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Posted for "Paul Lipps" <elippse@sbcglobal.net>:
Colyn! Sorry, my ducting was that way from the get-go, so I have no
before-after. My original cooling inlets were 4" by 2", but with my cylinders
not getting up to temp, I had to close them down to 4" by 1 1/2". That's a
total area of 12 sq. in. for 125 hp at 201 mph TAS at 10,000' dalt. If I could
go a little faster I could decrease them more, since I'd intercept more air at
higher stagnation pressure! My temp distribution is not good, with one of them
I can only get up to 160C max. My hottest one runs 190-200C, right where I
want it.
I estimate that wierd prop's efficiency at 90% in cruise, 80% to 84% in
climb at 110 mph IAS, 2400 rpm. Here's some pix of the props I designed for
the two winning Reno Biplanes. Tom's "Phantom" qualifying speed went from 220
mph in 2003 to 241 mph in 2004 on 245 rpm less. That's a 40% increase in
efficiency. Jeff Lo's "Miss Gianna" went 10 mph faster on 100 rpm less than
his best-of-two Macauley metal props, for a 17% efficiency increase.
Sorry, too, I don't have any data about piston clearance and blow-by vs
temp. I just think that Lycoming, Pratt, and Continental know what they are
talking about when it comes to recommended temperatures, and if someone or
some group has come up with something better, the manufacturers and/or the FAA
should speak up on the subject.
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