A basic 4 channel radio has Throttle,rudder,elevator and aileron. You would need another channel if you wanted retracts, and another channel if you want smoke, and so fourth and so on. The crystal determines what frequency your radio is on. For an LT40 you could use a cheap regular old 4 channel radio, but if you are planning on staying in the hobby you might want to look at a higher end radio like a 6,7, or 8 channel computer radio. I use JR radio's. You can see them at the Horizon hobby site. If you have any other questions the folks at Horizon are great people to deal with. If there is any way I can help you out let me know...John