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Old 12-13-2004, 01:20 PM   #1
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Engine overheat

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My saito 72 is overheating when it is in the cowl on my funtana 40. I was woundering if anyone could help me out with some tips or tricks.

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Old 12-13-2004, 02:01 PM   #2
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Not sure of the cowl set up on the funtana .......... however, this is how I do cowl setups on single cylinder engines.

If there are 2 openings in the front of the cowl, only 1 is usually located it front of the engine.

What I do is block the other opening with clear plastic (as used on Canopies) from the inside, this way all air entering the cowl goes over the cylinder head.

If you don't do this air is robbed from the exit as the opening without the cylinder head is the path of least resistance, therefore less air goes over the engine.


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Old 12-13-2004, 02:16 PM   #3
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1)spinner covering both openings? maybe go to a smaller/different style spinner.

2)direct the flow of air through both cowl openings (via a baffle) over the head.

3)is there a large enough exit hole for the air to escape? There's probably enough getting in but there's no way for it to get out. You might enlarge the "exhaust" hole in the bottom to allow for more air to escape.
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Old 12-14-2004, 07:39 AM   #4
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Rule of thumb is, the air outlet should be 2 to 3 time the inlet area.
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Old 12-14-2004, 08:41 AM   #5
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Air entering the cowl through the holes in the front will go where it will, not necessarily over the engine. The cooling air must be forced to flow over the upper crankcase. Install a duct/tunnel/tube call it what you will, immediately inside the cowl inlet. Ensure there are no leaks. Aim this duct right at the upper crankcase and as close as possible. This will force the air through the engine fins. This will also solve your overheating problem.

I can post pictures of one of my pressure cowls if interested.

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Old 12-14-2004, 11:35 AM   #6
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I would like to see one of those cowls Ed. Please post a picture of it.
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Old 12-14-2004, 06:17 PM   #7
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i have a funtana40 with a 70 os surpass and never had a problem with overheating. the front of the cowl has two holes and i cut out a hole for the exhaust pipe and muffler under the bottom of the cowl.

i also ran a satio 80 with no problems.

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Old 12-14-2004, 06:28 PM   #8
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Pressure Cowl

Hi Ted,

The Cowl description as requested.

This cowl is used on an F3D Pylon Racer. A .40 size engine with a full tuned pipe @30,000 rpm. Pipe and engine are fully enclosed. The cowl has an outer and inner shell.

Cowl 1 shows the two inlets. The ingoing air is directed to the engine with no leakage elswhere.

Cowl 2 shows the inner shell. The front part of the inner shell is a tight fit on the engine, around the crankcase and over the head. It fits around to the rear of the engine and over the pipe. There is about 1/8"+ clearance between the inner shell and the pipe.

Cowl 3 shows the ducted inlets at the inner shell. The head inlet is self explanatory. The two side inlets accept the ducted air from the vertical inlet and force the air through the fins of the upper crankcase. It is not necessary to have the air hit the case at the very front. There is a large transfer passage at the front of the engine and the fuel helps there. So the incoming air is forced through the case and head fins and then over the pipe and out the back end.

There is nothing new with this type of cowl in modelling applications. C/L Team Race and Speed fliers have been using them for decades. In full size aviation, ducting was used in WW1.

Ed S
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Old 12-14-2004, 06:30 PM   #9
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I will attest to what Jim said about the opening and voyager's #3 solution.

I did both of these things to my cowel and no more problem....ever! I had my engine so hot at one point, it was crackling and smoking like crazy. Thought I had ruined the engine! Didn't know what to do until Jim M told me what the problem was.

Not to run anyone down or to disrespect anyone's input as each of us have our own solutions that work very well, but with both the above approaches, I have personally found no need for tunnels or deflectors but then again have never tired them either! Probably a better method for long narrow front ends.

One opening in the front of the cowel directly in line with the cylender fins and 2 to 3 times the size of that opening in the bottom of the cowel to let the air out worked just great on my Saito 1.80 flying a Midwest 73" Giles 202. After my very next flight with these repairs, Jim checked the cylinder temperature and it was running quite significantly cooler!
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Old 12-14-2004, 07:16 PM   #10
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Thanks Ed. Pictures are worth a thousand words.
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