On June 26, 1996, at about 1400 eastern daylight time (EDT), a Cessna 182P, N40007, touched down hard on runway 27, at Baltimore Airpark, in Baltimore, Maryland. The private pilot, the sole occupant, was not injured. The airplane sustained substantial damage. Visual meteorological conditions prevailed and a flight plan was not filed. The personal flight was conducted under 14 CFR Part 91. The flight originated at Martin State Airport in Baltimore, Maryland, at 1330 EDT. The pilot reported that he was taking the airplane to Baltimore Airpark for a scheduled maintenance appointment, to have the oil changed. He stated that his approach to runway 27 was "...to fast...evolved into porpoising which ultimately resulted in a hard landing." The pilot taxied from the runway to the maintenance facility. He stated that when the mechanic inspected the airplane to perform the oil change, he noticed that the firewall was buckled.