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Pop pop pop pop pop pop pop pop


Witch
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That popping noise the blades make was unnerving when I first heard it. Now I really like the pops.

 

Question: What are the blades doing to cause the popping noise? Angle of attack? Flapping in the wind? Sonic booms? What is the mechanism of the pop?

 

Later

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Blade Slap - The dominant noise produced by helicopters consists of a broadband spectrum generated by vortex formation and shedding in the flow past the helicopter blade. In addition to the discrete frequency noises at harmonics of the blade passage frequency, superimposed on the broadband spectrum for helicopters is a rotational noise known as blade slap. This high amplitude periodic noise plus highly modulated vortex noise caused by fluctuating forces on the blade due to the cutting of one blade's tip vortices by another blade and transonic shock. Blade slap is a distinctive, low frequency throbbing sound which increases during certain descent, maneuvering and high-speed cruise operations. :huh:

 

chppm-www.apgea.army.mil/dehe/ morenoise/noise_dictionary.aspx

 

Fly Safe

Clark B)

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Blade Slap - The dominant noise produced by helicopters consists of a broadband spectrum generated by vortex formation and shedding in the flow past the helicopter blade. In addition to the discrete frequency noises at harmonics of the blade passage frequency, superimposed on the broadband spectrum for helicopters is a rotational noise known as blade slap. This high amplitude periodic noise plus highly modulated vortex noise caused by fluctuating forces on the blade due to the cutting of one blade's tip vortices by another blade and transonic shock. Blade slap is a distinctive, low frequency throbbing sound which increases during certain descent, maneuvering and high-speed cruise operations...

 

Good lord...!!! :o

 

High speed (around 70kts in the robbie), shallow decents are the biggest culprit. Somewhere I have a blade slap chart for the R-22 that shows the airspeed / decent rate combinations that cause it. If I can find it I'll throw it up here for all.

 

- Fly Safe

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Blade Slap - The dominant noise produced by helicopters consists of a broadband spectrum generated by vortex formation and shedding in the flow past the helicopter blade. In addition to the discrete frequency noises at harmonics of the blade passage frequency, superimposed on the broadband spectrum for helicopters is a rotational noise known as blade slap. This high amplitude periodic noise plus highly modulated vortex noise caused by fluctuating forces on the blade due to the cutting of one blade's tip vortices by another blade and transonic shock. Blade slap is a distinctive, low frequency throbbing sound which increases during certain descent, maneuvering and high-speed cruise operations. :huh:

 

chppm-www.apgea.army.mil/dehe/ morenoise/noise_dictionary.aspx

 

Fly Safe

Clark B)

 

Clark,

 

Can I axe you to splane dat in detail?

 

LOL

Paul

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I am glad someone brought this up. It seems to have been explained in good detail. One should try to avoid conditions which lead to blade slap. This is a big reason for noise compliants and with a simple change in pitch angle or airspeed once getting it you can get out of it. I make it a habbit to teach my students when they encounter blade slap to make a change to get out of it. Some say they like it, but this is also why you can hear a huey from over 10 miles away. There is actualy an AC out there. I will try to dig it up and post the link. Food for thought.

 

JD

 

Found it.

 

http://rgl.faa.gov/Regulatory_and_Guidance...Highlight=blade slap

Edited by JDHelicopterPilot
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So you're saying that the blade tips are cutting through the vortice from the previous blade and transonic shock? As Spock would say, fascinating. It seem similar to the prop tips on a Stearman that break the sound barrier, no?

 

That does clear up the fog, so to speak.

 

Later

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That popping noise the blades make was unnerving when I first heard it. Now I really like the pops.

You're probably also the person that revs your Harley at the stoplights just for show! :D

I gotta' admit, I love the sound as well. I can't understand why all those unfortunate helicopter-pilot-wanna-be's on the ground don't like it too! ;)

 

WW

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You're probably also the person that revs your Harley at the stoplights just for show! :D

 

Actually, I ride a KLR. Need I say more?

 

Hey, I read that AC and I guess the blades do slap in that profile. It also has some neat info about noise abatement. I guess I'll have to teach my students to be quiet.

 

Later

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