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Aircraft losing speed then altitude and freezes

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Aircraft losing speed then altitude and freezes

Postby PavlinS » Wed Apr 19, 2017 8:38 am

Split off from the topic always a new bug.

can someone explain this ??????
https://fgtracker.ml/modules/fgtracker/?FUNCT=FLIGHT&FLIGHTID=6890625
Last edited by Johan G on Thu Apr 20, 2017 6:56 pm, edited 1 time in total.
Reason: Split off from the topic "always a new bug".
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Re: always a new bug

Postby sanhozay » Wed Apr 19, 2017 8:57 am

You mean the red arc?

Simple answer:

Earth is round, the map is flat. The North Pole is a point in real life, but is stretched out along the top edge of the map in this projection. If you fly north in a straight line, you end up flying south.

https://en.wikipedia.org/wiki/Mercator_projection
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Re: always a new bug

Postby ludomotico » Wed Apr 19, 2017 11:03 am

Additional explanations to sanhozay post (which is perfectly correct):

Straight lines on Mercator maps are courses of constant bearing (loxodromes: https://en.wikipedia.org/wiki/Rhumb_line). That is: follow always the same bearing in your compass/heading indicator and it will be a straight line on a Mercator map. This is the main reason Mercator maps were used for navigation: trace a straight line, measure the angle and trust your compass.

But loxodromes are usually NOT the shortest route between two points, as you can see in the example shown in the wikipedia link provided above.

The shortest routes between two points are called orthodromes (https://en.wikipedia.org/wiki/Great_circle). They are NOT shown as straight lines on a Mercator map and they can NOT be navigated using a compass because their magnetic bearing changes constantly. Orthodromes are shown as straight lines on gnomonic projection maps. The very usual Lambert conformal conic projection (https://en.wikipedia.org/wiki/Lambert_c ... projection) is not gnomonic, but it is a very good approximation. This projection is widely used in aircraft navigation maps.

Navigators in the old times approximated an orthodrome route using a sequence of loxodrome steps they can follow using a compass (for example: http://www.transnav.eu/files/Approximat ... on,323.pdf) This is still the method taught in the flying schools.

Modern electronic navigators can calculate orthodromes automatically, but if you are flying a route so long that an orthodrome route and a loxodrome route differ significantly, you are probably flying under IFR rules and all this does not apply to you :)
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Re: always a new bug

Postby PavlinS » Wed Apr 19, 2017 11:23 am

sanhozay wrote in Wed Apr 19, 2017 8:57 am:You mean the red arc?

Simple answer:

Earth is round, the map is flat. The North Pole is a point in real life, but is stretched out along the top edge of the map in this projection. If you fly north in a straight line, you end up flying south.

https://en.wikipedia.org/wiki/Mercator_projection


Nope, I mean why the plane stops and losing it's spd when the fuel is manged and does not wanna move from there.
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Re: always a new bug

Postby Isaak » Wed Apr 19, 2017 11:50 am

Can you repeat your question? I can't get what you are asking: the plane stops and loses its speed because the fuel is managed? To me it looks like the plane went down for some reason and crashed in some mountains, but I might be mistaken. Are you sure you had enough fuel on board to perform the trip? Didn't encounter strong headwinds which resulted in extra flight time?
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Re: always a new bug

Postby PavlinS » Wed Apr 19, 2017 2:32 pm

Listen closely:
I am flying. There is fuel to remain. Conditions are good- I am on cruiuse altitude of 33000 feet. The spd is 0.87 IAS mach. The link shows a diagram - see the diagram! I lose my spd and plane was freezing on 16000 feet. This is the qwestion- why suddenly it's decide to do it? No V/s at all, no lost of fuel, no eny reason to do it!
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Re: always a new bug

Postby stuart » Thu Apr 20, 2017 11:31 am

Looking at the limited available data, I think you stalled the aircraft at high altitude.

If I zoom into the track, I see the following datapoints right at the end of the flight:

#4248:2017-04-19 06:34:58+00 Coordinate: 52.445909,52.115022 Altitude: 35275.64ft Speed: 495 knots
#4249:2017-04-19 06:35:08+00 Coordinate: 52.448432,52.092658 Altitude: 35263.21ft Speed: 485 knots
#4250:2017-04-19 06:35:18+00 Coordinate: 52.450966,52.070173 Altitude: 35270.73ft Speed: 488 knots
#4251:2017-04-19 06:35:28+00 Coordinate: 52.453508,52.047584 Altitude: 35282.53ft Speed: 490 knots
#4252:2017-04-19 06:35:38+00 Coordinate: 52.455255,52.031383 Altitude: 35210.67ft Speed: 351 knots
#4253:2017-04-19 06:35:48+00 Coordinate: 52.454396,52.028845 Altitude: 34177.2ft Speed: 56 knots
#4254:2017-04-19 06:35:58+00 Coordinate: 52.452772,52.029116 Altitude: 30617.98ft Speed: 22 knots

It looks like the aircraft stalled at 35,000ft, and no recovery took place. I'm guessing it was running on an autopilot in FL mode and after it stalled the autopilot kept on applying elevator and power. I don't know why it stalled, or what you were doing with the aircraft at that point.

