I & C Tech

Is proper cooling harder to achieve, i.e. requiring good baffling, when running at higher mix ratios and/or switching to synthetic?

Floater-RCU

Rcpilet, there is a gentleman on this forum by the name Big Bird who posted how to baffle a single cylinder on the 33% Super Decathlon thread. I think there are pics of it else where too.

The way he has done it is simple, well thought out and not too hard to do. If I needed to baffle a single it's the way I would go!

Floater

Tired Old Man

My Feedback: (1)

The oil mixtures and types used with an engine really have little effect on the cooling factors involved with an engine. To a small extent, yes, but not a major factor.

What is intended with baffles is to direct airflow efficiently through and around the engine to dissipate and carry away heat created from the combustion process. Without proper movement through the engine, the heat created while running would accumulate, and rise in temperature to a point that the internal componenets would begin to melt and sieze.

I'm going to use a twin as an example due to the fact that most of the single cylinder engines used always seem to be hanging out in the wind and thus do not require baffles.

On a cowled twin, the propeller acts very much like a large "plate" stuck out in front of an engine, blocking much of the entry airflow. An engine without baffles permits the air that does enter to act in the same manner that water does in seeking the path of least resistance. Without baffles, that path will usually be around the engine and not through it. For the engine to cool properly, the fins placed on the cylinder for the purpose of cooling need to have that air pass between them, not be diverted around them. This is where the baffle is an effective tool through the act of "forcing" the incoming airflow between the cylinder fins, absorbing and carrying away the heat radiated from the cylinders.

To increase the effectiveness of the baffles, a low pressure area created outside the cowl just aft of the cylinders will create a draft, or suction if you will, increasing the flow of hot air out of the cowl. That's why you often see an "air dam", or raised lip, on the bottom of some cowls at the edge of the hot air exhaust opening. That same dam, through the low pressure action, will increase the amount of cooling air entering the cowl.

Oil has a little to do with the process, but not really that much, especially compared to what a properly engineered and installed baffle will do.

RTK

My Feedback: (1)

Very nice explanation Pat. One more thing to include that will help keep an engine cool is to NOT run it lean.
Fuel mixture play a large roll in keeping our engines cool too.

SLINGSHOT-RCU

Here is a pic of my aerotech 42% Extra 330L.

jak_kkaall

I tried to make the edge of the baffles only 1-2 mm from the cylinder and following it's shape as I saw in the youtube video: ''Baffling your gas RC engine for better cooling''.
I needed something that can twist, change it's depth and also it's shape towards the center of the air intake hole so there are no spaces the air will go, except the cylinder. It had to be something that I can initially shape with ease. So I used 3mm wooden sticks as in the pictures, CA them at the base initially and created the baffle structure needed. Then epoxy them in place. I cut pieces of duplex white cardboard and glue them on the stiks. First I wasn't sure if it will get solid enough but after I epoxy all the cardboard pieces on both sides with thin epoxy the structure is rock solid. Then I paint them white.
The air exit panel is from aluminium with fins, place it with four hinges and two nylon bolts so I can remove the cowl as the muffler's extensions won't permit other way.
When I test it, I blow air from the front of the plane under the cowl and over the fins, and if you hold something light in front of the air intake holes it is slightly pulled in. Thank you!

acerc

I put telemetry on my Pitts with a twin just for temp and rpm. I was shocked to discover it is not the movement of the aircraft but rather the prop that cools the engine. In flight, every time I would throttle back the engine began to heat up, apply throttle and it cooled. At first I thought it was the acceleration and deceleration of air speed causing the heat up and cool down. So I went and did some vertical climb and descents, virtually no airspeed. And again every time I accelerate the prop the engine would cool, decelerate the prop and the engine would begin to heat up.
Not saying anything, just an observation.

MTK

Robert, that makes perfect sense....

the prop at idle is actually blocking the cooling ram air from getting in. The fan up front at idle also helps brake the model in landings...large frontal area.

If you stopped the prop in flight then you will get cooling but, of course you will have to land too, unless you had an on-board starter

speedracerntrixie

My Feedback: (29)

Robert, I would be curious to see what happens to engine temps while the airplane is in a hover. You just can't overdo cooling baffles with one of these large engines. One thing I did notice about the Prototype Pitts that Robert is modeling over on his thread is that particular Pitts bipe did not have side exit vents like most others.

acerc

Speed that was the vertical part of my post above. Holding a hover, the temp was good, throttle up a little and it would cool, throttle down and it would heat up. I have done this with two different engines and airframes with the same results. What got me the most was that after tuning and flying, tuning and flying, then putting the telemetry on and seeing just how cool the engine was running in general. But I do not over prop, very anal about propping to rpm, maybe that is where mine is different. I do not look forward to the cowl mods to close up those vents.
And that is one beautiful bird you have pictured there.

speedracerntrixie

My Feedback: (29)

Yes, it looks like you are going to have to cut some wedges out of the glass and then pull it back together to make the back edge smaller. I may be wrong but it actually looks like they narrowed the whole cowl on the full scale.

acerc

You would be correct in they narrowed the whole cowl. The upper outside is replicated with fake hinges and closed line. I can cut it on the closed line/seam and draw it over under and hopefully close up the side to rear, a bit of heat helps in the transition area. I am not remaking an entire cowl and maybe by the time I get to it I may even change my mind about closing the gap altogether.

acerc

Just after posting the above post I was heading out for a smoke and it dawned on me. I can't draw the sides in, my Valach engine needs that space. And I would rather have the engine with the bubbles than no bubbles and no Valach.