Cooling vent

[Paul Taylor]

What is the cooling ratio for venting a cowl?

[James Mills]

I've always been told (a minimum) make the exhaust hole behind the cowl twice as big as the inlet.

James

[Paul Taylor]

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.

Thanks guys.
Hey Ty - Did not want to bother Jim on the 4th. 

[Randy Powell]

1 to 3 (intake to exhaust) is a good number.

[Ted Fancher]

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

[Howard Rush]

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.

Not because of expansion.  For air to expand that much at 70 degrees F, it would have to get to about 1600 degrees.

[Bill Johnson]

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?