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Re: Aircraft losing speed then altitude and freezes

Postby PavlinS » Thu Apr 20, 2017 6:55 pm

The A/p was running with engaged F/d. I was asleep when it's happend. Mostly this common error is happening on 747 plane when I do flight from KSFO to EGLL. actually it's a common error in alot of my flights recently. I amusing the last release of FG - 2017 1.3. I do not find eny reason.
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Re: Aircraft losing speed then altitude and freezes

Postby Octal450 » Thu Apr 20, 2017 7:01 pm

Well, maybe the AP is stalling the aircraft?

The AP has no stall protection logic modeled.

Have you tried looking the instant replay? see the surface movement, maybe you can see what happen?

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Re: Aircraft losing speed then altitude and freezes

Postby PavlinS » Thu Apr 20, 2017 7:11 pm

I was running the replay. Did not help, because it wasn't has the good condition of the plane. Most the time this was on A/p, because I run it in 10 at night, and in 2 and half hours I was suposed to start descend and landing at OMAA. I have notice that a/p was not holding the CRZ ALT correctly, the plane have been moving it's altitude during the flight.
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Re: Aircraft losing speed then altitude and freezes

Postby Octal450 » Fri Apr 21, 2017 4:03 am

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Re: Aircraft losing speed then altitude and freezes

Postby Thorsten » Fri Apr 21, 2017 5:35 am

I was asleep when it's happend.


I suspect that's why they require real pilots to be awake when the plane is on AP... :mrgreen:
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Re: Aircraft losing speed then altitude and freezes

Postby PavlinS » Fri Apr 21, 2017 7:37 am

Thorsten wrote in Fri Apr 21, 2017 5:35 am:
I was asleep when it's happend.


I suspect that's why they require real pilots to be awake when the plane is on AP... :mrgreen:


Thank you for this. Never till now 777 has do that kind of problems on my machine for 3 years amount of flying in it. I think this kind of humor is little bit irrelevant. In the real life pilots also sleep during flight, for example from OMDB to NZAA. Is not possible to be awake in 18 hours! This was 13 hours flight, how you suppose I can be awake that long? also- the plane was totally inverted pointhing the land with it's nose. Without eny scenery downloaded, no matter Terrasync was active............. I do not understand how this can be possible in real plane? This is not possible in real plane,becouse real plane will hold the altitude always, not like this plane, going on 35000 feet when I put the A/p on 33000. I am sorry to tell this, but with every new vertion of the simulator more and more bugs i has onmy flights even with 777, I tought was the only plane not making eny errors till now!
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Re: Aircraft losing speed then altitude and freezes

Postby Thorsten » 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.
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Re: Aircraft losing speed then altitude and freezes

Postby Isaak » Fri Apr 21, 2017 9:25 am

If your plane stalled, which seems to have happened (the sudden side movement looks like an asymmetric stall to me), it is perfectly possible that it ended upside down. Sadly, there is nothing you can do about the autopilot stalling the airplane at the moment except for taking over manually (which requires you to be at your computer). I 've been there before during an overnight flight. It 's not fun, but it 's reality.

You say that the scenery wasn't loaded, there have been some issues with Terrasync in the last year, but these should have been solved by now.

It looks fun for me to take a look at the autopilot logics and design a stall recovery logic: full thrust, nose down until the target speed has been reached, climb back to previous assigned altitude maintaining the target speed. All this with flight envelope protection so the plane doesn't make contact with terrain. I don't know if such a logic exists in reality, so I 'd have to check that first, but if it does, I would like to take the challenge of creating it.

The fact that your target altitude was set at FL330 doesn't mean (also in reality) that your plane will fly at 33000 feet true altitude. With changing temperature and air pressure, the indicated altitude will almost always differ from the true altitude. So the fact that your plane goes up and down during cruise isn't a bug, it 's just varying temperature and pressure at different places around the world. Your plane is programmed to maintain a fixed indicated altitude, not a true altitude.
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