The pilot reported that the airplane porpoised three times on the second landing, and bounced once on the third and final landing. He reported that while taxing to the fuel pump, he noticed that he had a "flat tire" on the nose wheel.
During a postaccident examination of the engine and airframe, substantial damage to the firewall was discovered.
The pilot reported there were no pre-impact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation.