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No Glide Path with LinkVor False (resolved)

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Posted (edited)

If LinkVor = False with the GTN 750 there is no Glide Path guidance during an RNAV LPV approach. Setting LinkVor = true prevents using the RMI needles for situational awareness when the GTN750 is in GPS mode. Why should a VOR setting impact glide path guidance?

Thx,

Al

Edited by ark

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As stated before, this is aircraft dependent..

If the aircraft vendor uses the VOR variables for the autopilot, the GTN needs to override them..

Which aircraft are you talking about?

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1 hour ago, Bert Pieke said:

If the aircraft vendor uses the VOR variables for the autopilot,

Let me try to further explain: if the aircraft autopilot is custom made to directly command the aircraft controls and if the autopilot is only based on the VOR variables then yes this is true. Please note most aircraft only use the default autopilot in the back and only a few (usually Boeing/Airbus) do implement their own autopilot system like this.

The needle deflection though depends on which variable the aircraft gauge is using in the background and if it so happens it is using the VOR variables for an HSI needle, then there isn't much we can do but overriding the VOR variable (with the "Connect VOR" setting) in order to deflect the needle with the GTN output.

Please note the RMI should be consistent: the RMI#1 will show the NAV1 signal which will be the GTN signal in this case. You might want to use a RMI #2 then, otherwise, set the GTN to use NAV2 source instead and it will override VOR#2 leaving the RMI#1 alone, while still coupling the autopilot regardless.

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41 minutes ago, RXP said:

Let me try to further explain

I appreciate your patience!

In what way is a vertical (glide slope) mode considered a VOR variable?  I don't associate vertical guidance with a VOR?

Thx,

Al

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Posted (edited)
2 minutes ago, ark said:

In what way is a vertical (glide slope) mode considered a VOR variable? 

Is your VOR instrument having 1 or 2 needles? is the 2nd needle used to display a vertical deviation?

This is a VOR gauge (not a VOR station) with VOR variables storing the deviation values, therefore, to 'move' the VOR gauge needles to the GTN output value you have to enable 'overriding' the VOR gauge variables driving the needle deviation.

There is an equivalent set of variables for the HSI gauge.

If a developer is using the VOR#1 vertical needle variable value to drive the HSI vertical needle image, it works fine as long as you are dealing with the stock GPS or NAV1 station because in turn, the HSI and the VOR#1 variables share the same source behind the scene.

With our GTN and GNS V2, you have fine grained control (finer than the stock/default in fact).

Just as simple as this!

Edited by RXP
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2 minutes ago, RXP said:

Is your VOR instrument having 1 or 2 needles? is the 2nd needle used to display a vertical deviation?

This is a VOR gauge (not a VOR station) with VOR variables storing the deviation values, therefore, to 'move' the VOR gauge needles to the GTN output value you have to enable 'overriding' the VOR gauge variables driving the needle deviation.

Just as simple as this!

OK, I should have thought of that. I just don't fly any aircraft with an actual VOR gauge so didn't make the connection to a VOR gauge GS needle. As you figured out, I just thinking of a VOR station.  🤔

Thx again,

Al

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Just to update and close the above, I have been able to get the GTN750 vertical guidance to work as expected in GPS mode with LinkVOR False for the Flysimware Lear35 and Falcon50 aircraft. The general approach was to use HSI variables (e.g., HSI GSI NEEDLE instead of NAV GSI, etc) when the GTN is in GPS mode.

Al

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