A 4 channel radio is for throttle, rudder, elevator and ailerons. If you use a 5th and 6th channel they are for flaps, bomb drop, retracts and such. You can have a 4 channel radio that has 5 and 6 servos. Some planes have one servo for each aileron and a Y Harness to tie them together. Some of the 3D and larger planes use 2 servos for the elevators and they are mixed together with a radio that has the programming feature to mix 2 channels together. If you are just starting out, check out the beginners forum as it has a list of great starter planes. It is hard to learn RC without starting off woth the right plane. Good Luck, Dave