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Fluttering Instrument Display

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- what OS (Windows Xp/Vista, Mac etc.) are you running?
- what FlightGear version do you use?
- what graphics card do you have?
- does the problem occur with any aircraft, at any airport?
- is there any output printed to the console (black window)?
- copy&paste your commandline (tick the "Show commandline box on the last page of FGRun or the "Others" section on the Mac launcher).
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Fluttering Instrument Display

Postby parker » Fri Jul 27, 2018 4:57 pm

I am new to FlightGear.

Issue Description
The IAS indicator and airspeed indicator on the primary flight display are fluttering. Basically, they are increasing and decreasing very rapidly in value in a motion that could be described as vibrating even though the input is stable. It seems that the indicator is trying to show the speed then quickly jump back to zero with each update. Even when airspeed is forced to a constant, this behavior persists. All other instruments, such as those for altitude and heading, do not exhibit this issue and behave as expected.

What OS (Windows Xp/Vista, Mac etc.) Are you running?
Windows 7 Professional
Service Pack 1

What flightgear version do you use?
FlightGear Version: 2018.2.2
SimGear Version: 2018.2.2
OpenSceneGraph Version: 3.4.1
Build Id: 236
Build Number: 236
Revision: b000e132bba859bd0e3c7f28d780fa798954330

What graphics card do you have?
Graphics Card: AMD Radeon HD 6900 Series
OpenGL Version: 4.2.11762 Compatibility Profile Context
GLSL Version: 4.20
Max Texture Size: 16384
Depth Buffer Bits: 24

Does the problem occur with any aircraft, at any airport?
The problem is known to occur with the Cessna CE-750 CitationX. Other aircraft have not been tested for this yet.

Where did you download your aircraft/scenery from?
V2.0.1 “HD: via a Graphical Interface
http://ns334561.ip-5-196-65.eu/~fgscene ... 2.0.1.html

Is there any output printed to the console (black window)?
No. This issue does not produce console output.

Copy&paste your commandline (tick the "Show commandline box on the last page of fgrun or the "Others" section on the Mac launcher).
C:\Users\test\Desktop>"d:/Program Files/FlightGear 2018.2.2/bin/fgfs.exe"
--fg-root="d:/Program Files/FlightGear 2018.2.2/data" --fg-scenery="d:/Program
Files/FlightGear 2018.2.2\data\Scenery" --generic=socket,in,25,,5010,udp,myInputProtocol --aircraft=CitationX --airport=KDTW --callsign=NADI1 --fd
m=external --disable-panel --disable-hud-3d --timeofday=morning --enable-cl
ouds3d --config="d:/Program Files/FlightGear 2018.2.2/data/cameraViews.xml"
Created multi-app mutex, we are in writeable mode
CrashRpt enabled
FlightGear: Version 2018.2.2
FlightGear: Build Type Release
Built with Microsoft Visual C++ version 1900
Jenkins number/ID 236:236
System locale not found or no internationalization settings specified in default
s.xml. Using default (en).
StatsHandler::StatsHandler() Setting up GL2 compatible shaders
Volcanic activity off.
Electrical System ... ok
Flight Director ...Check
Nasal runtime error: props.setValue() with non-number
at d:/Program Files/FlightGear 2018.2.2/data/Nasal/props.nas, line 31
called from: d:/Program Files/FlightGear 2018.2.2/data/Aircraft/CitationX/Nasa
l/CitationX.nas, line 76
called from: d:/Program Files/FlightGear 2018.2.2/data/Aircraft/CitationX/Nasa
l/CitationX.nas, line 294

Additional Information
Airspeed in knots is sent to FlightGear via UDP packets with the --generic protocol. The protocol file looks something like this:

Code: Select all
<?xml version="1.0"?>
<PropertyList>
    <generic>
        <input>
            <line_separator>newline</line_separator>
            <var_separator>tab</var_separator>

            <!--other chunks would here but were omitted -->

            <chunk>
                <name>/velocities/airspeed-kt</name>
                <node>/velocities/airspeed-kt</node>
                <type>float</type>
                <format>%f</format>
            </chunk>

             <!--other chunks would here but were omitted -->

        </input>   
    </generic>
</PropertyList>


The value for airspeed seems to be received by FlightGear properly because it appears to be logged accurately. If you add logging to the PropertiesList file…

Code: Select all
<!--some content omitted-->
<?xml version="1.0"?>
<PropertyList>
        <logging>
           <log>
              <filename>D:\Export\datavalues.csv</filename>
              <enabled>true</enabled>
              <interval-ms>40</interval-ms>
              <delimiter>,</delimiter>
              <entry>
                 <enabled>true</enabled>
                 <title>Velocity</title>
                 <property>/velocities/airspeed-kt</property>
              </entry>
           </log>
        </logging>
        <sim>
        ...
        </sim>
</PropertyList>


… will notice in the resulting csv file datavalues.csv that the velocity is fairly constant and has the correct value of 179.9 kts.

Code: Select all
Time,Velocity
1,0
1,0
1,0
...
145.1,179.9964905
145.125,179.9964905
145.175,179.9964142
145.2,179.9964142
145.25,179.9963684
145.3,179.9962921
145.325,179.9962921
145.375,179.9962006
145.4,179.9962006
145.45,179.9961548
145.5,179.9960785
...


Based on this, I would expect the airspeed indicators to have a steady reading of about 179.9 kts but instead they display the fluttering behavior mentioned previously.

This problem is not encountered when FlightGear version 2.8.0 is used. Of course, many changes have been made since then and the Changelog for 2018.2 lists the Cessna Citation X as having "Significant Aircraft Updates" (refering to changes in avionics and MP model display), but it is worth mentioning.
Last edited by parker on Mon Jul 30, 2018 5:17 pm, edited 2 times in total.
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Posts: 1
Joined: Thu Jul 12, 2018 12:01 pm

Re: Fluttering Instrument Display

Postby wkitty42 » Fri Jul 27, 2018 8:47 pm

i have to wonder if the indicators are updating faster than your code is sending updates... in other words, you send a speed, the indicator catches it, the indicator looks for another one that isn't there and the needle goes toward zero, a new speed value arrives, the indicator catches it and puts the needle where it needs to be, looks for another value and there's not one arrived... loop loop loop...

so basically, can you send the values faster?

also, your logging is only once a second... there can be a lot of numbers sent in one second's time and you're missing them...
"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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