On Apr 27, 11:22 pm, "Morgans" wrote:
wrote



Unless that engine is really tight (pretty much zero ring
leakage) he'll end up with backpressure in the crankcase and will blow
the front crank seal out, losing oil at a good clip

I agree.

How come airplane engines don't have PCV valves, plumbed back into the intake
manifold, like cars? You could even use an oil separator, before the gas enters
the manifold, if too much oil was worried to be a problem.

An arrangement like that would solve the oily discharge on the belly, I would
think.

Might even keep the intake valves lubricated a little bit! g

I wonder what the answer is, and why that solution would be a problem. I'm sure
it has been tried, since it seems there is truly nothing new under the sun, when
it comes to airplanes.
--
Jim in NC

No PCV because the aircraft engine runs at high manifold
pressures most of the time, so there's too little differential (read
"manifold vacuum" to suck a PCV valve open and adequately purge the
gases. On an auto, when the throttle is fairly open, the PCV valve
pretty much closes. The valve has to be there to stop flashback in
case the engine backfires; the flame would ignite the gases in the
crankcase. Boom, big ugly mess and a major CG shift. In the auto, the
gases will, at full throttle or nearly so, back up through the
crankcase intake filter and into the air cleaner and get cleaned up
that way. The filters act as flame arrestors. When the engine gets
old, there's too much blowby and lots of it exits this way, and its
moisture freezes up the crankcase intake filter in colder weather.
BTDT.
It could be done, with some different plumbing, which adds
weight, expense, and certification hassles. When the EPA or whoever
decides that airplanes need all the antipollution stuff that cars
have, we'll see it on airplanes and our useful loads will drop
considerably.

Dan