The use of drones in a diverse range of applications such as agriculture, pest control, logistics for goods transport, or the monitoring of entire large-scale industrial plants is no longer a peripheral phenomenon. Predictions for the future foresee the widespread use of drones in both rural and urban areas. In addition to the technical challenges and the question regarding the safe and efficient integration of these new airspace participants into the airspace, the social acceptance of this innovative technology is crucial for its success.
The noise pollution or noise characteristics of drones and the associated perceived noise nuisance is an important factor for their acceptance. The Institute of Flight Guidance is therefore investigating, in various projects and undertakings, the actual noise development of a large number of different drones in various environments by flight-test trials, as well as in simulations by means of developed modelling methods.
Opportunities and risks of unmanned air transport
The DLR institutes for Flight Guidance and Transport Research, in collaboration with the Institute of Urban and Transport Planning at RWTH Aachen University, are analysing the future opportunities and risks of unmanned aviation for people and the environment. The focus of this project, commissioned by the German Federal Environment Agency, is on the relocation of specific supply chains and delivery operations from the ground to the air by means of parcel drones. Various baseline scenarios and distribution concepts are hereby being compared in order to evaluate their impact on social acceptance, health and the environment.
With the aid of the institute's own simulation tools, the relocation of traffic from the ground to the air is modelled in order to subsequently conduct a qualitative analysis of the expected effects. The focus of the investigation is hereby on factors such as noise immission, visual nuisance, energy consumption and resource input.
Extensive flight-test trials for noise measurement
In recent years, the Institute of Flight Guidance has been responsible for various flight-test trials at the DLR National Experimental Test Center for Unmanned Aircraft Systems in Cochstedt, Germany, with the aim of measuring and analysing the noise development of various drones. For this purpose, research initiatives were instigated in cooperation with the German Federal Environment Agency and regulatory authorities, in which the noise characteristics of the most diverse types of drones were recorded in field tests.
Within the framework of an initial flight-test trial in December 2020, three different drone types were tested acoustically. These were a very small recreational drone, a small parcel-delivery drone, and a large heavy-load drone with a theoretical maximum payload of 10 kg. The drones performed several overflight manoeuvres over microphones installed on the ground, thereby flying at different heights and at different speeds.
In a second test trial in July 2021, the focus of the noise measurements was transferred to realistic flight manoeuvres and routes. One example: A number of take-off and landing manoeuvres were performed in close proximity to a static microphone. In addition, very precise hovering manoeuvres were performed in the centre of a hemisphere of microphones, whereby the drones hovered only a few centimetres above the ground. Abrupt course changes and emergency braking manoeuvres were also executed in order to additionally be able to record the noise of the deployed drones during borderline flight manoeuvres.
In spring 2022, the DLR institutes of Flight Guidance, Aerodynamics and Flow Technology, Flight Systems, and Aerospace Medicine launched a further research initiative in which the noise emissions of ten different drones are being investigated. In this initiative, commissioned by a regulatory authority, standardized overflight manoeuvres and long-duration hover manoeuvres were performed in field tests using different multicopters, a fixed-wing drone, and a gyrocopter. The results of these acoustic measurements are currently still being evaluated.