I have read several articles/posts re cooling gas engines and I am especially impressed with the work Pe Rivers has done and posted on his site. With that as background, I am curious about how most of you get adequate/proper air cooling to your inverted-mounted 50cc engines-especially when it is in an Extra or Edge (or similar non-round cowled plane).

I am familar with the 2 to 1 rule for exit to inlet area, yet I've seen some installs that cut away just enough of the cowl to clear the head and muffler and they seem to be OK. On most Extra/Edge/Giles cowls, there is a fair amount of the front of the cylinder-head exposed to intake air. Is that enough? Or do they need to follow the 2 to 1 rule too?

I am presently working a cowl mod to my Extra to add a small air dam just aft of the DL50 cylinder to help pull air through the cowl to exit aft of the air dam.

What about baffeling inside the cowl to direct air flow around the cooling fins? I am thinking about putting something just inside the front cowl inlets that would force the air down. Is additional baffeling around the head needed too? Is this overkill??

My goal is adequate cooling to give me reasonably good engine life, but I don't want to do a lot of unnecessary work and add unnecessary weight.

What solutions have you come up with? I would love to see some pics of your installations.

Change that 2-1 ratio to 3 or 4-1 and you'll be closer to the mark.

For the best cooling I prefer an open fire hose and large quantities of cold water. Hard on the plane but by God the engine stays cool

Likely that you'll be just fine with the head exposed to weather under the cowl.

If the entire front of the cylinder is sticking out in the air and you have a big hole in the back of the cowl, it'll be fine.

I'm probably wrong though. Some expert (maybe even 2 or 3) will show up soon enough to tell you how much of an idiot I am, and how you need a stainless steel baffle system thats not more than 3/8" away from any cooling fin on the entire cylinder.

Good grief, Rcpilot, what's wrong with you? It's 3/16"!!!

This works great on my 260. The whole bottom of the plane is a low pressure area, it slants up about 15* I didn't need to bother with ducting around the engine all the air that comes in goes right on the engine and sucked out the back of the can tunnel.

Here's mine...

GP 27% Extra 330S ARF. I cut the air inlet holes shown. The air outlet is just the clearance area factory-cut in the bottom. Engine runs fine.

[sm=lol.gif]

krproton,
That looks nice. Looks like a Fuji. What size?

These aren't the best pics, but you get the idea. This works fine. No special baffling. Notice the 1/2" lip that hangs down all the way around the exit hole. It's perfect for creating that vacuum that we need to pull all the air out of the cowl. Seams to work. No signs of overheating. I'm running it a bit rich for now.

Thanx for all your replies.

Sorrich: It's hard to tell in the pic but how far back from the front of the cowl are the black baffels (or whatever they are) that it looks like you installed?


RCPilot: The 1/2 inch lip on your cowl is what I am trying to create. Mine does not have any factory pre-cut holes. Also, the louvers near the bottom rear of your cowl appear to be functional. Did you cut the slots or did they come that way?

Rcpilet,

It's 1/16" or less, dammit...[8D]

Your all wrong its 3mm.

From what I remember on my fluid dynamic studies, the main thing with any airflow is to ensure that it goes in between the fins and not just over the top of the head, air flows just like water it will take the path of least resistance, so if the head is sticking out the bottom of the cowl trim it as close as possible to the head to force air between the fins and prevent the air from entering the cowl and disturbing the flow from the front outlet, the dam at the front of an outlet will increase the flow from it by creating a negative presure behind it at the opening, look at the big radials and others on full size planes the louvres all function and the total area is somewhat less than 2:1 each subcequent louvre increases in outflow from its neighbour upstream as it is operating in a reduced pressure area caused by the louvre in front.

Mike

They are about an inch behind the lip of the cowl opening. I tried to create a plenum chamber so I would have high pressure air in front of the engine, and a slight vacuum at the exit of the can tunnel to suck the air in across the engine's fins. I know ducting would make it more effective, but what I did works well enough. Our 50cc engines make about 5 hp going full out, if it was a Formula 1 engine it would be making 15 hp, and if F1 used two strokes 50c would be making 30 hp, so our engines are loafing along and really aren't highly stressed.

This link might help:

http://www.supercoolprops.com/articl...delengines.php

This is how I am preparing my 58cc tow plane. The engine will have to work hard at low speeds. The cool air enters the cylinder fins, and is guided out of the cowl in a rear chute.
Cool air for the rear carb can enter the cowl on both sides of the shute, and will not mix with the hot air.

The complete build-along is [link=http://www.prme.nl/forum/viewtopic.php?t=195]here.[/link]

Thanx Pe. That's just what I needed to see.

Rich

Those louvered slots were factory cut. You can't see it real good in the pics, but they are all angled back to create a vacuum.

[/quote]

[sm=lol.gif]

krproton,
That looks nice. Looks like a Fuji. What size?


[/quote]

It's a 43cc.