When the aircraft has a circle flight or a touch down, the speed brake of aircraft is one of devices to decrease aircraft's speed using the aerodynamic drag as expanding the brake. The speed brake are usually installed in several military aircrafts, such as the F-15, F-16, KT-1, and T-50 aircrafts.
In the AFSD (Airframe full-scale development) stage of the T-50 aircraft, the speed brake was designed to withstand the external aerodynamic forces. The stress and strength analyses of the brake structures were not made by actually applying the aerodynamic forces in flight, but the expected forces were just applied to the structures. As the results, the cracks on the tip of the speed brake were detected due to lack of consideration of the actual boundary conditions in the operation stage of the T-50 aircraft. Therefore, the demand for the improvement of the design of the speed brake structures for the fatigue and crack was seriously increased.
In the present study, the characteristic diagram, which is one of the seven basic tools of quality management, was considered to select main causes of origination of the crack on the tip of the speed brake of the T-50 aircraft. The selected causes were analyzed and the effects for the causes on safety characteristics of the speed brake structures were investigated. To analyse the structural cause of the crack, the stress and strength analyses of the speed brake structures were performed using the MSC/NASTRAN program, and the maximum stresses were obtained. The results were verified by comparing with flight test data. Finally, the improved configuration for the crack of the speed brake structure of the T-50 aircraft were proposed.