2 AEROBATIC ACFT SUFFER A GND COLLISION AS TAXIING TFC.

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2 AEROBATIC BIPLANES COLLIDED ON THE GND WHILE PARTICIPATING IN THE UNITED STATES AEROBATIC CHAMPIONSHIPS. PRIOR TO TAXIING TO THE FAR SIDE OF THE TXWY; I CHKED FOR INCOMING TFC ON THE TXWY. I TURNED 90 DEGS R AND TAXIED STRAIGHT DOWN THE W EDGE OF THE TXWY/RAMP. I SAW A PLANE (BIPLANE) HOLDING AT THE RELEASE POINT. I STARTED AN S-TURN TO THE R. I HAD MADE 2 TURNS; LOOKING BOTH SIDES OF ACFT AND SAW NOTHING. I HAD JUST STARTED MY THIRD TURN WHEN I SAW THE SMA Y ON THE E SIDE OF TXWY GOING STRAIGHT S. THE PLT WAS LOOKING SLIGHTLY TO HIS L; AWAY FROM ME. I SAW THE R WING COMING AT ME; SLIGHTLY TO MY R. I DUCKED DOWN IN MY COCKPIT AS FAR AS THE SHOULDER HARNESS WOULD ALLOW. FOLLOWING IMPACT; MY AIRPLANE WAS FACING NE. THE SMA Y WAS FACING SE APPROX 30 FT S OF ME. THERE WAS A TEMPORARY TWR IN OP. AEROBATIC PLTS WERE INSTRUCTED IN THE BRIEFING TO MONITOR TWR (126.6) WHEN OUTGOING; AFTER DEP TO GO TO 131.92 FOR CLRNC TO THE AEROBATIC BOX BY THE CHIEF JUDGE. I WAS NOT AWARE UNTIL THE NEXT DAY THAT THE TWR WAS NOT PROVIDING GND FOR THE AEROBATIC PLTS. NO OTHER PLT I TALKED WITH KNEW THIS. OBSERVATIONS/RECOMMENDATIONS: FORWARD VISIBILITY IN SMA X-Y TYPE ACFT IS RESTR; HENCE; S-TURNS ARE ESSENTIAL WHEN TAXIING. HOWEVER; IT IS POSSIBLE TO GET INTO SYNC WITH ANOTHER S-TURNING SMA X-Y AND NEVER SEE EACH OTHER. IT IS RECOMMENDED THAT S-TURNS NOT BE MADE IN A REGULAR PATTERN SO AS TO PREVENT THIS. INCOMING AND OUTGOING ACFT SHOULD NOT BE ON THE SAME TXWY; PARTICULARLY AEROBATIC ACFT. THE ROLE OF THE TWR SHOULD BE CLARIFIED AS TO GND CTL; CTL OF WHICH ACFT; AND CORRECT FREQS. THE PLTS SHOULD BE MADE AWARE OF THE SIT. A HELMET IS A MUST. MY HELMET WAS 'MARKED' HEAVILY INDICATING MY HEAD 'BANGED' AROUND INSIDE THE COCKPIT. SUPPLEMENTAL INFORMATION FROM ACN 252380: THE SIT WAS SET UP BECAUSE BOTH INBOUND AND OUTBOUND TFC USED THE SAME TXWY; WHICH I POINTED OUT TO THE CONTEST OFFICIALS AFTER THE COLLISION; AND WHICH WAS SUBSEQUENTLY CHANGED TO MORE OF A RACE TRACK TYPE PATTERN WHICH SHOULD HOPEFULLY PRECLUDE A RECURRENCE OF THIS EVENT.