Well, I do recall practicing a T/R model, and deciding to practice a real fast race stop. It went great, and I let go the model in real quick time. Then I looked up and saw my pilot standing a few feet from me, just inside the circle. He had walked out for a conference. The model survived o.k., and it was a great learning experience. I now never let go the model without looking at the pilot first, it doesn't take any time.