The private pilot arrived at a turf strip to attend a fly-in event on the day of the accident. During departure, the pilot stated he applied full aft yoke during the takeoff roll and lifted off with a nose high attitude. Soon after takeoff, the airplane banked left and descended into a cornfield, which damaged the firewall. The pilot attributed his nose high attitude immediately after takeoff to an improper nose up trim setting, as he had not set the airplane's elevator trim to the takeoff position in accordance with the before takeoff checklist. The pilot reported no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.