RE: Skymaster Viper ..... unexplained crash??
For me it looks like one of the flap servos got striped doing the loop causing the plane getting into an spiral.
Something similar happened to me once with my CARF Lightning, I put the flaps and then the plane started to make a roll,
I remove the flaps and I could retrieve, when I landed one of the control horns was loose from the surface, but this was a matter of seconds.
This was my case.