It spun out of control, performing five or six tight loops before falling to the ground. The glider, meanwhile, wasn't at sufficient altitude to level out and glide, so it nose over and rammed into the ground. Luckily, it wasn't damaged. Neither was the power pod. For a while I tried to determine the cause of the accident.
Experiments are never failures.
I don't know why it happened. Maybe it was just bad luck. I'd like to fly Sunbird II again someday soon.