Chinooks. Not exactly stealthy, are they?
 

Caveat: I know naaaathiing, this is a genuine question.

I was working in my garden office this afternoon when I heard *that* sound (not unusual in my area). I was due a break, so I wandered out and looked west. A *long* time later a Wokka hove into view at reasonably low level. It occurred to me that in a hostile environment I'd had enough notice to order a MANPAD on eBay with a pretty good chance of it showing up in time. Is it just me, or does these things announcing their arrival quite so well make them a little... vulnerable?

Stealth wasn't in their spec, so it wasn't designed for it. *shrugs*
Comanche was designed as Low Observable and was a LOT quieter than any other helicopter I've ever heard (or haven't heard) but that one went away 20 years ago.

Reminds me of the story about the RNZAF in their UH-1Hs chasing deer poachers in NZ's national parks.
The poachers were in 500s - and had ample time to disappear due to the Hueys being so audible from miles away.
That 50 foot of blade slap was something else.
And yet the one time I strapped into one of those side-facing seats on the transmission tunnel with the sliding side door open - the big Huey was surprisingly quiet to ride in.
Noise projected outwards I `spose...
Anyone ridden in the Chinook- are they also relatively quiet inside in flight compared to outside when heard from ground?
Have heard a few Aussie ones flying over here in Sydney and up in Townsville.
What struck me was that they weren't so much really loud, just had a very distinctive sound... unmistakeable.

There is no way on earth you could call a Chinook quiet inside!

minigundiplomat is well placed to answer this question but from my memory, the noise signature of a CH47 over the sea in still wind (ie as controlled as it gets) was assessed to be either 10nm or 15nm for planning purposes (ie at 10.1 or 15.1nm you would not hear anything). wind direction and speed can have a profound effect on the way the noise travels.

Mentioned over on "spotters forum" that on Tuesday morning I heard a distant and familiar whopping noise while walking through some local woodland and surmised Chinook - check on ADSB confirmed it was indeed (apparently there were actually two) some 15 miles away over Park Royal in West London, heading south towards the Thames heli lane. Even allowing for me being on the highest point in Croydon, reasonably divorced from traffic on a nearby main road with (had there been no trees) a clear line of sight and a favourable wind, I was quite astonished that the sound could carry across the bulk of London and all the ambient noise of a weekday morning.

(Always used to amuse me that on the reality Cop TV programmes when the Met Police's "India 99" EC-145 was being used for tracking suspects on foot, the voice over would breathlessly announce that "they have absolutely no idea the chopper is there!" Really? They must be :mad: deaf then as the EC-145s, (and the earlier AS-355s and Bell 222s) are very audible from miles away - having had the things orbiting my area in the wee hours on countless occasions, I'd be amazed if many locals were still asleep.)

Many years ago, when based at a certain not so secret helicopter base, our dog would bark, the room divider window panes would visibly begin to vibrate, a certain faint rumble would be heard, then shortly afterwards a Chinook would call up to rejoin the MATZ.

A Chinook in level flight is quieter the heavier it is.

I read somewhere in Vietnam that the UH-1's would approach on an angle so that it was hard to differentiate from which direction they were coming from, might be true but I do not know.



..

On my one Chinook ride, we had the rear door open thoughout and it wasn't too bad, mind you everybody was wearing headsets which would have muffled the noise a bit.
A few years ago (about 2016 I think) I was out in my back garden 'slugging' (unfortunately we've never been blessed with a resident hedgehog) at 4.25am and on H3, about half a mile north of me and about 2 miles east of Bagshot Mast a pair of wokkas ambled along westbound at about 1000ft and I was amazed how little noise they made in the otherwise dead calm of the dawn; somebody on here said it was a new design of rotor blade.

Bell's 214ST Flight Test.
 

Spring - Summer 1982: Three flight test 214ST aircraft located South of Bell's flight test facility in Arlington Texas, 18401, 18402, and 18403 were finishing up their morning's flight cards and joined up to return to the test center. As we approached the control tower gave us the 'knock-it-off' command as we had just cracked the tower's window! Ott

I doubt that you heard them from 15 miles.
You probably heard the other two chinooks, 4 miles away, with their transponders swiched to stby and not showing on ADSB.

