Drones are loud. No matter which one you get, it will produce a noise that is going to be annoying for you and for people around you. But we can make them slightly quieter if we understand the source of sound and how different factors affect it. So, how to make drones quieter to make them less annoying? Let’s find out.
The primary source of noise on drones is spinning propellers. Drones with larger propellers spin slower to produce the same lift so they are relatively quieter. The shape of the propeller, surface finishing, pitch angle and distance from the arm also affect the frequency and intensity of the noise.
In this blog post, we are going to discuss the science behind drone noise and learn how to reduce the noise as well.
Factors affecting drone noise
Before we dive into methods to make your drone fly quieter, let’s first understand the factors that affect the frequency and intensity of noise that your drone makes.
- Propeller RPM: The RPM of your drone has probably the largest impact on the noise your drone makes. Higher RPM usually means higher frequency noise. As the frequency increases, the noise becomes more annoying. Smaller drones with small propellers have high RPMs and are more noisy compared to bigger drones.
- Propeller length & chord size: As noted in the above point, the propeller length has an indirect affect on the noise level. Larger propellers have to turn at lower RPM to produce the same amount of lift compared to smaller propellers. Lower RPM means lower frequency noise. Similarly, the width of the propeller (aka chord) also affect the noise level. Thin propellers are noisier than wide propellers.
- Surface finish: A part of the noise comes from the turbulent from around the propeller blade that runs through air. If the surface finish of your propeller is high, your drone will produce less noise. Any protrusion like stamped logos or any other marking will make the propellers more noisey.
- Tip design: The design and finish of the propeller tip is very important for acquostic purposes. The propeller tip is running at the highest linear velocity than any other part of the propeller and is more suseptible to vibrations and turbulance. Ovel shaped tips are quieter than straight cut tips.
- Distance from the arm: When a propeller passes over the motor mounting arm, it produces a compressed air column between the propeller and the arm. This high pressure when released after the propeller passes, adds an additional noise to the mix. The further the propeller is from the arm, less pressure will develop between the two surfaces and quieter the drone will run.
- Propeller balancing: Another source of sound is unbalanced propellers. High quality propellers come well balanced but if. you buy cheaper ones, they might not be as well balanced as they should be. This slight unbalance will create additional vibrations and add to the noise mix. Propellers can also become unbalanced if one of the sides is damaged during a crash or picks up dirt.
- Motor bearings: Faulty motor bearings can also produce additional noise that can add to the overall noise mix.
How to make drones quieter
Now that we know what makes drones so noisy and annoying, let’s explore a few practical ways to make your drone less noisy and quieter.
Chose a quieter drone
If noise is going to be a big problem for you due to any reason at all, select your drone carefully. Not all drones are equal. Some are louder than others.
If you want one of the quietest drones then we suggest that you buy a drone designed specifically for silent or near-silent operation.
For example, some manufacturers like Yuneec and DJI have developed new sound dampening technologies where they have minimized noise as much as possible. So if you are looking to buy a very quiet drone, stick to those models from trustworthy drone manufacturers. [Check the table below for the quietest commercial drones]
In some cases, it might not be worth spending money on making your existing drones quieter because some drones are just inherently loud and that might ruin their entire purpose. So before spending money on something that will not benefit you consider first whether wasting extra money makes any sense or not.
Install bigger propellers
Generally, bigger propellers are quieter than smaller ones. Smaller propellers usually have higher RPMs and produce more noise compared to larger ones rotating at lower RPMs.
This is a good solution if you are building your own DIY drone and have the freedom to adjust your frame length at will. If you have an off-the-shelf commercial drone from DJI or other manufacturers, your options for choosing bigger propellers are limited by the manufacturer’s specifications.
Install 3-blade propellers
Two blade propellers are noisier than three-blade propellers. More blades offer a bigger surface area so your motors can run on lower RPM to generate the same amount of thrust.
If your drone comes with 2-blade propellers, you might find 3-blade props from other third-party manufacturers. For example, O’woda makes carbon fiber 3-blade propellers for Mavic 2 Pro and Zoom. Similarly, you can find 3-blade props for your own specific drone model.
Use ‘low-noise’ propellers
Some third-party manufactures are making propellers that are designed for better noise reduction. They have shallow pitches and more pointy, hook-shaped wingtips to minimise the turbulence around the propeller edges.
