Helicopter Noise What is a Sonic Boom? Sources of Non-Aviation Noise Noise made by a helicopter , is very complex and is comprised of multiple forms of noise sources. Thickness Noise This type of noise is referred to as "thickness noise," and is the result of a sound wave pulse created by the repetitive rotary motion of the air being displaced by the wing blade surface.
Blade Loading Noise Another source of noise results from the lift and drag forces on the rotary wings and is called "blade loading" noise. Other Noise Other contributors of helicopter noise include engine and gearbox noise. Factors that Affect Helicopter Noise The noise from a helicopter depends on such factors as: The number of rotor blades The design of the rotors The engine type The helicopter's motion, such as Blade speed Speed of the helicopter The type of action the helicopter is executing The helicopter's surroundings, such as Weather Does the Impulsive Nature of Helicopter Noise Make It More Annoying?
References: Larkin, Ronald P. Glossary Words: frequency , helicopter , noise, rotary For definitions of words used in this section go to the NoiseQuest Glossary of Terms. The quieter a helicopter can be made, the more markets it will appeal to leading to better sales. Here are just some of the way in which helicopters have been designed to reduce their noise footprint:. More main and tail rotor blades mean the blades can be smaller.
Smaller blades produce smaller vortices that make less noise when intercepted by the next blade. As of yet, there is no helicopter in production that has a varying speed main rotor. Varying the speed is a complex area that changes many aerodynamic and vibration conditions, but as technology and design evolve, this may be a feature we see in future helicopter designs. The design uses multiple swashplates to control the pitch of each individual rotor blade during its rotation around the helicopter.
This system is still in a development phase but it would not surprise me to see this or a derivative coming into production over the next few decades. You may have seen this already if you have a keep eye when wandering around airshows etc. Blade tip design has created some funky looing main rotor blades over the last few decades all with the aim of decreasing rotor tip vortices and their associated aerodynamic problems.
By altering the shape of the blade tip engineers have been able to reduce the effect of compressibility to allow the blades to work more efficiently and produce less noise. If you wish to learn more about blade compressibility you can find a great article written by Phil Croucher Here at HelicoptersMagazine. As mentioned above in the tail rotor section the helicopter manufacturers are constantly looking to improve the design of the anti-torque system on their helicopters.
Whether it be a ducted fan, electric motor, or no tail rotor system at all this area of helicopter design will always lead to some interesting innovations. One of the simplest ways to reduce helicopter noise is to alter how it is being flown.
Certain flight maneuvers cause the noise produced by the main rotor to be extremely loud and this is actually one of the main reasons for noise complaints when flying over populated areas. This is just one example. Yet another testing program from the DLR Institute of Aerodynamics and Flow Technology in Germany has led to recommendations for helicopter manufacturers and operators to adopt:. Lower rotor noise thanks to a modified approach path — DLR on the way to the silent helicopter.
Helicopters are noisy machines and there is no getting away from that for the near future. Whether it is the noise created by the blade vortex interactions, blade tip compressibility, main rotor vortex interaction on the tail rotor, or the power turbine within the engine, the noise is there. But by trying to reduce the noise bit by bit on every component an overall noise reduction of the helicopter is welcomed news to those who live under active helicopter flying areas! If you would like more information on articles related to helicopters, please take a read of the ones listed here:.
Account icon An icon in the shape of a person's head and shoulders. It often indicates a user profile. Log out. US Markets Loading H M S In the news. Alex Davies. Sign up for notifications from Insider! Stay up to date with what you want to know. For the first time, the way the rotor blades produce sound has been caught on camera.
As a helicopter flies, a vortex forms at the tip of each of the blades, because there is a difference in pressure between the regions above and below them.
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