Given the time of day, the sound could have been reflected upwards by a layer of cold air at ground level. The converse is also true in that I can hear traffic from many miles away on a cold and frosty morning. Once the sun gets to work, the sound disappears.

I’ve heard some excuses for bad navigation before but that’s a really good one! :p

Not that it needs to be stealthy, but the S-92 isn't much better for ~1/2 the weight & the A400M can clearly be hear at around 3 million miles away.

I recall being told that when the BV234s were being trialled in the Frozen North someone, scheduled for the next rotation, heard one coming and went outside to watch it land. He gave up and came inside fifteen minutes later frozen to the core - and it landed thirty minutes after that.

Travelling to a Coningsby Airshow in the late 1980s when their ATC contacted us and said they had audible but not visual with our UH-1H on a bright sunny day….we were some 12 miles away!

Some sideways action allows the ‘buzz’ of the Tail Rotor to shine forth!

While they were introduced to Lippitts Hill as ”the quietest in their class” to the local residents, EC145’s were a clattery cacophony on the ground and only slightly noisier than their predecessor AS355Ns. However, once in the air they were quite quiet - especially from below and surprisingly inaudible at observation distances using that nice 15x(?) camera/footstep thingy.

Still not as quiet as the Explorers used by some ambulance helicopters.

A US study into D model rotor noise, amongst other things.

https://apps.dtic.mil/sti/pdfs/ADA191059.pdf


https://cimg0.ibsrv.net/gimg/pprune....77a52e4430.png

I used to live on the Western edge of the Bournemouth Control Zone in a rural gap between two built up areas. We often had military helicopters flying through this gap, especially at night around 2300 and at low level with no lights. I am currently reading the book The Workhorse of Helmand and discovered that Chinooks there operate in pairs and I believe that the ones flying low over my house was one of a pair with only one lit up. Of course this increased the noise level and the awesome effect of a Chinook coming right over your house with no lights was impressive. The change in noise level as they passed over head seemed to increase the dramatic effect. I have now downsized to a place just over a mile away so I still hear them but its not the same.

With careful planning and the right offshore wind/ topography, we took a Chinook full of interesting people to a bay N of Saxa Vord and were told by the exercise DS that no-one heard us until we made our first turn after departure some 4 miles offshore. Conversely, if you really want to be noticed - perhaps, say, by the participants in a Mount Pleasant dining-in night who've 'forgotten' to invite anyone from 78 - descend at 4-600fpm/ 100kt aiming at a point just short of the target then pull up into a 30deg bank climbing turn approx 400m short so that you don't overfly any buildings. Lifts the cutlery off the table, apparently.

Never believed the Eurocopter publicity about their 'quiet' helis - the 135 was always more audible than the NOTAR MD902, particularly around the home base(s). I'm pretty sure that the latter's 5-blade head producing vortices that didn't interact with any kind of external fan was the reason.

Living for many years in Camberley ie between Wokka world at Odiham and London Chinooks were always scooting up and down the M3 and very noisy -I would have been mostly off to one side. But is there any helicopter that's quiet? Where I live now, there are occasional Apaches and Chinooks plus assorted smaller mil types , Merlins etc, on their way to the various military bases or Yeovil? and then there are private ones which can be heard miles and miles away .

I am old enough to remember Fairey Rotodyne-now that was noise , Ospreys are incredibly noisy and someone has mentioned the A400 whose strange musical tones are a regular occurrence as they head out from Brize towards the southwest, a lot more conspicuous than the Hercs which were close to inaudible until right overhead especiallyat low level -

A certain Austrailian, DW upon the first time we took the OCU Chinooks to Upavon on detachment, he came up the valley at the bottom of the airfield at low level and bar seeing the odd rotor blade peaking over the field, nothing but a dull thud, then he then did just that, did a banked climbing turn by the bighouse to announce our arrival. It didn't go down well :E

The Dorset Police used to operate a NOTAR helicopter which was very quiet. They now use a more conventional one which is quite noisy.

