deep NACA
duct with a 7º ramp is 40.7" long. I wonder if the ramp can be
steeper? I don't recall ever seeing extremely long ramps on any
NACA ducts. I don't know how to conduct a pressure survey on the
exterior of a flying Tailwind. Directions would be most appreciated.
However, I am confident that I can achieve a low pressure
differential in the fuselage aft of the Rad.--Thanks again, Jerry
Don't forget Bill is only cooling 109 HP.
Check the web site Jerry for a sketch on a water manometer.
You can plumb into the static pressure tap on your altimeter
for a reference pressure. Use a bit of porous foam on the
ends of the pressure measuring tubes. You can also use a short
piece of small tubing with three or four small holes drilled
around the ends on the side of the tubing. Pinch the tube shut
or weld it shut. Place the end of the measuring tube where ever
you want to measure the pressure. Always measure the pressure
at the same airspeed.
Paul Lamar
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