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How Much Oil Pressure when Windmilling?

D

Dad's RV-10

Well Known Member
For those with old school oil pressure annunciator lights, what PSI switch should be used to reliably indicate an engine that is no longer running? How many PSI does a typical 320/360/375 produce with a windmilling prop?

I've ordered a "Smart Glide" switch with a backlit LED annunciation. In a perfect world, it would be configured to illuminate "Smart Glide" when the engine is no longer running. The switch LED illumination would function no differently than a typical low oil pressure annunciator light.
 
I think this may not work as intended. Typical windmilling props turn at higher RPMs than they do during ground taxi. Do you want your idiot light on during ground operations?
 
BobTurner said:
I think this may not work as intended. Typical windmilling props turn at higher RPMs than they do during ground taxi. Do you want your idiot light on during ground operations?
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Ideally, no. But it really wouldn't matter much. The intent is no different than a dedicated oil pressure annunciator light; to indicate oil pressure is lost and engine failure has occurred or is imminent. I assume most (properly functioning) oil pressure annunciator lights extinguish at ground idle RPM/PSI.

I'm just trying to determine what PSI would be suitable to close the switch and illuminate the light in flight. It looks like the Van's pressure switch, which has NO and NC terminals to allow for power to a Hobbs and illumination of a low oil pressure annunciator, is triggered at 15 PSI.

EDIT: The Van's IE SPDT PRES-15 SW description indicates a 15 PSI set point, but the Nason SM-2C-20F part number indicates it's 20 PSI.
 
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Given that there might be non-oil-pressure related reasons to push that button, and given that your system will presumably be configured to monitor oil pressure, I think you would be better served by a regular old Master Warning annunciator lamp.
 
mburch said:
Given that there might be non-oil-pressure related reasons to push that button, and given that your system will presumably be configured to monitor oil pressure, I think you would be better served by a regular old Master Warning annunciator lamp.
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The switch itself is momentary. The lettered "Smart Glide" backlighting doesn't affect the switch operation. It will function if dark or illuminated.

The other wiring options are constant illumination or no illumination.

Illuminating at the loss of oil pressure seems to make the most sense.
 
I don't know...

Dad's RV-10 said:
The other wiring options are constant illumination or no illumination.

Illuminating at the loss of oil pressure seems to make the most sense.
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Are you saying that if, during a night flight, the engine quits for any reason other than lack of oil, that button will be dark, unilluminated (hard to find?)?
 
If I were faced with a windmilling engine presumably not producing power the oil pressure would be the least of my concerns.
 
BobTurner said:
Are you saying that if, during a night flight, the engine quits for any reason other than lack of oil, that button will be dark, unilluminated (hard to find?)?
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I'm not sure I'm following. If the engine "quits" for any reason, it won't have sufficient oil pressure. I'm just trying to determine a reasonable switch pressure to choose to annunciate low oil pressure.

Based on the switch that Van's sells, it's seemingly somewhere between 15 and 20 PSI.

The cockpit has plenty of illumination and the switch is labeled.

SG Dark.jpg SG Lit.jpg
 
Windmilling Oil Pressure

Dad's RV-10 said:
I'm not sure I'm following. If the engine "quits" for any reason, it won't have sufficient oil pressure. I'm just trying to determine a reasonable switch pressure to choose to annunciate low oil pressure.

Based on the switch that Van's sells, it's seemingly somewhere between 15 and 20 PSI.

The cockpit has plenty of illumination and the switch is labeled.

View attachment 41136 View attachment 41137
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This makes no sense. If I do a power-off glide in my CS IO-360 RV-8 and don't pull the prop back, the engine windmills at 1350-1500 RPM (glide speed dependent) and maintains over 70 PSI oil pressure. The oil pump doesn't care if it's being turned by a windmilling prop or combustion driven pistons. As long as the crankshaft is turning and the oil system isn't compromised, it will produce pressure. If I pull the prop all the way back, it still windmills at 600-700 RPM and produces over 60 psi oil pressure. This was tested with mixture at ICO and 0 fuel flow.

