Oil pressure drop

Matt & Shay

I agree that a configuration problem seems hard to have happen on the G3X/GEA-24 system. What I remember is that you go to the configuration screen and for oil pressure you just select Rotax FADEC. After that I don't think you get to choose the sensor type (I'm going out to the hanger later today and will check this).  Also, I don't know if the correction from absolute to gauge pressure is applied by the EFIS or the Rotax ECU. That said, a sensor configuration problem or sensor failure seems the most likely cause of what is being observed. I just can't see altitude or engine heat affecting the actual oil pressure in a way so closely related to the altitude. 

I think I would call the G3Xpert tech line and discuss this with them.  They may have seen this before, and they can tell you how the G3X processes the signal.

I consulted with Midwest Panel Builders and they said it’s the ECU and there is no configuration associated with relative / absolute. 

Jeff Blakeslee wrote:

Matt & Shay

I agree that a configuration problem seems hard to have happen on the G3X/GEA-24 system. What I remember is that you go to the configuration screen and for oil pressure you just select Rotax FADEC. After that I don't think you get to choose the sensor type (I'm going out to the hanger later today and will check this).  Also, I don't know if the correction from absolute to gauge pressure is applied by the EFIS or the Rotax ECU. That said, a sensor configuration problem or sensor failure seems the most likely cause of what is being observed. I just can't see altitude or engine heat affecting the actual oil pressure in a way so closely related to the altitude. 

I think I would call the G3Xpert tech line and discuss this with them.  They may have seen this before, and they can tell you how the G3X processes the signal.

Yes, my recollection is that the only configuration was to select Rotax FADEC.  I also agree that the uncanny correlation with altitude smacks of a sensor or computation issue, I’m just at a loss to think what it might be.

Hi all

OK, once more, altitude absolutely has an effect on oil pressure.  The ambient pressure on top of the oil (in the oil tank) will diminish with decreasing pressure of altitude.  That will drop the oil pressure by that amount of drop.  The oil pressure is gauge pressure, it is a simple sender on the engine block and the reading to the ECU makes no calculations, it is a direct reading.  Perhaps verify your instrument by using BUDS and read the oil pressure recorded during an event to verify your instrument.  

As far as altitude affecting oil temperature, for sure this can happen.  At altitude the Trubo will be running at max given the stated ranges he is having an issue with.  The higher we try to compress the air the hotter things will run. Heat rejection is very difficult due to the thin air.  Oil temperatures running at max can cause the oils to thin and lead to some pressure drops.  It is most likly a combination of factors here and not just one thing.  

In high altitude Rotax powered drones special modifications are done to the oil line vent to keep higher pressures on top of the oil.  In normal manned flight this is not generally done with small piston engines.  Anything over flight level 14 is generally  controlled airspace and not recreational flying.  

Cheers

Rotax Wizard wrote:

Hi all

OK, once more, altitude absolutely has an effect on oil pressure.  The ambient pressure on top of the oil (in the oil tank) will diminish with decreasing pressure of altitude.  That will drop the oil pressure by that amount of drop.  The oil pressure is gauge pressure, it is a simple sender on the engine block and the reading to the ECU makes no calculations, it is a direct reading.  Perhaps verify your instrument by using BUDS and read the oil pressure recorded during an event to verify your instrument.  

As far as altitude affecting oil temperature, for sure this can happen.  At altitude the Trubo will be running at max given the stated ranges he is having an issue with.  The higher we try to compress the air the hotter things will run. Heat rejection is very difficult due to the thin air.  Oil temperatures running at max can cause the oils to thin and lead to some pressure drops.  It is most likly a combination of factors here and not just one thing.  

In high altitude Rotax powered drones special modifications are done to the oil line vent to keep higher pressures on top of the oil.  In normal manned flight this is not generally done with small piston engines.  Anything over flight level 14 is generally  controlled airspace and not recreational flying.  

Cheers

The effect is much less than what he is seeing.  He is seeing about 25 psi difference between 500’ and 14,000’.  Standard atmospheric pressure at 500’ is 14.44 psi.  Standard atmospheric pressure at 14,000’ is 8.64.  The difference is 5.8 psi.  That isn’t even close to 25 psi so while that may be a small part of the difference, something much more significant is at play.