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Old 04-05-2006, 08:32 PM   #1
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Have a problem with knowing how much cool air is required to cool an enclosed engine.Putting together a CMPro YAK 54 Fibreglass Arf.Opening at front of cowl is approx. 5.5 inches and going on the advice of Adrian Page of Page Aviation(Gee Bee Kit etc) I have made a close out very similar to full size plane .Theirs is louvered mine isn't.This close out should direct air directly onto cylinder and head.I don't even have a problem with drilling a 3/4 " hole directly in front of the cylinder on the curvature of the cowl to direct more air onto head.I have heard of a ratio of 1intake of cool air to 2 exhaust of warm air or even 1 to 3.The Glass work and Paint finish is so excellent on this arf I have a problem just hacking holes .So far I have 2 slots 3/4" wide by 4" long to enable the cowl to be put on with exhaust on engine and all so for exhaust to exit cowl.This cowl doesn't lend itself to much hacking sure wish those louvers where functional(not an option)

Hmm! pictures came out in the reverse order that I put them but hopefully they will help.Also the angle of the one with the closeout panel doesn't look as if it allows much air in .It is the angle I took it though
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Old 04-05-2006, 11:16 PM   #2
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Intake seems fine.

You might need some exit space though!!Popcan..

Maybe the more experienced will help here.
Have a great day!!!
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Old 04-05-2006, 11:57 PM   #3
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My inexperience is the same as Popcan's inexperience.

I agree with him. I'd open up the space between your existing exit holes, make sure you round off the corners in any holes you cut. If they are sharp corners, it's liable to crack.

If in doubt, fire that bad boy up and monitor it for overheating. As long as you don't lean it out like crasy, it shouldn't cause a problem for the motor. It just won't run worth a darn. If it runs like crap on the ground, you should open up them holes some more. (Exit first, and your ratio is what I know as well)

I'm no GURU, but I've ran a few underventilated cowls in the past. Tial and error rules my hobby room!

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Old 04-06-2006, 09:38 AM   #4
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With the cutout you are on the right track to direct cooling air towards the engine side, however, this will only partially work. To do baffling correctly, you will need a baffle that is cut out around the engine fins at the centerline of the cylinder head.

See this link from r/c showcase with an article from Ken Spears. It's for a gas engine but the principles are still the same.



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Old 04-06-2006, 10:54 AM   #5
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I have baffled quite few even down to 1/4" x 1-1/4" on my FAI's and Formula 1's. They are all 40 size at high rpm(+20k) You have lots of opening but I would install a baffle around the head for your airflow. Not sure how on this one but you won't need much. I try to get the flow around to the exhaust side to cool that area as that is where the high temps are. The ratio I work on is 1 to 3.
Hope this is some help.
John Davidson
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Old 04-07-2006, 12:37 PM   #6
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Hey guys thanks for all the help and links
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