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Hi Paul-
I can't answer your question about only cooling the heads, but you could read various NACA/ NASA studies on cylinder cooling. These are ones I read many years ago and only vaguely remember. Most date to WWII, when this was a vital subject:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810013485_1981013485.pdf investigates cooling for horizontally-opposed engines.
http://ntrs.nasa.gov/search.jsp?R=19930093136 is NACA-WR-L-767, aka ARR 3H16, dealing with cylinder cooling.
http://ntrs.nasa.gov/search.jsp?R=19930081408&hterms=naca-tn-620&qs=Ntx%3Dmode%2520matchallpartial%2520%26Ntk%3DAll%26N%3D0%26Ntt%3Dnaca-tn-620 is NACA-TN-620, investigating cylinder baffle design.
http://ntrs.nasa.gov/search.jsp?R=19930091858&hterms=naca+779&qs=Ntx%3Dmode%2520matchallpartial%2520%26Ntk%3DAll%26N%3D0%26Ntt%3Dnaca%2520779 is NACA-TR-779, effect of design of cooling fins.
Based on what I got out of them I measured the cooling fins, made a CAD drawing, calculated the air passage areas, then designed a tight-fitting set of aluminum shrouds (to increase cooling surface area) for an IO-360 Lycoming. Because of the installation I chose to try an updraft system. Yes, heat off the exhaust would have been an issue but I was young(er) and figured I could come up with something... Chances are if I'd ever fired it up the engine would have been toast but perhaps someone out there could do better. Something along those lines might work well with a plenum, mainly by directing flow around the bottom of the cylinders and heads. -Bill Wade
-----Original Message----- From: Paul Miller
Sent: Wednesday, January 23, 2013 8:27 AM
To: lml@lancaironline.net
Subject: [LML] Plenum only to Cylinder heads
Thinking about all the air leaks that typically show up in the IO550 Legacy cowl. A full size plenum has been accomplished by some folks. What about a plenum that went from the inlet and simply exited onto the three cylinder heads on that side? It would be smaller, maybe easier to build, lighter. You could use a silicone seal where it would fit on the barrel to keep a tight fit and wires could be kept away I believe.
How much better would the cooling be and would the lack of air to the rest of the crankcase or cylinder bases cause problems? Still need to route some bleed to the accessories and oil cooler which we do already but I'm talking about ducting the inlet straight to the head and avoiding most of the leakage points and perhaps achieving better overall cooling.
Second: Why does the alternator duct exit below the engine? The exit air may be warm but certainly less than CHT so why not duct the alternator exit back into the upper deck and regain the pressure loss that goes straight through the alternator and bypasses the cylinder fins?
Thoughts?
Paul
Legacy
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