pe reivers

Check again post number 24!
In a horizontal baffle, you need to direct the incoming air up over the fins, collect the air in the top of the cowl, and then force the air throigh the fins using the close-fitting baffle.
The lower cowl half should be dedicated to air extraction. It has an opening with an air dam in front of it, so the air is drawn out by the prop wash, which gets better when the plane is up to speed.

Another way to do it is shown in http://www.prme.nl/forum/viewtopic.php?t=148 , which is sort of a vertical baffle with jackets. In that post I also made scetches of different baffle arrangements. There are several ways to skin a cat. Main idea is to get the air to flow throigh the fins from a high pressure zone to a low pressure zone.
Without pressure difference there will be no flow! Without baffles, the flow will not do the engine any good, unless you have LOTS of it. Cooling fins on our plane engines are too small.
Example: do a search on "breitwand Kreidler" and see how a high power cylinder that is cooled by free air flow looks like.
It looks like this:

pe reivers

Here is another vertical baffle with jackets. Ducting was added to prevent hot air from reaching the rear carb. The cowl top has forward facing scoops to get cool air in behind the ducts to feed the carb. Any openings that could allow hot air from reaching the carp departement have been sealed.
http://www.prme.nl/forum/viewtopic.php?t=195

bob_nj

My Feedback: (62)

In the picture in post 24, how does the air get to the bottom of the cowl if it is theoretically sealed off at the top?

Attached is a picture of my used cowl on the right.
The bottom is pretty well cut up from the previous owner.
Would I still benefit from putting a low pressure lip on the bottom, or is it too far gone?
If the lip won't help, will the air get out after I build my ducts?

On the Somenzini Yak cowl, there are a boatload of closed off louvres running from from to back.
Would it be of any benefit for me to open them up?

Thanks for the help.
Bob

pe reivers

In post 24, the upper picture shows how to extract air from the cowl bottom is a horizontal baffle arrangement.
The lower picture shows how the air from the air intakes Left and right of the spinner is guided into the upper cowl half. For clarity, on one plane the upper cowl half is removed, so the baffle is visible.
Air is forced through the cooling fins by the pressure difference in the upper and the lower cowl half.

In your cowl, you could use a horizontal baffle plate if the cylinder is horizontal.
Block the lower cowl entry half up to the horizontal baffle. Fit louvres in the huge hole that the previous owner has cut. Open up all louvres below the horizontal baffle.

bob_nj

My Feedback: (62)

OK, I'll give that a try.

So you don't think opening the smaller cowl louvres will do anything for me?

Thanks
Bob

pe reivers

read my post again!
I'll rephrase:
Open up all louvres in the low pressure section of the cowl, but not the ones in the high pressure area.

bob_nj

My Feedback: (62)

My fault.

It's starting to sink in now.
I'm reading this at work, Shhhhh [X(]

I have to get it through my head that the upper cowl is "high pressure"
I'll look at the diagram and try to sort it out.

Thanks
Bob

RTK

My Feedback: (1)

Holy cow Pe, man that cylinder is ALL fin, what does that thing go in??

pe reivers

It is the cylinder of a 50cc Kreidler street bike without forced cooling, much used to hop up. The cylinder head looks similar, and has even more cooling area. The design is from the late 1960-ies and allowed about 12 hp to be extracted from the tiny 50cc without overheating. In motocross, we tuned to about 10hp for a more tractable bike.

craigteffe

My Feedback: (24)

here is a picture of My OMP Hybrid that i am currently building and the air tunnel for it. The plans called for most of the front to be open but i decided to build an air tunnel into the fins of the head.

RTK

My Feedback: (1)

That will work fine if you have good extraction of the hot air. Be sure to put a lip on/or louver the exit area.

Richard m Crapp

This is how i do a cooling instalation on a aircraft that uses a typical 'Lycoming ' type instalation

Richard m Crapp

Richard m Crapp

Sorry for the muddled posting above.
This is how i baffle an engine, this one is a Lycoming style installation but it can apply to any cowl.
The wood baffle must nearly touch the fins. I then wrap the fins in cling film and then apply a beed of gasket goo, let it set then remove the film and trim the goo with a blade.
I can be made even more effective by adding a wrap around baffle behind.

The effect of all this can be made three times better , ie, faster airflow if the extraction airflow from a low pressure area behind the engine if efectif.

pe reivers

The baffling is nice. The main issue however is to get a air pressure difference across the baffle.</p>

This week I "cured" a glow engine installation that had the famous 1:3 intake-exit rule. It ran hot regardless of a lip deflector in front of the large rear cowl opening. The airflow would bounce against the fitted landing gear, and thus destroy any pressure difference, despite the air dam.</p>

The problem was solved using two scrap pieces of wing trailing edge. One fitted against the carbon landing gear to get a smooth flow path, A second piece fitted halfway between the airdam and the landing gear in order to create a louvre air exit.
This created such pressure differece, that all overheating is now a thing of the past, even without baffling the engine. Had it been a gas engine, baffles would have been installed.</p>

jak_kkaall

I tried to make the edge of the baffles only 1-2 mm from the cylinder and following it's shape as I saw in the youtube video: ''Baffling your gas RC engine for better cooling''.
I needed something that can twist, change it's depth and also it's shape towards the center of the air intake hole so there are no spaces the air will go, except the cylinder. It had to be something that I can initially shape with ease. So I used 3mm wooden sticks as in the pictures, CA them at the base initially and created the baffle structure needed. Then epoxy them in place. I cut pieces of duplex white cardboard and glue them on the stiks. First I wasn't sure if it will get solid enough but after I epoxy all the cardboard pieces on both sides with thin epoxy the structure is rock solid. Then I paint them white.
The air exit panel is from aluminium with fins, place it with four hinges and two nylon bolts so I can remove the cowl.
When I test it, I blow air from the front of the plane under the cowl and over the fins, and if you hold something light in front of the air intake holes it is slightly pulled in. Thank you!

Tony Hallo

Looks like there might be so snow on the ground there?

jak_kkaall

From December until April there is always snow here, and a lot. Last year I I've flown my Cessna Skylane with skis on big snow, first fly on 50 cm snow. I always fly during the winter with skis, since I got my first plane 9 years ago and it's beautiful. Here is a video if you have the time...http://www.youtube.com/watch?v=bGyoiWCIg2g

Tony Hallo

Too cold for my old bones, looks like fun though.

jak_kkaall

Yes it is a lot of fun and since I can fly in winter I have a good reason to wait for it and not to put the planes away half a year until summer.