A320-211 flight path during ILS approach is not precise

[gierschi@flightgear]

Dear guys,

i made the following observations during ILS approaches in strong mean crosswind conditions (between 20-40knots in the lower atmosphere):

1.) San Francisco Airport (Frequency 111.70, Runway 28R, Wind direction 209°): The autopilot of the Boeing 707 seems to work very well. But i do not understand why the airplane is not flying parallel to the center line of the displayed ILS sector showed in the map (You can also view this sector in the MulitPlayer map). It flies always parallel to the left line and also not exact on it. What is the reason for that? The good thing is that at the end of the glide slope the touchdown is quite centered. This is different for the A320-211. Flying this airplane results into a path which is shifted to the left in the direction of travel and compared with the whole three lines of the ILS sector. The touchdown happens on the left border of the runway.

2.) Frankfurt Airport (Frequency 111.55, Runway 25C, Wind direction 160° : ) The autopilot of the Boeing 707 seems to work perfectly. The airplane is aligned along the middle line of the ILS sector and is doing an exact crabbed approach. Therefore also the touchdown is centered. Again, the path of the A320-211 is shifted to the left in the direction of travel compared to the center line of the ILS sector. The touchdown is also too far left but still on the runway.

So, what are the reasons for these differences? Is it a problem of the realization of the airplane or of the airport? My aim is to use an airplane which is based on the model JSBSim, which is very precise concerning an ILS approach and of simulating the influence of the wind field to the aircraft, which is still/widely used as a passenger plane and which can be easily start form the air. Therefore the A320-211 is my first choice but it should show a comparable behavior like the 707 with respect to the ILS approach.

Thank you very much in advance. I did some screen shots during the flights so that you can imagine the above described situation better. Unfortunately, i don't know how to upload/show them here in the forum.

[Thorsten]

But i do not understand why the airplane is not flying parallel to the center line of the displayed ILS sector showed in the map (You can also view this sector in the MulitPlayer map). It flies always parallel to the left line and also not exact on it. What is the reason for that?

From the description, probably because it has no integrator component in the controller which would null residual errors, so you're seeing the equilibrium a P(D?) controller reaches.

[Octal450]

Hi
Is this my A320Family? If so, can you give more information like pictures, videos?

Also, note that 28R at KSFO the ILS doesn't line up with the runway, purposefully, as in real life.

Kind Regards,
Josh

[legoboyvdlp]

Dear guys,

i made the following observations during ILS approaches in strong mean crosswind conditions (between 20-40knots in the lower atmosphere):

That may be why. For a CAT II autoland, the limit is 25 knots including gusts; for a CAT III autoland the limit is 20 knots with gusts. Maximum limit for a manual landing is 33 knots, gusting 38 knots.

[gierschi@flightgear]

by it0uchpods » 14 Sep 2017, 20:23
Hi Is this my A320Family? If so, can you give more information like pictures, videos?

Yes of course. How and where can I send it to you?

by it0uchpods » 14 Sep 2017, 20:23
Also, note that 28R at KSFO the ILS doesn't line up with the runway, purposefully, as in real life.

Ah okay, thanks for this hint. So the autopilot of the Boeing 707 seems to do its job also at this site.

by legoboyvdlp » 15 Sep 2017, 09:27
That may be why. For a CAT II autoland, the limit is 25 knots including gusts; for a CAT III autoland the limit is 20 knots with gusts. Maximum limit for a manual landing is 33 knots, gusting 38 knots.

Yes thanks I know . Nevertheless, it should work at least comparable to the Boeing 707.

[legoboyvdlp]

My point is that its unreasonable to expect something that you wouldn't do in real life, and probably wouldn't work to work on this simulation of the A320.
However, others have noticed issues with autoland, we're looking into it
Jonathan
IDG

[gierschi@flightgear]

by legoboyvdlp » 18 Sep 2017, 09:57
something that you wouldn't do in real life

Yes this is definitely true . Therefore I assume the worst case scenario for my investigations to have an averaged wind at about 10m of nearly 20 kn (no gusts) so that an ILS approach also of CAT ||| is still possible. Then, of course, for higher heights the magnitude of the wind velocity is increasing. But this doesn't matter because usually crosswind limits are based on the reported wind speed close to the ground (mainly 10m height).

[gierschi@flightgear]

Here is a link where you can find the pictures

https://www.dropbox.com/sh/16ie9v7xhowuibb/AABSoqOwA-YiXwNqZeyw2Feta?dl=0

[Octal450]

Hi,
That is not my A320. I can tell by the menu bar, my aircraft say Airbus A3XX. That is the old unrealistic A320-family.

Mine is called IDG-A32X

Kind Regards,
Josh

[gierschi@flightgear]

Ah great, i didn't see this. Thanks Josh for this hint.

