On April 18, 1996, about 1500 mountain daylight time, N733FF, a Cessna 172, operated by Sky Harbor Air Service, Inc., Cheyenne, Wyoming, landed hard in Cheyenne and was substantially damaged. The commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan had been filed. The personal flight was conducted under 14 CFR 91. The pilot stated that he was practicing touch-and-goes at the Cheyenne Airport. During one the approaches, the airplane "had a steeper than normal approach which I corrected, but landed 'flat.' The nose contacted and I over-corrected, creating a porpoise." The pilot stated that he then executed a go-around, re-entered the traffic pattern, and landed uneventfully back at the airport. After he taxied in and shut down the airplane, he noticed damage to the propeller blades and alerted the operator. No preimpact mechanical malfunctions were reported by the pilot. Upon detailed inspection by an FAA aviation safety inspector from Denver, Colorado, a wrinkle in the firewall and a bend in the fuselage nose gear support structure was revealed.