Flight validation of a structural health monitoring system for CH-53 Helicopter main rotor gearbox support

摘要

A critical crack was identified in the main gearbox support beam of the largest Israeli Air Forcern(Sikorsky CH53) Helicopter. The crack has developed on the main supporting beam monthsrnafter it had been repaired. Interestingly, this crack was anomalous in its position and directionrnand could not have been predicted by conventional Finite Elements (FE) based fatigue analysis.rnAs a necessary step to better understand the actual loading conditions acting on this complexrnstructure and the implications on the growth mechanism of the crack, an in-flight fiber opticrnbased Structural Health Monitoring (SHM) concept was developed. Multiple Fiber BraggrnGrating (FBG) sensors, embedded in composite “Smart Patches”, were installed to fullyrnmonitor the structural behavior of the cracked beam during dedicated flight tests. These flightrntests varied in their takeoff weights and involved carefully selected maneuvers, designed tornhave the highest load impacts on the beam. This paper reports the flight data evaluation as partrnof this SHM concept and introduces the new insights obtained throughout the entire process:rnfrom the design stage to the implementation. By analyzing the flight measurements obtainedrnfrom all smart patches, the factor which most affected the crack growth could be directlyrninferred. It is expected that this successful experience will potentially lead to broader usage ofrnin-flight SHM systems, which will serve as a preventive, as well as investigative, tool.