I put an os 91 on it and installed servos exactly per the instructions. The plane was very tail heavy - needed 12 ounces or so in the nose, but it still flies great even with the extra weight. It only needs about 1/2 throttle to take off, but there's not enough juice by the standards of most folks who like to overpower their planes. I still think you'd be way underpowered with an os 70.