First Noise Study 2023

The first study focused on a basic comparison of the noise performance of commonly used drones and small aircraft with a pilot on board. The measurements took place in April 2023 and were conducted as a certified test under the expert supervision of the Government Testing Laboratory of Machines.

What was measured:

• Sound pressure level (LpAeq,T) in non-urban area and built up area
• Sound power level (LwA) in standardised conditions
• Reference ambient noise (background noise) before each measurement

Where the measurement took place:

• Non-urban area: ATZ Letkov airport zone
• Built up area: urban area of Pilsen, Cukrovarská Street

What machines were tested:

• 12 unmanned aerial vehicles (UAS) – e.g. DJI Mini 2, Mavic 3 Classic, Matrice 300 RTK
• 4 manned aircraft (GA) – e.g. Zlin Z-42M, WT9 Dynamic
• Noise was measured at different altitudes (10-300 m), depending on the type of machine and the environment

Measurement results:

• The average noise level of GA aircraft at 150 m was about 60 dB, and at 300 m about 52 dB.
• UAS reached a noise level between 45-60 dB at 30-50 m.
• Light quadcopters were the quietest (e.g. Mini 2, Mini 3 Pro).
• the noisiest larger machines such as the Matrice 300 or Inspire 2.
• In urban environments, the values were on average 3.6 dB higher than in open countryside.
• Some drones were acoustically almost lost in the background noise at operational altitudes (30 m).

The study confirmed that smaller drones have significantly lower noise levels than GA aircraft, even when flying at significantly lower altitudes. It also showed that the noise level increases with the weight and class of equipment. This data was used as a baseline for the design of the measurement methodology and for further testing in the following year.

Second Noise Study 2024

The second study built on the first phase, but its scope was significantly broader. In addition to conventional UAS and GA aircraft, it included remotely piloted models and atypical unmanned vehicles – including vortices, ornithopters and heavy transport drones.

A major contribution was the refinement of the methodology using photographic scaling and GNSS altitude calibration. This allowed a more accurate assessment of the relationship between flight height and measured noise.

What assets were tested:

• 21 UAS (incl. DJI Flycart 30, Matrice 350, LIAZ SkySpotter 150)
• 4 electrically powered aircraft models (e.g. Ambrosia, Elexant)
• 8 GA aircraft of various designs (e.g. Zlin Z-43, JK-05L, Calidus vortex)

How the measurement was carried out:

• Measurements in the sky (for drones with stabilisation capability) – at heights of 17-25 m
• Overflight measurements – in real flight above the measuring equipment, altitudes 25-300 m
• Non-urban area: Zbraslavice airport
• Inner city: Kolín, area with proximity to busy roads

Measurement results:

• Light drones and models showed the lowest noise values – WingtraOne Gen II reached 40.1 dB, DJI Mini 4 Pro 48.8 dB.
• The LIAZ SkySpotter 150 helicopter had the highest noise level – up to 84.7 dB at all times.
• GA aircraft reached noise levels between 56 and 82 dB depending on altitude and machine type.
• Remote-controlled models were often quieter than the average UAS, even at higher weight.
• The C0-C1 classes remained the quietest group, while C2-C3 were 10-20 dB noisier.

The second study therefore not only confirmed the 2023 findings, but also broadened the range of aircraft types measured and refined the methodology. Moreover, the results are compatible with European EASA databases and can be used for standard-setting and urban traffic planning.

Conclusion

The results of the two noise studies confirm that unmanned systems, especially light quadcopters and autogyros, generate lower noise loads. In most operational scenarios, these machines are able to generate lower sound pressure levels, even though they operate at lower altitudes where noise is usually perceived more intensely.

At the same time, however, the noise level of UAVs is not constant and universally low.

On the contrary, the results showed that the acoustic performance is strongly dependent on:

• the structural type of the aircraft (copter, autogyro, vortex),
• weight (often correlated with the class of equipment according to the European C0-C4 classification),
• power unit performance and overall flight configuration.

While lightweight drones of C0 and C1 class (e.g. DJI Mini 2, Mini 4 Pro) were in many cases acoustically indistinguishable from the background urban environment, heavy machines such as the LIAZ SkySpotter 150 or DJI Flycart 30 already generated noise values comparable to or higher than conventional GA aircraft.

Moreover, both studies showed the importance of environmental context. In an intown environment, even a quieter drone can be drowned out by traffic noise, while in an extravarious environment its acoustic manifestation is more perceptible. This finding demonstrates the necessity to always perform acoustic assessments in relation to the specific environment and planned traffic.

The data set obtained during both measurement stages forms an important basis for:

• the production of noise maps and the assessment of operating limits in urban and suburban areas,
• the definition of geographical zones for drone operations according to the level of noise pollution,
• standardising measurement methodologies across the EU and linking to EASA databases,
• developing technical requirements for new generations of UAS in terms of noise emissions.