A FULL SCALE AIRFRAME HIGH CYCLE FATIGUE TEST METHODOLOGY AND ITS APPLICATION TO THE SH-2G HELICOPTER

A full scale high cycle fatigue test of the SH-2G helicopter has been performed as part of an overall Structural Life Assessment Program. The test subjected a fully representative SH-2G airframe to constant frequency vibratory loads which best reproduce the critical strains experienced in flight at the main rotor primary forcing frequency, four per rev. The vibratory loads were applied for a period of 10 million cycles along with steady loads of lift, main rotor torque and pitching moment, with the test vehicle suspended in such a way as to simulate a free-flight condition. The object of the test was to apply the proper magnitude and phasing of vibratory loads to the airframe so as to subject the airframe to a representative, but highly accelerated, fatigue loading. The key idea is to properly apply a single typical realistic high cycle load condition with regard to frequency, phasing, and dynamic load paths so that as many simultaneous fatigue evaluations as possible occur. This, along with a separate low cycle fatigue test, will provide a means of assessing the long term structural integrity of the SH-2G airframe. This paper will address the high cycle fatigue test from concept to realization. From a flight data base, this includes the methodology of selecting representative loading conditions, transforming these conditions into applicable test loads with conformable timing phases using a Generalized Force Determination technique, test set-up, and test results.