DURING AN AEROBATIC FLT, THE PLT-IN-COMMAND WAS ASKED TO DEMONSTRATE RECOVERY FROM AN INVERTED FLAT SPIN. THE MANEUVER WAS INITIATED AT APRX 5000 FT. AFTER THE ACFT MADE APRX 3/4 OF AN INVERTED TURN, IT ROLLED UPRIGHT AS THE PIC STARTED TO 'FEED IN THROTTLE.' HE RETARDED THE THOTTLE, HELD FORWARD STICK & RIGHT RUDDER & THE ACFT ROLLED INVERTED AGAIN. AGAIN, POWER WAS APPLIED & THE PLANE ROLLED UPRIGHT AGAIN & 'WOUND UP TIGHT.' REPORTEDLY, THE PIC RETARDED THE POWER & APPLIED OPPOSITE RUDDER, BUT WAS UNABLE TO STOP THE SPIN, WHICH WAS TO THE LEFT & BETWEEN A NORMAL & FLAT SPIN ATTITUDE.AT APRX 2000 FT, THE PIC ORDERED A BAILOUT, BUT THE 2ND PLT REMAINED IN THE ACFT. FINALLY, THE PIC BAILED OUT AT APRX 500 FT & WAS SERIOUSLY INJURED. THE ACFT STOPPED ROTATING JUST PRIOR TO IMPACTING THE GROUND IN A NOSE DOWN, WINGS LEVELATTITUDE. TO RCVR FROM A FLAT, UPRIGHT, LEFT SPIN, THE PROCEDURING WAS: THROTTLE - IDLE, STICK - FULL LEFT TO FORCE THE INSIDE WING DOWN, HOLD UNTIL A NORMAL SPIN DEVELOPS, THEN RCVR FROM NORMAL SPIN; EXPECT 2500 FT ALT LOSS DURING RCVRY.