Helicopters can take off and land vertically or hover in the air. This gives them a number of advantages over fixed-wing aircraft. The disadvantage is that they are relatively noisy. With that in mind, the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is working with German Armed Forces Operations Command (Einsatzführungskommando der Bundeswehr; EinsFüKdoBw) to investigate how noise propagates from helicopters and what changes might be possible. The results of this collaboration are intended to increase the safety of armed forces personnel during deployments.
Noise from helicopters in flight is often audible from a great distance. The sound propagation also depends on the speed, the rate of climb or descent, and the weight of the helicopter. "In addition, there is a significant directional characteristic. This means that a helicopter tends to be perceived as creating more noise in one direction compared to another," says Project Manager Jurrien Olsman of the DLR Institute of Aerodynamics and Flow Technology in Braunschweig. This directionality changes along with the flight conditions. In forward flight, for example, a helicopter tends to radiate more noise forwards. DLR researchers carried out flight tests and measurements in cooperation with Bundeswehr Technical Center for Aircraft and Aeronautical Equipment (Wehrtechnischen Dienststelle für Luftfahrzeuge und Luftfahrtgerät; WTD 61) and pilots from Helicopter Squadron 64 at Manching Airfield (Bavaria).
An H145M helicopter from the German special forces followed a number of different flight paths as part of the research while carrying various payloads. Based on the measurement data, the project participants are developing a new digital model for visualising sound radiation in further studies. Acoustic datasets for other Bundeswehr helicopters will also be created. These digital models can then be used, for example, to optimise flight profiles and estimate response times in processes such as operational planning.