Skylor
 
skylor said:
This makes no sense. If I do a power-off glide in my CS IO-360 RV-8 and don't pull the prop back, the engine windmills at 1350-1500 RPM (glide speed dependent) and maintains over 70 PSI oil pressure. The oil pump doesn't care if it's being turned by a windmilling prop or combustion driven pistons. As long as the crankshaft is turning and the oil system isn't compromised, it will produce pressure. If I pull the prop all the way back, it still windmills at 600-700 RPM and produces over 60 psi oil pressure. This was tested with mixture at ICO and 0 fuel flow.

Skylor
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There’s your answer! The windmilling prop is driving the oil pump because it is geared to the crankshaft - and it doesn’t take that much RPM to generate enough oil pressure to lubricate the engine. Oil pressure is a very unreliable indicator of engine failure (although lack of oil pressure quickly lead to an engine failure.

Believe me - if the engine stops producing power, you are going to know it right away - no warning light needed! (This is not a wing-mounted engine that is out of sight….) Then just hit the Smart Glide button.

Paul
 
skylor said:
This makes no sense. If I do a power-off glide in my CS IO-360 RV-8 and don't pull the prop back, the engine windmills at 1350-1500 RPM (glide speed dependent) and maintains over 70 PSI oil pressure. The oil pump doesn't care if it's being turned by a windmilling prop or combustion driven pistons. As long as the crankshaft is turning and the oil system isn't compromised, it will produce pressure. If I pull the prop all the way back, it still windmills at 600-700 RPM and produces over 60 psi oil pressure. This was tested with mixture at ICO and 0 fuel flow.

Skylor
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Yes, a rotating engine produces oil pressure. I understand that the oil pump is mechanical. That's why I asked the question to begin with; "How many PSI does a typical 320/360/375 produce with a windmilling prop?"

I'm trying to determine if a non-running engine with a windmilling prop produces more than 15-20 PSI, since this is the setting of typical oil pressure switches used to activate oil pressure annunciator lights.

All I really want to know is how many PSI of oil pressure does a typical Lycoming 4 cylinder engine produce when windmilling?
 
Ironflight said:
There’s your answer! The windmilling prop is driving the oil pump because it is geared to the crankshaft - and it doesn’t take that much RPM to generate enough oil pressure to lubricate the engine. Oil pressure is a very unreliable indicator of engine failure (although lack of oil pressure quickly lead to an engine failure.

Believe me - if the engine stops producing power, you are going to know it right away - no warning light needed! (This is not a wing-mounted engine that is out of sight….) Then just hit the Smart Glide button.

Paul
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Yes, Paul. I should never have mentioned the Smart Glide switch. Obviously, I am not depending on the illuminated light to make me aware that the engine is no longer producing power. I'd simply rather not have the light illuminated 100% of the time.

I figured the simplest way to make it illuminate when it's most likely to be used (in the event of an engine failure) is to tie it into an oil pressure switch. Obviously, if the engine failure is catastrophic (no rotation), there will be zero oil pressure.

Seemingly, as long as the prop is rotating in flight, there will be enough oil pressure to prevent a typical 15 to 20 PSI switch from closing. That's all I wanted to know.

Thanks.
 
In my experience the red light goes out almost immediately when cranking the engine, so I'd say at least 25 psi.
 
When you say "a non-running engine with a windmilling prop" what you really mean is an engine that is not producing power. Maybe you can best accomplish what you want by measuring fuel flow instead of OP since fuel flow and power are directly related. Just a thought. Good luck.
 
rmarshall234 said:
When you say "a non-running engine with a windmilling prop" what you really mean is an engine that is not producing power. Maybe you can best accomplish what you want by measuring fuel flow instead of OP since fuel flow and power are directly related. Just a thought. Good luck.
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Good thought. Thanks for the suggestion.
 
Lycoming pre-oils overhauled or new motors by removing the spark plugs and turning the motor over with the starter. This should produce 30-40 PSI oil pressure so I would think windmilling will be above your threshold.
 
