Flight Test Investigation of Add-On Treatments to Reduce Aircraft Airframe Noise

Abstract

A major task within the European Community funded Project SILENCE(R), was to flight-test high-lift devices low-noise modifications and landing gear noise reduction fairings. This work was part of the airframe noise reduction investigation that was initiated in 2001, with a design based on both computational and experimental work, aiming at modifications that fit the actual Airbus A340-300 test aircraft. Landing-gear fairings were designed and manufactured by both Airbus and Messier-Dowty. They are add-on elements that can be mounted on the existing gears without affecting the operation of the landing gear. The add-on treatment modifications (designed and manufactured by Airbus) on the high-lift devices consist of covering the numerous cavities in the slat-retraction system and flap-side edge space, that have been identified to be responsible for a significant part of the noise. The tests were conducted in September 2003 at Tarbes airport. To investigate the noise perceived on the ground, Airbus’ noise system of microphones was used. To help the result interpretation and detection of possible spurious effects, a large array of microphones was operated by ONERA and DLR. On board measurements (pressure and acceleration sensors, strain gages, etc.) were also implemented to assess local effect of devices. Back-to-back tests were achieved in 11 flights, by successively removing all modifications in small groups. Examples of the effect of SILENCE(R) devices is assessed for typical landing configuration and also for specific aerodynamic noise configurations, that were designed to separate the effects of landing gear and high-lift device noise reduction.