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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 |
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Venting of Lycoming 0-290 D Engine
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 |
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Venting of Lycoming 0-290 D Engine
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Venting of Lycoming 0-290 D Engine
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 |
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Venting of Lycoming 0-290 D Engine
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 |
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Venting of Lycoming 0-290 D Engine
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 |
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Venting of Lycoming 0-290 D Engine
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. |
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Venting of Lycoming 0-290 D Engine
"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. |
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Venting of Lycoming 0-290 D Engine
"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. |
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Venting of Lycoming 0-290 D Engine
"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 |
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