Mconner7 said:
Lycoming pre-oils overhauled or new motors by removing the spark plugs and turning the motor over with the starter. This should produce 30-40 PSI oil pressure so I would think windmilling will be above your threshold.
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Yep, seems so. Appreciate the replies.
 
I get down to 35-40 psi at 550 rpm during landing rollout with 200 degree oil. At 800 rpm, it's making over 50, and anything at 1000 or above it's at 70 psi. Running or windmilling, the pressure should be the same unless it stopped running because of an oiling issue.

With cold oil and the plugs pulled, my engine cranks 400-500 rpm and makes around 50 psi
 
EMS alarms

In relation to what I think you are trying to achieve, I expect that the Garmin EMS is similar to the Dynon EMS that I know can drive an external warning lamp if an alarm threshold is exceeded. Alarms can be configured for low/high: oil pressure, fuel flow, fuel pressure, EGT, CHT etc. Perhaps you can connect the external warning pin to light up the Smart Glide button?
 
agent4573 said:
...With cold oil and the plugs pulled, my engine cranks 400-500 rpm and makes around 50 psi
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Wow...good to know. Thanks!

PaulvS said:
In relation to what I think you are trying to achieve, I expect that the Garmin EMS is similar to the Dynon EMS that I know can drive an external warning lamp if an alarm threshold is exceeded. Alarms can be configured for low/high: oil pressure, fuel flow, fuel pressure, EGT, CHT etc. Perhaps you can connect the external warning pin to light up the Smart Glide button?
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Yes, that's something I'll look into. I did mention that possibility when I briefly spoke with the radio installation tech. He said that all of the GEA 24 triggers are 5V and the switch illumination needs 12V.

I guess I could possibly use a 5V signal to activate a relay. I don't know a lot about the GEA 24 (I'm not the builder) and I don't want make a Rube Goldberg contraption just to illuminate one switch, but if there's a simple solution, I'll surely consider it.
 
Dad's RV-10 said:
Wow...good to know. Thanks!



Yes, that's something I'll look into. I did mention that possibility when I briefly spoke with the radio installation tech. He said that all of the GEA 24 triggers are 5V and the switch illumination needs 12V.

I guess I could possibly use a 5V signal to activate a relay. I don't know a lot about the GEA 24 (I'm not the builder) and I don't want make a Rube Goldberg contraption just to illuminate one switch, but if there's a simple solution, I'll surely consider it.
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Out of curiosity I looked at the G3X manual for the GEA24 and it appears that the external annunciator pin gets pulled to ground, so 12V from airframe power would be connected to the switch for illumination. I'm no Garmin expert though!
 
PaulvS said:
Out of curiosity I looked at the G3X manual for the GEA24 and it appears that the external annunciator pin gets pulled to ground, so 12V from airframe power would be connected to the switch for illumination. I'm no Garmin expert though!
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I'll check out the GEA 24 manual.

Might be a simple solution after all. Thanks!
 
rmarshall234 said:
When you say "a non-running engine with a windmilling prop" what you really mean is an engine that is not producing power. Maybe you can best accomplish what you want by measuring fuel flow instead of OP since fuel flow and power are directly related. Just a thought. Good luck.
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That’s not necessarily true either.. You could have a mag failure, or some other failure that may still have fuel flow, even though the fuel isn’t being ignited. I thing EGT or even CHT would give you a true indication of lack of power. Heck, a broken fuel line downstream of the ff meter would produce an engine failure, with lots of indicated fuel flow.
 
Dad's RV-10 said:
Is it possible to configure the GEA 24 for an external ground trigger when the EGT drops below a predetermined value?
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You can have Master Caution and Master Warning lights, which will illuminate based on the criteria you set. For your unusual application you will probably have better luck using a small microcontroller to parse the RS-232 output for the particular conditions you are interested in (see Appendix C in the G3X installation manual) which any clever teenager ought to be able to do.
 
mburch said:
You can have Master Caution and Master Warning lights, which will illuminate based on the criteria you set. For your unusual application you will probably have better luck using a small microcontroller to parse the RS-232 output for the particular conditions you are interested in (see Appendix C in the G3X installation manual) which any clever teenager ought to be able to do.
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Thanks. I'll do some reading. Looks like a fun project for my inner teenager to figure it out.

