If you’ve ever heard a helicopter flying overhead or been in close vicinity to a helicopter when on the ground, you know just how loud they are.
In fact, helicopters are so noisy that you can’t even normally speak while inside of them without wearing a great aviation headset.
But what is the reason helicopters are so loud?
Helicopters are some of the loudest aircraft around, primarily because of their main rotor.
The main rotor spins, which then results in the air pressure dropping above each blade, and rising below it.
To even out this difference in pressure, air flows around the blade, creating a concentrated vortex.
When the vortex meets the next blade, you get a vibration – an incredibly loud sound
Helicopter noise is even believed to be linked to hearing loss.
There are efforts being made to produce quieter aircraft by using new design choices, so future helicopters are likely to be much quieter than current ones.
5 Reasons Helicopters Are So Loud
A helicopter’s main rotor generates most of the aircraft’s noise.
Noises Caused by the Main Rotor
A helicopter’s rotor spills vortices off its back and tip while rotating in the air, causing two areas of sounds.
The back of each main rotor blade creates an aerodynamic condition called Blade Vortex Interaction (BVI).
During BVI, the vortices leaving the trailing rotor blade get hit by the vortices of the next rotating blade, producing a slap or snap sound.
There’s an entire wall of vortices in the path of each blade, since vortices are created down a rotor blade’s entire length.
The more vortices that get hit, the greater the sound they produce.
Choppers with fewer rotor blades produce the most noise.
That’s because having fewer rotor blades requires helicopters to have longer blades to compensate.
These longer blades create more vortices, resulting in more vortices crashing with one another and producing louder and deeper noises.
Related: How Fast Do Helicopter Blades Spin?
Blade Tip Vortices
A helicopter’s blade tips also generate vortices.
These vortices are even easily visible during helicopter flights in humid air.
The tip vortices produce sound either during BVI or when they interact with the tail rotor.
Noises Caused by the Tail Rotor
Tail rotors cause noise the same way that the main rotors do.
The tail rotors also generate BVI, but since tail rotors often rotate faster than main ones, tail rotor BVI produces higher frequency noise.
The tail rotor also experienced disruption from the main rotors because the tail rotor descends backwards from the main one.
Tail rotors also experience secondary BVI when vortices from the main rotor when the main rotor’s vortices interact with those on the tail rotor.
Noises Caused by the Engine
Helicopters have two types of engines: piston engines for smaller helicopters and turboshaft gas turbine engines for all other helicopters – both engines produce a notable amount of noise.
Air is drawn to the front of the engine by one or multiple compressors, which creates noise because the compressors squeeze the air into the engine.
When air exits the engine, it passes through the power turbine, which transfers energy from the passing air to the main transmission, resulting in high frequency noises.
Lastly, a helicopter engine’s exhaust system also produces noise. The large amounts of gas exiting the exhaust produces large amounts of noise.
How Loud is a Helicopter?
The Helicopter Association International (HAI) reports that a helicopter flying at 500 feet produces 87 decibels of noise.
At 1,000 feet, helicopters produce 78 decibels of noise, which is almost the same as a vacuum cleaner, which produces 75 decibels of noise.
But, the perceived noise of passengers and pilots during a helicopter flight is as high as 97 decibels, so helicopters are generally noisier for people inside them than outside observers.
We go into more detail into our How Loud is a Helicopter article.
Helicopters Are Still Very Loud When Inside One
Most commercial aircraft emit less than 80 decibels of noise, although the perceived noise of helicopters is 97 decibels, as mentioned above.
Some of the world’s noisiest helicopters are high-powered military choppers, which have internal noise levels between 104.6 to 106.5 decibels.
The Loudest Helicopter in the World
The Sikorsky S-65 is the world’s loudest helicopter.
At takeoff, the S-65 comes in at 95.9 EPNdB, 92.6 EPNdB during a level flyover, and 94.0 EPNdB during approach.
EPNdB means effective perceived noise in decibels, which is used for aircraft noise certification.
The Quietest Helicopter in the World
The quietest helicopter in the world depends on what category the helicopter falls under.
The Stealthy Blackhawk (or Silent Hawk), which was used during a raid in Pakistan, that took down Osama Bin Laden, is the quietest military helicopter.
The Airbus H130 is one of the quietest civilian helicopters with its shrouded tail rotor and automatic variable rotor speed control.
It has a noise signature 6 dB below ICAO limits
The MD 600N is another very quiet helicopter.
This is down to ts advanced NOTAR anti-torque system, and the fact that it’s a light single-engine turboshaft aircraft.
How Helicopter Noise Can Be Reduced
There are multiple ways to reduce helicopter noise, mostly through design alterations.
Helicopters can be made quieter by adding more main and tail rotor blades, reducing blade lengths, and having slower main rotors.
Adding more blades means that each blade’s length can be designed to be shorter, which results in smaller vortices that cause less noise.
Shorter blades also mean that the blade tips travel more slowly, which further reduces blade tip vortices and further reduces noise.
A slower main rotor would reduce the number and size of vortices produced by a helicopter’s rotors.
Engineers are also testing a design called “Active Rotor Blades” that uses multiple swash plates to control each rotor blade’s pitch to reduce noise.
Future helicopters may be considerably quieter than current ones if the design is successful.
Flying in a Helicopter Can Damage Your Hearing
According to this study, flying in a helicopter can cause hearing damage.
The study analyzed data of 234 pilots which showed a high correlation between high-frequency hearing loss and higher flight hours, indicating that experienced pilots suffer higher hearing loss.
The study also found that hearing loss was especially pronounced in left ears in helicopter pilots than pilots of other aircraft.
So, flying in a helicopter long enough can damage your high frequency hearing.
You Can’t Have a Normal Conversation in a Helicopter
It’s too noisy to have a normal conversation in a helicopter without using noise-suppressing headphones.
All helicopter pilots and passengers wear headsets during flights.
These headsets have noise-canceling features that minimize helicopter noise and let the pilots, crew, and passengers speak to each other.
Stealth Helicopters Are Much Quieter
Stealth helicopters are designed to minimize detection by reducing noise, radar, and other identifiers.
There are no publicly available statistics about stealth helicopter noise levels, but most analysts estimate they produce between 20 to 50% less noise than standard helicopters.
For example, the Boeing–Sikorsky RAH-66 Comanche emits half the rotor noise of existing choppers.
The Comanche achieves this by having a five-bladed rotor.
Its design also eliminates interaction between its main and tail rotors.
Michael is an esteemed aircraft engineer and aviation expert with an insatiable passion for all things aviation-related.
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