Automatic Fatigue Test Control System (AFTCS)

Bell Helicopter's next-generation Automatic Fatigue Test Control System (AFTCS) is presented. Fatigue testing places a helicopter part or specimen under repeated, controlled cyclic loading to determine if and when it will fail. A National Instruments PXIe embedded processor and LabVIEW software are used to control up to 48 linear/rotary hydraulic actuators in real-time. The actuators apply structural loads that are sensed by up to 256 strain gauges on the helicopter specimen. The structure and instrumentation respond to prescribed cyclic loads that range in frequency from 0.5 to 30 Hz, with a minimum resolution of 0.1 Hz. The fatigue test controller design is based on the well-known Linear-Quadratic-Gaussian control (LQG) methodology. Its feedback and filter gains are computed using a state-space model of the specimen identified separately. The controller computes any necessary changes in the actuator motions (at every time sample), maintaining acceptable margin between the measured and desired strain gauge responses. The system is demonstrated on a Bell Helicopter 429 tail rotor blade.