Venting of Lycoming 0-290 D Engine

Hello
I have been helping a young fellow EAA member with the restoration of a
EAA Biplane , he is using a rebuilt Lycoming 4cyl. , 125 H.P. 0-290 D engine
in this plane and has a 3/8 " O.D. aluminum tube running from the firewall
and exiting just ahead of the tailwheel , he wants' to keep the underside of
this fabric covered plane as clean as possible , the vent elbow that exits
the top forward area of the crankcase has an I.D. of approx. 5/8 " , he
plans to put a reducer to make the step from 5/8 " I.D. to approx 1/4 " I.D.
on the alum tube , this tube will go from the firewall to the tailwheel ,
the question is this , does the engine vent just relieve pressure and will
the long narrow tube cause any problem ?, am not an expert in the dynamics
of this of this area of the engine , any thoughts or help would be
appreciated .
Thanks
Phil Lohiser
EAA 12873

On Apr 27, 2:09 pm, "Phil" wrote:
Hello
I have been helping a young fellow EAA member with the restoration of a
EAA Biplane , he is using a rebuilt Lycoming 4cyl. , 125 H.P. 0-290 D engine
in this plane and has a 3/8 " O.D. aluminum tube running from the firewall
and exiting just ahead of the tailwheel , he wants' to keep the underside of
this fabric covered plane as clean as possible , the vent elbow that exits
the top forward area of the crankcase has an I.D. of approx. 5/8 " , he
plans to put a reducer to make the step from 5/8 " I.D. to approx 1/4 " I.D.
on the alum tube , this tube will go from the firewall to the tailwheel ,
the question is this , does the engine vent just relieve pressure and will
the long narrow tube cause any problem ?, am not an expert in the dynamics
of this of this area of the engine , any thoughts or help would be
appreciated .
Thanks
Phil Lohiser
EAA 12873

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 and maybe even
getting so much on the windscreen that he can't see where he's going.
If he flies long enough he'll run out of oil. And if by some miracle
it doesn't blow out, and then he flies in subfreezing weather, that
long tube is going to ice up immediately (water vapor condensing in
the tube, the vapor being an unavoidable byproduct of combustion) and
the sure thing will happen: blown seal and lost oil.
Cessna and Piper and Mooney and Beech and American Champion and
Taylorcraft and about a hundred others over the years have used
minimal lengths of 5/8" and 3/4" and 1" vent tubes for some very good
reasons, and those tubes often have a small hole well above the outlet
in case the outlet, being in the cold slipstream, ices up. A long tube
under the belly would ice up all along its entire length.
A slightly oily belly is much preferable to an engine failure.
It's pretty hard to improve on what the major manufacturers do with
their airplanes. They're concerned about oily bellies, too, but you
don't see long tubes under them. You can get the Airwolf oil/air
separator setup to supposedly extract the oil from the venting air,
and we have one on a 172, except that it doesn't work all that well.
Needs a vacuum pump on the system, too, to get the pressure to drive
the oil back from the separator to the case.

Dan

wrote:
On Apr 27, 2:09 pm, "Phil" wrote:

Hello
I have been helping a young fellow EAA member with the restoration of a
EAA Biplane , he is using a rebuilt Lycoming 4cyl. , 125 H.P. 0-290 D engine
in this plane and has a 3/8 " O.D. aluminum tube running from the firewall
and exiting just ahead of the tailwheel , he wants' to keep the underside of
this fabric covered plane as clean as possible , the vent elbow that exits
the top forward area of the crankcase has an I.D. of approx. 5/8 " , he
plans to put a reducer to make the step from 5/8 " I.D. to approx 1/4 " I.D.
on the alum tube , this tube will go from the firewall to the tailwheel ,
the question is this , does the engine vent just relieve pressure and will
the long narrow tube cause any problem ?, am not an expert in the dynamics
of this of this area of the engine , any thoughts or help would be
appreciated .
Thanks
Phil Lohiser
EAA 12873


