redcesar

I do not know how I must do that Pe, I hope that the baffles I made be enough to do there work in the cowl, but maybe I closed the gap in the cowl underneath the engine with a piece of ABS to the underside of the "jackets".

Regards,
Cesar.

Jaketab

My Feedback: (2)

The below pics are of a DA in a WH Extra. I have experience overheating thus having the motor quit several times. The motor is currently at the factory being serviced.
I'm going to expose more of the cylinder and make a baffle/dam just in front of the exhaust tubes.
Can anyone give their estimate by looking at the pics as to whether on not the present cowl cut outs were suffcient to provide adequit cooling?
I also plan on blocking off inlet areas around the propeller. Is their any reason I should not do this?
Any other areas of this cowl I should modify?
This discussion has been very informative.

Thanks - Jaketab

Big_Bird

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It appears that the firewall is solid behind the engine with only a little clear space behind the top of the head. This could be restricting a lot of air flow. Aluminum or hardwood dowel standoffs would work a lot better by providing far more uninterrupted air flow. I know it would be a lot of work to change out but would be better than ruining an engine.

I think that the outlet area is OK providing you have minimally obstructed air flow. Of course an air diverter tab at the front of the outlet will help.

pe reivers

The cylinder looks well exposed on the face of it, but the airflow is directed over the cylinder, and not through the fins by the deflecting part just behind the spinner. That very small hole does not change the situation much. It is about the only air going directly to the cooling fins, but because the air flow has to pass a sharp orifice, it gets diverted and slowed down much, loosing nearly all of the cooling ability. Make that front opening as large as feasable, and take care of air removal behind the cylinder.

pe reivers

The baffles cannot work all by themselves. They need to make contact with the cowl around them. Foam, cardboard, anything that will close the gaps. In the picture below I made a cardboard system with baffle and short jacket inside a round cowl, which can be seen through the somewhat transparent cowl.

In front of the baffling system the cylinders are cooled by the air turbulation of the prop. Behind the baffling system the hot air is drawn out through the slit between cowl and fuselage, which probably is quite efective. Louvres like in a suchoi will provide excellent air extraction as well.

Jaketab

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The engine is mounted by 3 inch aluminum standoffs. The below pic references the engine inside the cowl. Does this help provide for better explanation of poor cooling?
Again - what do you think about blocking the air intakes on both sides of the spinner? It would appear that much of the airflow is entering here and going over the engine with little reaching the fins?

Jaketab

Big_Bird

My Feedback: (1)

Jaketab, that big hole above the engine is doing little for the cooling. The air that comes in there is only serving to crowd out some of the cooling air going over the fins of the engine. Close up the big hole. Paint the dam flat black for looks. Pe's baffle would be very effective but more work. It is the same idea that I offered with the article on RC Showcase earlier in this thread.

That last photo was very informative.

Jaketab

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Ken,

The reason I ask is I see many inverted single cylinder (50cc) motors in Extra's without blocking off the air intake on each side of the spinner. Many appear to work just fine without overheating. It does not appear to be the general practice to block this area. The Extra type cowl appears to serve it's purpose for horizontally opposed twin cylinder engines where the air goes in and over the cylinders. In the case of my Extra with the inverted cylinder hanging down, it seems to be requiring additional airflow to keep temps down. Just wanted to hear from others if they have blocked off this area with good cooling results. Didn't want to do something to make matters worse.

I've already made an airdam out of 1/8 balsa covered with thinned epoxy and painted flat black to block the openings. I'll open up the cowl in front of the cylinder a little more and place a baffle in front of the bottom air exit.

Thanks again - Jaketab

Big_Bird

My Feedback: (1)

I guess what it comes down to is that you have had troubles with over heating and they haven't or they didn't know that they were having over heating. At first glance of your pictures I was a little surprised that you were having this much over heating. All Pe and I were trying to do was to give you some options to try. By all means, if you think the air dam will make the situation worse, then don't try it.

Other things to think about are: Are you tuning the engine for max RPM? If so, try richening it up a couple hundred RPM. Are you over propping the engine? Is the gas/oil mix what the manufacturer recommends?

pe reivers

The inverted engine can have both openings open for looks. You do need to place one baffle plate at the cylinder centerline location, so no air will bypass the engine cooling fins. The cowl cutout can be quite closefitting to the cylinder if the head sticks out. Behind that baffle, you need air extraction with a rim at the foremost opening edge to prevent air entry there. (example Big-bird). That way, the muffler receives it's share of cooling as well.

RTK

My Feedback: (1)

I have doing some reading and experimenting with baffling and temps. One of these days I am going to publish it on an engine manufactures web site (which I was asked too) with articles on full scale done by the largest personal aircraft manufacturer. Time permitting. Briefly reading over this thread there are many good example of of baffling. Basically, the old rule of 2x, 3x or 4x exit vs opening is not really valid. Directed air flow at the right speed is much more critical.

pe reivers

RTK,
Some Interesting links that may be helpful (snatched from my forum):
http://www.rcshowcase.com./html/faq....0is%20cooling?
http://www.liquidcooledairpower.com/lc-longertbo.shtml
http://www.liquidcooledairpower.com/lc-topendheat.shtml
http://naca.larc.nasa.gov/reports/1929/naca-tn-328/
http://naca.larc.nasa.gov/reports/1938/naca-report-612/
http://www.pilotfriend.com/aero_engines/images/j5.jpg
http://www.tpub.com/content/construc.../14264_213.htm
http://www.lnengineering.com/pinz.html

