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Old 12th Oct 2015, 19:43
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I have noticed a very distinct loud put put noise from this vietnam vet when it approaches you but once it has passed you that noise subsides. what's the science behind that then?
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Old 12th Oct 2015, 20:18
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There's a few Vietnam vets on this forum and they all make noises, some of them from both ends.

But in the case of the Huey, it's related to shockwave of the advancing blade tips as it comes towards you.
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Old 12th Oct 2015, 20:23
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When G-HUEY was doing the rounds we could make ourselves heard at about 10 miles from our destinaations!
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Old 12th Oct 2015, 23:25
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Good observation. Our local medical Bell 412 is exactly the same. You can lie in bed and hear it coming for miles, but once it's gone overhead the sound is gone fairly quickly. My observation is that is appears louder directly in front of it. When it's flying past and isn't approaching, it doesn't seem as loud.
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Old 12th Oct 2015, 23:30
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As the Huey was built in Texas I suppose it was bound to be Loud.....but as the old time Cowboy's used to say "It ain't bragging if you done it!".

The sound of the Huey is Iconic and once heard is never forgotten.

Redhill Tower always knew we were coming....long before we called on the Radio.

Huey 509 has rattled more than a few Wine Glasses at Heli-Tech and other Displays over the Years especially when flown in the "Not Fly Neighborly" Mode.
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Old 13th Oct 2015, 01:20
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Woka Woka

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Old 13th Oct 2015, 02:54
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Currently working our Huey on a job moving 4,000,000 lbs of dirt at the Port Chicago Naval Weapons Station. Google is your friend for the history buffs amongst you:

Port Chicago Explosion and Naval Mutiny

And YES...I am making LOTS of noise: Slow ROD high speed will do it.....

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Old 13th Oct 2015, 05:43
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Most 2 bladed systems are loud. The 222 is just as loud as the UH1 and the 430 is quiet close to the 412 in noise...
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Old 13th Oct 2015, 06:55
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A 206 flew over the other day and what I hear first is the buzz from the TR, and shortly after that the MR beat. Does 'disappear' quite quickly once past.
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Old 13th Oct 2015, 07:37
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On a good day over water you can hear one at about 25 nm.

The science - Christian Doppler in 1872
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Old 13th Oct 2015, 08:28
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I once saw a gaggle of over 600 of the things headed west into Never Never Land.....and some Army Colonel said something about we would surprise the Enemy.

Yes....he was a special kind of Stupid!

It reminded me of a scene out of the Wizard of Oz for some reason.
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Old 13th Oct 2015, 08:38
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What you are hearing is the advancing blade beating the air into submission.......
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Old 13th Oct 2015, 09:10
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Simple: Doppler shift

Simply put, with the aircraft advancing towards you, the sound you hear are pressure waves which are covering a shortening range and changing frequency and intensity, as it passes you the range is now increasing so the pressure waves of sound changes the frequency and intensity in the opposite sense.
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Old 13th Oct 2015, 16:39
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"Noise" is - I believe - defined as "unwanted sound".

I would never describe the sound made by a Huey as noise, except possibly in the case of SASless' "special" Colonel.

...and Rigga, I can't believe we ever tried drawing attention to ourselves in any unseemly manner e/r to Tractor Shows, Balloon Fiestas or the like
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Old 13th Oct 2015, 18:11
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Can get our 205 "loud " on a nice crisp -20c day. But you want really loud, 214ST......drillers on a job I was on wondered why HTSC 214 had 'Thunder Dawg' written on the nose. They soon figured it!!
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Old 13th Oct 2015, 22:06
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Not necessarily you T&B, but definately Rob over the flatlands of Cambridgshire on the way up to Coningsby.
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Old 14th Oct 2015, 08:21
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Not really only Doppler shift - the loud thumping 'wok wok' noise certainly sounds louder when it's coming at you, then as it passes overhead and heads away the tail rotor noise becomes more apparent and the 'wok' drops away relatively quickly compared to when it's approaching. It doesn't seem to be simply a pitch shift thing which would be explained by Doppler - I reckon it must also propagate more in the forward direction of flight. There's a doctoral thesis for someone - investigate Huey noise!

The Chinook makes a bloody loud thump too, but there's not the tail rotor buzz superimposed, so you can tell the difference before you see them.
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Old 14th Oct 2015, 13:39
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ISTR it is a function of Blade Vortex Interaction (BVI) - the same thing that causes blade slap on some helicopters when manoeuvring - where the advancing blade smacks into the vortex left behind by the previous blade.

I suspect the relatively low disc loading of such long, wide blades means the vortex dissipates slower (not spat down out of the way quickly).

It certainly becomes quite tiresome flying one - the constant thwack, thwack and the nodding caused by the blades passing over the cockpit doesn't make for a relaxed and noise-free flying environment.
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Old 14th Oct 2015, 13:57
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Crab.....which helicopter is it you find quiet and blade strobe free?

If you want noise....fly a Chinook sometime!

It is much like the C-130....louder inside than outside!
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Old 14th Oct 2015, 15:46
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All things are relative I suppose Sasless.

Fancy taking 2 large-bladed, noisy rotors and strapping them to the same fuselage......... genius
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