I was noticing that the little sample bleep of power was unusually week or almost absent (Ice light 50 , Hubin FM9,)  Otherwise all seemed OK . A couple of flights later I had an unscheduled flame out during the inverted flight .Lost a rudder, and created a job for myself painting etc.I guess the week bleep should have been a warning.I'm pretty sure that I was getting signals from the ESC that all was not well in electric land.I replaced both units , and all is well again , except for a messy looking Sultan.  Keith

FIrst thing I checked was the battery. Keith