On June 16, 2001, about 1600 eastern daylight time, a Robinson R-22A, N2242P, was substantially damaged when it rolled over while hovering at a private helipad in Atwater, Ohio. The certificated airline transport pilot was seriously injured. Visual meteorological conditions prevailed and no flight plan was filed for the local personal flight that originated at the pilot/owner's helipad and conducted under 14 CFR Part 91. During a telephone interview, the pilot said the purpose of the flight was to experiment with ballast added to the helicopter. He said that in its normal configuration, the helicopter tended to ascend and descend from a hover in a left-skid low attitude. The pilot said that with the proper placement of ballast, the center-of-gravity could be adjusted to attain a more wings-level attitude during takeoffs and landings to and from a hover. According to the pilot, he placed the weight on the pad to the right of the helicopter prior to engine start. He said he intended to fly one trip around the traffic pattern, land the helicopter, set the throttle at idle, de-plane, install the ballast weight, then fly the helicopter around the pattern to note the difference in helicopter attitude in both hovering and forward flight. According to the pilot: "My helicopter always landed heels first. I read in the maintenance manual that you could put a 10-pound weight in the front of the helicopter to level the attitude. So I figured, I'm going to fly this thing around and back down to the ramp, leave it at idle, and put the weight in. "I took the damn weight and set it on the ramp next to my helicopter. I started the helicopter, picked it up to a hover, drifted to the right, hit the weight, and rolled over. It was instant, it happened in a millisecond." When asked if he was familiar with the phenomenon of dynamic rollover, the pilot said: "I sure am. What I should have done was lower the collective, but I think I tried to maneuver out of it." The pilot held an airline transport pilot certificate with a rating for airplane multi-engine land. He held a commercial pilot certificate with ratings for airplane single-engine land, single-engine sea, instrument airplane, glider, and rotorcraft-helicopter. The pilot's most recent first class medical certificate was issued May 2, 2000. He reported 18,935 hours of flight experience, 236 hours of which were in helicopters. The pilot said there were no mechanical deficiencies with the helicopter. The weather at the Akron-Canton Regional Airport, about 15 miles southwest of the accident site included a few clouds at 5,000 feet with variable winds at 6 knots.