I have at last got my program to run successfully transfering binary data across 3-wire RS232 (no hardware handshaking), using Basic4PPC, of course, and my F-S Loox PDA. This PDA also has host and slave USB. The host works OK to a USB keyboard but I think would need a special driver (goodness knows how that would be integrated!) to do arbitrary host working to, say, a printer.
So I think USB to control the plane might be problematic. A PDA which has RS232 would be much easier. RS232 to D-to-A converter could (almost?) be off-the-shelf. Don't know about WiFi, Bluetooth or IR, but I think that RS232 would take least power and have least chance of interference too.
What are the insurance, health and safety and regulatory aspects of flying an autonomous plane? I wouldn't want to help with anything illegal!
Cheers, Mike.