Probably more complicated than it needs to be but I think it would be cool for the switch to stay dark until "needed." It sounds like a CHT or EGT trigger would work best.
 
Dad's RV-10 said:
Thanks. I'll do some reading. Looks like a fun project for my inner teenager to figure it out.

Probably more complicated than it needs to be but I think it would be cool for the switch to stay dark until "needed." It sounds like a CHT or EGT trigger would work best.
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CHT is a bit slow to react. Which cylinder EGT are you going to use as a trigger? How do you distinguish a single cylinder EGT falling off versus a complete engine failure? As Paul said - if the engine quits, you will know it. You don’t need a light illuminating to tell you that.

In 20,000 hours plus of flying - I’ve had several partial engine failures. One piston, one turboprop, one turbofan. It was obvious in all three.
 
KatanaPilot said:
CHT is a bit slow to react. Which cylinder EGT are you going to use as a trigger? How do you distinguish a single cylinder EGT falling off versus a complete engine failure? As Paul said - if the engine quits, you will know it. You don’t need a light illuminating to tell you that.

In 20,000 hours plus of flying - I’ve had several partial engine failures. One piston, one turboprop, one turbofan. It was obvious in all three.
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Thanks Krea. This has nothing to do with me needing some kind of external indication to alert me of an engine failure. Like I said, I don't "need" the light to tell me the engine has quit.

The desire is simply to not have the switch lit all the time. The other option is to not have it lit at all.
 
Switch Annunciator

Dad's RV-10 said:
Thanks Krea. This has nothing to do with me needing some kind of external indication to alert me of an engine failure. Like I said, I don't "need" the light to tell me the engine has quit.

The desire is simply to not have the switch lit all the time. The other option is to not have it lit at all.
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Why not use the annunciation in the switch to indicate when “Smart Glide” is enabled (turned on rather than when it’s needed?

Skylor
 
skylor said:
Why not use the annunciation in the switch to indicate when “Smart Glide” is enabled (turned on rather than when it’s needed?

Skylor
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My understanding is that the signal would have to come from the GTN, which I'm not sure is possible.
 
Does someone have a wiring diagram for the Smart Glide button? I looked on line but didn’t find one.

If the man wants to wire other than intended, let’s at least look to see if it is possible.
 
Webb said:
Does someone have a wiring diagram for the Smart Glide button? I looked on line but didn’t find one.

If the man wants to wire other than intended, let’s at least look to see if it is possible.
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Thanks. Upon further reflection, I see no reason to over complicate things.

I believe there is dimmable panel light circuit in the plane. I'll probably just look into pulling power from that circuit. The switch will be dark during the day and dimly lit at night. No need to reinvent the wheel.

Appreciate the feedback.
 
I love problems like these because it highlights how hard engineering can be sometimes. A simple question like "is my motor running?" is so easy for a human to determine and so hard for a computer to know.

If you wanted to use EGT, you would probably have to put in a different "dual" probe, or take the data from the serial bus after the temp was calculated. Even with a dual probe, you would probably need a dedicated control box with a digital output since the voltage range is so small. Someone better informed than me can chime in, but I have a feeling the EGT channels in the GEA24 have special hardware in order to deal with the small voltages, so using a random analog in channel isn't going to work.

If you're on a fixed pitch prop, you could put a throttle position sensor on there and use a box to compare throttle position to RPM. That would be a pretty reliable indicator. You'd have to spend some time building the lookup table for RPM vs throttle vs airspeed in order to make it accurate though.

I think I would just wire it to the GAD27 lighting channel though. The button lights up when your back panel lighting is on so you don't lose it in the dark. Otherwise just know where it is so you can press it.
 
agent4573 said:
I love problems like these because it highlights how hard engineering can be sometimes. A simple question like "is my motor running?" is so easy for a human to determine and so hard for a computer to know.

