Cowl Design: "X" in = ? out.
01-27-2003, 12:26 AM
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Cowl Design: "X" in = ? out.
Is there a particular rule about open frontal area vs. exit area on a cowl? I am building a cowl for a scratch plane. I will have about 20 square inches open area in front. By open are I mean air will be allowed to flow into the cowl. How much open area should I have for the air to exit the rear of the cowl?
Ryan
Ryan
01-27-2003, 02:29 AM
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Cowl Design: "X" in = ? out.
I'm assuming by 1.5 you mean the outlet area is 1.5 times the inlet area. Would using 1:1 or less hurt in any way e.i. flight performance, damage to cowl due to ram effect, etc?
Ryan
Ryan
01-27-2003, 05:10 AM
#4
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Cowl Design: "X" in = ? out.
"Would using 1:1 or less hurt.."
Is 1:1 less than 1.5?
.
Actually no one knows, with any real authority.
I've seen very successful planes with 0 inlet area, and 0 outlet area, and a very close helmet cowl, with only the cylinder head exposed.
Total running time maybe 20 seconds... FAI speed planes at the 1960 FAI Internationals in Budapest.
Bill Wisneiewski's "Pink Lady" had such a cowl. And he won.
.
Your 20 inch opening is a LOT. That's probably a large airplane. With some spillover to be expected out the front due to heating of the air and consequent expansion inside, and the air has to go -somewhere-..
By why be parsimonious on the outlet?
Just because there can be a lower limit doesn't require that you go there.
Is 1:1 less than 1.5?
.
Actually no one knows, with any real authority.
I've seen very successful planes with 0 inlet area, and 0 outlet area, and a very close helmet cowl, with only the cylinder head exposed.
Total running time maybe 20 seconds... FAI speed planes at the 1960 FAI Internationals in Budapest.
Bill Wisneiewski's "Pink Lady" had such a cowl. And he won.
.
Your 20 inch opening is a LOT. That's probably a large airplane. With some spillover to be expected out the front due to heating of the air and consequent expansion inside, and the air has to go -somewhere-..
By why be parsimonious on the outlet?
Just because there can be a lower limit doesn't require that you go there.
01-27-2003, 03:22 PM
#6
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Cowl Design: "X" in = ? out.
At a 1:1 ratio, the air in the cowl will get hot, expand, have no where to go, and dam up the flow, therefore no cooling. You are better off blocking off part of the inlet, so that any flow is forced to travel around the object to be cooled.
Les
Les
