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Air hole in cowling (pics)

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Old 09-11-2012, 09:25 AM
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a70eliminator
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Default Air hole in cowling (pics)

How much of this cowling do I neeed to take out for adequate cooling airflow? I have an area penciled in if it shows up. Ever seen louvers cut in the sides?
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Old 09-11-2012, 10:19 AM
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Default RE: Air hole in cowling (pics)

5 to 1 is the industry average ratio to area coming in vs. area going out. 

My $.02

Ray W.
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Old 09-11-2012, 11:20 AM
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Default RE: Air hole in cowling (pics)

Getting the air out is very critical in order to cool the engine, you must have a good flow. I had always thought it was 3 to 1 Say just for an example, 1 inch hole in the front of the cowling you will need a 3 inch hole for the exit. So measure what the hole size is in the front of your cowling and cut the exit openings to proper size. It could be 5 - 1 but that seems rather large but you get the idea.
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Old 09-11-2012, 11:29 AM
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Default RE: Air hole in cowling (pics)

A 3:1 ratio is more in keeping with the hobby's general rule of thumb.

Karol
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Old 09-11-2012, 12:21 PM
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Default RE: Air hole in cowling (pics)

Agreed, I use about 3:1
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Old 09-11-2012, 01:23 PM
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Default RE: Air hole in cowling (pics)

Depends on the airplane, cowling shape, baffling and engine.

If baffled correctly to force the air through the cylinder cooling fins, you can get away with as little as. .5:1 (yes 1/2 the exit area as the inlet). If you dont want to go through all that trouble, 3:1 is the good "works for everything" number
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Old 09-11-2012, 03:48 PM
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Default RE: Air hole in cowling (pics)


Been trimming away a little at a time and notice alot less rigid now, not sure how much more i can take without adding some stiffeners of some sort, I'm hoping this is will do, maybe I'll do a couple 1/2 inch wide slits somewhere just to get that air ratio up a little more, it is a 4 stroke glow engine.
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Old 09-11-2012, 04:01 PM
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Default RE: Air hole in cowling (pics)


Quote:
ORIGINAL: a70eliminator


Been trimming away a little at a time and notice alot less rigid now, not sure how much more i can take without adding some stiffeners of some sort, I'm hoping this is will do, maybe I'll do a couple 1/2 inch wide slits somewhere just to get that air ratio up a little more, it is a 4 stroke glow engine.
Just looking at it without measuring I would say you might need a little more exit area opened up. Don't know if you do this already but when mounting any of my cowls I drill a hole about the same size of small yellow nyrod and put thin ca on it and tap it in the hole then cut off excess. This way the screw will not back out and you will never have thread holes that get sloppy. Next thing I do is use the washer that has the rubber backing attached to it and when you tighten the screw it will not back out because of the nyrod and the rubber on the washer will hold the cowling a LOT better and you will not get the screw hole in the cowling enlarged.
That's my 2 cents worth
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Old 09-11-2012, 04:15 PM
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Default RE: Air hole in cowling (pics)


Quote:
ORIGINAL: a70eliminator


Been trimming away a little at a time and notice alot less rigid now, not sure how much more i can take without adding some stiffeners of some sort, I'm hoping this is will do, maybe I'll do a couple 1/2 inch wide slits somewhere just to get that air ratio up a little more, it is a 4 stroke glow engine.
What you have here will be just fine. Remember, it's a glow engine and not a gasser. Glow runs cooler.

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Old 09-11-2012, 04:21 PM
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Default RE: Air hole in cowling (pics)

Now he tells us, anyway we should have been more observant and seen the pushrod tube sticking out in the pic he sent

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Old 09-11-2012, 07:52 PM
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Default RE: Air hole in cowling (pics)

You would do better to put some baffles around the engine so that air is forced to flow through the fins and not just around the engine. I have an OS FS-120 Surpass in my P-47 and it stays very cool. My air inlet is just the space around the dummy engine cylinders at the bottom but all the air goes through the engine cylinder fins.
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Old 09-12-2012, 04:00 AM
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Default RE: Air hole in cowling (pics)

I'm trying to guess the plane ?..Weeks special, pitts..?
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Old 09-12-2012, 05:50 AM
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Default RE: Air hole in cowling (pics)

I suggest you check out this sitehttp://prme.nl/forum/viewforum.php?f...bfed2dc01f99d1Pe is very knowledgable in this area and helped me out alot. Just cutting a bigger outlet is not always the solution and and can actually make it worse, besides ruinning the looks of a good cowl. Baffeling is the way to go, just think about your weedwacker, they are baffled to provide max cooling. Good luck.
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Old 09-12-2012, 09:31 AM
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Default RE: Air hole in cowling (pics)


Quote:
ORIGINAL: Fleet

5 to 1 is the industry average ratio to area coming in vs. area going out.

My $.02

Ray W.

wrong!!!!

a few guys hit on it here. Take a little time and make a baffle that is glued to the front of the cowl and make the baffle where it is placed just inline with the cylinders. do this so that the baffle will goto the the cylinder and be in the middle of the cylinder (the direction the piston moves).

Air is a fluid and think of it as water flowing through the cowl. look at your inlet holes and then look where your exit hole is. The air will enter the inlet and then go straight to the exit as best it can. this will only allow the air to touch the front lower section of the cylinders. by adding a baffle as i described it will force the air to flow through the fins on the front of the cylinder and most of the air to flow over the top and down the back side of the cylinder down to your exit.

another thing about air is that it doesnt like being forced to do anthing but go in a straight line. think of how you can create a slight negative pressure at the exit. this will help pull the air where you need it. just by adding the baffles as i described you will increase your cooling of the engine by 100-200% over what you have now.
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