What makes a drone sound

Whatever the reason sciences started looking into the ways that we can reduce drone noise levels and we will cover some of the research here. In , a study by a Chinese research group looked at the design of quiet drones by understanding the physical aspects of drone noise generation and propagation. In their paper they present a framework to evaluate the scattering effect of the rotor noise of a flying drone using different modelling and mathematical techniques. By understanding the effect of the body on rotor noise and the scattered noise generated from the reflected noise they have presented a way of analysing exactly what needs to happen to reduce the drone noise from different drone body types.

In their paper, they use a drone body type that is very similar to the DJI phantom series. This is what the drone noise pattern looks like:. You can see that there is a load amount of noise reflected upwards and very little which is reflected downwards during a flight. In scientists from Israel note that designing a quiet and efficient propeller is a demanding task because these two goals often lead to contradictory design trends.

The study looked at a multidisciplinary design optimisation process for the design of a quiet propeller. This design is subject to power, structural, and side constraints but they were able to design a quiet propeller for an electric mini unmanned air vehicle.

The design variables include things like blades geometry, blade cone angle, propeller radius, the number of blades, and the rotational speed of the motor.

The motor characteristics were also found to have a very important influence on the optimisation of the propeller and it should therefore be taken into account when designing the silent propeller. A recent paper published in looked at the stock DJI phantom to propellers and compare them to a stop propeller which was modified with a trailing edge notch. A comparison of the two propellers showed the research is that the trailing edge notch and stop propellers have a similar sound pressure level at all distance measured.

The trailing edge notch of the propeller did seem to shift the frequency higher and was the only significant difference between the two types of propellers.

This effect seems to be reduced as you increase the amount of propellers. A DJI hexacopter was also flown with the stop and trailing edge notch propellers. The hectic was 20 dB noisier than the phantom to but there was no discernible difference in sound pressure level between the two propellers. This means that any significant changes to the trailing edge of the propeller are unlikely to cause a significant increase or decrease of noise.

This is because they rely on the displacement of a significant amount of air which inherently will cause noise. Just think about a fan or other fast-moving object and there will always be noise. Drone technology will need to come on in an unimaginable leap if drones were to become completely silent. However, there are scientists working on reducing the amount of noise and we can even get a drone to the point of being almost inaudible as it flies about 30 m in the air.

That is incredible considering the amount of potential applications in an urban setting that drones may be able to fill. Andy started droneflyingpro. He has been a drone pilot for many years and has flown many types of drone. His favorite is still the DJI Mavic Air for the portability and functionality packed into a small and portable drone!

We are supported by our readers and every time you visit we earn a small amount of money through ads and affiliate programs. Thank you! There can be the production of small harmonics at times, unlike when there is only one motor that brings out a single frequency. The electric control unit controls the many propellers that produce the single frequency spectrum. Nowadays, most drones come with a revolutionary blade design which comes in handy in noise reduction.

The case is different if you are using old drone designs. Usually, older drone models have electric motors that make the main engines produce a lot of noise. To fix this, install a motor glider in the drone. Then adjust the drone settings to maybe slow or medium speed, and it will automatically produce less noise when functioning. You can incorporate this method with other ways that help to make the drone quieter so that you may be able to make better videos.

Other people recommend this method to reduce noise from drones, which has been working for many. Usually, drone propellers from a specific manufacturer carry the logo of that manufacturer. To reduce the noise, try to remove the logo and smoothen the surface using sandpaper. The drone will be propelled much more smoothly, producing less noise. I remember one time I was flying a popular drone which had some raised logo marks on it. The propeller was therefore not smooth and would produce a lot of noise.

Usually, the edge needs to be as smooth as possible, and you should not cause any scratches. I tried using sandpaper to make the edge smooth, and it really helped to reduce the noise level quite a bit. If the shape of the blade is not in a smooth form, it contributes to the noise the propeller creates. But, if the blade is wide, flat, and smooth, it will most likely produce little to no noise. Also, most times, thin blades make more noise when the edge is in motion than thick blades.

Ensure that before flying the drone, you clean up the propellers. Also, ensure that you remove any scratches that it may have after flights. Moreover, it is essential to regularly balance the propellers to reduce the voice and frequency of the noise they produce.

If all these efforts do not work well, replace the propeller with a large slow one. If all the methods above fail to work, another better option is creating your own propeller that fits your drone.

The only way that their noise is avoided is they fly high enough. While jet-powered aircraft create intense noise from aerodynamics.

Considering that much of the noise of a propeller aircraft is of aerodynamic origin due to the flow of air around the blades.

An interesting fact about the propellers is that when they spin at full speed, the blades can reach speed that is near or over the speed of sound, and that is the cause of the noise they make.

In cases where the tips go over Mach 1, the shock waves create little sonic booms, which is the main reason why some aircraft sound a lot louder than they have a right to be. Many times most of us wish our drone could be more silent. First we need to know are they really quieter and are they more efficient? And buzzing noise of blades can be a bit annoying, especially if you are often exposed to it.

So the question is are silent propellers better? For that we have to consider a couple of things, and what are the difference and similrities between the original props and new low-noise props. They weigh about the same, new props are made with a new aerodynamic design, also feels thinner, and the length of the low-noise blades are about 3mm longer than the original blades.

The negative side of these props of course not with all drones can be: slow vibrations that can be seen in the camera and props breaks more easily. Without forethought, public outcry and regulation, the buzzing of drones may soon fill city and suburban skies — adding to the din in many places, and disturbing the peace of even those wealthy suburbs whose residents can afford the convenience of rapid home delivery.

Even neighborhoods that have managed to avoid being under airport flight paths will find themselves surrounded by the buzz. Public parks, designed to provide places for recreation, community gatherings and quiet contemplation, may no longer provide any escape from the hum of daily life.

You might not be able to enjoy birdsong in the morning with your coffee , but even worse, the birds themselves might not be able to hear each other , either. Any home delivery service raises a great many questions about sustainability and the costs of consumption in energy, material and human lives.

Until now, though, those deliveries have been by car and truck over existing roads and are covered by ordinances on sound levels. Adding drones will bring a third dimension to shipping — but also to the level of noise in the world. Festival of Social Science — Aberdeen, Aberdeenshire.

Edition: Available editions United Kingdom.