Noise Assessment for a Laser Reflector Installation (JCAB Global Express)

Abstract

A flight measurement was conducted at Feb. 26th 2003 by Aerodata and DLR with a JCAB aircraft (Bombardier Global Express) to investigate whether additional external noise occurs due to the presence of a laser reflector. This laser reflector is mounted in the fuselage of this aircraft normally in retracted position inside the aircraft; during flight inspection operations it can be extended to provide a passive target for ground based laser sensing devices. The extended laser reflector is used during approach when the landing gear is extended as well. So the test flights were performed only in the approach mode alternately with retracted or with extended reflector at grass runway 26 of Braunschweig airport. The procedure occurred at the following conditions: flight velocity 140 kts, flight path descent with an angle of 3 degree. The experiment was conducted in two parts with an interruption for refueling, to stay in a range of aircraft weight between 80000 lbs to 74000 lbs. The first result is as follows. The sound exposure level (SEL) does not depend on aircraft weight in this range. The second result is a constant averaged SEL for retracted and extended laser reflector - for all valid approaches 86.8 dB SEL - at a statistical 90 per cent confidence limit not exceeding +/-0.20 dB. That means there is no acoustical change by extending the laser reflector.