Cooling Baffles...How 2??
 

A lot of talk on engine temps has me convinced that I need to learn more about this subject. How do you direct the air with the baffles and know that you are doing it right? If you've got pics, I'm sure it would be helpful. My minds eye tends to be nearsighted at times.[8D] I'm having a hard time trying to figure out to do it effectively and not waste a bunch of time sticking baffles here and there.

RE: Cooling Baffles...How 2??
 

All air entering the cowl must flow by the cooling fins of the cylinder and head. No air can get through unless it goes between the fins

RE: Cooling Baffles...How 2??
 

Yeah, that much I've got. I've read that you can't rely on prop blast to push air in, you must create a vacuum inside the cowl to draw the air in. True or false? If true, and I have a large (over 4x the intake) exhaust air area, can I assure this is taking place. I'm don't believe I'm getting hot on the ground, I just want to make sure I understand the principle.

RE: Cooling Baffles...How 2??
 

Here's a picture of the cowl from a 35% yak. it's a round cowl and the engine is a boxer twin. So I had to block off the upper and lower portions. I use 1/16 balsa to frame up the ducting, then reinforce it with two layers of 6 oz fiberglass from the inside.

RE: Cooling Baffles...How 2??
 

Look at a full scale plane, inside of the cowl are partitions that seal around the engine so that the only way the air can get out of the cowl is by passing through the cooling fins;)

RE: Cooling Baffles...How 2??
 

Here is mine, I made a cardboard template and kept trimming it until I got the shape I wanted, then I traced it on a piece of thin plywood, cut it out with a scroll saw, trimmed it a little more until it was exactly perfect. Then I covered it with monokote, I ironed the crap out of it to make sure it wasn't going to bubble or peal, then I epoxied it in place with epoxy and microballons, and added a couple of small pieces of triangle stock at the back corners on the bottom. It looks like I painted it, has held up in over 100 degree days a couple times, and it gets a lot of compliments and questions "how did you do that". People think it's molded in with the cowl or something.

RE: Cooling Baffles...How 2??
 

You did nice work.

RE: Cooling Baffles...How 2??
 

The whole point of baffels is to direct the air comming in to the cowl through the fins, air that enters the cowl without being directed will not pass through the fins just ove them, its a bit like water it will take the path of least resistance the air between the fins will stagnate and turbulate without cooling, so a close fitting baffle with an open front to direct the air though the fins from the cowl opening will work best. I am in the UK so most of the time the temps don't get up to anything that would worry the engine, but when if does its supprising how many of my flying pals experience problems, "it was running alright last week"

Mike

RE: Cooling Baffles...How 2??
 

I have baffled mine so well, the engine runs significantly leaner with cowl on than call off !! :( Hasn't flown yet ....

RE: Cooling Baffles...How 2??
 

A field report:
Aerobatic extra plane, engine DA50, side mounted, very neatly built. prop 22x10. The cowl fits closely around the fuselage with a small central bottom bulge to let air out between cowl and fuse. Canister mounted inside the fuselage.
First flights the engine showed it's distress by almost quitting, severe loss of power. Cylinder temperature in flight in excess of 150C, measured with a Venom gauge as used by car racers. (simple 25 dollar device)
Something had to be done, so:

Now the only air intake open is the one in front of the engine cylinder, and about 2x3 inches surface. The other air entry is closed. The lower air entry edge slants upward toward about halfway the diameter of the cylinder and snug up to the fins. The rear and side of the engine have horizontal baffles at engine centerline, with openings for carb and cylinder head.
One row of small louvres was built in the lower cowl starboard side for extra air extraction. Louvres are very effective in extracting air and creating a low pressure zone, especialy in an area where the full prop blast flows over them. The air extracting area is about as large as the air inlet (6 square inches). With the plane in flight and stationary, the air outlets are invisible and the plane's clean lines are undisturbed.

Final results:
Engine temperature now is down to 118C on a leaner mixture, and runs like a champ. With good cooling 130C is not too high, so it still seems a bit rich.
On the ground, you can distinctly feel the (quite) hot air exhausted from the cowl. This engine will live long if the pilot keeps the plane alive.

RE: Cooling Baffles...How 2??
 

PE,

I too have a DA-50 mounted inverted in a WH Extra. What I thought was sufficient cowl cut out and cooling is apparently not. I’m going to try blocking the open area around the prop, expose more of the cylinder to the front, and make a baffle/air dam to the rear of the Pitts exhaust.

Would you post a picture of the application in your last post above?
Also, anyone with pictures of singles with baffles would be welcome.

Thanks - Jaketab

RE: Cooling Baffles...How 2??
 

