Mi-8 "chirping" sound

[nielot96]

Does anyone know what makes the Mi-8/17/24 emit the characteristic chirping sound?  I found three theories.  The first is that it is a rotating drive link on the swashplate.  The second talks about the holes for anchoring the blades.  The third one, heard and discussed with the lecturer operating the Polish Mi-2 and SW-4 helicopters, talks about the aerodynamics of the rotor, the whistle generated by the blade tips.  However, he was not able to confirm it 100% because he is an engineer of the fuselage and engine, not aerodynamics.

 

Thanks for solving the problem in advance and greetings from Poland

[sLYFa]

7 hours ago, nielot96 said:

The first is that it is a rotating drive link on the swashplate. 

This

[AlphaOneSix]

It’s the swashplate drive link 

Edited April 16, 2021 by AlphaOneSix

[AlphaOneSix]

I’m working today as you can see  

[nielot96]

Wow, very nice to see it. I just  begin servicing in air force on this magnificent helicopter and just wondering about this specific noise. Could you make a little bit longer record from interior, because there the noise is very audible:) Greetings 

Edited April 16, 2021 by nielot96

[AlphaOneSix]

Well I made a longer video but it was in-flight and the wind noise drowns out the whistle noise from the drive link. I should have closed the doors.

Edited April 17, 2021 by AlphaOneSix

[Morrov]

It is the swashplate follower thing, you can see the how the sound correlates with it's movement very clearly in this video.

It's the same mechanism in the Mi-24, except it spins faster so the sound is more frequent, as you can see here.

 

I love hearing the Hinds fly over my head, the chirping/whistling makes it super easy to identify them.

[bmbpdk]

I can tell you that the EH101 Merlins makes the same sound, ive heard that several times when they come by where i live.

[Richard Dastardly]

23 hours ago, bmbpdk said:

I can tell you that the EH101 Merlins makes the same sound, ive heard that several times when they come by where i live.

Very audible from above the Merlin ( they tend to fly past here under the cliffs, so I rarely get to hear one like everyone else does! ). Quite sure there's other helicopters that have a similar sound but off the top of my head can't remember one right now.