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Aircraft losing speed then altitude and freezes

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Re: Aircraft losing speed then altitude and freezes

Postby CaptB » Fri Apr 21, 2017 9:51 am

I'm not familiar with the real 777, but from what I understand there should be some protection laws, not sure if those are designed to help recover from a stall, such as for instance the Alpha Floor on the Airbus 3xx, which still would not ensure stall recovery without the pilot's active participation.

It would be good to understand why the stall happened to see if it's an AP bug or something else, it's unusual for this to happen in cruise. Are the effects of icing on the wings/pitot tubes simulated?
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Re: Aircraft losing speed then altitude and freezes

Postby Richard » Fri Apr 21, 2017 10:20 am

PavlinS wrote in Wed Apr 19, 2017 8:38 am:[color=#008000]
can someone explain this ??????
https://fgtracker.ml/modules/fgtracker/?FUNCT=FLIGHT&FLIGHTID=6890625


Looks like a loss of engine power which caused a stall whilst the AP was trying to hold altitude.

Just as in real life we need FDR or rather the FG equivalent of the FDR - which in this case is a saved replay; but it might not have the entire flight because of the default duration.

So change /sim/replay/duration to the maximum expected duration of your flight in minutes (will require more memory) and hopefully this will record the entire flight.

You could also change /sim/replay/buffer/low-res-sample to a higher value to reduce the amount stored (this is in seconds). Set this to 30 would seem to be more reasonable for a long flight - but still capture enough. However try it with the default of 5 seconds first and see how much memory you end up using.
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Re: Aircraft losing speed then altitude and freezes

Postby Richard » Fri Apr 21, 2017 10:22 am

CaptB wrote in Fri Apr 21, 2017 9:51 am:I'm not familiar with the real 777, but from what I understand there should be some protection laws


Generally if there is a failure detected the result will be autopilot disengage with associated aural warnings and flashing lights on the master caution.

I haven't looked at the 777 but I'd imagine that the autopilot simulation is the usual simplistic one that just does the navigation and doesn't have all of the extra logic that the real ones do.
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Re: Aircraft losing speed then altitude and freezes

Postby PavlinS » Fri Apr 21, 2017 11:10 am

I have only 4 GB's of RAM. My flight recorder tapes are long 1 hour. I save parts form the flight. The taxi+takeoff, cruise , descending+app+landing+taxi. I can not efford to change thiese settings, because I think will be happend memory consumption.
About the altitude- see this diagram of a proper flight with 777 I make sometime previously:
https://fgtracker.ml/modules/fgtracker/?FUNCT=FLIGHT&FLIGHTID=6887661

On the diagram you see that it was on 31000 feet. As I managed the ALT. This time it was 3000 feet above the ALT I put. It was having problems to reach the ALT I put all the time. During cruise the plane was shaking all the time. And you see this on the fist diagram. I do not understand why? I Use manual takeoff to 12000 feet. Then I engage FLCH and that's it! Never was do that kind of staff previously. The flight on this reply was made with FG 2016 4.4 . Now I use 2017 1.3. That's the reason I put a reply in " Always new bug". Because this flight was on the newest vertion!
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Re: Aircraft losing speed then altitude and freezes

Postby PavlinS » Fri Apr 21, 2017 11:19 am

Thorsten wrote in Fri Apr 21, 2017 8:12 am:
This is not possible in real plane,becouse real plane will hold the altitude always,


I think you might be mistaken about what real planes do.


I am talking especially for A/p. In real conditions every country you are passing by ask you to change the altitude if it's necessary. But here I am talking about a bug on the system, Even if I was awake there is no way to change suddenly -8000 V/s without eny reason-fuel is manged, F/d works. If this happend on your maschine what you will do? Changing spd till the plane decides to listen your command? I am talking for unoperable plane, not for something else- I was alseep, computer decides to crush my plane. Without eny logic reason! And how the plane will stall with A/p when it's on cruise altitude? Without a loss of fuel! This is not logical, Thorsten, there is no logic reason for it! If was QNH problem I should know, but QNH is not a factor during cruise. There is no mountih highter than 35000 feet! Everest is on lower altitude than this! And I was not passing by there! I was in totally different country! And why you are talking for real pilots work when this is a simulator? It is not real!
O, I forgot to say something important - Stall it's happening when the pitch is not on the sea level! How the pitch will be changed when it's on A/p holding altitude, oin pitch 0? V/s is the only explonation of this! Why plane do a v/s when it's holding altitude! This is not possible in real plane!
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Re: Aircraft losing speed then altitude and freezes

Postby CaptB » Fri Apr 21, 2017 12:05 pm

PavlinS wrote in Fri Apr 21, 2017 11:19 am:Changing spd till the plane decides to listen your command?!


