Continental 0-200 breather tube question

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Gone Flyin

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Gone Flyin
Need to replace the aluminum breather tube in my C150. Been told it is too short.

How far below the belly should the tube extend?
 
Found something on Cessna 170 site that says the tube should extend 2" below the belly of the plane.

A hole (freeze hole) should be drilled about 10" up from the end of the tube to relieve pressure should an ice plug block the end of the tube.

Another site says that ice hole needs to be as close to the muffler as possible and still another says the hole needs to be reverse-relieved to make it invisible to any exiting oil or fumes.

There is a mod for the breather called "Breather Modification" that suggests a longer connection between the engine and the right angle fitting will reduce oil consumption by limiting the amount that gets "flung" out the front breather opening with the existing shorter connection.

Right now, I'll deal with the first issue of tube length and hole placement.
 
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Unfortunately, the article you reference does not answer my question. How far below the belly should the tube extend?

From what I can find on the net, there are some that feel extending the tube below the belly and "into the wind" will create a vacuum and make things worse. Others feel it might create back pressure. On my buddy's C150 the tube is facing sideways and above the bottom of his cowling/belly.

I still believe the tube should stop well before the bottom of the cowling as it is only acting as a drain. My current (and soon to be history) tag team A&P and IA disagree and want it extended. For now, I will comply to make them happy and cross this airworthiness issue off the list... but, I still need to correctly resolve this for my own piece of mind.
 
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Gone Flyin said:
Unfortunately, the article you reference does not answer my question. How far below the belly should the tube extend?

From what I can find on the net, there are some that feel extending the tube below the belly and "into the wind" will create a vacuum and make things worse. Others feel it might create back pressure. On my buddy's C150 the tube is facing sideways and above the bottom of his cowling/belly.

I still believe the tube should stop well before the bottom of the cowling as it is only acting as a drain. My current (and soon to be history) tag team A&P and IA disagree and want it extended. For now, I will comply to make them happy and cross this airworthiness issue off the list... but, I still need to correctly resolve this for my own piece of mind.
Click to expand...

If there's a hole drilled in the tube a few inches up from its end, it isn't going to generate suction. Suction wouldn't make much difference anyway. If you end the tube above the bottom of the firewall, the oil gets on the firewall and seeps through the riveted seams and gets inside the fuselage and makes a mess under the floor. It attracts dirt and forms a really sticky, hard-to-remove sludge. It can saturate some of the insulation on the inside of the firewall. You don't want any of that.

It's not just a drain. It's releasing the gases that blow past the piston rings. Those include a lot of water vapor, the last thing you want inside that engine.
 
The C 150 that I flew for years, and did oil changes on, had a breather that extended about 2 inches below the sheet metal. There was a small breather hole further up, exact location not sure of, but at least 6 inches. The cowling had a hole for that breather pipe to pass through.

The plane was a 1960 model, and I first flew it when it had less that 100 hours on it, and the preflight included checking for obstructions on that breather pipe.

We considered making it longer to reduce the oil condensing on the belly of the plane, but never did. Our A/P at the time recommended that change.
 
Agreeing with Dan Thomas, the water vapor from blow by is what freezes and blocks the end, plugging it in the winter, thus the mandatory vent hole in the warm space inside the cowl. I have landed, and seen ice globs on that pipe in the winter.
 
Dan Thomas said:
...It's not just a drain. It's releasing the gases that blow past the piston rings. Those include a lot of water vapor, the last thing you want inside that engine.
Click to expand...

geezer said:
...There was a small breather hole further up, exact location not sure of, but at least 6 inches. The cowling had a hole for that breather pipe to pass through.
Click to expand...

Alright, so the suggestion is to have it extend below the belly. As to having a hole in the cowling, if that was actually the case, not sure why that was needed. The pipe on my C150 was clamped to one of the nose wheel supports so came out well away from the existing lower opening. No extra hole needed.

It would seem, then, the best place and direction for the tube to exit is as far back and under the belly as possible (i.e clamped to the lower nose wheel strut support) and facing somewhat aft, as opposed to straight down.

The freeze hole should probably be up nearer the muffler to take advantage of the heat, or is that likely to create a flame out from those fumes?

The hole being reverse-relieved to make it invisible to any exiting oil or fumes, as I stated, above.

Comments, please.
 
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Gone Flyin said:
Alright, so the suggestion is to have it extend below the belly. As to having a hole in the cowling, if that was actually the case, not sure why that was needed. The pipe on my C150 was clamped to one of the nose wheel supports so came out well away from the existing lower opening. No extra hole needed.

It would seem, then, the best place and direction for the tube to exit is as far back and under the belly as possible (i.e clamped to the lower nose wheel strut support) and facing somewhat aft, as opposed to straight down.

The freeze hole should probably be up nearer the muffler to take advantage of the heat, or is that likely to create a flame out from those fumes?

The hole being reverse-relieved to make it invisible to any exiting oil or fumes, as I stated, above.

Comments, please.
Click to expand...
Some airplanes had a smaller cooling air outlet in the bottom cowl, and so they provided holes off to the side for the breather tube and battery box drain.

That tube doesn't have to extend "as far aft as possible." Just get it below the bottom of the firewall. Lots of 185s had maybe four inches below the firewall and it was bent back at 30 or 40 degrees.

That freeze hole doesn't need to be anywhere near the muffler. The gases exiting the tube are already pretty warm from the engine. The danger is that in really cold weather the water vapor condenses in the tube and freezes in the end of it, out in the slipstream, and blocks it. The small hole relieves the pressure. Many airplanes started out with cold-weather kits that included insulation over the tube to keep the thing warm so that freezing was unlikely, since the gases would still be pretty hot when they got to the end.

You are overthinking this. Your mechanics know what it should look like, since they've seen hundreds of them and are familiar with the parts catalogs, maintenance manuals and a lot of other stuff. They didn't get their education off YouTube. When an owner starts second-guessing an experienced mechanic, based on his experience with cars or motorcycles or just intuitive or assumptive knowledge, he's just going to create more headaches for himself.
 
Your plane will fall from the sky on an orphanage if the breather tube is not the perfect length. Sheesh, definitely time for a new mechanic.
 
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