Comparative Study of Different Techniques for Development of Optimal Load Spectrum

This paper aims at presenting a methodology to develop load spectrum for an aircraft using flight data. An aircraft undergoes various kinds of loads during its service life out of which the normal acceleration loads (g-loads) contribute the most in limiting the structural life. This time history of acceleration loads acting in the z-direction is termed as the Nz profile. Load spectrum development plays a vital part in accurate estimations of fatigue life for aircrafts. The Nz profile of the sorties of an aircraft were extracted from Flight Data and Cockpit Voice Recorder (FDCVR) data. Different filtering techniques were employed for the reduction of data including discrete filtering, peak-trough filtering, linear reduction filtering and modified-racetrack filtering in time and frequency domain. This was followed by the application of different cycle counting techniques including range-mean counting, range-pair counting and Rainflow counting to deduce the best technique. Finally, a load spectrum was made which can be used for fatigue life evaluation. The methodology may be used to process acceleration data for any aircraft.