Oil pressure fluctuations

by Alexander Kluge in 912 / 914 Technical Questions 6 years ago

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Re: Oil pressure fluctuations

by Alexander Kluge » 6 years ago

Alexander Kluge

8 20 28

Yes, with the mechanical gauge, it looks similar, with the VDO sensor and analog instrument (like in your clip) its stable.

I understand your approach - but as only a small minority of Rotor 912 engines have this issue, I wonder why we have this phenomenon with the same engine but nearly all relevant parts exchanged - this is highly unprobable. I just don't want to overlook some other reason.

Maybe the condition of the oil pump in conjunction with the oil pressure valve makes some engines more prone to resonance than others.

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Re: Oil pressure fluctuations

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.96k

This sounds like Deja Vu all over again! :whistle:
https://www.rotax-owner.com/en/rotax-forum/3-4-stroke-technical-questions/5484-severe-jittering-oil-pressure?limitstart=0

Some owners have changed every part of the oil system at great personal expense to them and even persuaded another owner at their airport to swap oil pumps from known good engines with no improvement.

As stated, this is a reoccurring theme that most owns eventually just accept as normal.
I am willing to offer a solution, you just need to ask. Bill <Whertzel1@yahoo.com>

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

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Re: Oil pressure fluctuations

by Wayne Hubbs » 6 years ago

Wayne Hubbs

5 10 0

When I first built my gyroplane with a 914 engine my EIS system showed 75 psi steady oil pressure with no variation, I have video of how steady the pressure was and around 200 hours it dropped to 40 psi in an instant but now goes up and down continually about 5 pounds. I changed the sender, changed to latest bullet regulators, and installed a direct reading car oil pressure gauge which read 52 and steady pressure. I now have flown another 300 + hours with the variation jumping up and down as I trust the car gauge reading.

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Re: Oil pressure fluctuations

by Genival Pacheco » 6 years ago

Genival Pacheco

4 87 135

I had this problem a while back.
My plane was equipped with an EMS TL Electronics and VDO sender and there was a variation in the oil pressure of approximately 7 psi that was driving me crazy.
After everything verified I decided to change the EMS and install an AVMAP engibox that gave a lot of work to function properly and refused to work with the VDO so decided to install a Keller type that solved the problem. Still a slight variation in the pressure reading of approx. 3 psi which is acceptable.
Tired of this issue,at the time, instead of removing the VDO sensor that had output to an oil pressure lamp kept the sensor and installed the lamp.
This way, I know immediately after starting the engine if there is oil pressure (go no go) which is the most important and from then on the EMS reading indicates if the pressure value is within the parameters.
So the good old lamp became my backup of the oil pressure. I recommend to everyone not only the oil pressure but also a lamp to verify the operation of the alternator.
Old technologies that are still great.

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Re: Oil pressure fluctuations

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.96k

You hit the mark. With a mechanical gauge, we see fluctuations.
They "look" like harmonic oscillations. That implies that the sample rate of all the systems we compared (Bluetooth sensor-phone; VDO sensor with Dynon and with analog instrument; kavlico and Rotax with the Dynon) is to slow to show the fast pressure changes. What we saw as "fluctuations" may in fact be an oscillation...

Alexander,
Just out of curiosity...

Your Electrical gauge readings are running on the high side and are just under the "Normal" High Limit of 5 bar.
4+ Bar would be expected at 5000rpm on a 60°C Engine.
4+ Bar at 3500rpm at 80°C seems a little high.
I would expect to see the pressure in the 3-3.5 range under those conditions.

I suspect that the "Filter" in the electronic gauges would be a simple capacitor filter that tends to pump up to near the peak voltage. Essentially giving you the highest (not the average) reading it saw during the sampling period.

Did you notice if the Mechanical gauge (despite the Oscillations) was generally reading lower pressures than the digital gauges?

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

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