Odd oil pressure behaviour on two 912iS’s.

[dzubot]

There are two identical pipistrel aircraft with 912iS engines and mt constant speed hydraulic props here in Alberta Canada that have very odd oil pressure behaviour that we cannot figure out. Wondering if it’s possibly due to the oil pressure sensors or software at this point.

Symptom: oil psi is not constant on both aircraft, they both have good indicated pressure on the ground before take off, indicating around 40-50psi. I can’t speak directly for the other owner as to exactly the specs he gets but we both see similar numbers. I see 30 psi at 6000-7000’asl and at 15,000’ I got as low as 14 psi this week while crossing over the Rockies. The other pipistrel owner replaced his oil pump in hopes it would bring up the psi but it did not improve his pressure readings. So we are stumped at what this could be.

Anyone else out there seeing similar things on their 912is engines?  Both aircraft have the same dynon skyview 10” displays and sensor packs for the 912iS.

My next step will probably be to install an analog gauge to determine if the dynon is indicating the correct pressure. But the rotax guys here also do not know what would be causing this on both aircraft.

 

[jakej]

The pressure that you are seeing on the ground - is that what is expected ? Hot or cold oil ?
If yes then I think the next check is what you’ve already worked out, use a mechanical gauge ( calibrated is best) to confirm or not whether what is displaying on the Dynon is correct.
The correct sensor type has been entered into Setup Menu I presume ?

 

[dzubot]

Hi Jakej, Yes it's expected although i'm surprised at how the oil pressure changes on the ground too. At idle I have about 45 psi but at full throttle for take off the oil pressure climbs to about 70, i've never seen oil pressure fluctuate like this in any other aircraft. The other pipistrel owner has same issue, so it's either wiring issue with the sensor, or the sensors are faulty, or maybe it's how pipistrel has routed the oil lines. We can rule out bad oil pumps and pressure spring since the pipistrel dealer has replaced this on his with no change. I think we will have to install analog gauge to confirm it's not the actual oil pressure fluctuating and possibly a dynon sensor or software or wiring issue.

 

[jakej]

If that is the case then I’m guessing it’s a pressure system design issue however it’s hard to know not being there [ch128521]
Please post your findings here when you get a resolution to the issue - it may help others too.

 

[dzubot]

I'll be installing an analog gauge this week to verify the oil pressure against the dynon indicated pressure. Will post results.

 

[vlittle]

I'll be installing an analog gauge this week to verify the oil pressure against the dynon indicated pressure. Will post results.

From rotax-owner.com:

Alexander,
If by "Fluctuations", you mean that the Dynon display appears to be generating random numbers between 3.x and 1.x with no apparent pattern at all...
and the needle on a mechanical gauge appears to be vibrating wildly within a similar range of pressures...
This is a common complaint of a small but significant number of owners.
It typically only appears at higher RPMs and only with Hot Oil.
Most just deny it is a problem and accept it as normal.

The inherent problem is in the design of the Oil Pressure regulator piston.
Rotax no longer uses this style regulator in its later designed engines. (912is,915)
Once the regulator Ball or Mushroom Valve begins to regulate, it moves OFF of its seat and is no longer supported or stabilized.
If the vibrations in your particular installation happen to synchronize with the spring in the regulator, it becomes a "Bobble-Head" and the pressure flutters like a flag in the wind.
You can change the Pump Housing, spring, ball, or Mushroom valve all you wish. The problem will remain.

I have a drop-in solution that replaces the Rotax Oil Regulator with a different proprietary design.
There are currently three prototypes in the field with a few hundred hours of flutter free operation on them.
If you would like to discuss using my solution, please contact me at WHertzel1@yahoo.com.

V