Hi! I made an Android app that allows you to control Infinite Flight running on another device (iOS or Android) using a joystick. Give it a try and let me know if it works for you.
I use it to control Infinite Flight running on my iPad with my T.Flight Hotas X joystick plugged into my Samsung Galaxy S6.
The app is optimized for low battery consumption and high performance. Its source code is open (GPLv3).