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Posted for "Paul Lipps" <elippse@sbcglobal.net>:
Speaking of cooling, here's some shots taken by Peter Garrison, except
DSCN1527 and 101-0181, of my cooling/exhaust system. Those two were taken when
the cylinders were wrapped with aluminum, whereas now it is carbon fiber. The
inlet ducts feed the cylinders between the push-rod tubes. The cylinders are
wrapped from the tubes into the box below the cylinders, where the exhaust is
introduced; that's the little curved duct that feeds into the main one. The
combined flows exit the cowl through the 5" X 2 1/2" stainless duct with a
variable exit aperture that can close down to 5" X 1 1/4" in cruise. Mixing
the exhaust with the cooling air drops the temperature to about 400F-550F and
quiets it down somewhat. It takes out the sharp bark you usually hear on
un-muffled experimentals and softens the noise. The inlets are 4" X 1 1/2" for
12 sq. in. total inlet area for 125hp. Pict 0011 shows the lower portion of
the oil-cooler inlet-duct, which is fed from an external stagnation/pitot
duct, not a "NACA" or submerged-divergent duct. Oil temperatures run 90C to
100C above ambient. On the oil-cooler outlet duct, you can see the arm which
operates a flapper valve to divert the heated air into the cockpit for cabin
heat. CHTs are usually:#1-180C; #2-160C; #3-200C; #4-190C. #3 will sometimes
get to 220C/428F in a climb on a hot day when there's an inversion with
80F-100F at 1000' to 3000'. The others may get to 190C-200C, except #2, which
seldom exceeds 170C. I'm making a new cowl with an 8" prop extension that will
have a single 12" long by 1" high annular inlet right behind the spinner on
the top of the cowl which will feed a duct that smoothly divides and feeds
both cylinder banks. I hope to get better CHT match with it. There are two
other small cooling inlets. One is a 3/8" tube just ahead of the alternator
for its cooling, and another is a 1" X 1/4" on top of the cowl right behind
the spinner. It feeds cooling air to the four ignition coils on top of the
crankcase through 1/4" tubes, cooling air to the two LSE ignitions on the
firewall through 3/8" tubes, air to the oil separator through a 1/4" tube, and
air to the fuel pump and gascolator through 3/8" tubes to prevent vapor-lock.
So far, vapor lock has never happened, though it did happen to me several
times in my friend's Lancair at some of these 100F airports. All of the air in
the cylinder ducts is contained within the ducting and none gets out into the
rest of the cowling.
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