Today I was buddy boxing with my instructor for the second time and lost my plane. It was a very calm day. My instructor took off and checked the trims again and said he thought there was some sort of radio interference. The plane would loop very tight as if someone had applied full elevator. This didn't happen in the next 2 or so minutes of flying and he gave it to me. I made one gentle turn and was headed back in the opposite direction when it did it again. He immediately took it but had no control over it. I watched it spiral to the ground from way up. He said he had no control at all. The battery showed almost a full charge (tx and rx) and all the servos are working. After we brought the plane back, we watched the servos for interference but didn't see anything. The rubber grommets were in place, the receiver was wrapped in foam as was the receiver battery. There was no fuel near the receiver.
I think my engine is ruined. It is hard to turn and took a hard lick on the spinner nut. The needle valve broke off too.
Any ideas? This plane flew fine 4 days earlier on a much more windy day.