If you purchase a 4 channel radio like Jr Quattro or Futaba skysport for your trainer and graduate on to your second plane....Can you use the same radio on your second plane?
Yes you can.
I'm thinking I would have to purchase a flight pack for the second plane set up to match the radio? Does buying the correct crystal accomplish this?
Yes it does, just specify what channell when you order it.
Just my opinion here but If you can afford it I would probably by the 6 channel.