Yeah this happened to me today as well. I was breaking in my new .91 Saito and it was on it's second tank of fuel. It had about 20 minutes of run time on it. Near the end of the second tank I deided to open her up to see what kind of thrust it would pull. It was impressive for about 15 seconds, then "POP" it just quit. The spinner had come loose. The prop didn't throw, but both the nuts had come loose, and the blade would spin freely..