PVT PLT OF A SMA SEL EXPERIMENTAL ACFT MADE AN UNPLANNED FORCED LNDG IN A CORNFIELD AFTER HE COULD NOT LOCATE THE PVT ARPT TO WHICH HE WAS FLYING.

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I WAS FLYING AN AIRPLANE USING GPS FROM 7A1; DONALDSON; GA; TO RITTER AIRPARK (PVT) APPROX 5 MI SW OF ASHEVILLE; NC. I FLEW TO A WAYPOINT KEYED INTO THE GPS. THE WAYPOINT COORDINATES KEYED IN WERE 35 DEGS 18.6 MINS N BY 82 DEGS 37.7 MINS W. THEN I TURNED AND FOLLOWED THE GPS TRACK GOING FROM THE WAYPOINT DIRECTLY TO ASHEVILLE ARPT; A LINE BTWN THESE 2 POINTS CROSSES DIRECTLY OVER TOP OF RITTER ARPT (MY INTENDED DEST) 4.6 STATUTE MI OUT FROM ASHEVILLE; RIGHT ON THE EDGE OF THE CLASS C AIRSPACE. WHEN I GOT TO WHAT SHOULD HAVE BEEN 'RITTER' PER DISTANCE FROM ASHEVILLE AND LINE BTWN THE 2 POINTS; I COULD NOT FIND RITTER AIRPARK. CIRCLING AROUND AND SEARCHING ACCOMPLISHED NOTHING FOR ME. I WAS AT THE SUPPOSED LOCATION EXACTLY ON TIME PER FLT PLAN. I CIRCLED FOR 15 MINS. NOT FINDING THE AIRPARK AND RUNNING CLOSE TO FLT SVC 'BEGIN SEARCH' TIME AND WITH ONLY 45 MINS OF FUEL LEFT; I MADE A PRECAUTIONARY LNDG IN A CORNFIELD TO CALL FLT SVC AND GET DIRECTIONS TO 'RITTER.' RITTER TURNED OUT TO BE APPROX 1 1/2 MI NE FROM WHERE I HAD BEEN CIRCLING. WHY? I USED A CURRENT ATLANTA SECTIONAL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE LEARNED THAT HE COULD NOT RELY ON USING COORDINATES FOR GPS NAV FROM MEASURING THE SECTIONAL CHART SINCE THE CHART WAS NOT DESIGNED FOR THAT TYPE OF ACCURACY. HOWEVER; IF THE RPTR HAD USED THE PUBLISHED COORDINATES OF THE NEARBY ARPT AND TAKEN A DISTANT FROM THAT IT MAY HAVE BEEN MORE ACCURATE. THE RPTR ALSO STATED THAT THE PVT ARPT WAS USUALLY HARD TO SEE SINCE IT WAS A GRASS STRIP. HE SAID THAT HE WAS REEXAMINED BY THE FAA; GIVEN A LETTER OF RECORD OF THIS INCIDENT FOR HIS AIRMAN CERTIFICATE FILE SINCE HE DID DO DAMAGE TO THE ACFT DURING TKOF FROM THE CORNFIELD. THE EXPERIMENTAL ACFT FLOWN WAS A BREEZE THAT RESEMBLES THE WRIGHT BROTHERS' ACFT.