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  #1  
Old 05-07-2022, 02:25 PM
EchoJuliet EchoJuliet is offline
 
Join Date: Oct 2021
Location: Everett, WA
Posts: 28
Default Oil tank vent tube

Has anyone had success modifying the oil tank vent tube (FF-1218-1) in order to reduce the amount of oil film that accumulates on the aircraft belly? Wondering if changing the tube length (shorter or longer), or a 45 deg. cut on the end the tube would make any difference.. I typically have the oil level at 1/4 to 1/2 on the dipstick flat (warm burp) and am using very little oil - and that small amount is being vented out the tube.
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  #2  
Old 05-07-2022, 08:45 PM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,390
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How about putting the end of the tube into a bottle that is fastened to the firewall?
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  #3  
Old 05-07-2022, 08:57 PM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest
Posts: 2,328
Default My plan

Quote:
Originally Posted by Mich48041 View Post
How about putting the end of the tube into a bottle that is fastened to the firewall?
I plan to do this for my first flights and phase 1 prior to paint. This way I minimize the belly being blasted with oil prior to paint.
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  #4  
Old 05-07-2022, 08:59 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
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Default

How bad is the oil film? I get a little, but no drops or goo.
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  #5  
Old 05-08-2022, 03:07 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
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Default

Quote:
Originally Posted by PilotjohnS View Post
I plan to do this for my first flights and phase 1 prior to paint. This way I minimize the belly being blasted with oil prior to paint.
I would re-think putting oil tank vent tubing into an overflow bottle. The Rotax 9-series engines are dry-sump and only use light pressure in the crankcase to scavenge oil back to the holding tank. I’m pretty sure Rotax wants oil tank vent to be completely unrestricted and discharge into negative pressure of slipstream. Any restriction in the oil tank, or increase backpressure in the oil tank, could easily upset the flow of returning oil to the tank, and worse yet, could increase pressure in the crankcase and blow out seals. You might end up having a bad day when black oil fills the windscreen….
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 790

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  #6  
Old 05-08-2022, 06:22 AM
Mich48041 Mich48041 is offline
 
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There shouldn't be enough oil in the overflow bottle to cover the end of the vent tube.
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  #7  
Old 05-08-2022, 09:06 AM
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Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
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Default

Quote:
Originally Posted by Mich48041 View Post
There shouldn't be enough oil in the overflow bottle to cover the end of the vent tube.
Correct... I would not restrict the air flow from the oil tank vent in any way. I strongly suspect that Rotax wants the end of the tube in the negative pressure slipstream to keep the oil tank at a low or negative pressure to facilitate crankcase scavenging, which is marginal at best. Remember that Rotax stipulates 122F oil temperature for high speed engine operation. This is necessary so oil viscosity is low enough that egress of oil is at least equal to oil pump volume so oil does not pool and overload the crankcase. Again, a bad day when crankcase pressure overcomes the seals because drain back to tank doesn’t have sufficient flow.
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 790

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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  #8  
Old 05-08-2022, 12:14 PM
EchoJuliet EchoJuliet is offline
 
Join Date: Oct 2021
Location: Everett, WA
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Default

Quote:
Originally Posted by RFSchaller View Post
How bad is the oil film? I get a little, but no drops or goo.
It's just a little, just enough to see it's there (not dripping). I usually clean it about once a month. Here we have a high-tech modern engine and we're still cleaning oil from the belly of our aircraft. Seems like Rotax should have a better solution.
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  #9  
Old 05-08-2022, 01:05 PM
PilotBrent PilotBrent is offline
 
Join Date: Dec 2011
Location: Hackettstown, NJ
Posts: 531
Default

Quote:
Originally Posted by EchoJuliet View Post
It's just a little, just enough to see it's there (not dripping). I usually clean it about once a month. Here we have a high-tech modern engine and we're still cleaning oil from the belly of our aircraft. Seems like Rotax should have a better solution.
While I get ribbing from pilots in my neighborhood about my RV-12 cruise speed, I typically remind them of my fuel burn and clean aircraft belly. Do respect experimenting with things like this, but cleaning ROTAX belly oil off of my aircraft is way down the list of concerns or complaints. (Its hard to believe how little oil this engine uses between changes.)
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  #10  
Old 05-08-2022, 03:32 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Default

Quote:
Originally Posted by EchoJuliet View Post
It's just a little, just enough to see it's there (not dripping). I usually clean it about once a month. Here we have a high-tech modern engine and we're still cleaning oil from the belly of our aircraft. Seems like Rotax should have a better solution.
Cars used to have a “Road Tube” which vented the crankcase. If memory serves… it was ~3/4” diameter, angled downward, with a 45 degree chamfered discharge end. Nasty…. Then in the mid 60’s the PCV valve replaced the Road Tube in the name of environmental protection. The crankcase was vented through the one-way PCV valve into the intake manifold where the fumes were mixed with carbureted fuel/air mixture and burned in the combustion process. The valves needed frequent cleaning and replacement. I doubt if an aircraft engine would be good candidate for such a high maintenance item and where crankcase pressure varies depending on altitude.
__________________
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 790

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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