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Engine Failure

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Engine Failure

Postby ORZMUD » Tue Apr 23, 2019 7:13 am

I build from source, it shows 2019.2.0 running fgfs.
In a flight where I was practicing right/left turns the C172P experienced an engine failure.
I'm curios as to why the engine died since I don't have enabled system failures.

The flight tape can be found here:
http://www.saaib.net/file/c172p-20190422-223532.fgtape

Uploaded video of the session:
https://www.youtube.com/watch?v=Zn0tVHWY-cI

The engine finally dies on minute fgtape: 48:30, Youtube: 44:45

Any comments/suggestions are welcome.

Regards,
Last edited by ORZMUD on Tue Apr 23, 2019 2:37 pm, edited 2 times in total.
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Re: Engine Failure

Postby Alex H » Tue Apr 23, 2019 7:26 am

The only thing I can think of is this (and don't ask how i found out :) )

In 'Aircraft options' do you have 'save state of aircraft between sessions' selected?

If you do, then the fuel state is saved and you have to fill up between trips, otherwise you will run out.
Regards

Alex
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Re: Engine Failure

Postby ORZMUD » Tue Apr 23, 2019 2:25 pm

Hi Alex,

I just replayed the tape and at the moment of the engine failure there were about 15 gl of fuel on each tank.
Did check the Aircraft Options and the "Save state or aircraft between sessions" is not selected.

Thanks for the pointer tough!

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Re: Engine Failure

Postby wlbragg » Tue Apr 23, 2019 4:00 pm

Carb icing on? Were you using the carb heat?
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Re: Engine Failure

Postby ORZMUD » Tue Apr 23, 2019 4:19 pm

The first sputters coming from the motor where before take off, in the youtube video is at minute 3:43.
Carb heat was on cold.

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Re: Engine Failure

Postby wlbragg » Tue Apr 23, 2019 4:29 pm

The reason I asked is because carburetor icing is modeled in the c172p. If you had the option on you can experience icing (carb heat off and icing capability on) and I don't think there was any limit to the amount of icing that can occur. Do you remember much sputtering around the time of the engine failure? What altitude were you flying at and were you using any mixture?
The combination of incorrect mixture at altitude and carb ice could cause the engine to fail.
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Re: Engine Failure

Postby ORZMUD » Tue Apr 23, 2019 4:34 pm

Mixture was fully rich, max altitude during the turning practice was 6000ft, engine malfunction started on the way back to airport around 5500ft and finally went out below 1500ft on final approach.
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Re: Engine Failure

Postby wlbragg » Tue Apr 23, 2019 4:39 pm

That sound a lot like icing. Do you remember sputtering? If that really was the icing model that stopped the engine, I am impressed. Not happy if you experienced a catastrophic failure though.

If you don't mind me asking, what did you do, did you make it down safely?
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Re: Engine Failure

Postby ORZMUD » Tue Apr 23, 2019 5:03 pm

There where sputtering before take off, which I recover from by increasing throttle while holding on the runway.
In the way back when the engine started sputtering I went for a climb to gain additional altitude, which by increasing throttle it fixed it for a little while.
I was able to reach final and when the engine went out I glide to the runway.

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Re: Engine Failure

Postby wlbragg » Tue Apr 23, 2019 5:17 pm

Engine sputtering in the c172p in FlightGear is caused by one of two things that I know of, carb icing or low oil. Either can cause engine failure if your have the "Complex engine procedures and failures" checked. A long slow approach is where you would be more likely to experience icing in the carburetor. "Save state between sessions" isn't necessary for the oil to get low, I think that only requires "Complex engine procedures and failures".
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Re: Engine Failure

Postby ORZMUD » Tue Apr 23, 2019 5:22 pm

I noticed the "Complex engine procedures and failures" is checked for the C172P.
Reading on your comment about oil, I checked again and the oil pressure gauge was lower before engine failed than before take off.
Is this an oil leak simulation? How can I check from the logs?

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Re: Engine Failure

Postby wlbragg » Tue Apr 23, 2019 5:54 pm

I loaded your tape, fascinating!

I checked again and the oil pressure gauge was lower before engine failed than before take off.

I think that was associated with idle approach VS full throttle takeoff and cruise throttle.

Is this an oil leak simulation? How can I check from the logs?

No, we model low oil from repeated use. I think we add some random water also.

We don't record all the properties associated with these two systems (oil and carb ice) but we do record coughing, and it was definitely an event associated with coughing. It got severe right as the engine shut off. I looked at the property tree and didn't notice enough of a change in oil pressure or EGT to think it was oil related. But it appears that we don't record the icing numbers only the engine status.

I think it was icing.

That's why that carb heat is there and is to be used on approach if there is any doubt about conditions. Really, always use it on a long approach is a good rule of thumb I think.
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Re: Engine Failure

Postby wkitty42 » Tue Apr 23, 2019 6:20 pm

looks like it would be a good idea to add additional numbers to the recordings so these types of things can be replayed and analyzed thoroughly...
"You get more air close to the ground," said Angalo. "I read that in a book. You get lots of air low down, and not much when you go up."
"Why not?" said Gurder.
"Dunno. It's frightened of heights, I guess."
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Re: Engine Failure

Postby Thorsten » Tue Apr 23, 2019 7:44 pm

Usually you only know afterwards what you should have added though...
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Re: Engine Failure

Postby wlbragg » Tue Apr 23, 2019 9:00 pm

I'm really tickled that it is modeled so well that it caused that kind of failure. That is the type of systems modeling I love to see in FlightGear. I think it is what helps to set FlightGear apart.
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