C172 PLT TAKES OFF OVER A GROUP OF 5 PERSONS WITH PWRED PARACHUTES.

Narrative

I WAS PREPARING TO DEPART A FLY-IN AT LOG CABIN ARPT; AN UNPAVED PVT STRIP; IN A C172; WITH 2 ADULT PAX ON BOARD; AND OTHER ACFT LINING UP BEHIND ME. THE UNOFFICIAL 'CTLR' ASKED ME TO TAKE A POS AND HOLD ON THE RWY WHILE A GROUP OF 5 PWRED PARACHUTES TAXIED TO THE FAR END OF THE RWY WHERE THEY PLANNED TO DEPLOY THEIR CHUTES AND TAKE OFF. WHEN THEY ARRIVED AT THE FAR END; THE 'CTLR' ASKED IF I HAD SUFFICIENT RWY TO TAKE OFF OVER THEM. I INDICATED THAT I DID. THE 'CTLR' THEN ASKED ONE OF THE PWRED PARACHUTE PLTS IF IT WAS OK FOR ME TO TAKE OFF OVER THEM; AND HE REPLIED IN THE AFFIRMATIVE. SO I TOOK OFF USING MY BEST SOFT AND SHORT FIELD OBSTACLE CLRNC PROCS; AND CLRED THE PWRED PARACHUTES; BUT ONLY BY ABOUT 50 FT. TREES ON EITHER SIDE OF THE RWY PREVENTED ME FROM TURNING TO EITHER SIDE. THIS WAS MUCH TOO NARROW A MARGIN. IN RETROSPECT; I UNDERESTIMATED MY LOAD AND THE EFFECT OF THE ROUGH AND HILLY TURF; AND ALLOWED MYSELF TO GET RUSHED INTO A SIT WITH NO EMER ESCAPE RTE. I SHOULD HAVE EXERCISED SOME PATIENCE AND WAITED FOR A CLR RWY.