Yes, you have to create conditions where the wings will have sufficient lift again, this is achieved by reducing pitch and applying TOGA. On some aircraft like the A320 the Alpha Floor protection will assist, but still not do it for you.
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Re: Aircraft losing speed then altitude and freezes

Postby Richard » Fri Apr 21, 2017 12:32 pm

PavlinS wrote in Fri Apr 21, 2017 11:10 am:I have only 4 GB's of RAM. My flight recorder tapes are long 1 hour. I save parts form the flight.


I've downloaded and inspected the kml from the flight tracker you posted in the first message. This indicates that there was a loss of engine power; however I can't say exactly why without the fgtape.

If you are having troubles with longer tapes then reduce the resolution as I posted. If you change low res from 5 to 60 you should be able to save 12 times longer than you currently have with the same memory usage.

It appears to be a fault somewhere, but without the fgtape nobody is going to be able to say definitively what happened.
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Re: Aircraft losing speed then altitude and freezes

Postby CaptB » Fri Apr 21, 2017 1:21 pm

Just out of curiosity, did you have your center fuel pumps on?, If you do an autostart these seem off by default which means that you will starve your engines enroute when the wing fuel tanks get empty.
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Re: Aircraft losing speed then altitude and freezes

Postby PavlinS » Fri Apr 21, 2017 1:31 pm

CaptB wrote in Fri Apr 21, 2017 1:21 pm:Just out of curiosity, did you have your center fuel pumps on?, If you do an autostart these seem off by default which means that you will starve your engines enroute when the wing fuel tanks get empty.


I was using them, but I have turn them off after. Also - I have try to restore the plane with changing V/s. It was on -8000 and it was unchangeable.
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Re: Aircraft losing speed then altitude and freezes

Postby Thorsten » Fri Apr 21, 2017 1:46 pm

But here I am talking about a bug on the system, Even if I was awake there is no way to change suddenly -8000 V/s without eny reason-fuel is manged, F/d works. If this happend on your maschine what you will do? Changing spd till the plane decides to listen your command?


If the AP is not working as it should, I disengage it and take over manually - or try to (just three hours ago, I had the Shuttle entry AP kill me when I switched it to low energy logic before I could even figure out what it was trying to do...) As I would hope people do in reality.

So yes, I'd try to recover from stall by descending at a steep angle to recover speed and then pull out gradually. Usually does the trick.

I am talking for unoperable plane, not for something else- I was alseep, computer decides to crush my plane. Without eny logic reason! And how the plane will stall with A/p when it's on cruise altitude? Without a loss of fuel! This is not logical, Thorsten, there is no logic reason for it!


Look, the reason there's pilots in cockpits who aren't supposed to be asleep is just that - you can't trust the machine to get it always right. You just can't.

The problem is not that computers act without logical reason - they're in fact very logical devices, they just have the annoying habit of executing commands literally and without thinking what they mean. So there probably was a perfectly good logical reason for what happened, the AP was trying to do *something* which it considered part of its instruction set - it was just not what you were expecting.

There's no reason to believe that the plane would have been inoperable for a human pilot - direct control problems are far more rare than AP problems (though they occur as well in fly-by-wire setups).
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Re: Aircraft losing speed then altitude and freezes

Postby PavlinS » Fri Apr 21, 2017 3:01 pm

Thorsten, even when I try manually the plane does not recover. You think I was not? Also, for second time - I was put the plane to hold ALT. When I found it in that shape it was on -8000 V/s without eny reason.
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Re: Aircraft losing speed then altitude and freezes

Postby Thorsten » Fri Apr 21, 2017 4:15 pm

Thorsten, even when I try manually the plane does not recover. You think I was not?


I think you told me you were sleeping when it happened. Quoting yourself:

I was asleep when it's happend.


So yes, unless you have pretty amazing sleepwalking habits, I was not under the impression that you tried to recover manually.
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Re: Aircraft losing speed then altitude and freezes

Postby PavlinS » Fri Apr 21, 2017 5:25 pm

This happend after I was awake. I try to restore it.
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Re: Aircraft losing speed then altitude and freezes

Postby dilbert » Sat Apr 22, 2017 7:09 pm

Curious.
The flight data gives every appearance of what would happen if the engines throttled back or failed and the autopilot tried to maintain altitude, dropping to 351K while maintaining 352.0 ft, then deaccelerating to 56 at 34177; then aircraft falling right after vertical stabilizer no longer effective. Was this around the time for commencing a normal descent (in which case throttle would be reduced, but autopilot should be reset to control airspeed, not altitude), or just happen when aircraft would normally have been maintaining assigned altitude?
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Re: Aircraft losing speed then altitude and freezes

Postby PavlinS » Sun Apr 23, 2017 4:58 am

Hi, dilbert.
It was not time for descend, it was remaining 2 and half hours to start descending. The plane was crush without a reason.
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