RE: A powered Thermal Glider as a first plane ?
The Radian is an excellent beginner/intermediate glider, we have a couple at my club's field they are very good performers.
After reading through all of this thread I think some folks here are making too much of big deal about converting from glider to glow powered flight or vice-versa.
I don't know how most of you folks fly, but IMO it pretty much takes full attention to keep track of a glider especially at higher altitudes and around cloud bases. In R/C there just isn't too much time for a mental vacation be it glider or glow/gas powered airplane. Yes the glider is slower, but if your effectively tracking around trying to find thermals you have to fly the bird.
Personally I think a pilot gains a good deal of valuable experience flying gliders in learning how to fly the wing vs. a power curve. Case in point the "Miracle on the Hudson" full scale yes, but the principles are the same.