THE PLT TOOKOFF WITH AN ESTIMATED 7 GAL OF FUEL ON BOARD. WHILE PERFORMING AEROBATIC MANEUVER, HE ENTERED A VERTICAL, CLIMBING, POWER-ON MANEUVER. WITNESSES REPORTED THAT THE ACFT CLIMBED TO ZERO AIRSPEED AT ABOUT 2500 FT AGL. REPORTEDLY, THE ACFT THEN SLID BACKWARD AND ENTERED AN INVERTED FLAT SPIN. POWER REMAINED ON FOR ABOUT HALF OF THE DESCENT. WHEN THE POWER WAS REDUCED, THE ACFT ENTERED AN UPRIGHT SPIN AND CONTINUED TO DESCEND IN THIS MODE UNTIL GROUND IMPACT. INTERVIEWS WITH OTHER PLTS, FAMILIAR WITH THE FLT CHARACTERISTICS OF THE PITTS, REVEALED THAT AT A LOW STATE OF FUEL, THE CENTER-OF-GRAVITY IS IN THE AFT RANGE. THEY REPORTED A POWER REDUCTION IS NECESSARY TO RECOVER FROM AN INVERTED SPIN. THEY ALSO STATED THAT INTENTIONAL SPINS WERE NOT A NORMAL PART OF THIS PLT'S AEROBATIC ROUTINE. NO MALFUNCTION OF THE ACFT OR PLT IMPAIRMENT WAS FOUND DURING THE INVESTIGATION.