sengli

My Feedback: (27)

This is my first gasser . Although I have been doing RC for for 30 plus years, so bear with me on this one.
Well I have done some research here on this site and read many of the articles on baffles and cooling threads. I have a Aviation models 33% Yak 54 which has a large radial type cowl. I have a ZDZ 80 super in this for power. Most of the head of the inverted mounted engine does stick thru the cowls bottom. The first flight this past weekend showed the cylinder head temp at around 260F at idle. Ambient air temp was around 85F. I thought the engine seemed to run as if it was too hot. I currently have a TBM 24X10 wood prop on this. I am also still running the break in oil ratio of 32: 1 pennzoil with premium gas. I ran the engine this last winter on a test stand for break in purposes, so it has over a gallon of gas thru it currently. I would like to see if anyone else out there has any photos of there cowl baffling with this setup or anything similiar.

Hooked-On-RC

My Feedback: (16)

you could add some baffling to that cowl to force air directly through the cooling fins on the front of the cylinder. That seems like a pretty hot cylinder head temp and I think if you talk to RC Showcase they want to see it in the 165-180 degree range. remember with heat comes wear and that could shorten your engines life drastically not to mention causing you a world of issues with deadstick landings. If you look at the 100CC Quique Aircraft yaks the face of their cowl is completely blocked off except for a slot for air to pass over a twin cylinder engine. In your case block off the entire cowl and open a space at the bottom, place baffles in there to direct the air right over the cylinder cooling fins. The rest of the of the area behind the engine does not need cooling so dont worry about it, just be sure the air is forced past those cylinder cooling fins also be sure your exit air hole is large enough for the air flow, it should be, by a rule of thumb, 2.5 times the size of the inlet air...inlet air =6 square inches...outlet air should be 15 square inches...you will notice a difference. Yes I noticed that even though the top of your cylinder head protrudes through the bottom of your cowl, that does NOT guarantee air is flowing over it to keep it cool

Richard D Bahmann aka/Wrongway

My Feedback: (42)

I have the same airframe but 3W-80 on a 26x10 two blade prop. (your ZDZ is supposed to have similar or more power than my 3W...could it be your prop is too small?)
While still on the break in period we were seeing 190 plus or minus 10 degrees after flight. Correct baffling would certainly help but we did not use any.
I am curious to know if the manufacturer reccomends ground running the engine for break in. I know that my buddy with your same eninge on the same plane was told by TBM to set the engine and break it in in the air. He was further told not to do any lengthy full power ground (or air) run ups for at least a gallon or so as it would overheat the engine.
260 is too hot an engine temp in my book for a gasser.

hope this helps.

Richard

pe reivers

With the cooling OK, I mean using baffles and a sound pressure difference over them, temperatures as high as 350F should pose no problem whatsoever. Not after landing, but during flight. After landing measurements are useless. Also it will put your engine in distress if you do not use baffles in the cowl.
Finally, all baffles will do no good if there is no air extraction from the cowl that sucks the hot air out. Do not count on the prop blast. It has no effect other than to stir up the air in front of the engine. (which has a cooling effect all by itself)

juanes1969

I hope these pictures help. I have tried the plane like this and it seems to work, I wish the temps went down a few more degrees. I am not sure if this baffle is the best way, so if there are any pros out there that can share ideas on how to make it better, please let me know
John



BTW, the plane is and SD-Models 33% YAK with a 3W-85xi... less than 1 gallon thru it.

sengli

My Feedback: (27)

Well it is very interesting to see other people do not have any baffling to speak of in their cowlings and the cylinders don't even stick out at all. I am not sure I have a real problem, there is no easy way of testing the temps when it is airborn. I have modified my beautiful cowling in order to expose the entire cylinder, and have installed baffles on either side of the cylinder as well. I will test this set up this weekend.

juanes1969

This is my 30% with a DA50. This one I know works great.

JoeAirPort

My Feedback: (41)

Your exit area is good, you just need a baffling up front, just block everything except the cyclinder and nothing complicated. Also opening up a slot in front of the cylinder is good.

Hooked-On-RC

My Feedback: (16)

Yes Joe AP is correct, you have good airflow over the cylinder you need to block off the rest of the cowl to direct airflow ONLY over the cylinder. what would happen if you leave that cowl open like that is air will get trapped inside the cowl and not allow a "flow" of air over the cylinder, more likley it will disrupt airflow becasue of air turbulence. Block off the airflow to the rest of the cowl and you should be good to go!