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Main source of helicopter noise


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#1 chris pochari

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Posted 10 May 2018 - 20:23

I've always heard blade vortex interaction is the main source of noise.

The four main noise types are: BVI, HSI (High speed impulsive) thickness noise and of course tail rotor noise. Of these four, which is the biggest contributor as a percentage? Or is it even scientific to rank order them?

Listen to the sound of the H160 compared to the AS365 without the BVI reducing swept tips (Blue edge), the difference is clearly noticeable. 

IBC can also reduce HSI noise, is the added complexity just not worth it? The video below of the BO-105 equipped with IBC clearly demonstrates it is highly effective. 


#2 Eric Hunt

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Posted 10 May 2018 - 21:09

BVI is the cause of the "WOCKERING" sound, and comes at certain combinations of forward speed and rate of descent, allowing the blade to hit the descending vortex of the previous one. Not usually in level flight.


A Huey has the thumping sound from a big rotor creating a lot of lift. You can'd sneak up on anybody in one of these, or a B222 or 212 or 214ST. Swept tips will reduce this noise. 


Those fans at the tail are a huge source of noise, as are tail rotors, doing similar RPM to an aeroplane propellor (1800RPM). The hissing sound is from the compressors and bleed bands.


Surprised to see people walking around the running aircraft without ear protection?

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#3 overtorque


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Posted 10 May 2018 - 23:55

The noise-reducing technology in modern helicopters is unbelievable. It took me aback when I saw a Calstar fenestron eurocopter doing patterns. You hear nothing! While meanwhile old junker Cessna 150s everyone and the state over can hear them.


Don't get me started on the whop-whop-whop of a Huey and heaven forbid you try to sleep when a Chinook is anywhere airborne in your city.

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#4 Discap


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Posted 12 May 2018 - 16:25

A MD 600N that I have flown, flew over the local golf driving range while I was hitting balls. It was so quiet that not one golfer flipped them off. I would opine that 6 blades and no tail rotor helps keep,them quiet.
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