Good day Warwick,
(the following assumes you use the P92 from FGAddon, i.e. downloaded in the launcher).
The airspeed indicator in FG is a 3d model (AC3D format) along with a texture (PNG format) and an animation file (XML format). In order to change the indicated unit from km/h to kts, you can either edit the instrument yourself by editing the texture, e.g. with GIMP or Photoshop and editing the animation file so that the needle shows the correct speed, or you can replace it by an instrument from another aircraft or from the "instrument library" in Aircraft/Instruments-3d. The latter is probably easier, as there are many knots airspeed indicators used in other aircraft and available in the library. To do so
1) Use from another aircraft: Find the folder containing the instrument, this is usually located in the aircraft's path /Models/Interior/Panel/Instruments/asi, a shortened version of that path or similar. E.g. looking at the Cirrus-SR22, you can find it in Aircraft/Cirrus-SR22/Models/Interior/Panel/Instruments/asi. Use this to replace the folder to Aircraft/Tecnam-P92/Models/Interior/Panel/Instruments/asi. As the xml files located in that folder (asi.xml) are named the same for both, you don't need to change anything else except maybe the offsets in the <model>-block including the asi, which you can find in Models/Interior/Panel/panel.xml, l.52ff.
2) Use from Instruments-3d. Use your favourite file manager to navigate to $FGDATA/Aircraft/Instruments-3d/ and look for a suitable instrument. For the asi, you can use asi or asi-pa24. You don't need to copy that folder anywhere because it's a shared folder for all aircraft in FG. In Aircraft/Tecnam-P92/Models/Interior/Panel/panel.xml, l.52ff., replace the
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<path>Instruments/asi/asi.xml</path>
in order to point to the other instrument, e.g.
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<path>Aircraft/Instruments-3d/asi/asi.xml</path>
. You may need to adjust the offsets if the model is a bit off.
The aircraft's stall speed is defined by the FDM. The Tecnam P92 from FGAddon uses YaSim, which defines the stall speed directly. Have a look at Aircraft/Tecnam-P92/Systems/FDM/p92W-yasim.xml for the tricycle variant, p92A-yasim.xml for the amphibian variant. Line 28ff. defines the approach configuration, one of YaSim's two solution targets. According to
http://buckarooshangar.com/flightgear/y ... ruise.html, it's a good start to use 1.3 * stall speed as the approach speed. This only works within reasonable limits, troubleshooting issues is described here:
http://buckarooshangar.com/flightgear/y ... oting.html. The whole guide, available at
http://buckarooshangar.com/flightgear/yasimtut.html is in my opinion one of the best resources when working on YaSim FDMs.
Flap speeds is a bit ambigious. Do you mean
* maximum flap speeds (i.e. Vfe)? These are defined using Limits (see
https://wiki.flightgear.org/Howto:Define_limits) and are currently not configured for the Tecnam P92, as far as I can see. Note that these only create a warning, structural damage due to overspeeding needs to be simulated separately and is somewhat more advanced
* minimum flap speeds, i.e. stall speed with flaps extended? These are defined as a combination of the above mentioned approach configuration, which mandates that the flaps are fully extended during approach in order to reach the solution (which is in the current case flying at 30kts at an aoa of 2):
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<control-setting axis="/controls/flight/flaps" value="1.0"/>
as well as the flaps effect, which is defined in line 63 (flap0):
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<flap0 start="0.084" end="0.498" lift="1.2" drag="1.25"/>
Caution: note that flap1 is not a flap in the traditional sense, but the ailerons.
Or do you mean changing the white, green, yellow and red arcs on the airspeed indicator? This requires editing the instrument's PNG (or sometimes RGB) texture.
Have a good day