When we talk about “drones” we assume that we talk about relatively small multirotors. Of course, first we have to define what it means when we say “so loud”. It’s not the same when your drone flies a few feet away from you and when it’s 250 feet up or a few hundred feet away from you. Therefore the drone sound will be loudest when the drone flies few feet from you. So let’s explain why the drones are so loud. The loud noise that drones produce comes from the fact that rotors are slicing through the air so we hear buzzing noise. When we talk about electric motors, they are very quiet by themselves; but when you use only a multirotor without its propellers on and all you’ll hear is a slight whine.
The job of a propeller is to convert rotational kinetic energy to thrust. If we at least understand the basics of mechanics, we know that there are always some losses, so a typical large propeller that are used for a full size airplane might be over 80% efficient, and as an example a small multirotor propeller may be 60-70% efficient. While the rest of the energy goes into generating heat and noise, and that’s the sound you hear in drones. So basicly when you hear two propellers that are spinning with about same input power and you notice that one is way louder than the other, it is clear to conclude that the louder proppeler is the less efficient one.
Main characteristics of propeller efficiency are: blade count, diameter, pitch, shape, and operating RPM. Most efficient are single blade props but in practive, they are hard to implement so 2-blade props are more common. Therefore, smaller props are less efficient than large props for a lot of reasons like, viscosity, compressibility, and so on. Therefore, if you want to reduce the noise of the drone, it is important to select the appropriate props.
Drone Noise Is Driving People Crazy
A research has been carried and NASA study has confirmed what you already suspected, that drone noise is driving people crazy. This is also one of the reasons why people before choosing a drone are looking at that factor. So why are drone noise so irritating when cars create plenty of noise also and we are surrounded by each step around them. One of the reasons is that drones are much slower then cars, and you have to put up with the sound for longer time than a car which passes much faster next to you, and you’ve probably grown up listening to cars all your life, while the drones are quite new and that buzzing noises sound strange. The only way that their noise is avoided is they fly high enough.
Why do Propellers Make noise?
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. The reason for that it’s the propeller and the local air velocity over 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.Because of that it creates something called a wave drag and it’s one of the fundamental barriers that limit propeller performance. 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.
Are Silent Propellers Better?
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. The reason for that is they are so thin, and they could start vibrating by interferance only by the slightest damage, and we can’t see that with the bare eyes. If you want to keep your drone quieter, these are my silent propellers recommendations that are available on Amazon: Best Silent Propellers for Drones
World's Quietest Drone
When we consider one aspect that makers found hard to manage, it’s the sound. Force 1 F100 ghost is currently the quietest drone in the World, and fairly cheap. It comes in packet with camera mount for GoPro Hero 3 and 4. This is a brushless drone with brushless motors and it does have independent ESC (Electronic Speed Controllers), that gives you better performance with brushless drone.
Force 1 F100 have 2 batteries and they’re 1800mAh Li-Po Battery that can give up to 15 minutes of flight per launch. Average charging time is about 3 hours. Remote control is labeled. What this drone have is the possibility to rotate 360 degree and make cool stunts. The controller is simple and works, but it’s not really anything special. This drone is a bit too large to fly inside, so do not make your first flight inside, instead go outdoors. I also recommended that you start your flight from somewhere stable.
We can conclude that silent drones do not exist for now and technology is at a point where manufacturers can produce drones with thick bodies which somewhat reduces noise. With these things they are masking their vibrations while running. So today drones are quieter unlike before, but not enough. The only thing we can do to reduce noise of the drone is to properly select propplers. Also, another way (and more expensive) is to buy a quiet drone. My personal opinion is that in the near future we will not see the drastic reduction of noise in the drones, but I would love to hear your opinions in the comments below.