Engine failure on Astro DA42-VI

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nworthin
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Re: Engine failure on Astro DA42-VI

Post by nworthin »

Karl wrote: Wed Oct 26, 2022 2:21 pm
alexair101 wrote: Wed Oct 19, 2022 10:11 pm
Vlada-T wrote: Thu Oct 13, 2022 5:06 pm
Yes it is correct.
I met so many people that kept saying that propeller Autofeathers... I think even emailed Diamond and some point and they said that, but PoH clearly read to me as if master off is a must for feathering.
It autofeathers if it loses gearbox oil pressure, as would happen with an engine failure. Turning the engine master off simulates a failure.
Are you SURE it auto feathers with loss of oil pressure. I'm not so sure....
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Re: Engine failure on Astro DA42-VI

Post by thommy152 »

Wouldn’t you still have gearbox oil pressure with a windmilling prop? Thus, you would still need to turn the engine master off to feather if you have an engine failure with a windmilling prop?
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Karl
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Re: Engine failure on Astro DA42-VI

Post by Karl »

nworthin wrote: Thu Oct 27, 2022 2:35 am
Karl wrote: Wed Oct 26, 2022 2:21 pm
alexair101 wrote: Wed Oct 19, 2022 10:11 pm

I met so many people that kept saying that propeller Autofeathers... I think even emailed Diamond and some point and they said that, but PoH clearly read to me as if master off is a must for feathering.
It autofeathers if it loses gearbox oil pressure, as would happen with an engine failure. Turning the engine master off simulates a failure.
Are you SURE it auto feathers with loss of oil pressure. I'm not so sure....
Think about how it works. The only thing keeping it in fine pitch is gearbox oil pressure. No oil pressure and it moves through course to feather unless the pitch lock prevents it.
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thommy152
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Re: Engine failure on Astro DA42-VI

Post by thommy152 »

Karl wrote: Fri Oct 28, 2022 7:54 am
nworthin wrote: Thu Oct 27, 2022 2:35 am
Karl wrote: Wed Oct 26, 2022 2:21 pm
It autofeathers if it loses gearbox oil pressure, as would happen with an engine failure. Turning the engine master off simulates a failure.
Are you SURE it auto feathers with loss of oil pressure. I'm not so sure....
Think about how it works. The only thing keeping it in fine pitch is gearbox oil pressure. No oil pressure and it moves through course to feather unless the pitch lock prevents it.
Does loss of engine oil pressure necessarily mean loss of gearbox oil pressure? I don’t think it does, but correct me if I’m wrong.
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Re: Engine failure on Astro DA42-VI

Post by CFIDave »

Loss of engine oil pressure does not mean loss of gearbox oil pressure (unless the engine stops), since they are completely separate systems on Austro engines. Engine oil gets very dark and dirty from JetA soot, whereas the gearbox oil remains much cleaner (pale yellow) and is good for 300 hours.

For that reason, the Austro prop governor shares relatively clean gearbox oil instead of dirty engine oil. (In contrast, Lycoming DA40s --without a gearbox -- use engine oil for the prop governor.)

So as long as you have a windmilling prop generating gearbox oil pressure, an Austro engine prop shouldn't automatically feather. But I don't know this for sure, since fortunately I've never experienced Austro engine power loss. :)
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Karl
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Re: Engine failure on Astro DA42-VI

Post by Karl »

thommy152 wrote: Fri Oct 28, 2022 5:22 pm
Karl wrote: Fri Oct 28, 2022 7:54 am
nworthin wrote: Thu Oct 27, 2022 2:35 am
Are you SURE it auto feathers with loss of oil pressure. I'm not so sure....
Think about how it works. The only thing keeping it in fine pitch is gearbox oil pressure. No oil pressure and it moves through course to feather unless the pitch lock prevents it.
Does loss of engine oil pressure necessarily mean loss of gearbox oil pressure? I don’t think it does, but correct me if I’m wrong.
You are right, loss of engine oil pressure doesn't mean loss of gearbox oil pressure but I doubt the engine would run for long without engine oil anyway. All this means is that you have options, you can run the engine and use any power available to gain altitude or switch it off and feather it.
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Re: Engine failure on Astro DA42-VI

