Ground power provides electrical power to a parked aircraft, so its systems can be operated without depleting the battery even if the engine(s) are turned off.
The ground power plug must be plugged into the aircraft first, then a relay can be closed to actually connect an electrical bus to the external power source.
Plugging the power in
Aircraft made for X-Plane 12.07 and earlier always have voltage on the ground power receptacle if the aircraft is stationary (ground speed is less than 1 knot).
Aircraft made for X-Plane 12.0.8 need to call for ground services to have the ground power plugged in. In order to that, preconditions must be met:
- The aircraft must be stationary (ground speed less than 1 knot)
- The aircraft must not be on a runway (it needs to be on a ramp or taxiway area, or on grass)
Then, the user can request to “service the aircraft”. This will cause power to become available. Whether an animated ground power unit will show up in the 3d world to service your aircraft depends on
- the aircraft author must have specified a location for the generator cart to be parked relative to this aircraft. That’s in Plane Maker, in the “dock ports” tab, “has ground power cart” must be checked and the coordinates specified
- the airport must have a route for ground service vehicles to reach your aircraft parking position
In the absence of the above, the electrical power will still work, but no animated generator cart will be visible.
Making contact
Once the power is available, the available voltage will be readable in the sim/cockpit2/electrical/GPU_generator_volts dataref. If this reads 0, nothing is plugged in. This information can be used by aircraft to power “hot buss” items that might be available even before the switch in the cockpit is activated. This can also be used to indicate the availability of ground power to the pilot, such as the switch lighting up.
Now, the dataref sim/cockpit2/electrical/GPU_generator_on can be used to switch the GPU relay to on. Now, all connected busses will be powered from GPU power, all equipment can be used and the batteries will be getting charged.
Third-party overrides
At some third-party scenery airports, or with some aftermarket aircraft, the use of X-Plane default ground services might be undesirable. For these, the ground power can be overridden by plugin logic, so the third party product can decide ground power availability rather than X-Plane’s ground service system.
To take control of the GPU power, the plugin needs to set sim/operation/override/override_GPU_volts to 1 and then write the desired voltage to sim/cockpit2/electrical/GPU_generator_volts or 0 if the GPU isn’t supposed to be plugged in right now.
In order to not fry any virtual circuits, the plugin should check the dataref sim/aircraft/electrical/acf_nom_gen_volt to find out whether the user aircraft expects 12V, 28V, 110V or anything else.