I actually wasn't aware that induction motors don't use permanent magnets. RC model aircraft is a hobby of mine, and all I knew is that the commonly-used brushless AC motors certainly use permanent magnets.
At low power levels, permanent magnet motors (specifically brushless motors) tend to have higher efficiency than induction motors, additionally, they don't require complicated control systems to operate efficiently at varying speeds. Thus you are unlikely to see an induction motor in an RC model anytime soon.