The Roo II being a delta wing, needs some distance to take off. I had a few of them with P80 and P120 and they flew fine on either. The only thing is that mine took off in about 400 to 450 feet on asphelt with a P120 or P80. They will fly only when they are ready AND the CG is per plans. If you have a short grass runway, you will need to throttle up to 75% before brakes off, track it well then go to 100% power as soon as you can.

The P70 is rated at 18 lbs at best, so assume you get 16 lbs and keep the Roo light and you should be ok with a good well maintained grass field of at least 500-600 feet.

Landing is easy with any of the enignes with the proper procedure. Good luck!