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HUEY UH-1H NOISE
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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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. |
When G-HUEY was doing the rounds we could make ourselves heard at about 10 miles from our destinaations!
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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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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. |
Woka Woka
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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..... http://i76.photobucket.com/albums/j3...psgqczve7y.jpg http://i76.photobucket.com/albums/j3...pste6knib6.jpg http://i76.photobucket.com/albums/j3...ps3vvtsmpd.jpg |
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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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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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. |
What you are hearing is the advancing blade beating the air into submission.......
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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. |
"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 :E |
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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Not necessarily you T&B, but definately Rob over the flatlands of Cambridgshire on the way up to Coningsby.
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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. |
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. |
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! |
All things are relative I suppose Sasless.
Fancy taking 2 large-bladed, noisy rotors and strapping them to the same fuselage......... genius;) |
and the nodding caused by the blades passing over the cockpit I'd guess a decently balanced and correctly tracking 2 bladed rotor should not infere more mechnical vibration to the fuselage than any other number of blades. |
I think the blade passing frequency as the downwash impacts the cockpit roof is a quite well-documented source of vibration and noise - well tracked or not.
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The Chinook had a tendency to cause Flicker Vertigo with the right sun direction beaming down through the Forward Rotor System and reflecting off the Attitude Indicator.
Flicker vertigo, sometimes called the Bucha effect, is "an imbalance in brain-cell activity caused by exposure to low-frequency flickering (or flashing) of a relatively bright light."[1] It is a disorientation-, vertigo-, and nausea-inducing effect of a strobe light flashing at 1 Hz to 20 Hz, approximately the frequency of human brainwaves.[2][3] The effects are similar to seizures caused by epilepsy (in particular photosensitive epilepsy), but are not restricted to people with histories of epilepsy. This phenomenon has been observed during helicopter flight; a Dr. Bucha identified the phenomenon in the 1950s when called upon to investigate a series of similar and unexplained helicopter crashes. Flicker vertigo in a helicopter occurs when the pilot or front passenger looks up through the blades of the main rotor as it turns in the sun causing the light to strobe. The strobe light effect causes persons who are vulnerable to flicker vertigo to become disoriented, lose control of the aircraft or have a seizure. A similar situation can occur in fixed wing flight whenever flickering light conditions exist. An example would be looking through a slowly spinning propeller while the airplane is landing facing the sun.[4] According to The US Naval Flight Surgeons Manual, flicker vertigo is a rare occurrence.[5] Flicker vertigo has been considered as a principle for various forms of non-lethal weapon.[6][7] A related crowd-control device was invented by Charles Bovill, which "employed a combination of ultra-sonic waves and strobe lights to induce acute discomfort, sickness, disorientation and sometimes epilepsy."[8] |
crab@, may I surmise that you don't have a lot of time in the 205/212 series?
For most of us it's the Mack truck of the skies, and should have a Mack bulldog on the nose ;) Cockpit blade noise is purely a background issue since most of the work done is of a short range/aerial work type. I managed to throw water at the ground again yesterday and hit it every time; any blade noise was only noticed when a bit of 'fly neighbourly' was called for :ok: Flicker vertigo is neatly negated by having a sunshade in the overhead...... cue howls of outrage for reducing vision, etc, from those who don't flog around in 35C+ :p |
Have to agree John, although i have friends who say it would be the Peterbuilt of the sky...
Busy in OZ yet? or just a normal start to the fire season? |
crab@, may I surmise that you don't have a lot of time in the 205/212 series? Flicker vertigo/flicker epilepsy is also well documented on some French roads where the spacing of the trees causes the low sun to flash at exactly the right frequency if you are driving around the speed limit. ISTR it was one of the things covered in initial aircrew medicals for the British Military - they wired you up to an EEG and then flashed strobes at you to see if it triggered a fit. |
Indeed, the same test is part of the medical for a Netherlands commercial licence. Mind you, their medical takes a whole day from specialist to specialist; no doubt the CAA are the same these days?
Whilst we've danced around the UH1/205 series blades for unique noise, for sheer decibels the 214B on the fireline doesn't need a siren prior to a drop :cool: |
Come on guys!!!
It's not NOISE, it's .....the sound of FREEDOM! Wock! wock! wock! or in an Agusta-Bell, Wop! wop! wop! The best noise complaint generated was from a B222 in a high hover over North Sydney back in 1985 when on trials for the Polair boys- apparently the police switchboard lit up like a Xmas tree, and Base called us to ask what the heck we were doing to make so many people ring up? The answer was simply - hovering. And then when I got back to base, a bird decided to commit suicide by dividing itself on the angled tip of the blade. A Cocka-one became a cocka-two. More feathers and guts than you could poke a stick at, and a really strange POP! sound. |
or in an Agusta-Bell, Wop! wop! wop! |
If Memory serves me right....the 412 requires an overhead shade for IFR flight. Not that we ever did but I do recall a Warning or Caution Note to that effect.
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214ST
In '80 or '81 three 214 ST's, 18401, 18402, 18403 joined up in return flight to Arlington airport from morning's data flights. (Development flights pre-production 214ST) I was FTE onboard 18403, broke the control tower's glass. We were at medium GW but the other two A/C were both heavy at the time.:=
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Here are 2 more, one from a B214B in winter and the other from a B205 at altitude
JD B214B B205 |
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