Abstract: F- X is an advanced supersonic fighter. For verifying the structure inte grity, a full scale structural fatigue testing in suspending state is condusted with 42 points automated loading rig to indicate the fatigue critical items of the structure and the service. In the testing, the flight by flight load spectrum including 22 load conditions and the integral tank pressure are adopted. To improve the testing accuracy and reliability, a set of advanced and automated loading fatigue test control system with the Direct .Digital Control (DDC) method is designed. The system is operated by a HIDIC-80 computer and the test is very successful.This paper will briefly itroduces the testing procedure, the supporting method of the aircraft, the safety-preserving system in the testing, the design chacte ristics of the DDC automated loading control system and provides the failure details of the structure and the failure analyses.

Key words: full-scale fatigue test, Direct Digital Control, automated loading, flight-by flight load spectrum, safety-preserving system