Okay, since there seems to be some confusion, let me see if I can make things simple.
27MHZ can be used for air and ground models, but I wouldn't recommend using with anything that leaves the ground
27/49MHZ is used on most toy store R/C's like Nikko and Radio Shack products
50/53MHZ can be used for either but requires a HAM LICENSE
72MHZ is AIRCRAFT ONLY
75MHZ is SURFACE ONLY

OH, and Rodney, Futaba is a negative shift system