How do you do it and do you baffle all of them? I fly a number of gassers, mostly single cylinders with the engine protruding from the bottom of the cowl and have never felt the need to baffle them. Recently I was talking with a fellow club member and he said he baffles all of his gassers whether the head is exposed to free air or not. Since I am fixing to build a 35% plane with a 100cc twin (yet to be purchased) I am interested in the proper way to ensure it doesn't overheat. I'm also curious if I have been treating my single cylinder engines wrong all this time. Engine manufacturers never include any information regarding this important matter with their engines, and when you contact them, they tend to be a little evasive in their answers.

All input is appreciated, but experienced input is preferred. Picture examples would be great.

There is a nice article about doing this on the rcshowcase website.

Also BME's site.

CSTEVEC-

I do not baffle the single cylinder engines that protrude either. I baffle ALL cowled engines I have. If I can find some pictures later I will post them.

If the cylinder head is sticking out a baffle does nothing but direct airflow over the crankcase...which isn't needed. If the head is completely enclosed by the cowl, such as with twin cylinder "boxer" type engines and side mounted singles, then build a baffle.

Well now see? Thats kinda what I am talking about. I have five, a ZDZ 40 single in an Extra, a ZDZ 60 single in an Extra, Two Brisons and one RC Showcase Roto 35, all of which are enclosed in cowls but have either their heads exposed or at the very least an air inlet in front of and equivilant to the size of the cylinder, along with an appropriately sized outlet. Now I am about to put a good sized twin into a good sized cowl and since the air inlets are going to be in front of the cylinders common sense says it should take minimal baffling to make sure the air goes where it should. However, I have been hearing all these horror stories and a few tales of baffling that seems to be awfully elaborate in order to prevent damage to the engine. I have seen some mighty nice engines and planes at flying events and it just never seemed that they got that elaborate with it.

That's when you need baffling most. Just because the cylinders are behind the opening doesn't mean any air goes through the fins... as soon as air enters the cowl it's going to take the path of least reistance... a beeline directly for the outlet skiping the cylinders all together. You need something to force that air through the fins.

First and most of all, get a temperature gauge or gun. There will be no way to determine what might be needed without a way to find the temperatures of both heads. The exposed singles don't need any airflow help, so leave them alone.

Air will, like water, normally take the path of least resistance. If it has the opportunity to pass relatively free and unobstructed over, under, or around an engine rather than pass through those restrictive cylinder fins, it will do so. Some cowl designs are better than others in positioning the cylinders in the direct path of cooling air. Some engines may sit too high or too low to benefit from the incoming air. This is where the engine temps come into play.

Get the temperatures of each head with the engine fully exposed, running at a reasonably high, and preferably max rpm. Try to get your measurements from as close to the spark plug as possible. This will most often be the hottest location on the head, and one head will usually be hotter than the other one. Use these temps as a baseline.

Install the cowl and repeat the temp checks. If the temperatures are hotter, and they probably will be, you need a baffle. The baffle will need to be installed in a manner that directs the air through the cylinders and out the back, not just to the cylinders. You may need to build a baffle that completely prevents the air from passing below or around the tops of the cylinders. You may also need to build a "plenum" to properly direct the air through the jugs and out the bottom of the cowl.

Each plane/engine combination is different, so there's not much anyone can do about specific measurements. Good pics can be found at several sites. Brison R/C Engines in the 6.4 engine section is one. The Wild Hare Forum in one of the G-202 threads is another, and the other engine manfacturers site already noted.

Some will jump on this one, but you want to keep the temps at all times from exceeding 325 degrees farenheit. That's even pushing it a little. Engine melt down will occur at somewhere very near 400 degrees f. It won't hurt a darn thing to rum at 300, but do try to stay under 300.