My Tower Trainer .40 Mk II ARF was initially set up completely stock with the standard engine mount and standard thrust angles built in. I had a .46 FX on the nose, which was a ton of power for this lightweight airframe. When I went to maiden the trainer, it just about launched itself straight off the ground and shot up like a rocket.

I had to add plastic washers behind the engine mount on the top two bolts to put a significant amount of "downthrust" into the engine setup. After that, I was able to trim out the airframe and get it to fly in a very neutral and well-behaved manner despite it's flat-bottom wing.