Scat tube flange locations

[Gary Wallace]

I have dual cabin heat muffs, and ducting fot an oil cooler, therefor two 2" flanges and a 3 or 4 inch flange on engine baffles for two heat muffs and an oil cooler duct. Any recommendations on location of the three flanges on the baffles. Also, any recommendations on 3 or 4 inch scat for oil cooler. Lycoming O36 . I am considering a 2 inch ofd right side rear of baffle and the other two left rear baffle.rather than off the front of baffles for length of scat. Any suggestions. I will be mounting oil cooler on firewall with a damper of some sort. Just not sure if there is any reason they would need to be, or any advantage to drawing the air in from the front of baffles at the nosebowl inlet. Thanks again

[S Lathrop]

There was a 4 place Bearhawk with an external air scoop to feel the oil cooler. That seems like a good approach.

For hot weather operations I think that a separate air source for the oil cooler really makes sense. When cabin heat is wanted, cylinder and head cooling won't be such in issue so I think taking air for cabin heat or carb heat is alright. When cooling is an issue, I think all the air available air should go for engine cooling.

Just my thoughts. And I don't have a lot of experience that is relevant to this issue.

[zkelley2]

The heat muffs need air over them all the time, so it doesn't matter if you're piping to the cabin/carb, the alternative is still taking air and then overboard to cool the heat muffs.

[Aero_tango]

FWIW, I have 4” scat from the rear left side baffle to my FW mounted oil cooler. No issue with oil cooling or CHT, even in summer, 30c OAT. This is for a O-540.
Also a 2” scat from the rear right side baffle to heat muff for cabin heat and another 2’’ scat tube from the front left baffle (ramp) to heat muff for carb heat.
Plenty of cabin heat down to -15c OAT (this is with a Vetterman muffler / heat muff...the van’s wrap around heat muff isn’t that great from my experience in a RV7)
Mike.

[S Lathrop]

That is good information. Thanks for posting.

[Gary Wallace]

Thanks. Ive got vettermans exhaust. Hope enoigh heat using both heat muffs for cabin heat. One more thing. Is it necessary or recommended for bugscreen on flange inlets for cabin heat or oil cooler. I think not???

[Aero_tango]

I do have bug screens on the 2’´ flange, not on the 4’´ .

[Gary Wallace]

Thank you!

[tailwind]

I put a naca vent on either side of the lower cowl for cabin heat. Two inch scat tube to a “y” transition into a 3 inch cabin entry. You have more than enough air movement. It is very important that you seal every chance for leaks in the cabin area. Any small leak will rob you of your heat.

[Ray Strickland]

Bug screens on everything.

[Gary Wallace]

Anyone have a source for bugscreen? Not seeing any at aircraft spruce?

[Aero_tango]

Home Depot....works for me.

[Gary Wallace]

Sounds good
.

[tailwind]

Here is what I did. Clint is probably correct in saying that you probably only need one muff if you seal up your air leaks. My plane seems to have leaks all over

[zkelley2]

The exhaust under your heat muffs will need repair a lot sooner if they dont have constant airflow. You need a way to let the air go overboard unless it's on 100% of the time. It for sure wont last 500 hours. And then you have the CO problems.

[tailwind]

In addition, I went to our local aircraft parts supplier (Menards) and purchased some window screen to keep our bugs.
purchase 1 naca vent. They are plastic and will not stand up in our engine compartment. Don’t ask how I know. Wax the interior several times with a good paste wax. Fill the inside with body putty. Allow it to set up. After it has cured place the mild and vent into the freezer. Let it cool over night. Then place it over a a warm area. What you are trying to do is expand the plastic to loosen it from the body putty. Remove the naca vent from the mold. Sand and repair as needed. The 2 inch neck will be slightly small if desired you can build this area up. I did not and I still have good air flow. Wax the mold several times. This is very important. Without a good wax coating your vent will not separate from the mold. Wax a piece of glass and place your mold on the glass. Lay up your fiber glass over your mold. Reinforce the 2 in neck area. Lay up the cloth is that it lays out flat on the glass so when cure you can dress the mounting surfaces. Place a garbage bag over your part and allow extra plastic around your part. Tape the plastic down to the glass. Suck it down with a vacuum cleaner. Use west system fast cure epoxy so it sets up quickly and you will not need to run the vacuum cleaner so long. Also place near a warm area to encourage setting. Not near open flames.

[tailwind]

Should have proof read better, sorry.

[Bcone1381]

Hey Bob, would you consider writting it up again and placing it it Tips/Techniques? That a neat way to do it, and I've never seen that method used before.

[jaredyates]

Or how about a Beartracks article!

[tailwind]

I ageee that the exhaust stack will crack and burn out without air flow. The air will either go out into the cabin or dump out through the shuttle door. In this picture you can’t see the design of the cabin heat shuttle door to see the overboard dump.

[Gary Wallace]

Fabricated oil cooler housing and damper complete