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NEw Standby Lidar InstrumEnt

Final Report Summary - NESLIE (NEw Standby Lidar InstrumEnt)

The knowledge of the aircraft airspeed is necessary at every moment of the flight, including take-off and landing phases. Current airliners airspeed measurement architecture is based on several and redundant sensor systems (total pressure sensors, static pressure sensors and temperature sensors, air pressure ducts, ADM transducers, ADR reference unit computers). Such independent airspeed 'chains' are thus provided for both the captain, and first officer. For safety purposes, an additional 'standby' channel is mandatory, the crew getting thus the capability to switch and replace its own failing system by this standby one. However, for existing aircraft air data standby architecture, primary and standby channels are composed of similar equipments with similar failure modes. In order to improve this redundancy, the study and design of new airspeed systems, implementing new technologies, is now currently expected by research labs and manufacturers.

The aim of the NESLIE project was to contribute to the development of a multi-axis laser function, able to measure true air speed (TAS), angle of attack (AOA), and side slip angle (SSA), for air data stand-by channel. The use of LIDAR based standby architecture with drastically different failure modes, compared with existing systems, will increase aircraft's safety by reducing the probability of common mode failures.

The specifications of the efficient signal processing algorithms that may provide air-speed measurements and other useful flight parameters from a lidar signal were analytically presented. Studying the expected signal characteristics and using appropriate modelled data the proposed algorithms were extensively simulated and tested showing satisfactory results.

The specified signal processing algorithms have to be implemented in a well suited hardware. The huge computational throughput at a considerably high clock rate and the demanding, real-time fast signal processing application necessitates the usage of powerful FPGA (field-programmable gate array) boards. Special consideration is given to the data collection time and to the processing speed of the FPGA processor which constitutes the time it takes to perform the FFT spectrum analysis and all the needed additional functions. The inherent parallelism of the logic resources in the FPGA as well as the flexibility it presents allow for high performance processing.

The NESLIE project objectives have been met: the optical air data system (OADS) architecture has been specified and designed. The technological bricks have been developed and validated (integrated laser, integrated optics, optical head and windows, real time signal processing, air density acquisition theoretical study. Only the IR detector was not developed, but a back-up solution was defined and used, so XenICs failure had no consequence on the overall project achievements.

A lidar mock-up was integrated and flight tested. The flight tests results validate the OADS concept: the mock-up provided measurements in all atmospheric and altitude conditions. The analysis of the mock-up measurements show very interesting performances with respect to the specification objectives. The NESLIE project showed very promising results and represents a large progress with respect to the state of the art in OADS. In addition to those results, a large signal database is now available for the development of improved signal processing algorithms in the frame of the on-going DANIELA Seventh Framework Programme (FP7) project.

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