Thanks - I was wondering about whether I should have tried the pavement, but the thought of the harder surface scared me - I wasn't sure if it was going to slide, so I decided flipping it in the grass was the better choice. I figured that I could slow the plane down so much that I might avoid a flip. It was close, but happily worked out in the end. Funny thing is I am pretty sure I loctited the retaining collar. I will definitely file a flat spot as suggested.