for your spad, you'll need basically four channels (servos). One for the rudder, one for the ailerons, one for the elevator, and one for the throttle. Servos are little electric motors that move control surfaces and other things that need to move. They are hooked to a receiver that receives signals from your radio. The receiver and radio have to be on the same channel to talk to each other. this is where the crystal comes in. Whatever channel your radio is on, you'll need to purchase that crystal for your receiver. Normally, a flight pack will come with one standard seven or eight channel PPM receiver, and four standard servos. They run about 100 dollars. The crystal for your receiver will cost another 10 bucks or so. Hope this helps some, I really couldn't tell what you wanted to know exactly.