Compared to a propeller of an airplane or the rotor of a helicopter, the proprotor of a tiltrotor aircraft is a very complex system working under very different operational conditions varying from high speed cruise flight conditions in airplane mode to hovering and low speed manoeuvres in helicopter mode. Additionally, the transition between both, the airplane and the helicopter mode, causes a lot of challenging load conditions on this system. Thus, the real-time monitoring of the reactions of the proprotor system to these varying operating conditions is of great importance. Especially the monitoring of the flapping movement of the rotor allows enhancing the performance of the tiltrotor aircraft and increases the operational safety. For that reason, the development, design and manufacturing of a contactless measurement system for real time monitoring of the proprotor flapping angle is being performed within FLAPsense.
Measurement setup
Sketch of the measurement setup used in the FLAPsense senor system and example of markers arranged within the Target Areas (small image)
The FLAPsense sensor system has to be integrated into the proprotor assembly and will be co-rotating with the rotor. It will be based on a highly accurate optical sensing method providing the actual flapping motion of the rotor hub to the avionic system. Additionally, the system would be able to measure the rotor lag and the axial displacement of the rotor hub in operation. 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 flow field 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).
The DLR Institute of Aerodynamics and Flow Technology is coordinating the project, developing the hardware and software for the sensor system and creating a prototype.
Sensor unit
FLAPsense sensor unit enclosure design (a – composite enclosure (in broken view); b – viewing window (in broken view); c – optical lens (second one is not depicted); d – camera sensor boards; e – microprocessor boards and master controller)
