16:40
Experimental Aeroacoustic Measurements – Field 3
16:40
20 mins
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Prediction of acoustic dynamics during horizontal flights of a contra-rotating propeller UAV
Camilo Ignacio Andino Cappagli, Alireza Amiri-Simkooei, Mirjam Snellen
Abstract: The use of Unmanned Aerial Vehicles (UAVs) has increased rapidly in recent years, driven by expanding applications in civilian sectors such as logistics, infrastructure inspection, environmental monitoring, and emerging urban air mobility concepts. As UAV operations become more frequent and numerous, usually flying low-altitude operations over urban populations, their acoustic impact has become a critical concern, influencing operational planning and mission effectiveness. Predicting UAV noise from first-principle basis is challenging due to the interaction between the different drone subsystems and its interaction with the environment. These challenges motivate the development of empirical modeling approaches as a practical tool and a complementary approach to purely physics-based methods.
In this work, a series of experimental tests of horizontal flights at constant speed performed by a contra-rotating propeller (CRP)-based drone were analyzed. The effective directivity of the overall sound pressure level and its A-weighted counterpart (OSPL and OASPL), and sound pressure level (SPL) at different frequency bands were characterized. From the symmetries of the radiation patterns, simple functions were used to approximate the spatial directivity reflected in a modulation in the pressure time-series. These were coupled to a series of telemetry-based variables which constituted the input for a new empirical model of the sound dynamics during real operations. A machine learning model proven accurate to predict the OASPL dynamics during ascent, descent, and hover was used. Preliminary prediction results showed that the model accurately predicted the OASPL during the studied flights. Quantitative analysis of input variable importance indicated that few specific variables are critical to generate accurate predictions of short- and middle-timescale dynamics of the acoustic metrics.
These findings suggest the existence of a hierarchy of importance between the telemetry-based variables to predict the sound dynamics of drones during real operations. This means that the sound pressure level dynamics can be recovered based on few specific telemetry variables. Furthermore, these preliminary results show that the model can perform accurately and precisely in the studied horizontal flights. Overall, the model constitutes a tool to aid in the planning of drone operations and their control to reduce the acoustic levels and fluctuations on the ground.
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17:00
20 mins
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On the Repeatability of Drone Noise Measurements in Outdoor Test Environments
Gert Herold, Julian Benz, Steffen Büchholz, Stefan Becker, Ennes Sarradj
Abstract: Reliable characterization of drone noise emissions requires measurement procedures that yield repeatable results under realistic operating conditions. While emission-based measurement approaches are increasingly applied in current research, the reproducibility of results obtained from outdoor measurement campaigns remains insufficiently understood, particularly with respect to sensitivity to environmental conditions and measurement geometries.
This contribution investigates the repeatability of drone noise measurements conducted in outdoor test environments. Two measurement campaigns involving the same multicopter platform were performed using identical signal processing and evaluation procedures as well as nominally identical flight configurations, while the measurement setup and meteorological conditions varied. The evaluated dataset includes repeated fly-bys under comparable conditions as well as measurements conducted under different environmental and geometric configurations.
The analysis focuses on the consistency of derived acoustic metrics and emission characteristics across the different measurement cases. Observed variations are discussed with respect to changing weather conditions, flight trajectory deviations, and sensor placement, enabling an assessment of which factors most strongly influence measurement repeatability in practice. The results provide quantitative insight into the robustness and limitations of outdoor drone noise measurements and help to identify boundary conditions under which repeatable emission characterization can be achieved.
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17:20
20 mins
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Measurements of outdoor drone noise
Christine Huth, Sonia Alves, Julian Babl, Emilian Zehetbauer
Abstract: Currently available for the measurement of outdoor drone noise are
- the Guidelines on Noise Measurement of Unmanned Aircraft Systems by the European Union Aviation Safety Agency (EASA) released in June 2023 and
- the international Standard ISO 5350 Noise measurements of UAS (unmanned aircraft systems) – first edition 2024-01
To compare the procedures of both recommendations, measurements with various C0/C1 class drones were carried out. Both the measurement procedures and the results will be discussed.
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