Airbus Flight Tests Turbulence Prediction System on A340

Airbus is flight testing a LIDAR (light detection and ranging) technology to measure clear-air turbulence (CAT) ahead of an aircraft to warn pilots of its presence.

The Toulouse-based aircraft manufacturer, which discusses the program in its November 2006 Airbus Letter, which can be accessed on its Website, says the flight testing will continue until end of 2006.

The "Gust Sensor," as Airbus calls the system, uses ultraviolet (UV) LIDAR devices, installed in a forward-looking position to measure air speeds ahead of the aircraft in order to detect CAT.  The development program is being carried out jointly by Airbus and EADS' Corporate Research Centre (CRC) as part of the Aircraft Wing with Advanced Technology Operation (AWIATOR), in which Airbus is a major partner.

This system works by emitting bursts of single frequency UV light at a certain rate, 50 to 150 meters ahead of the aircraft, which allows the relative motion of the air with respect to the aircraft to be measured in the backscattered radiation due to the Doppler Effect.

The system is equipped with an interferometer that uses the principle that two waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out, assuming they both have the same amplitude. The interferometer and an image processing technique in the system make it possible to determine the relative speed of the air causing the turbulence, and doing this in different directions allows the system to measure the lateral, vertical and longitudinal air velocity values separately.  Then using data from the aircraft's FCPC (flight control primary computer), the aircraft's own movements can be taken into account so the turbulence values can be derived.

During the flight tests, the LIDAR system is housed in a dedicated fairing attached to the underside of the A340's forward fuselage that has been designed to have the least possible aerodynamic effect.  In future developments of the system, when its components are reduced in size, it likely will be installed in aircraft's radome.  This phase of flight testing started in November and is scheduled to continue until the end of the year. 12-20-2006.

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