Blade root integrated optical fiber bragg grating sensors - a highly redundant data source for future HUMS

Fiber Bragg Gratings (FBG) show an excellent potential for accurate strain measurement in aerospace and other applications. This paper will describe an approach to derive remaining useful lifetime values for dynamically loaded components by using FBG strain sensor data from helicopter blades. A complete chain of transformations is presented together with a substantiation approach for certification. The transformation chain is based on properties of piecewise linear mechanical systems for which observability conditions are fulfilled. For this class of problems, FBG measurement values can be used to calculate rotor hub loads and how they are transferred to dynamic components. Before the results are used to calculate the so-called remaining useful life, failure analyses are necessary in order to evaluate the required level of redundancy on sensor level. An experimental set up is presented based on a bearingless main rotor blade root with embedded FBGs. First lab tests raise confidence in the acquired signal accuracy and availability which demonstrates enough potential to let lifetime calculations derive from them. In order to finally comply with regulatory constraints, the complete setup needs to have an architecture with satisfactory data integrity.