THE OWNER RPRTD THE PLT FLEW THE ACFT AT A COMPANY PICNIC WITHOUT AUTHORIZATION. COMPANY PSNL SAW THE EXPERIMENTAL, AMATEUR BUILT ACFT TAKEOFF FROM THE COMPANY STRIP, THEN MANEUVER FOR A LOW PASS OVER THE AREA AT ABOUT 150 TO 200 FT AGL. SOME ESTIMATED THE PASS WAS MADE WITH A SPEED IN EXCESS OF 100 MPH. THE NEVER EXCEED (VNE) SPEED FOR THE ACFT WAS 95 MPH. AS THE ACFT APCHD THE AREA OF THE PICNIC, WITNESSES HEARD A BUZZING OR FLUTTERING SOUND. AS IT CONTINUED OVERHEAD, WITNESSES NOTED THE LEFT AILERON HAD BECOME DETACHED FROM THE OUTBOARD END & HAD FOLDED AFT. SUBSEQUENTLY, THE RGT AILERON FAILED IN A SIMILAR MANNER. THE ACFT ENTERED A CLIMB & SOME WITNESSES NOTED A POWER REDUCTION AS IF THE PLT WAS TRYING TO SLOW THE ACFT. HOWEVER, THE ACFT ROLLED & ENTERED A DSCNT WHICH WAS DESCRIBED AS A STALL/SPIN CONDITION. RPRTDLY, THE PLT WAS AWARE OF THE ACFT'S TENDENCY TO ENCTR AILERON BUZZ OR FLUTTER WHEN ACCELERATED ABOVE 100 MPH.