"as the fuel burned off, she started nosing down and finally bored into the ground under power".
Looks like stall recovery leaves something to be desired. More decalage (i.e. angle of incidence) and a more forward CG might be worth a trial.
The point of thrust is at the nozzle. The CG does appear to be a trifle far back - the set up as you have it is like a chuck glider.
The following user(s) said Thank You: TerryInBavaria, Tendera