CONTEMPORARY TECHNIQUES FOR CONDUCT OF HELICOPTER AIRFRAME FATIGUE TESTS

Sikorsky Aircraft, under contract to the U.S. Navy, conducted a fatigue test on the SH-60B “SEAHAWK“ airframe. The test was performed to determine areas of the airframe susceptible to fatigue, evaluate modifications to improve fatigue properties, and establish inspection requirements to maintain structural integrity. The test article was a complete airframe representative of the latest production configuration and was subjected to a programmed spectrum of simulated steady-state and transient conditions representative of the SH-60B design mission. A programmable controller exercised authority over five synchronized shaker systems and seven quasi-static servo systems. Landing gear loads were applied within the spectrum and were reacted at the main rotor head. The suspension system was designed to isolate the test frame from N/rev loads and react the applied landing and inflight transient loads. A mini computer-based measurement system was used to monitor test conditions and produce hard copy output of parameter statistics in engineering units. The data acquisition computer and programmable controller were linked to allow full automation. Analysis of failure modes exposed during this test led to several preproduction design modifications which will increase the structural integrity and maintainability of the aircraft. The increased reliability, flexibility and automation resulting from the use of computers for load control and measurements proved to be a significant improvement over previous techniques. Their present and future potential for increasing the productivity of full scale airframe testing has been established by this test.