They also have a smooth and shiny surface finish which also facilitate laminar airflow over the surface to reduce noise further. Check these silent propellers for a better noise reduction.
DJI is also introducing low-noise propellers across its popular models. They reduce the noise by as much as 4 dB (which is A LOT actually). Combined this with their redesigned sinusoidal ESC, and they have managed to reduce noise on their newer drones by up to 10 dB (like on DJI Mavic Pro Platinum)
Autel is also shifting towards low noise propellers following the footsteps of DJI. The old propellers on their most famous Evo 2 drone were oval in shape. The new low-noise propellers are more pointy toward the edge just like the DJI’s.
Remove any logos on propeller
As we discussed above, the surface finish of your propeller has a great impact on how air flows around it. A better surface finish can produce a more laminar flow and will result in a silent motion of the propeller through the air. In contrast, a propeller with a rough surface finish will produce more noise due to turbulence.
If your propellers have any brand logo or number marking on them, they will not run silently. You can either buy propellers with a smooth surface finish (link this one) or sand off the logo or mark with 600 grit sandpaper. Make sure that your sanding process does not produce further rough surfaces so do it with patient and delicacy.
Balance your propellers
If you are using off the shelf third party propellers especially cheap ones, make sure you balance them perfectly before installation. An unbalanced propeller has more weight on one side and creates vibration during high RPM rotation. These vibrations are bad because of two reasons.
- They produce additional noise.
- They put additional stress on motor and motor mount.
If you are building your own drone or modifying the one that you have, it is important to get high-quality balanced propellers and check them before installation. This will reduce overall vibration and noise production due to an unbalanced prop/motor combination which can make your drone very noisy.
Balancing a propeller is easy with a small prop balancing tool like this one. Just put your propeller on the stand and see which side is heavier and sand it with fine sandpaper. Repeat this process till you can station the propellers horizontally. The below video goes into the prop balancing in detail.
Clean your propellers & motor
A dirty propeller will create unbalanced and rough surfaces both increasing noise. If you use your drone outside in dusty or muddy conditions, make sure you clean it regularly to keep the blades free from dirt and stones which can impact their performance and make them noisy. A simple toothbrush can come in handy in this regard for thorough cleaning.
Regularly inspect all the parts that connect your propellers to your motors including motor shafts, nuts and bolts, propellers themselves for any signs of wear and tear which is an indicator that they need to be replaced. If your motor shaft has dust or sand in them, clean your drone motor as well.
Use brushless DC motors
Drones usually use two different types of motors; brushed motors and brushless motors. Brushless motors are expensive, more efficient and have less noise compared to the cheaper brushed motors.
If you are building your own drone, it is a better idea to use brushless motors. They cost a little more but they run very smoothly, produce very little electromagnetic noise ( also known as coil whine) and give you a better flight time on the same battery.
Change noisy drone motor/bearings
Faulty motor bearings can produce additional noise which might be difficult to filter out with other remedies. Like all mechanical moving parts, your motor bearing tends to dry over time and run with friction. This not only produces noise but also increase current draw which reduces your flight time.
If your motors have been running for a long time and are noisy than before, it’s perhaps time to replace them with a new one.
Which drone is the quietest?
The DJI Mavic Pro Platinum is undoubtedly the quietest drone in the market right now. It comes with the new DJI low-noise propellers and a redesigned ESC that operates on a sinusoidal wave to cancel out the coil whine from the motor making the Mavi Pro Platinum the quietest drone.
Guys over at wetalkuav.com did testing with a few popular DJI models and determined how much noise each drone make at a 2 ft distance. Below table is the recap of values they recorded (see their original post here)
|Noise @ 2 ft
|DJI Mavic Air
|Mavic Pro (old props)
|Mavic Pro (new props)
|Mavic Pro Platinum
|Phantom 4 Pro (old props)
|Phantom 4 Pro (new props)
|Phantom 4 Pro V2.0
All drones are inherently noisy and there is nothing that you can do to make them completely silent. But we can reduce the noise to levels where they are acceptable and don’t interfere with your application of the drone. Quiet drones are important for many things like recording events or monitoring wildlife or just for recreational flying without annoying your temperamental neighbours.
With the tips above, you can reduce the noise level of your drone and fly with more peace and quiet.