If you will be flying off grass id highly recomend going with the os .46fx, or tt pro .46. At the very least get the os 46la. Id stay away from the .40la. If the grass gets thick and or high you will have a tough time taking off. It will however to teach you to fly off the wing and not the motor. I had a weak engine in my trainer when learning and many times could not even gain enough speed to take off, had to hand launch it a few times. I bought a os .46fx and had no problems what so ever, plus the engine will fit nicely into your next model.

good luck!!