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HomeAircraftHelicopterHelicopter Main Discussion › Why do rotor blades sound different when inverted?
04-24-2011 03:36 PM  7 years agoPost 1
Rogman88

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West Monroe, LA

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What's the physics involved with why blades have a more "farty" sound when air is pushed through negative collective. If I'm in the pits not watching a heli, I can tell if the pilot is flying upside down just by the sound of the blades. Certainly there is a phenomenon, or theory here why sound comes off the blades when inverted?

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04-24-2011 03:40 PM  7 years agoPost 2
ppridday

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Detroit Lakes MN

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Could be because there is not the mass of the heli underneath them to break up (diffract/attenuate) the sound waves coming from them.

Just a thought...

Paul

"There's someone in my head, but it's not me..."

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04-24-2011 03:41 PM  7 years agoPost 3
Wingman77

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Pulaski Tennessee

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there are two things that cause this, firstly it could have a bent spindle shaft, secondly it could be an align helicopter.

you can't tell the difference on any of my helis.

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04-24-2011 03:41 PM  7 years agoPost 4
Dood

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Wescanson

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I haven't heard what you're describing, but just a theory, perhaps you hear a different sound because inverted, the rotor wash is not passing over the canopy, boom, tail rotor, etc like it does when you're upright.

It's like when you're driving your car under a bridge. The sound of your car doesn't actually change, it's just that you hear it in a different way.

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04-24-2011 03:44 PM  7 years agoPost 5
Wingman77

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Pulaski Tennessee

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well that "farty" or blade slap sound is simply from blades coming out of track.

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04-24-2011 04:08 PM  7 years agoPost 6
OH-6 Cayuse

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san antonio tx, USA.

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I don't know but it's a glorious sound like music to my ears

!!For some people the sky is the limit, for me it's home!!

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04-24-2011 04:14 PM  7 years agoPost 7
max232

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Pensacola

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+1.

I'm a huge fan of that sound I don't know the physics behind it, but I love it

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04-24-2011 04:22 PM  7 years agoPost 8
Wingman77

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Pulaski Tennessee

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from a pilots perspective, I would pay twice as much if I had to for a heli such as a vibe or rave that can keep the blades quite.

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04-24-2011 04:27 PM  7 years agoPost 9
Thumpernator

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Senoia, Georgia, USA

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I believe it's simply a case of pulling "clean" air vesus "turbulant" air.

Dave
I keep on thinking, but nothing's happening. Knuk, Knuk, Knuk

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04-24-2011 04:34 PM  7 years agoPost 10
OH-6 Cayuse

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san antonio tx, USA.

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Hey wing man what do you mean vibes don't make the sound, both beat the air into submission the very same way look at this video he's a great guy by the way! And you can clearly hear the difference from inverted and normal noise!

Watch at YouTube

!!For some people the sky is the limit, for me it's home!!

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04-24-2011 05:08 PM  7 years agoPost 11
Justin Stuart (RIP)

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Plano, Texas

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Because the tail rotorwash is not disrupting the air off the main blades.

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04-24-2011 07:08 PM  7 years agoPost 12
LaurenceGough

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UK

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Another vote for the tail rotor wash affecting the sound... Same goes for backwards inverted hurricanes, they sound different than upright ones..

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04-24-2011 07:18 PM  7 years agoPost 13
D.Magee

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kansas city mo.

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Could it be the sound of the engine coming through the blades?

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04-24-2011 08:00 PM  7 years agoPost 14
Dirthead

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Thornton Co.

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It could be because the mass of the heli is above the main rotor as opposed to below it, and the blades have to work in a diffrent way to keep it balanced.

Keep ur head out the dirt only in the grass

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04-24-2011 08:14 PM  7 years agoPost 15
heli-cuzz

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Pittston, Pa. USA

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Its a mystery!!!

Fury 55 NIB Furion6 CGY750 fbl helicopter-Frenzy CGY750 fbl nitro-Frenzy fbl NOBAR90

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04-24-2011 09:28 PM  7 years agoPost 16
Rogman88

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West Monroe, LA

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backwards inverted hurricanes, they sound different than upright ones..
Perfect example. I kind of like the blade farting sound of backwards inverted hurricanes.

High Voltage just works better

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04-25-2011 12:19 AM  7 years agoPost 17
helidevil

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Brunswick, ME

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it could be when the heli's upside down and moving the heli its self (skids, body and boom) could be disrupting the air making a weird flow into the blades (turbulence of some sort) causing that farting sound..as opposed to upright when there is nothing disrupting the air, just a clean flow to the blades making no sound

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