Post by Karl »

CFIDave wrote: Fri Oct 28, 2022 6:42 pm Loss of engine oil pressure does not mean loss of gearbox oil pressure (unless the engine stops), since they are completely separate systems on Austro engines. Engine oil gets very dark and dirty from JetA soot, whereas the gearbox oil remains much cleaner (pale yellow) and is good for 300 hours.

For that reason, the Austro prop governor shares relatively clean gearbox oil instead of dirty engine oil. (In contrast, Lycoming DA40s --without a gearbox -- use engine oil for the prop governor.)

So as long as you have a windmilling prop generating gearbox oil pressure, an Austro engine prop shouldn't automatically feather. But I don't know this for sure, since fortunately I've never experienced Austro engine power loss. :)
I am pretty sure that the designers thought about this and tested it, being able to feather a prop on a twin is part of the certification requirements.
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Re: Engine failure on Astro DA42-VI

Post by Vlada-T »

We are up in the air again. Engine replacement landed at 97T EUR. Still waiting for the RCA from Austro. Very quite actually from the manufacturer.

https://www.youtube.com/watch?v=goUK8VtAlm0
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Re: Engine failure on Astro DA42-VI

Post by MikeMeadows »

CFIDave is correct, the prop will not automatically feather if either engine or gearbox oil pressure is lost for any reason. The POH describes the feathering process quite well:

"To feather the propeller the engine must be shut down with the appropriate ENGINE MASTER switch. This will open the electric governor valve. All oil will flow back from the propeller hub, allowing the blades to move into the feathered pitch position. At the same time the electric valve at the pressure accumulator closes, and the oil pressure is restored in the accumulator.

Feathering is only possible at propeller speeds above 1300 RPM.

CAUTION
If the engine is shut down below an RPM of 1300 the propeller pitch remains below the start lock position. In this case the speed must be increased to increase the propeller RPM."

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Re: Engine failure on Astro DA42-VI

Post by Davestation »

MikeMeadows wrote: Sat Mar 11, 2023 3:56 am CFIDave is correct, the prop will not automatically feather if either engine or gearbox oil pressure is lost for any reason. The POH describes the feathering process quite well:

"To feather the propeller the engine must be shut down with the appropriate ENGINE MASTER switch. This will open the electric governor valve. All oil will flow back from the propeller hub, allowing the blades to move into the feathered pitch position. At the same time the electric valve at the pressure accumulator closes, and the oil pressure is restored in the accumulator.

Feathering is only possible at propeller speeds above 1300 RPM.

CAUTION
If the engine is shut down below an RPM of 1300 the propeller pitch remains below the start lock position. In this case the speed must be increased to increase the propeller RPM."

Mike Meadows
CFI CFII MEI
Houston, TX
That description makes it sound more confusing to me. The whole point of autofeathering is if you lose oil pressure, ie the engine shut down. I think the POH is describing a loss of oil pressure but making it sound backwards. Oil is flowing back from the hub because of the loss of pressure. The counterweights are what automatically drive it into feather, you just need to be above 1300rpm for the high pitch stops to be disengaged.

And when it says accumulator pressure is “restored” it should say “stored” as the accumulator is holding system pressure all the time while the engine is running. The valve needs to close to lock in that pressure so that when you go to restart the engine the valve will open and dump the accumulator pressure to unfeather the prop. Oil pressure is what keeps it out of feather, so loss of oil pressure puts it into feather.

I suppose they’re saying you have to turn the master switch off to feather it (on purpose) because that’s the expected scenario. I don’t think that means if you don’t turn the master switch off feathering will be prevented in case of engine failure. Although unless you starve it if fuel the only likely scenario where the engine quits involves an electrical failure so at that point the switch is effectively off anyway.
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