THE PLT WAS PRACTICING AEROBATICS FOR AN UPCOMING AIRSHOW. HE LANDED AT ELOY ARPT AFTER HE HAD COMPLETED ONE ACROBATIC SEQUENCE. THE AIRSHOW'S NARRATOR, AN EMINENTLY QUALIFIED ACROBATIC PERFORMER, TOLD THE PILOT THAT HIS RECOVERY FROM THE FINAL INVERTED FLAT SPIN MANEUVER BEGAN AT TOO LOW AN ALTITUDE. THE PLT TOLD THE NARRATOR THAT HE INTENDED TO USE AN OIL FILLED SMOKE SOLUTION DURING THE RECOVERY FROM THE FLAT SPIN MANEUVER. THE NARRATOR CAUTIONED THE PLT AGAINST USING SMOKE DURING THE MANEUVER, BUT THE PLT STATED THAT IT ENHANCED THE MANEUVER FROM A SPACTATOR POINT OF VIEW. THE PLT DEPARTED ELOY AND BEGAN ANOTHER ACROBATIC SEQUENCE. THE PLT ENTERED THE FINAL MANEUVER, AN INVERTED FLAT SPIN WITH THE SMOKE ON. THIS TIME HOWEVER HE BEGAN THE RECOVERY AT 500 FT, ABT 300 FT LOWER THAN HIS PREVIOUS RECOVERY. THE AIRPLANE ROLLED OUT TO THE RT-SIDE-UP POSITION, BUT THE AIRSPEED WAS INSUFFICIENT TO ARREST THE RAPID VERTICAL SPEED DESCENT. THE WRECKAGE EXAM DSCLSD NO EVIDENCE OF ANY AIRPLANE/ENG. MALFUNCTION OR FAILURE.