A. To use Fly by Wi-Fi iPad app, you need to install Fly by Wi-Fi Server in your PC.
B. Fly by Wi-Fi Server works with FSUIPC to communicate with Flight Simulator.
You can enjoy Fly by Wi-Fi with FSUIPC Free Version without any problems.
C. For your convenience, here is some description how Fly by Wi-Fi connects to Flight Simulator.
Fly by Wi-Fi client(iPad) <-> Fly by Wi-Fi Server(WinPC) <-> FSUIPC <-> Flight Simulator
D. Installation Checklist
1. Check iPad and Flight Simulator Installed PC exist in the same network.
2. Download & Install Fly by Wi-Fi Server Ver. 1.2
2-1. Launch Fly by Wi-Fi Server.
3. Download & Install FSUIPC
4. Launch Flight Simulator
4-1. In the first launch after installed FSUIPC, Flight Simulator will be ask you to activate FSUIPC or not.
4-2. After meet Flight Simulator main page, check Fly by Wi-Fi Server. – it should be connected to Flight Simulator.
5. Check your IP address in Fly by Wi-Fi Server, and set it in Fly by Wi-Fi Client Settings.
I hope this description will help for you.