Is there a possibility to start the aircraft (e.g. A320-200-CFM) directly form the air with the aim to practice approaches? For the A320-family it was possible by just using the Autostart function and some console commands like
--airport=EDDF
--runway=25C
--vc=220kt
--altitude=3000
--heading=298.0
--offset-distance=28

Furthermore I get the following error informations in the console:

FlightGear: Version 2017.2.1
FlightGear: Build Type Dev
Built with GNU C++ version 4.8
Jenkins number/ID 0:none
Starting automatic scenery download/synchronization to '/localdata/giersch/FlightGear/.fgfs/TerraSync'.
-----------------------------------------------------------------------------
Copyright (c) 2016-2017 it0uchpods Design Group
-----------------------------------------------------------------------------
Trim Results:
Angle of Attack: 2.8 wdot: 2.58e+01 Tolerance: 1e-03 Failed
Throttle: 0.5 udot: -5.48e+00 Tolerance: 1e-03 Failed
Pitch Trim: 0 qdot: -1.91e-01 Tolerance: 1e-04 Failed
Roll Angle: 0.1 vdot: -5.79e-02 Tolerance: 1e-03 Failed
Ailerons: 0 pdot: 2.24e-09 Tolerance: 1e-04 Passed
Rudder: 0 rdot: 3.66e-10 Tolerance: 1e-04 Passed

Trim Statistics:
Total Iterations: 61
Sub-iterations:
wdot: 125 average: 2.0492 successful: 61 stability: 2
udot: 0 average: 0 successful: 0 stability: 2
qdot: 0 average: 0 successful: 0 stability: 2
vdot: 122 average: 2 successful: 61 stability: 2
pdot: 0 average: 0 successful: 61 stability: 2
rdot: 0 average: 0 successful: 61 stability: 2
Run Count: 2222
Nasal runtime error: nil used in numeric context
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 220
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 177
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
Nasal runtime error: setprop() value is not string or number
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 289
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 261
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
Nasal runtime error: nil used in numeric context
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 220
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 177
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
Nasal runtime error: setprop() value is not string or number
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 289
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 261
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
Nasal runtime error: nil used in numeric context
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 220
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 177
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
Nasal runtime error: setprop() value is not string or number
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 289
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 261
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
Nasal runtime error: nil used in numeric context
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 220
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 177
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
Nasal runtime error: setprop() value is not string or number
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 289
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 261
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
Nasal runtime error: nil used in numeric context
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 220
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 177
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
Nasal runtime error: nil used in numeric context
at /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 220
called from: /localdata/giersch/FlightGear/fgdata-v2/Aircraft/IDG-A32X/Nasal/FMGC-b.nas, line 177
called from: /localdata/giersch/FlightGear/fgdata-v2/Nasal/globals.nas, line 119
ND Canvas Initialized!
Error: caught signal 11:
/lib64/libc.so.6 : ()+0x35550
/lib64/libpthread.so.0 : ()+0x113d8
fgfs : OpenThreads::ScopedLock<OpenThreads::Mutex>::~ScopedLock()+0x29
fgfs : FGVoiceMgr::FGVoiceThread::wait_for_jobs()+0x5c
fgfs : FGVoiceMgr::FGVoiceThread::run()+0x8c
/localdata/giersch/OpenSceneGraph/OpenSceneGraph-3.4.0-install/lib64/libOpenThreads.so.20 : OpenThreads::ThreadPrivateActions::StartThread(void*)+0xb5
/lib64/libpthread.so.0 : ()+0x80db
/lib64/libc.so.6 : clone()+0x6d


Are they important to you or even to me?

Best regards,
Sebastian

[Octal450]

Hi,
These appear if you start paused.... You can't start paused the sim. I haven't had the time to fix it. Sadly, no. Because the aircraft is so complex, starting in air is not supported. (And won't be)

Starting normally on the ground is the best way to go.

Kind Regards,
Josh

Kind Regards,
Josh

[Octal450]

I went ahead and fixed those nasal errors (I think), it may be able to start paused now, but not in air.

Kind Regards,
Josh

[gierschi@flightgear]

Hi,

thanks for the hint.

I have some more questions to the aircraft so that I can try/test an ILS approach with it. Sadly, I am not familiar with controlling and starting such a complex aircraft. The only thing I want to do is to use it for scientific reasons investigating the wind influence during approaches. I found a function in the aircraft configuration dialog that allows me to prepare the aircraft for Takeoff automatically (By the way, is there a video tutorial that show the whole starting procedure?). But when i am in the air I have problems to control the aircraft with the autopilot because i have no idea of some functionalities. When i turn on the autopilot the plane adjust directly to the altitude i specified. But when I try to use the speed and heading control I just get a message

''Please make sure you have set a cruise altitude and cost index in the MCDU'' or
'"Please make sure you have a route set, and that it is Activated!"

What can I do? Is it better to use the autopilot dialog and is there an explanation how to us it? Thanks for the help in advance

Kind Regards,
Sebastian

[Thorsten]

Sadly, I am not familiar with controlling and starting such a complex aircraft.

I'm guessing that if you 'just' need a test aircraft to research whatever scenario, you're better off finding one that you can init in-air and tweaking the AP where needed.

(I absolutely don't want to keep you from learning and enjoying a high-quality airliner, but complex systems modeling is really not what you need for trajectory simulation... and you'll use a significant amount of time just to set up the scenario you want...)

[legoboyvdlp]

''Please make sure you have set a cruise altitude and cost index in the MCDU'' or
'"Please make sure you have a route set, and that it is Activated!"

That means you need to set up the flight management computer:


For your purposes, I reccomend you use OP CLB modes and HDG SEL modes: instead of hitting "push", hit "pull", and that should do it.

TBH, I don't think this is the right aircraft for scientific research: I completely agree with what Thorsten said.