Air oil separator may not be necessary
Edd said:
I'd like to install a good air-oil separator on my 0-360. Any advice on which ones work OK...including for light aerobatics?
Why do you want an air-oil separator. I had one which I collected the drain into a jar. What little came out was nasty, meaning I would not run it back to the engine. The volume that was collected out of the separator was small between oil changes (mostly water and crud). The belly had only a very little film of oil on it. My oil use was a little over a quart between 25-hour oil change. So if you have little oil on the belly and little oil out of the separator drain, why have a speparator. Most of that quart and change was burned by the engine. I am not using a separator on my new project.
If your engine is healthy and you are not leaking oil into the bottom of the cowl (which will also coat your belly) you will see only a little oil on the belly. Your never going to make it zero. Any little bit of oil, no matter what its source will get on the belly at 200mph.
Try flying with out one first. If you are already flying and find oil on the belly, fix the oil drips and leaks, clean the inside of the lower cowl, route the breather right up to the hot exhaust (use a metal tube at this end). Routing the breather tube near the exhaust burns what little comes out. This is per Van's suggestion, and it worked well for me. If you are really getting a lot of oil out the breather you may have an engine problem. Look into the engine problem before covering up the symptom. I have seen tubes get routed down the gear leg or out the tail on aerobatic planes. You end up with a oil on the gear leg or tail wheel.
When you say Aerobatics I assume you mean positive G maneuvers. I would admit if you are going to push the zero G's may be some separator might help, but if you are going that far with your Acro, may be you should go all the way with an inverted oil system.
All the little AOS devices are expensive and add weight. If you read the hype for the $360 M20:
http://www.m-20turbos.com/separator_facts.htm
Does that look like $360 worth and the "scientifically engineered 5 chamber oil separator galley" they talk about in their literature?
(click to enlarge) I talked to this guy at Oshkosh and he was rude and talked down to me with a bunch of
. I have a degree in mechanical engineering and this guy just got mad when I asked him how it worked, like why is it "centrifugal". From their web site:
"M-20 crankcase models use a 5-stage, ambient pressure process, which includes two oil collection stages, a tiny sump with a capacity of only a few drops of oil controlled by a weir, an air scrubber and a anti-siphon device. Others have faked a "centrifugal" design....."
Give me a break. "Weir" is simply a wall or dam. All the other stuff, "air scrubber", "centrifiugal", "tiny sump" and "anti-siphon device", is
. "AIR-SCRUBBER", please. As far as glowing reports from some articles?
Right, well I guess if your engine is sick and pumping out qts from you breather may be it will catch some of it. A healthy oil tight Lycoming will not need it. May be the M20 is the best thing ever invented, but it sure looks very close to the design Tony Bingelis published in the EAA magazine years ago. Since there is no patend pending my guess is this is nothing special.
POT SCRUBBER:
A lot of guys put the cheap round separator on (
http://www.aircraftspruce.com/catalog/eppages/hboilbreather.php ) and stuff it with a stainless steel scrub pad. I hate the idea of anything blocking the breather. There is nasty stuff coming out, blow-by with combustion products. You don't want back pressure. You want the stuff to "breath" and get out. As the scrub pad gets goo'ed up in the separator, back pressure gets worse.
The Myth of running 6 quarts in your engine:
Well it is not a myth, it is true. Running over 6 qts results in it just blowing out. Small Lycoming's that run more than 6 quarts tend to throw the excess off quickly. Also despite M20's hype shaming you for running only 6 qts, as part of their sales pitch, 6 qts is plenty. Not to forget most have added large spin on filters and oil coolers, which makes the actual system volume more than the 6 qt in the sump. Don't worry 6 qts is plenty.
Why does Lycoming have an 8 qt capacity if it was not meant to run 8 qts? Ans: FAR Part 23 requires (paraphrased):
"...an engine oil capacity not be less than the endurance of the airplane under critical operating conditions and maximum oil consumption of engine under the same conditions, plus a suitable margin to ensure adequate circulation and cooling..."
Therefore you have the 8 qt mark on the dip stick to account for the regulatory oil reserve, but 6 qts is the optimal max amount, most know from experience. Back in the day some engines, like round ones, had oil tanks and used oil like gas, so a reserve oil supply made sense. For a little Lyc start with 5.5 qt min for local short flights and no more that 6 qts for long flights. With 6 qts you have 4 qts usable. If you loose more than 4 qts in 4 hours you have serious troubles. An extra 2 qts will not make much difference.
Good Luck George.