Quote from http://www.allstar.fiu.edu/AERO/Propulsion1.htm
Quote:
Many of the best fighters of World War II were powered by liquid-cooled engines and by the mid-1940s the debate was over and air-cooled engines were the victors. One major development assisting the air-cooled engines was the development of the NACA cowling. This was an enclosure for the engine that limited the flow of air over the engine cylinders to the air actually in contact with the cooling fins of the cylinders. This advanced was very important in improving the efficiency of air-cooled aircrafts

RTK

My Feedback: (1)

Thanks Pe

Flypaper 2

The way PE does it and is done in full size practice is called pressure cooling. All the air going into the cowl must be blocked off from going anywhere but through the fins and crankcase. There is, for instance on a Cub, an aluminum plate that goes from the engine to the cowl so the upper half is sealed off from the lower half. Long time ago worked on a Cornell with a six cyl inline Ranger engine. When the mags were shut off, it would slow down till it almost quit, then rev back up to full throttle, slow down till it almost quit, then rev up again. It would repeat this continually if you let it. The only way you could shut it off was to shut the fuel off and let it run out of gas. The reason was, as it slowed down the back cyls would overheat, bit of carbon would start glowing, ignite the gas like a glow plug. it would go out when it got a shot of cold air and repeat the cycle.

pe reivers

I would rather call it vacuum cooling, because the air is drawn through the fins by the low pressure begind it.
I received an engine for evaluation, together with plane pictures. These show the desastrous effect of the standard cooling rule.
Oil Castrol TTS, it helped to let the piston survive this ordeal save for a few light scratches
Spark plug dark brown, proof of excellent carb tuning.
Piston top carbon is ash gray, piston inner side black, just short of "death ash"
The cylinder max temperature was gray, corresponding too 400°C!! Needless to say, this engine did not make it past the 2 gallon mark.
Interesting to see is the bleaching of the anodize of the head. This is caused by heat above 180°C, before the steel will start to turn yellow at about 200°C

Big_Bird

My Feedback: (1)

Pe, that looks like like a blatant example of how NOT to cool an engine. Probably most of the air was going through that big open hole and out the bottom of the cowl. The big hole should have been closed. The bottom of the cowl should have been opened up a lot more and rectangular in shape so that a turned down baffle (lip) could have been installed. The carb sure does take up a lot of space. It almost looks like that engine was too big for the cowl.

I realize that the guy was more interested in aesthetics than cooling. Sure is tough on an engine. The colors on the sleeve sure tell the tale.

pe reivers

That is why I posted this example. Most fliers are convinced that this is enough, while clearly it is not.
I realy am on a crusade to promote real baffling setups for ALL gas engines, and I hope this helps.

pe reivers

In the meantime, I repaired the engine, and the customer did a lot of work on baffling, jacketing and air extraction in the proper way. Temperatures now are down to lower than 100°C.
For full report see http://www.prme.nl/forum/viewtopic.php?p=506#506
Pictures will be added soon.

BillHarris

RE: Pe Reiver's post #40:

The attached images are of a Thunder Tiger 91 four-stroke on a SIG 4*60 that I finally got around to putting the fiberglas cowl on. It is a tight fit around the cylinder, and similar to the cowl setup shown in Pe's post, but not exactly like _that_. I've blocked off the top, bottom and left (opposite side) exit openings on the rear of the cowl. I have left as much of an outlet opening behind the cylinder as I could, but it isn't "three times the area of the inlet". Since I have the upper' lower and opposite outlets blocked, I don't have baffles on the left inlet or along the centerline; they can't be installed, the fit of the cowl is tight, and I need the extra room to wiggle the cowl on.

I _think_ that there will be good airflow into, around and out, but I've not flown it yet with the cowl in place, so I have no idea. I don't expect (hopefully) a problem, but the first flight I'll fly a very few minutes, bring it in and measure cylinder temps.

Feedback appreciated...

--Bill

pe reivers

You won't hav a problem here. Air extraction is excellent and it is a methanol engine. They run much cooler due to the substantial internal cooling by the fuel.

BillHarris

Great, I didn't think I'd run into a problem. The plane is 10 years old and I've been planning to install this cowl for 7 years. I'm in the process of putting baffles around a Brison Twin engine and have been reading everything available on baffles and I got last minute jitters on this old project.

I used to work with aircooled Volkswagen engines, and being familiar with VW's sheet metal shrouds and baffles is helpful in designing the baffles on the current project. I'll post what I've done when I finish it.

Thanks,

--Bill

Jburry

OK, so that's a pretty good covering of cowled gasoline engines. What about a gasoline engine in a non-cowled installation?

I humbly submit my new Byron Originals Pipe Dream. In test running (hasn't flown yet), the engine temps seamed reasonable to me (no thermo here). Is it necessary to add an air scoop around the cylinder on this G38? It wouldn't be difficult with a bit of aluminum flashing and a few fasteners, but is it necessary?

Thanks!

J

RTK

My Feedback: (1)

That set up will be fine.

bob_nj

My Feedback: (62)

Pete

In post #10 you talk about the type of baffling that is horizontal.
Can you explain that a little more, and how would one know if it's needed?

I picked up a used Yak, and cowl is kind of cut up.
Attached is a picture of my cowl, and a used one.
Can I still effictively use the small lip on the bottom to create a low pressure area to get rid of the hot air?

Thanks for any ideas
Bob

bob_nj

My Feedback: (62)

I guess Pete is on holiday.

OK, flypaper2 - In post # 39 you say;
Maybe you can explain to me the benefits of what you mention. I'm just not sure I understand what to do, or why.

Thanks for any help.
Bob