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Attitude indicator at high altitude

Discussion about creating 2d and 3d cockpits.

Attitude indicator at high altitude

Postby jam007 » Tue Apr 11, 2017 1:49 pm

The standard AI uses vacuum to drive it. This can be driven by electric voltage to fake vacuum suction as is commonly done to simulate an electric AI.
Eg.
Code: Select all
    <vacuum>
        <name>vacuum</name>
        <number>0</number>
        <rpm>systems/electrical/outputs/ac-main-voltage</rpm>
        <scale>25.0</scale>
    </vacuum>

But it seem that its hard to get the AI to work above approx 12 000 m regardless of the scale factor used to drive it due to the low air pressure.

The advantage of using the standard AI is that it comes as a package with properties, calculations and instrument errors.
How to best solve this/or replace for an aircraft with a high ceiling (20 000 m)?
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Re: Attitude indicator at high altitude

Postby V12 » Tue Apr 11, 2017 2:29 pm

Check Concorde. This aircraft has perfectly modelled all instruments. XB70, U2 or SR71 using standard FG instruments.
Fly high, fly fast - fly Concorde !
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Re: Attitude indicator at high altitude

Postby jam007 » Wed Apr 12, 2017 4:32 pm

Thanks. The Concorde uses engine-thrust in lb for suction property if I understand it correctly. I guess that is suction enough :)
It is the simplest solution. just a high enough value. I tried 5000 previously but should have tested 10 000...
But as the instrument needs ca 3-4 in to work properly there must be a limit around 15000 m unless negative pressures are allowed.
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Re: Attitude indicator at high altitude

Postby jam007 » Fri Apr 28, 2017 7:06 pm

Just found themaster reference gyro MRG. That is electrically powered. But I do not know how to get it included in the aircraft. The associated properties are not included in the property tree as far as I can see. How do you enable it?
A more general question. How to enable/disable a selection of standard instruments?
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Re: Attitude indicator at high altitude

Postby Thorsten » Sat Apr 29, 2017 5:08 am

Provide the FDM a path to your instrumentation definitions like

Code: Select all
<sim>
   (...)
   <instrumentation>
    <path>Aircraft/MyAircraft/Instrumentation/my-instruments.xml</path>
   </instrumentation>
</sim>


and then activate and configure the instruments inside that file like

Code: Select all
<?xml version="1.0"?>
 
 
<PropertyList>
 
 
   <airspeed-indicator>
     <name>airspeed-indicator</name>
     <number>0</number>
     <total-pressure>/systems/pitot/total-pressure-inhg</total-pressure>
     <static-pressure>/systems/static/pressure-inhg</static-pressure>
   </airspeed-indicator>
 
   <altimeter>
     <name>altimeter</name>
     <number>0</number>
     <static-pressure>/systems/static/pressure-inhg</static-pressure>
     <quantum>0</quantum>
     <tau>0</tau>
   </altimeter>
</PropertyList>


(you may need to do the same for the systems section to get things like /systems/static/pressure-inhg initialized - there's a couple of them on by default but it's possible that you request something exotic).

You can also drive the instruments with your own properties if you have a separate systems simulation. The SenecaII has a good example you can work from.
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Re: Attitude indicator at high altitude

Postby jam007 » Sat Apr 29, 2017 7:44 am

Thanks!

If I add an instrumentation xml-file I assume I have to activate and configure all instruments I want as this replaces the default instruments?
Can I use only the instrument name node to get standard configuration or do I have to look up all properties for the different instruments? Yes. Seneca II uses that.

Thorsten's info solved the high altitude problem for attitude indication too:
Code: Select all
  <attitude-indicator>
    <name>attitude-indicator</name>
    <number>0</number>
    <suction>systems/electrical/outputs/inst_ac</suction>
  </attitude-indicator>

:)
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Re: Attitude indicator at high altitude

Postby jam007 » Sat Apr 29, 2017 12:26 pm

Created a short wiki page. Please help expand and maybe correct.
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Re: Attitude indicator at high altitude

Postby D-EKEW » Sat Apr 29, 2017 3:05 pm

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Re: Attitude indicator at high altitude

Postby jam007 » Sun Apr 30, 2017 2:51 pm

Since there is a reference to http://wiki.flightgear.org/System_dependent_instruments I think that is enough. I added these links to the System dependent instruments page.
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