On June 12, 1999, about 1230 eastern daylight time, a homebuilt RV-6, N173AB, was substantially damaged while landing at a private unlisted grass strip in Bradford, Pennsylvania. The non-certificated pilot was not injured. Visual meteorological conditions prevailed and no flight plan had been filed for the local flight that departed the Bradford Regional Airport (BFD). The personal flight was conducted under 14 CFR Part 91. The unlisted grass strip was located about 7 miles south of BFD, and the airplane was landing to the east. When interviewed by a Federal Aviation Administration Inspector, the pilot stated that just prior to landing, a "gust of wind" forced the airplane's nose gear down into the turf runway. The nose gear dug into the ground and the airplane flipped over onto it's back. The pilot said he did not experience any mechanical malfunctions with the airplane. The pilot did not posses a pilot certificate. He reported 75 hours of total flight experience, with 7 hours in the make and model of the accident airplane. Additionally, the pilot's last medical certificate was issued in 1977. Review of the airplane's maintenance records revealed that the airplane did not have a current condition inspection. Winds reported at BFD, at 1253, were from 130 degrees at 7 knots.