THE PLT & 3 PSGRS WERE BEGINNING A X-COUNTRY FLT. THE PLT SAID HE MADE A 'QUICK OUTSIDE CHECK' OF THE AIRPLANE THAT DID NOT INCLUDE A FUEL SUMP DRAIN. HE TAXIED ONTO RWY 1, WHICH SLOPED UPWARD TO THE NORTH. HE ESTIMATED THE WINDS WERE CALM. THE PLT SAID HE STARTED HIS TAKEOFF RUN 300 FT DOWN THE RUNWAY, MADE A 'RUNNING' MAGNETO CHECK, BUT HE DID NOT MAKE A CARBURETOR HEAT CHECK. HE SAID THE PLANE ONLY CLIMBED ABOUT 30 FT AGL. HE NOTICED IT WAS NOT CLIMBING AS FAST AS THE TERRAIN ROSE, SO HE DECIDED TO LAND IN A FIELD TO AVOID POWER LINES IN THE FLT PATH. SUBSEQUENTLY, THE LEFT WING HIT THE GND & THE LANDING GEAR WAS TORN OFF. THE DOOR JAMMED, BUT A PASSERBY HELPED THE OCCUPANTS FROM THE CABIN. AN INVESTIGATION FAILED TO REVEAL ANY PRE-ACDNT PART FAILURE OR MALFUNCTION. DENSITY ALT WAS ABOUT 8700 FT. ABOUT 37 MI WEST, THE WIND FROM 200 DEG AT 5 KTS.