The next challenge for Nick - True GPSS simulation
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Hi Nick,
I come with a challenge! I'm a user and huge fan of all of your aircraft addons. I love the realism and how you have progressed innovation, with each new release!
There's just one area that I can see, that is not currently realistic in your aircraft, and that concerns how older APs (featured in your aircraft) interface with modern GPS units (by modern, I mean GNS through to GTN units).
As you might be aware, the APs that you feature, such as the KFC150 (a number of your aircraft), KAP140 (Caravan) and STEC-60 (Commander) do not have native GPS steering technology. The NAV mode in these units can use only one reference for navigation - the HSI/OBI. This means they can successfully track straight line GPS legs, using the HSI. In order to bring GPS Steering functionality to these units, a "GPSS converter" box is used, behind the panel. The GPSS converer takes the highly accurate navigation information from the GPS (which is output as bank level rates), convert that into a DC Heading error command, and send it to the AP's Heading channel (not NAV). For this to work, such GPSS converters provide a switch in the cockpit, typically labelled "HDG/GPSS".
When the switch is in the HDG position, the convert is inactive and the heading bug will control the HDG channel of the AP. When the switch is set to GPSS, the converter disables to heading bug (and in fact the whole HSI) from the AP and instead passes it heading commands that correclate with the so-called magenta line. This means that in this mode (AP set to HDG and the converter set to GPSS), full GPSS steering emulation is provided.
Such real world units are the Garmin GAD29 and the STEC-901.
At present in Black Square addons, these old autopilots are providing full GPS steering in NAV mode, which would not work in the real world.
The solution?
Aircraft like the Bonanza, Baron, Commander, Dukes and Caravan need a "HDG/GPSS" switch on the panel. To get MSFS's default GPS NAV capability, it shold be necessary to have the AP in Heading mode, and the HDG/GPSS switch set to 'GPSS'. With the GPS CDI switch set to GPS and the AP in NAV mode, the unit should be behaving just like VLOC mode, providing only straight line tracking of a GPS track.
As far as I know, the only addon aircraft that simulate this true GPSS behaviour are the A2A Comanche and Aerostar.
But I dream of the otherwise fantastically immersive and realistic Black Square planes one day having this realism.
Thanks for your consideration!