Pilot And Flight Instructor Were Conducting An Instructional Flight During Which The Pilot Performed Upset Recoveries And Basic Aerobatic Maneuvers Analysis: The pilot and flight instructor were conducting an instructional flight during which the pilot performed upset recoveries and basic aerobatic maneuvers. During the flight and subsequent taxi, the pilot reported intermittent rudder resistance that he described as a “catch” and an audible “pop.” A post-flight inspection revealed that the lower rudder hinge had separated from the rudder post. Postaccident examination revealed that the rudder post had fractured along the weld toes that attached the middle knuckle of the lower rudder hinge to the post. Although the service manual required inspection of the rudder for damage and cracks, it is likely that the fatigue cracking was obscured by the fabric covering and was not readily apparent during routine visual inspection.