The Future Roles Of Flight Monitors In Structural Usage Verification

Structural substantiation of helicopter dynamic components for fatigue has traditionally combined three elements component strength, aircraft flight loads, and an assumed usage spectrum. While component strength and flight loads are measured, most substantiating usage spectra are based on general military or civil specifications, contractor experience, or user and pilot surveys. All of these methods are filled with assumptions, and cannot begin to address the mission profile variabilities. Since helicopter dynamic component replacement times can be very sensitive to the assumed usage spectrum, it is necessary to define a "realistic mission profile". Past efforts in this direction have included detailed load/criteria studies, mission simulation flight tests, and pilot/user questionnaires. The development of flight monitors will provide major opportunities to understand aircraft usage. This paper discusses past and current limited aircraft monitoring programs at Sikorsky. It then describes future monitors under development which will provide fleet-wide continuous usage monitoring, and regime recognition algorithms which will provide rate of occurrence data for all critical flight conditions. It is emphasized that monitor data must be used cautiously. The engineer must use quality data, based on statistically significant survey programs. But most important, the traditional conservatism of the substantiation process must not be stripped away haphazardly. The reliability of a substantiation depends upon a balance of realism in the usage spectrum and conservatism in the overall substantiation process.