DLR's Contribution to European Aviation Noise. Research on Fixed and Rotary Wing Aircraft.

Plans to design future very large commercial aeroplanes have triggered highly sophisticated research in several areas of acoustics, one of which pertains to the aerodynamically induced noise of the approaching aeroplane with landing gears and high lift devices deployed. This type of noise, termed "airframe noise" has evolved into a major source of concern in attempting to meet new stringent ICAO noise limits after the great successes of engine noise reduction. DLR was involved in a number of pertinent substantial research projects to specifically study such sources and find ways for their control. Here excellent large acoustic wind tunnels (the German Dutch Wind Tunnel, DNW, being a prime example) had been indispensable to investigate the relevant aeroacoustics and to develop technically feasible noise reduction measures to reduce landing gear noise and the noise from high-lift devices on wings. In coping with the noise of modern high-speed helicopters, dedicated as well as cooperative DLR research on rotor systems has helped to clarify the complex physical mechanisms responsible for the generation of the highly intrusive impulsive noise ("blade slap"). Means to control the sources of the underlying mechanisms of "high speed impulsive noise" and of "blade vortex interaction noise" have been studied in aeroacoustic wind tunnels and in part successfully transferred to real flight-operational helicopters. Noise from propeller-driven General Aviation aeroplanes has been thoroughly studied in (full-scale) acoustic wind tunnel experiments and new - hitherto unknown - generating mechanisms related to the non-uniform shaft rotation of piston engines which drive the propeller - been identified, amenable to technical control solutions. This keynote survey paper will discuss and exemplify through selected projects and their results DLR's involvement in these various scientific research areas