Take a look at my forum http://www.prme.nl/forum/index.php for pictures etc.
The plane is not mine, so it is not that easy to take pictures. If I have them, I will post on my support forum.

RE: Cooling Baffles...How 2??
 

Thanks all for the advice. Pe, the pics in your forum offered the answers I was looking for. While none of the airplanes I own are in the 3D category, and most are flown in a fashion to accommodate good airflow, I'm going to spend some time this weekend fitting some baffles into a couple of my newer gas engines. An ounce of prevention...[sm=idea.gif]

RE: Cooling Baffles...How 2??
 

even in straight flight my 35cc test engine ran much more consistent with the pictured jacket baffling.
Before, it would loose some power when hot. After mounting the jacket it ran the same from start to landing.

RE: Cooling Baffles...How 2??
 

Here is an article that I wrote for RC Showcase on baffles.

http://www.rcshowcase.com/html/faq.html#baffles

RE: Cooling Baffles...How 2??
 

Indeed that's the basics in your article, which can be refined for better looks and improved air flow.
Too many pilots think cooling will happen all by itself if you fly a plane, because there is a lot of wind to go around. Few know that it is not so.

I think this thread is very valuably and will save quite a few engines from being fried.

RE: Cooling Baffles...How 2??
 

One thing to add is this:
in small engines the cooling is less important than in larger engines. There is a rule in this madness which goes like this:
Engine power generated is a function of it's swept volume (read cc), which is it's physical size to the third power (L^3). Power and cooling requirements are directly related.
The available cooling surface is a function of engine size as well, but to the second power (L^2).
So as engine size increases, power increases more than available cooling surface, and there invariably will be a size when air cooling will not do any more. That is where liquid cooling steps in, and the liquid is cooled by air again, but in a much more controlled fashion, because the cooler dimensions are no longer engine cylinder size related.

In between, all we can do is to make the best of the available cylinder fins, and direct the airflow past them as efficient as possible in order to create as large an air flow temperature difference as possible, because temperature difference times the masss of air is the heat taken away from the engine.

RE: Cooling Baffles...How 2??
 

OK I'm catching on. Here's a picture of a current setup. Do I block off the opening to the right of the engine completely? And, will the round opening in the lower cowl assist in drawing air through the cowl? It is directly in front of the where the cooling air will exit.




I'm glad I asked this question. Turns out that what I thought would work and what I'm learning will work are two different things. I'm getting a whole bunch of great ideas here, and all it's costing me is a little time. Thanks guys!

RE: Cooling Baffles...How 2??
 

I have done it this way.

Regards,
Cesar.

RE: Cooling Baffles...How 2??
 

Wow Ruud, you are a true professional.
In the pictures is just visible the air extraction ring between cowl and fuselage.
Can you post a picture how you prevent the air from going around your jackets?

RE: Cooling Baffles...How 2??
 

you indeed need to block that extra opening, as well as the opening below.
The engine seems to have no baffles to force the incoming air through the fins.
How is your air extracted?

RE: Cooling Baffles...How 2??
 

This is the model that the original question was based on. I have yet to install any baffling yet, and it hasn't left the ground. I broke in the new 26GT2 on the stand and have ran two tanks through on the airframe without cowl, and one with it. I just purchased a temp gauge, and have yet to take readings.

I kind of figured that the round hole (about 1" in dia.) would help "pull" the hot air out of the cowl with it's orientation. Can you explain to me why it won't so I understand? Is it because of cavitating air caused by the prop? I hate to show my inadequacies, but since my slip is already showing...[sm=confused.gif]

Thanks for taking the time to help.

RE: Cooling Baffles...How 2??
 

Again, my $.02. The small hole adds a small amount of air but provides no venturi effect to help pull air through the cowl. It may actually reduce the air going over the cylinder. Close it up along with the one opposite the engine. Make sure that you have a BIG air outlet. Notice the turned down aluminum at the front of the outlet. This produces a low pressure area which helps pull the air out. While you are at it, glue a baffle (1/8" balsa works) to the cowl between the cowl and the cylinder to make sure that the air does not duck down and go under the cylinder.

RE: Cooling Baffles...How 2??
 

This picture shows a good way to make a large exit opening even more effective. Most important, the airflow cannot enter the opening from the outside and thus spoil the air extracting function. Each preceding louvre baffle supports the action of the next in line. The plane and picture is by NORC.
http://prme.nl/pictures/norc2.JPG

This picture shows a good air entrance. In a single cylinder, such a huge entrance is not needed of course.
http://prme.nl/forum/images/baffle-3w.JPG

RE: Cooling Baffles...How 2??
 

Pe, that is very impressive. I like the way the internal baffle forces the air down through all of the cylinders so that the back ones are not starved for air.