On August 26, 1997, at 1400 Alaska daylight time, a tundra tire equipped Piper PA-18 airplane, N9771D, sustained substantial damage when it nosed over during touch and go landings at a gravel landing strip on the Knik River, five miles south of Palmer, Alaska. The airplane was equipped with 30 inch tundra tires. The solo airline transport certificated pilot sustained minor injuries. The flight was conducted under 14 CFR Part 91 as a personal flight. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed. The pilot told the NTSB investigator that he intended to warm the engine for an oil change. He departed the Sky Ranch private airstrip subdivision in Palmer at 1357 and flew to the gravel, off airport landing site, to perform touch and go landings. During the first landing, the airplane veered left, and the pilot applied full right rudder and brake. The tail subsequently came up, began to settle, then the airplane nosed over. The pilot reported that there were heavy scuff marks in the gravel where the left tire had touched down, indicating heavy braking. He described rotating the wheels on the inverted airplane by hand, and that the left tire rotated somewhat normally, but stopped more quickly than the right. The pilot indicated on his NTSB Pilot/Operator Report that there was no mechanical malfunction or failure.