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General control line discussion => Open Forum => Topic started by: Paul Taylor on July 04, 2013, 07:39:15 PM
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What is the cooling ratio for venting a cowl?
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I've always been told (a minimum) make the exhaust hole behind the cowl twice as big as the inlet.
James
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I have been using a 1 to 3 ratio. Heat really expands and needs a lot of area to escape. I got this info from some top flyers. Ask Jim. H^^
Thanks guys.
Hey Ty - Did not want to bother Jim on the 4th. H^^
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1 to 3 (intake to exhaust) is a good number.
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A raised "lip" at the front of the outlet (generically known as a NASA vent) will create a lower pressure over whatever sized hole you've got room for and will accelerate the air through the cooling pathway.
Ted
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I have been using a 1 to 3 ratio. Heat really expands and needs a lot of area to escape. I got this info from some top flyers. Ask Jim. H^^
Not because of expansion. For air to expand that much at 70 degrees F, it would have to get to about 1600 degrees.
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A raised "lip" at the front of the outlet (generically known as a NASA vent) will create a lower pressure over whatever sized hole you've got room for and will accelerate the air through the cooling pathway.
Ted
Ted, are you referring to NACA? They did a lot of work on vents, ducts and endorsed Jack Northrop's pressure cowl work.
As an aside, has anyone attempted application of the pressure cowl principles to these smaller aircraft?