Fiber Optic Strain Sensing with Pass-through Fiber Optic Rotary Joint

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Integrated Network Systems-of-Systems OBJECTIVE: Develop a system to acquire Fiber Optic Strain Measurements on a rotating rotor system and route the measurements to the non-rotating frame via a pass-through Fiber Optic Rotary Joint (FORJ). DESCRIPTION: Develop a system to acquire high fidelity optical strain measurements for a full-sized helicopter main rotor blade and calculate blade tip displacements. The intent of using optical measurement systems is to reduce reliance on electrical strain gage based measurement solutions for health monitoring/research data, as well as reduce the maintenance requirements that are associated with electrical slip rings. The system will need to have these attributes: 1) display and record data from up to 8 simultaneous channels, 2) sample and acquire strain and displacement data at sampling rates greater than 500 Hz, 3) have Optic Strain sensors sized for full-scale rotors (range from 4 ft to 15 ft in radius), and 4) display rotor tip displacement at a 10 Hz update rate. PHASE I: Demonstrate a 4 channel pilot system at 100 Hz with the ability to obtain fiber optic strain measurements in a rotating high vibratory environment. PHASE II: Develop and demonstrate a prototype system that meets the specifications given in the description with a small ruggedized footprint. PHASE III DUAL USE APPLICATIONS: Phase III may involve production contracts with US Army to support the Future Long-Range Assault Aircraft (FLRAA) or Future Attack Reconnaissance Aircraft (FARA) program. A system like this could be used as a safety of flight recorder on coaxial rotor systems [1] to prevent blade tip collisions at high forward flight speeds. REFERENCES: 1. 1. S.B. Kim, D. Geiger, P.O. Bowles, C.G. Matalanis, B.E. Wake; Tip displacement estimation using fiber optic sensors for X2 technology TM rotor blades AHS International 72nd Annual Forum, 16-19 May, West Palm Beach, Florida, USA 3 (2016), pp. 1914-1923 KEYWORDS: Fiber Optic Strain Measurement; FLRAA; FARA; X2-IBC