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Oil psi drops the higher I climb

in 912iS Technical Questions 7 years ago
There are two pipistrel virus aircraft here with 912is engines with hydraulic constant speed props and dynon skyview avionics with sensor package that have the same issue, when we climb to higher altitudes the pressure drops significantly. I have 40-50psi on the ground 2500’asl , at 6000’asl oil psi indicates 30, and at 14,500 I got 16 psi. The change is only to do with altitude not with temperature as we are in Alberta Canada and fly in cold temps and don’t have low psi. The other owner replaced his oil pump and spring with no improvement. The only way we will be able to verify that the dynon is reading correctly is if we install analog gauge and fly it to high altitudes, but the video recommends not to do this in flight, only for ground checks. Well we cannot check this issue on the ground. Any suggestions?
2B145EDF-A414-4294-A493-4FB36032A29D.jpeg (You do not have access to download this file.)

  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    Interesting!

    You are seeing a 30 psi drop at altitude.
    The absolute pressure change due to altitude.is ~5psi going from 2000 to 14000 feet.

    The Oil Pressure is reported to the Dynon through the CAN Bus from the Oil Pressure sensor on the engine.
    The Log file in the ECU of the 912is should have the pressure value the engine thinks it is seeing.
    You should be able to see this with the BUDS Program.

    If it is a sensor issue, swap sensors from a plane with known good Oil Pressure readings.

    Fuel Pressure in the 912is is a Differential Pressure.
    Oil Pressure in the 912is is a Relative Gauge Pressure.
    The Dynon applies a correction to the Fuel sensor based on the Manifold pressure.
    It might be configured incorrectly to apply a MAP pressure correction to the Oil Pressure.
    This would be apparent as the Oil Pressure would change significantly with major throttle changes.
    What Oil Pressures are displayed as the throttle changes from Idle to Wide Open?
    This would be apparent on the ground also.
    It is common for the pressure to increase ~10 psi as the Engine RPMs increase from Idle to WOT.

    Crazy ideas to check that are probably fine...

    Is the Vent line from the Oil tank restricted?

    I see the Oil Temp is above 100°C.
    Could you be boiling off water in the oil as the altitude increases and the engine runs hotter?

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
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  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    Appreciate all the info! Possible to swap sensors with another one but we are both getting the same results, loss of pressure as we climb. I will have to check out the MAP pressure correction to see if it’s applying a correction. I would’ve thought that the dynon sensor software they provide would automatically set up the sensors correctly for this engine no? If it’s not applying corrections then I think we need to install analog gauge and go for a flight to see what actual pressure is doing.

    Interesting that should only see 10psi change from idle to full open. At idle I’m around 40psi and full throttle it goes up to about 70. Then once I’m airborne it starts to reduce when throttle comes back to cruise. It’s not water in system as I regularly get temps over 110to burn off deficiencies. The breather tube works and isn’t blocked, also have small hole on top of breather tube where it comes out of the tank in case it does ever get blocked lower down as I’ve had a Cessna freeze up before and get oil all over my windshield.

    Don’t have access to buds and nearest Rotech Center is about 800km away, and they are in the middle of bc so not always easy weather wise to get to them.

    Appreciate the help. Will report back tomorrow what I find on the MAP settings.
      
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  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    ... Possible to swap sensors with another one but we are both getting the same results, loss of pressure as we climb.... I would’ve thought that the dynon sensor software they provide would automatically set up the sensors correctly for this engine no? If it’s not applying corrections then I think we need to install analog gauge and go for a flight to see what actual pressure is doing.

    Interesting that should only see 10psi change from idle to full open. At idle I’m around 40psi and full throttle it goes up to about 70. Then once I’m airborne it starts to reduce when throttle comes back to cruise. ...
    Don’t have access to buds and nearest Rotech Center is about 800km away, and they are in the middle of bc so not always easy weather-wise to get to them...


    Just a gut feeling that the Oil pressure is fine and the problem is either in the sensor or the display system.

    Every 912is owner should Own, or have close access to a shared BUDS Dongle. There is just too much information that you can not see without it. Rotax should include one in every engine package. It really is not an optional item.

    The Mechanical gauge will easily tell the tale.
    There is a unused port that faces the prop on the Oil Pump, just above the Oil Inlet Hose, that is easily accessable to add a temporary gauge.
    Just climb to altitude while staying within gliding distance of the airport just in case a hose blows off.

    Just because you have two planes acting the same does not mean you do not have two bad sensors.
    Do not assume anything is good until it is proven to be good.
    Swapping with a Known good sensor would be easy and definitive.

    For the record, I do not think the Dynon is misconfigured but I am also not willing to rule it out until proven otherwise.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
    Report

  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    The other pipistrel owner has a buds dongle I’ll have to see if he checked the data from his flights. He has a suspicion that it’s not the sensor but possibly the way the sensor is wired or grounded perhaps. I have been told the pipistrel factory have been trying to solve this on their end as well, so I’m not entirely sure if it’s just us or if it’s a fleet wide problem with 912iS installations in a pipistrel. Apparently they are trying to route the oil lines differently, I’ve sent an inquiry to the company to find out what they are doing, if others have this issue, and what can be done to solve it.

    I’m fully with you that the engine should come with dongle. I even started petition page trying to build steam for this. At least the dynon will now show what details about faults when they occur in the engine.

    I did not know about this extra plug for analog guage thanks for bringing to my attention. That will help for testing to compare the two.
      
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  • Re: Oil psi drops the higher I climb

    by » 7 years ago

    The Aircraft manufacture has nothing to do with the Oil Sensor, wiring, or ground.
    The Oil sensor and wiring are 100% Rotax Factory installed items.
    The sensor is wired through the Engine Harness to the ECU and the data leaves the engine via the CAN Bus.
    So it would not be a general Pipistrel problem, it would be a general 912is problem.
    If it is a sensor wiring or grounding issue it will show in the BUDS Data.
    At least you will know if the problem is internal or external to the engine.

    That unused oil port is used to supply the Oil to the Turbocharger in the 914 engine.

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Clicking the "Thank You" is Always Appreciated by Everyone.

      
    Report
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