Hi. Welcome to Mobiflight !
Let me say at first.... Building homecockpits ( and understand the systems like Mobiflight, FSUIPCm and so on) is simmular to learn flying.
Your situation is the same like if a guy try to do his first Aloane Flight without instructor but not know what "knots" and "heading" means or where the Landinggear leaver is located.
Or in a other example.... You ask me to explane a ILS Landing precedure.... but you still not know what Flaps are!
so... Mobiflight is a nice Software.... With MF Users must not be a professional programmer (like in the past where Homecockpits was just a hobby for Compuerfreaks ). With MF you can easy create configurations that controll your hardware.
BUT !!!
That not means you can do this complete without knowledge !
Things like WHAT is FSUIPC is a basic! and that must be understand "before" you beginn with Mobiflight or starting to build a panel at home!
I high recommend to you to take a bit time and read this forum.... Get on cockpitbuilder Boards .... Use Google..... And start to understand the full thematic.
Also you should have some skills in basic programming logic like "IF ELSE Conditions" and also understand mathematical logics and systems like Binary and Hexadecimal.
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To your Questions
Mobiflight is basicly designed for FSUIPC Comunication.
FSUIPC is a system ( by Pete Dowson) that was build like a "Compiler" for Microsoft FSX and Lockhead P3D .
In case that in the past ( and already today) most cockpitbuilders use this system nearly all the Homecockpitstuff is based on it.
Your Xplane11 is the OTHER System. It work not with FSUIPC so basicly Mobiflight can not work with it.....
BUT... You already found XPUIPC. This is a tool from a guy how like to use FSUIPC based systems with his Xplane.
So he write Xpuipc programm that Read/write the Xplane internal Data to a "simulated" FSUIPC Plattform.
Programms like Mobiflight now see your XPUIPC and "think" this is original and work like you will use FSX or P3D.
The Problem: This XPUIPC not include all the stuff that is available in the original FSUIPC. Specialy with AddOn Aircrafts it mostly have big problems.
Cause this Aircrafts not use Standard Data.... But only Standard stuff is include in this XPUIPC System.
Thats the awnser to your question: Some things work cause here you sue the "standard" System.... But special things in your addons will not be supported.
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Solution:
1. With some programming skills or by using Files from Other users (who build this themself) you can rework the XPUIPC System. Then Mobiflight can handle that stuff.
2. You can use a alternate to Mobiflight that is designed specialy for Xplane. ( Not use this but i think "ArdSim" will help maby.... google for that)
In that case you not need XPUIPC cause this Programm talk "direct" to Xplane..... So you can also work with Addon specific things diectly !
3. You rethink your simulator. Xplane got good facts... But today already the most and best addons are based on FSX/P3D .... Also most AddOns support its data direct to FSUIPC. I personaly think with P3D you can build your first Homecockpit much more comfortable)
You got the choice !