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For me, a Lancair is both beautiful and fast. Many put in
thousands of hours sanding and painting to enhance their plane's beauty, but if
they would put in one-tenth that number of hours designing and building an
efficient and low-drag cooling system, they would have the best of both worlds.
I have seen some of the most beautiful birds, on the outside, have such horrible
gunk for a cooling system. Don't use scat tubing anywhere; its pressure drop is
horrendous. Put in a small blast tube for the alternator, and
also for the fuel pump and gascolator to prevent vapor lock. Wrap the
cylinders with fiberglass or carbon fiber to keep the air in close contact with
the fins. This increases your cooling efficiency and so requires smaller inlets
with less drag. You can use Safety Poxy for this, or RTV, or hi-temp epoxy from
someone like Master-Bond. Are your cylinders running less than 360F?
Too cool! Close down your inlets! You want the cylinders at about 385F for
best efficiency. These aircooled cylinders have incredible piston clearances.
They are designed to give the best performance in the 360-400 range. Use
it! At the bottom of the cylinder, don't have a sharp edge on the baffle
but roll it outboard at least 180 deg to keep the air from separating as it
emerges. Cooling air that flows past wires, tubes, motor mount, and the sharp
edge at the bottom of the firewall to get out of the cowling requires
a greater low pressure to extract it - drag! Put cooling air outlets right below
the cylinders or duct it out. For some reason the inlet and plenum are well
designed, and then it's just assumed the air will find its way out! Don't
steal cylinder cooling air from the upper plenum to feed the oil cooler.
Feed it with a separate inlet with a diverging duct, then give it a converging
duct and outlet pointing to the rear; don't just dump it into the area ahead of
the firewall. Don't use the so-called "NACA" duct unless you understand its
pressure recovery vs duct flow ratio. It's just one of three of the family of
"submerged" ducts. Its proper name is divergent curved-wall submerged
duct. There is also straight-wall divergent submerged duct and a parallel-wall
submerged duct. Is the outer lip of your NACA duct sharp or is it rounded
and shaped like an inverted leading edge? If it's sharp, it's
wrong! Do you have intercoolers? Look what Darryl did with his. He exhausts
each of them through a converging nozzle on top of the cowling facing the
rear. Do you know how a jet engine works? You add heat to air which increases
its energy and then employ this added energy to increase the exhaust velocity to
create thrust. Your cylinder cooling fins, oil cooler, and intercoolers are, in
effect, little jet engines. Use that heat to reduce your cooling drag. Use
the exhaust to help extract the cooling air. Why just pump that 1/3 of the
fuel's energy overboard. A properly designed augmenter will decrease the
xhaust outlet temperature and also slightly muffle the exhaust sound
without having resonant amplification. There are other ways to make an augmenter
than the tube variety. Charley Airesman in his Sub-powered EZ uses a tube-type
augmenter to pull air through his radiator. No overheating on the ground in
his EZ! 'Nough said!
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