RPool

I did a search here and on google, but failed to find any posts that had a template I could use to create more airflow in my cowl. I've seen photos, but I was hoping someone had a template I could tape onto my cowl so I wouldn't butcher it too badly. Anybody have a PDF or something? Thanks!

spaceworm

What model or cowl with what engine are you looking at? I think too many variables the way you asked the question.

RPool

Yeah, I knew I did a bad job of explaining. I want to open up the bottom of the cowl as an air exit...to promote air flow and keep the engine temps down. I could cut a big hole, but want to do it in a more attractive manner.

goirish

What kind of plane?

RPool

It's a 26% Sbach. Does the type of plane matter? I ask only because you are the 2nd person to do so; that makes me concerned I don't know something important?? I want to do something like that shown in the lower part of the attached photo. I can blow up or reduce an image if you are concerned about size.

spaceworm

How about picking a hole pattern you like and printing it on clear adhesive film. Then, stick it where you want it and cut loose. MAN has an article on engine cooling in their current issue. Talks about baffles and such, which are more important than hole size. But you need two or three times (I think) the exit area of holes than entry area even with the baffles. Good luck.

RPool

"How about picking a hole pattern you like and printing it on clear adhesive film."

We've gone full circle now. If you read my first post, you'll see I am asking where I can find a template of some sort...what you called a hole pattern (not a hole pattern for engine objects like jug or exhaust. only for the air exits) ...so I'll have something to print up. My initial post states my intention is to tape it to my cowl so I can transfer it there. I sure appreciate your time and feedback though.

pe reivers

see http://www.prme.nl/forum/viewtopic.php?t=148and http://www.prme.nl/forum/viewtopic.php?t=37for comprehensive explanations. It will not provide templates, but make your work a lot "easier".

Cowl cutouts for engine cylinder are easy to make. First make a paper pattern that fits over the head of the mounted engine sans cowl. Tape that patern to the fuselage and see that it fits the engine nicely.
Now fit the cowl, with engine removed, and trace the pattern (that is still taped to the fuselage) to the cowl. Cut out, refit the engine, and hey presto, the cowl will fit nicely.

Edit: corrected first link to cooling systems

RPool

Still looking for a template for cooling cut-outs only. Thanks for all your help.

mrbigg

My Feedback: (21)

Use Pe's way of doing the cylinder head for your cooling cut out. Make your own template. Start big and trim it so it looks right. I usually come straight back off both sides of the cylinder to line it up and go from there. It's not rocket science.

mrbigg

My Feedback: (21)

I looked at the photo and the "vent style" openings you are wanting look to be about the same width as a Dremel sanding drum. Mark the lines with a marker and plunge in with the Dremel.

Tired Old Man

My Feedback: (1)

Pe's site, 3w manuals and website, both provide ideas of what to do. There are far too many plane and engine combinations to provide templates. Sometimes you just have to think about something, be creative, and perform some trial and error. The inlets are important only in they need to direct all the incoming air through the cylinders, not over or around them. Exiting is trickier, The hot stuff has to be directed to where is has to go and the exit velocity has to be enough to move more volume that what entered. That's where Pe's site comes in pretty handy. It explains low pressure areas. The 3-1 ratio is not cast in stone. Done right the exit area can be less than the inlet area. Few will ever obtain that kind of efficiency though.

It can't always be buy and fly or grab and go. Sometimes you have to do a little more work than originally desired.

Lnewqban

RPool,

If you give me the basic dimensions I can create a template of the inlet louver for you in AutoCAD and post it in PDF.

I would use the good advices above to make sure that the dimensions of the louver would provide the inlet volume of air that your engine needs.
As a rule of thumb in air conditioning, air louvers (with fins more or less paralell to the air stream) only alow about half of the volume of air of same size free opennings.

Regards!

RPool

Great feedback. Let me ask you this; in your opinion is it a good idea to close off the openings between the fuse and the area under cowl (like those in first picture)? Will this give me more control over airflow exiting the cowl? Also, should I screen in the openings in the cheeks adjacent to the prop? As you can see, the engine gets a great front row seat in the cowl. Flow should go right through the fins. I am considering running a band of exit holes right behind the cylinder to keep the air pulled straight past and out. Thoughts as to whether this setup will actually work are appreciated.

Michel

Hi
Have a look at this ,........................ and they are FANTASTIC ,

http://www.thunderboltrc.com/index.p...x&cPath=89_147

Michel

pe reivers

cooling vents like that grealy improve airflow by creating a low pressure zone.

Michel

Hi

Yup,....................... they really suck

RPool

Should I close off the openings between the cowl and the fuse?

mrbigg

My Feedback: (21)

Yes. You can just iron some covering over the holes. That's what Extreme Flight did on their 50cc Yak.

Charlie P.

Go to Tower and check the downloads for Great Planes assembly manuals. The Great Planes Super Sportster I am working on has a template at the back of the manual.

Usually, it's whatever you can get away with to get air in. There is no "standard template" as it depends on model size and cowl shape . . . and what engine you have stuffed inside. You want more exit opening than enterance as a rule of thumb so the air doesn't "pack up".

motoaire

My Feedback: (24)

p e reivers: Thank you for posting the diagrams and info, very helpfull !

RPool

Pe and other knowledgable men. I am using louvers like those in post 15 for air exits. They will be located on both sides of the cowl. I want to know your thoughts about covering two air inlets on either side of my prop as demonstrated in photo 3. I'm thinking that will maximize airflow over the engine and keep the air moving low in the cowl...it also keeps outflow vs inflow at least 2 to 1.

pe reivers

If the engine is baffled, the air in front of the engine is just a plenum chamber that should contain turbulent air.
The air exit louvres should excavate all the required cooling air. They alone determine the amount of cooling.
It is surprising how small the air inlet needs to be. Increasing the inlet area will hardly increase cooling, and ruin the precious 1:2 ratio. However without any ill efects on cooling if the engine is baffled well.
On narrow cowls where all airflow is balanced, the air heating should be accounted for by increasing duct cross sections, OR increase pressure difference across the baffle.

RoyR

I have a question, I have been flying glow engines since I was a kid. Started RC in the 70s. Of course for years most of my engines were out in the open, so cooling was no problem.
However, I have built a number of airplanes with a cowl, and I just put them on stock without adding baffling, or holes or vents, and have never had a problem with an engine overheating.
I have never flown gas, so I don’t know if they have their own particular problem. But my question is; if there were a problem with engines overheating inside a cowl wouldn’t the manufactures take that into account? I have seen many people fly their gassers without modifying the kit and seem to have no problem.

I’m not trying to be nasty. I plan on getting into gas soon, and just want to know how important all this is?

Isn’t adding the louvers and baffling just a way of customizing your aircraft and making it more “your own”?
I completely understanding modifying something to make yourself feel better about it not breaking, etc. But before reading this post I have never heard anyone very concerned about the cooling on a stock cowl.

Thanks
Roy

Charlie P.

With glow overheating may not make itself known for years as it may be a gradual decrease in compression as the engine wears out prematurely.  Also frequent dead-sticks.

Overheating can be a real issue - gas or glow.  If you are using a hot plug for ignition it can make a big difference.  What will it do?  Engine knoks out frequently.  Parts work loose,  Hard or impossible to restart.  Premature wear. 

I have even seen damage to painted cowls getting baked from proximity to hot head and exhaust.