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 and maybe even
getting so much on the windscreen that he can't see where he's going.
If he flies long enough he'll run out of oil. And if by some miracle
it doesn't blow out, and then he flies in subfreezing weather, that
long tube is going to ice up immediately (water vapor condensing in
the tube, the vapor being an unavoidable byproduct of combustion) and
the sure thing will happen: blown seal and lost oil.
Cessna and Piper and Mooney and Beech and American Champion and
Taylorcraft and about a hundred others over the years have used
minimal lengths of 5/8" and 3/4" and 1" vent tubes for some very good
reasons, and those tubes often have a small hole well above the outlet
in case the outlet, being in the cold slipstream, ices up. A long tube
under the belly would ice up all along its entire length.
A slightly oily belly is much preferable to an engine failure.
It's pretty hard to improve on what the major manufacturers do with
their airplanes. They're concerned about oily bellies, too, but you
don't see long tubes under them. You can get the Airwolf oil/air
separator setup to supposedly extract the oil from the venting air,
and we have one on a 172, except that it doesn't work all that well.
Needs a vacuum pump on the system, too, to get the pressure to drive
the oil back from the separator to the case.

Dan

I wanted to check the Pitts plans.
There is a breather tube shown on the plans running just
below thr left side stringer.
I _think_ it's 1" od aluminum tube.

If anyone has the Pitts plans handy???

Richard
--
(remove the X to email)

Now just why the HELL do I have to press 1 for English?
John Wayne

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

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

You have hurt my feelings again....... :((

cryin lil ben

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

Dear Phil,

Your friend has the physics backwards.

Lycoming's use of a vent diameter of 5/8" should be taken as the
minimum needed to properly vent blow-by from the crankcase. Anything
attached to that outlet must then INCREASE in diameter according to
length... or be provided with some active means of pressure reduction
that is independent of throttle position. A venturi would work (and
has been used for this purpose in the past) but they tend to clog-up
or freeze. A metal funnel (!) has also been used on a small vent line
but slow speeds calls for a pretty big funnel (ie, about a 6" funnel
for a 1/2"x15' vent-line at about 60 mph) but it looks weird as
hell. If you have sufficient vertical height you can use a passive
oil separator... but keep in mind they make dandy condensers of water
as well as oil. Ditto for the active types, which generally use some
form of rotary motion to condense/capture the vapor, plus a scavenge
pump to get it back to the sump or oil tank.

Unstated -- but implied by the aircraft-type -- is the need to install
a flop-valve on the vent line to deal the occasional negative-g
maneuver. Without it, he's going to blow his oil overboard. If he
insists on using a small-diameter vent line, he'll probably blow his
seals at the same time.

-R.S.Hoover
-EAA 58400

PS -- There is also the tray type of oil separator/catchment that fits
under the firewall. It can hold a quart or more of oil which you
discretely drain between shows.

"Morgans" wrote in message
...

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.

Jim ...........

If you've ever seen the oil that collects in an oil/water separator, you
wouldn't want it back in an engine. I realize that some of the water in the
separator is condensation from the air coming back up the vent from the
outside after shutdown, but even so, the watery sludge in the reservoir is
really gross. Best to spend a few bucks and a couple of hours building a
simple firewall-mounted separator (plans available in old issues of Sport
Aviation when they had such things).

Wiping the bottom of a fuselage is kind of a Zen thing for me. Takes me back
to a simpler time.

Rich S.

"Morgans" wrote in message
...

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.


A) They don't have to.

B) PCV as found on automobiles won't work well at higher loads (no vacuum),
but new sytems for large diesel trucks are now coming onto the market to
meet emission standards - they have the same lack of vacuum...

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"stol" wrote in message
...

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

You have hurt my feelings again....... :((

Whoops!

Sorry.

That should have read "nothing new under the sun, when it comes to the _old_
designed air cooled opposed aircraft engines.

Or something like that! ;-)

Speaking of auto engine aircraft, how do you handle the crankcase ventilation
issue? Vent overboard, or recirculate?
--
Jim in NC