If your thinking of gas..think of this 1 channel for throttle, 1 channel for choke, 1 for rudder, perhaps 2 for ailerons and 2 for elevator, perhaps one for smoke thats 8..see what I mean..channels go fast..
I have a 50cc Pitts Python...1 throttle 1 choke 1 rudder 2 elevators 2 ailerons.1 optic kill switch..that's 8..
If you were to get a 9 or 10 channel 2.4 that would be all the radio you need for years....