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LOC and GS antenna location in navradio code

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LOC and GS antenna location in navradio code

Postby Soitanen » Mon Aug 29, 2016 7:37 am

Navradio give heading and glideslope needle deflection, when following ILS approach. What point is used as antenna location? Asking, because 737 have LOC and GS antenna in front radome, and flying on glideslope (50 feet above treshold) in reality gives only 35 feet between gears and ground at this moment.
Boeing 737-300. Reworked cockpit, FDM, autopilot and much more. WIP.
Boeing 737-800. WIP. Canvas PFD and ND.
Antonov An-24B. Made from scratch. Very good FDM. 3D model by Adrian. WIP.
Project Russia (some cities, based on OSM with custom objects).
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Re: LOC and GS antenna location in navradio code

Postby Thorsten » Mon Aug 29, 2016 3:22 pm

But the avionics knows the current attitude, and it knows where the gear is relative to the antenna - so the software can display what is reasonable rather than where the antenna happens to be.
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Re: LOC and GS antenna location in navradio code

Postby Soitanen » Mon Aug 29, 2016 6:28 pm

But Boeing in FCTM shows figure, that airplane follows glideslope by nose (where antennas is located), and 35 feet is from that book.
Boeing 737-300. Reworked cockpit, FDM, autopilot and much more. WIP.
Boeing 737-800. WIP. Canvas PFD and ND.
Antonov An-24B. Made from scratch. Very good FDM. 3D model by Adrian. WIP.
Project Russia (some cities, based on OSM with custom objects).
Soitanen
 
Posts: 489
Joined: Sat Jun 16, 2012 6:50 am
Location: Saint-Petersburg, Russia
Version: git
OS: Linux Mint 17

Re: LOC and GS antenna location in navradio code

Postby Thorsten » Tue Aug 30, 2016 5:25 am

It's easy to make the instrument show whatever you want it to show (e.e. offset the needle) - far easier than tailoring the nav radio code to every aircraft.

I'm fairly certain any FG-side code uses the position reference point (aka, whatever position/ contains) without any offsets. That point in turn is defined by the FDM in relation to other points of interest (aerodynamical reference, 3d model reference,...)
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Re: LOC and GS antenna location in navradio code

Postby Alant » Tue Aug 30, 2016 9:30 am

The source code has no correction for aircraft ILS antenna position.

On the other hand the radio altimeter does, and possibly could be used as a template for improving the nav receiver.

With a large aircraft this error will be quite noticeable when near the transmitter.

A temporary fix could be to add range based corrections to the needle deflection before displaying passing it to the instruments or autopilot. Otherwise raise a "feature request", or update the code yourself and send it to the maintainer for approval.

Alan
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Re: LOC and GS antenna location in navradio code

Postby Alant » Tue Aug 30, 2016 2:31 pm

Which 737 is this ?

I ask because your 737-800 has a VRP a long way off zero.

Code: Select all
        <location name="EYEPOINT" unit="IN">
            <x>  98 </x>
            <y> -20 </y>
            <z>  56.18 </z>
        </location>
        <location name="VRP" unit="M">
            <x> 19.8099 </x>
            <y> 0 </y>
            <z> 0.0785 </z>
</location>
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Re: LOC and GS antenna location in navradio code

Postby Soitanen » Tue Aug 30, 2016 6:01 pm

Yes, it's mine. It's far away due to visual model zero coordinate position.
Boeing 737-300. Reworked cockpit, FDM, autopilot and much more. WIP.
Boeing 737-800. WIP. Canvas PFD and ND.
Antonov An-24B. Made from scratch. Very good FDM. 3D model by Adrian. WIP.
Project Russia (some cities, based on OSM with custom objects).
Soitanen
 
Posts: 489
Joined: Sat Jun 16, 2012 6:50 am
Location: Saint-Petersburg, Russia
Version: git
OS: Linux Mint 17


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