What causes the high, strong whistle sound of an helicopter engine at full speed?

Posted 6Jun18.

A great example:

The Ranger Flight Company, Maneuver Center of Excellence

I love the previous answers… especially Neil’s:
“You are hearing the ludicrous spin of the compressor section of the turbine.”

This sound is more noticeable as a helicopter – such as the Blackhawk – performs a hovering turn. As the nose of the helicopter turns towards the viewer, the relatively unobstructed “view” of the inlets allows for the sound of the engines to become more pronounced.

Like this, at 0:42 – 0:48:

One thing I might add to the sound of the compressors is that there are tons of moving parts in the transmission. In the video above, even as the ‘Hawk is 90̊ to the camera, that whine can still be faintly heard. The breakdown of the major internal parts of the drive system is a plethora of RPM’s when the birds is at 100%:

Main module: 258 RPM

Input module: 5,750 RPM

Hydraulic pumps: 7,188 RPM

Generators 11,809 RPM

High speed shaft: 20,900 RPM

[Edit] I almost forgot the inlet guide vanes. If one is bent slightly, the whistle becomes a screech. When I first started as a UH-60 crewmember, that screech actually sounded a lot like Dick Dale’s “Nitrus” (starting at 1:49) and forever imprinted that song as the theme for subsequent troubleshooting.

Yes, Dick Dale and helicopters. The sustained band-saw like guitar of Girls Against Boys’ “Bullet Proof Cupid” reminded me of the sound of the tail rotor as I frequently walked a safe distance behind birds that were running up. I’m weird like that.