Oil Pressure sensing, burning up fossil fuel using AI to calculate stuff..

[John McClanahan]

Hey Group - This is what I ate for breakfast this morning.  Maybe you’ll find it interesting -

Here’s where I am with my C-182 rehab project - hooking up the yellow spaghetti on the new engine..

So, I’m hooking up the oil pressure sensing - Oil pressure is picked up from the oil gallery through a restrictor fitting.  You have a restrictor fitting on your airplane, right?  Hint - if your fitting is blue, it’s not a restrictor fitting.  It should be steel, not anodized aluminum.  Why?  Aluminum can fatigue and break..  Here’s what the correct fitting looks like.  Spruce sells them but they’re not cheap (~$98).  Hole is .040.

The restrictor fitting does two things for you.  First, the small hole protects you (sort of) from rapid oil loss in the event of a broken hose.  Second, the restriction reduces pulsations that will kill your pressure sensor.  You know that right?  Vic Syracuse addressed this in an article in Sport Aviation if I recall correctly.

Ok.  So I was wondering this morning if it was necessary to fill the hose with oil before I connected it to the sensor?  Obviously, with the restrictor fitting (electrically analogous to a resistor), if there is air in the line (analogous to a capacitor), there would be delayed response (time constant to you engineering types) to pressure changes at the sensor.  But how much?  Is it really necessary to fill the hose with oil?

So I asked AI (ChatGpt) to analyze this situation based on Phillips XC at 70° and 180°, with a 24” AN-4 hose varying from no air in it to full of air.

That burned up some fossil fuel to calculate - 1 minute 47 seconds at the data center..smoke was coming out of the power plant stacks..

When I got the data, I had AI create an Excel spreadsheet/chart showing the data.  Here’s a chart -

This is what the chart shows - the vertical axis is how long it takes the sensor to get to 90% of the actual oil pressure.  In other words, how long before you get a pretty accurate reading..

The horizontal axis is % of trapped air in the example 24” AN-4 hose from 0 to completely full of air.

So for example, the upper, blue line is oil at 70°F and 20 psi.  It takes 8 seconds for the sensor to read 90% correctly.  That’s quite a long time in aviation.

Obviously, when the engine is warm (oil at 180° F), it takes way less time, ~ 1/2 second.

So, I think there are two things worth considering here.

First, do we need to fill the hose with oil?  My opinion is, yes, it’s worth doing because it will make the system much more responsive when starting up, especially on a cold day.  That makes me think that in the past, I was thinking it was taking some time for the engine to develop oil pressure when it was actually, mostly, air in the line.   Makes you think, doesn’t it?

The second point I think worth considering here is the power and value of AI.  Tommy Turner put me onto this and I’ve found it very helpful.  It doesn’t take much skill to use it.  Just ask it questions.  However, be careful and make sure you validate the answers before you use them to make life changing decisions.

I’m interested in your comments.

Thanks -

John McClanahan

[vic syracuse]

Filling that hose gets messy. Here's a trick I use. Remove the lower spark plugs Have someone crank the engine with the ignitions OFF. It will spin faster with the plugs out and you will get oil pressure. Loosen the fitting on the oil pressure hose at the sensor and it will quickly pump the air out of that hose and once you see some oil coming out at the fitting, tighten it and you are done. :)

Vic

Vic Syracuse

https://baselegaviation.com

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