If you wanted to use EGT, you would probably have to put in a different "dual" probe, or take the data from the serial bus after the temp was calculated. Even with a dual probe, you would probably need a dedicated control box with a digital output since the voltage range is so small. Someone better informed than me can chime in, but I have a feeling the EGT channels in the GEA24 have special hardware in order to deal with the small voltages, so using a random analog in channel isn't going to work.

If you're on a fixed pitch prop, you could put a throttle position sensor on there and use a box to compare throttle position to RPM. That would be a pretty reliable indicator. You'd have to spend some time building the lookup table for RPM vs throttle vs airspeed in order to make it accurate though.

I think I would just wire it to the GAD27 lighting channel though. The button lights up when your back panel lighting is on so you don't lose it in the dark. Otherwise just know where it is so you can press it.
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Yep, see my post just above yours. Decided to KISS. There's no GAD27 as it's a non-touch G3X (GDU 370 & 375).

I believe there is a a dimmable panel light circuit which I can hopefully tap into.
 
Dad's RV-10 said:
Yep, see my post just above yours. Decided to KISS. There's no GAD27 as it's a non-touch G3X (GDU 370 & 375).

I believe there is a a dimmable panel light circuit which I can hopefully tap into.
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Uhhh….have you checked to see if SmartGlide is even available with the non-touch units? I don’t think it was last year - when I upgraded my 37x’s to 470’s in the RV-3, that was one of the new things we got…. (We already had the capability in our Touch G3X in the RV-6).

Maybe they’ve ported the software over to non-Touch now, but I haven’t looked.
 
Ironflight said:
Uhhh….have you checked to see if SmartGlide is even available with the non-touch units? I don’t think it was last year - when I upgraded my 37x’s to 470’s in the RV-3, that was one of the new things we got…. (We already had the capability in our Touch G3X in the RV-6).

Maybe they’ve ported the software over to non-Touch now, but I haven’t looked.
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I'm having a GTN 650Xi installed.

My understanding is that the Smart Glide capability is inherent to the Xi box, regardless of whether its driving a Touch or Non-Touch G3X.

EDIT: You could be right that Smart Glide is incompatible with the non-Touch G3X. From Garmin's site; "Further, experimental aircraft with G3X Touch and a G3X autopilot can also enable Smart Glide technology when appropriately equipped."

I'm not entirely sure how it gets wired but if the feature isn't available with non-Touch G3X, I'll see if it's still possible to have it pinned-out now so the wiring will already be there if/when making the inevitable upgrade to a Touch system.
 
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Let’s talk about that switch. Just like the ones I saw every day in the USN. Where do you get those? Who prints the label for you?
 
Dad's RV-10 said:
I You could be right that Smart Glide is incompatible with the non-Touch G3X. From Garmin's site; "Further, experimental aircraft with G3X Touch and a G3X autopilot can also enable Smart Glide technology when appropriately equipped."

I'm not entirely sure how it gets wired but if the feature isn't available with non-Touch G3X, I'll see if it's still possible to have it pinned-out now so the wiring will already be there if/when making the inevitable upgrade to a Touch system.
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For your G3X non-touch system, the GTN can provide the Smart Glide feature and your G3X system can follow its navigation guidance.

If you had a G3X Touch system, you wouldn't need the GTN for the Smart Glide feature, as that capability is implemented totally within the GDU 4xx (and is more useful in certain ways than the GTN version, in my opinion).
 
mburch said:
For your G3X non-touch system, the GTN [Xi] can provide the Smart Glide feature and your G3X system can follow its navigation guidance.

If you had a G3X Touch system, you wouldn't need the GTN for the Smart Glide feature, as that capability is implemented totally within the GDU 4xx (and is more useful in certain ways than the GTN version, in my opinion).
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That's how I understood it to function.

Thanks for confirming, Matt.
 
Would a failed exhaust valve create high EGT and an engine not producing power? There would be rotation (windmilling prop), ignition and fuel.

I think we've run down the rabbit hole and determined there is too many failure modes of a piston engine to have one reliable sensor indicating the failure. Short of a torque gauge, which our engines/propellers are incapable of measuring.
 
I have to apologize to the OP, it was my idea to wire the light to the oil press switch. One never stops learning..
 
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