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Optical Sensor System for Realtime Proprotor Flapping Angle Monitoring

Periodic Reporting for period 2 - FLAPSENSE (Optical Sensor System for Realtime Proprotor Flapping Angle Monitoring)

Reporting period: 2019-09-01 to 2021-02-28

The main objective of the project FLAPSENSE is to design and manufacture a contactless measurement system for real time monitoring of proprotor flapping angle. The system will be integrated in the proprotor assembly and co-rotates with the rotor. It will be based on an highly accurate optical sensing method providing the actual flap motion of the rotor blade to the avionic system. The FLAPSENSE system in the project will finally be flight tested in the frame of the NextGenCTR Demonstrator.
The FLAPSENSE project will enable real time monitoring of the movements and deformations of a proprotor hub during real operation. It will enable a direct observation of the rotor and deliver new insights in “what’s going on in the rotating frame”, especially if the rotation axis is tilted and thus will contribute to the flight safety of rotorcrafts. One of the main impacts of the FLAPSENSE concept is to contribute to delivering superior vehicle productivity and performance. FLAPSENSE will realise measurements in a non-intrusive way reducing components interconnecting the hub and the proprotor, reducing wear and as such reducing weight, operational costs and maintenance.
Besides the direct contribution to the measurement objective, the FLAPSENSE project will be a pioneering activity for the application of other optical measurement techniques (e.g. overall blade deformation, local surface pressure, transition or flowfield around the blade). On the one hand it will solve difficulties in the installation of optical measurement systems in the rotating frame, on the other hand the real-time image processing software to be developed can also be used for other camera installations (e.g. landing gear measurements, wing deformation measurements, control surface monitoring, active control).
In work package 1, which is the overall management work package of the project, all relevant contractual issues (i.e. the consortium agreement and the implementation agreement) have been adressed in the first months. Furthermore, the FLAPsense teamsite, a password secured SharePoint website for data and information exchange, as well as project planning tool, has been implemented. Additionally biweekly technical update online meetings have been established as main communication forum.

In work package 2, requirements applicable to the flight critical NGCTR Contactless Flapping Sensor have been identified jointly by the FLAPsense partners and the topic manager. These requirements are the baseline for the sensor system design and will later lead to the definition of the means to show compliance with the certification rules for flight critical hardware like the FLAPsense sensor system will be. After completion of the initial technical requirement specification and the exchange of important geometry data the system concept study has been performed. Five different methods based on optical methods, accelerometers and simple angular sensors have been evaluated against the technical requirements and during a sensor concept review (SCR) two of them have been chosen to be further developed - concept 1 a camera approach and concept 2 a laser triangulation method. First studies related to the image processing performance and the feasibility analysis of the laser triangulation method have been conducted and a master test plan for the next period as well as an initial list of means of compliance have been created.
After the successful completion of the FLAPsense project, a novel airborne contactless measurement system will be available that enables real time tilt measurements in a rotating environment. Besides the integration of the FLAPsense sensor in a rotor hub, other application examples of the sensor system and the associated developments (real time deformation measurements, rotating image acquisition) might be the investigation of airframe structures and control surfaces during flight, the monitoring of wind turbines or even the measurements of the behaviour of wheels and tires during road testing.
Five possible sensor concepts (from the left to the right: stereoscopic approach, distance sensors,
Example results of the trade studies (left – image processing test, right – laser triangulation)