They are definitely not quiet when they are orbiting at 1000' in the immediate vicinity of your house at 3am!

The Kent Surrey & Sussex EC135 is also occasionally on task locally; it's much quieter while orbiting, bit of a hum and occasional blade slap.

stealth chinook anyone

https://theaviationist.com/2011/05/18/mh-47x/


https://theaviationist.com/wp-conten...05/mh-47x3.jpg


cheers

There has been a version of the Gazelle in 1983 with a built in whisper mode.
Cant see why they shouldn’t use this on an actual chinook.

https://cimg2.ibsrv.net/gimg/pprune....1ad61af1a.jpeg

Can be quite quiet.
 

I had one sneak up on me once and I never heard it coming. It came from behind a 500' ridge, on the down(fairly brisk)wind side, flying way below ridge height. As it got nearly on top of me, it pulled up very steeply, popping up from out of view with a sudden rush of noise and displaying the dark underside of the body, which blotted out the sky. It frightened the life out of me, then changed heading 180 degrees and flew off to the south until it disappeared over the horizon. I rather suspect that the pilot did this on purpose.

The Chinook is akin to the C-130….99% of the noise is kept inside!

The Huey is the Queen of racket making!

Once caused some wine glasses to tap dance off tables in a posh tented venue….and got asked for a Encore!

As to low level….rice straw on the cargo hook qualifies.

On the all too infrequent occasions a Merlin has visited EGOS Field 24 (hint) they've always struck me as very quiet for their size. It would be interesting to find out what causes the faint 'wisping' noise (for want of a better word) made as they set up the approach.

When asked why 25 pax had been put in ZD576 in 1994, MoD claimed it was because they wanted to discuss business en route.

Chinooks must have got louder since then.

Re the relatively-quiet Merlin, an ex-boss of a Puma Sqn who made Gp Capt while still in post once told us that in his time in Whitehall the subject of a new buy of Chinooks came up. After reading an MoD comparison of the merits of more Chinooks vs Wastelands (sorry, tuc, but after time on Lynx it's an opinion I hold strongly) Merlins the Minister was minded to go for the UK aircraft "as it was the quietest of the 2 contenders". Fortunately he was persuaded otherwise.

I never heard that claim from MoD about the requirement of the NI pax to discuss business en-route: farcical.

Is that an early version GoPro attached to the tail?

Many years ago i was on the ground at the south end of the Great Glen in Scotland awaiting the arrival of a Bristow Bell 214 to assist us in recovering one of our machines that had come to grief.

Cloud cover sitting on the tops of the mountains reflecting the sound.

We heard it coming.... It arrived 25 minutes later!!!

For a long period in the '90s, there was a vociferous noise complainer who lived in Camberley and complained about all fixed wing aircraft passing within about 5 nm and ignored Chinooks.
Mind you he had an ulterior motive which I'm not allowed to reveal on these pages.

No problem T&B. They never once let me down, but I know many who had different experiences. My experience of Lynx, apart from some avionics, ended 40 years ago. It had a poor reputation for some years because support was an afterthought. And the French instruments.... They had no concept of configuration control.

Odiham's finest fly over or near me a lot of the time. I agree they can be heard a long way off, but picking the actual track can be difficult (possibly due to reflection of buildings). I even find the infrequent 2300ish night flying quite soothing :).

I have to say I find the noise of passing 'executive' helicopters far more disturbing / irritating.

Originally posted by SLXOwft

Absolutely agree on this but I am surprised by the favourable comments on the Merlin. I live right in the centre of the procedure turn onto the ILS for 08 and this is often used by Merlins. I find the noise loud AND irritating while the Chinook is just loud.

However, none of them are as irritating as the noise from a Duchess in fine pitch which we used to hear a lot before the flying schools disappeared.
As far as Westlands is concerned, my experience is as a quality manager of one of their suppliers. For many years, all our work was done under our MoD approval and was no problem. However, after they built a helicopter under the Mod system they discovered that it was for a civilian customer and the CAA would not accept it, they insisted that everything we did had to be under our Westlands approval. This brought us under an auditor who had no technical or engineering experience and the small amount of work we had wasn't worth the agro.