Chinooks. Not exactly stealthy, are they?

[C152_driver]

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?

[Lonewolf_50]

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.

[tartare]

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.

[iwanm]

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

[nowherespecial]

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.

[treadigraph]

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.)

[ShyTorque]

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.

[NutLoose]

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.



..

[chevvron]

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.

[Otterotor]

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

[inbalance]

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.
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.

[B Fraser]

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.

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.

[ShyTorque]

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...

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

[Thrust Augmentation]

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.

[meleagertoo]

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.

[Rigga]

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!

[Rigga]

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

[Rigga]

(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.)

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.

[chevvron]

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.

[chinook240]

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

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


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[pulse1]

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.

[havoc]

where’s Sasless?

[Thud_and_Blunder]

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.

[pax britanica]

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 -

[NutLoose]

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.

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

[pulse1]

But is there any helicopter that's quiet?

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

[treadigraph]

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.
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.

[chopper2004]

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 chinook anyone

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


https://theaviationist.com/wp-content/uploads/2011/05/mh-47x3.jpg


cheers

[inbalance]

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.

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[nevillestyke]

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.

[SASless]

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.

[ACW599]

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.

[tucumseh]

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


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.

[Thud_and_Blunder]

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.

[campbeex]

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.org-vbulletin/1024x679/img_8788_9dbe96f30596624812a2555a22bd82a1ad61af1a.jpeg
Is that an early version GoPro attached to the tail?

[OvertHawk]

The Huey is the Queen of racket making!
.

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!!!

[chevvron]

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-
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.

[tucumseh]

Wastelands (sorry, tuc, but after time on Lynx it's an opinion I hold strongly)

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.

[SLXOwft]

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.

[pulse1]

Originally posted by SLXOwft


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

[chevvron]

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 live just south of H3/the M3 motorway and they generally operate tuesdays most weeks plus occasionally wednesdays, 2300 eastbound and about an hour later going home.

[Shackman]

Whilst living surviving in a quarter at Odiham in early 1980, long before we ordered any Chinooks for ourselves, the quiet of the neighbourhood one Sunday was disturbed by a distant noise (which sounded initially to me like desynchronised piston engines). This noise got louder, and louder, until eventually some 15 minutes later the sky filled with formations of C-47s, UH1,s and other rotary assets passing in a stately fashion - certainly more helicopters in the air than we had on the ground. The !st Air Cav just letting us know they were around as they proceeded up to SPTA for an exercise. The noise was .........impressive. Some weeks later Mrs S and I were in the centre of Woking when I heard that (by now) distinctive noise of a Chinook somewhere up high. Eventually a lone Chinook up at 10000 ft or so appeared - almost 35 minutes later! Whereas one approaching at 100ft was almost overhead when you first heard it.

That taught me a lot about noise propagation from the aircraft for when I also started flying them. Go high, spread the noise around, go low and you can surprise a lot of troops (but frighten a lot of animals).

[ShyTorque]

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.

Might that be because you’re not in one?

[Good Vibs]

We used to joke in RVN with our Hueys that when the VC farmer could hear us he had time to dig out his SKS from his secret hiding place, clean it of its protective oil, test fire it and be waiting for us once he could see us.

But over the jungle with trees he could hear us but not be sure of our location so had very little time to aim and shoot.

[gopher01]

While stationed at RAF Abingdon we used to provide facilities for the SAS to practice hostage release using the airframes in storage there. First notice of this was the arrive of nondescript trucks and Range Rovers in our hangar with nondescript bods climbing out of said Range Rovers.
This was followed by lots of interesting gear being laid out on hangar floor and ladders being attached to the Range Rovers. The exercise then commenced with the Range Rovers approaching the airframe at speed with the SAS festooned around them to assault the airframe. Simultaneously an approach was made by a Chinook which hovered over the airframe to lower more SAS onto the aircraft. If the highjackers didn't realise what was going on by then they certainly did then as the target aircaft vibrated in the downwash and the sound echoed round Oxfordshire!!
Certainly not a stealth approach.
All very interesting to watch.

[Dan Gerous]

I had a heads up of a helicopter exercise at Charterhall in Aug 2016 and headed over to get some happy snaps. I arrived with plenty of time and around noon heard the distinctive sound of an approaching Chinook. However it wasn't till 20 minutes later a Puma pitched up without any warning, then a Sea King followed by a Merlin which disgorged some troops and then finally the Chinook which unloaded more troops. There was also Lynx flying top cover, and apart from the Chinook I couldn't hear any of the other helicopters until they were almost next to me . These landed and took of again and I was then treated to the sound of the Chinook being thrown around with gusto, which obscured to me by a large wood. The process was repeated in reverse with the sound of the Chinook disguisung the approach of the other helicopters. Again, until you could see them, you wouldn't have known they were there.

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[Good Vibs]

Beautiful machines they are. And fun to fly:)

[DogTailRed2]

The idea with a helicopter is you put it where the enemy isn't. If you put it where the enemy is then it's part of a package with aircraft suppressing the area.

[andy148]

There's no nicer sound than the freedom bird coming in to lift you home. Standing out the back of the Chinook in the frozen Arctic and getting defrosted while breathing in the exhaust fumes was bliss. But the whine of the turbines was a hearing killer; it just seemed to get through any hearing protection you wore.

Back in 07, in a place far, far away. We were due a resupply; as the ROZ controller, I advised the flight (Chinooks & AH) not to approach from the North as this would put them directly over a world of pain. Sure enough, we heard them and then saw them coming in from the North. Sure enough, we see tracer fire heading their way. And there goes the underslung load of all our food, water, and ammunition right into downtown 'Sh*tsville'. That night during the 'stand too', our interpreter started laughing while listening to the ICOM. He says the TB are eating our food and wondering how we can live on this sh*t.

[gsa]

I lived in a fairly remote cottage on the side of Wensleydale for about 20 years and got lots of air traffic passing night and day. As long as the Herc and Chinooks weren’t that high and fast we found them quite quiet, even multiples with few lights on sometimes sneaked up unannounced at night. But put them at 1000 feet and fast, you could hear them for ages. Not as bad as the F15s though, they were noisy.

[minigundiplomat]

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.

The sound is pretty hard to mask, but directionally it can be very difficult to pin down, particularly in undulating ground and of course, at fifty feet visual acquisition is often a late spot.

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 it's hats not the same.

That's a great book, by the way.........:D

[Dan Gerous]

Just ordered that book and look forward to reading it.

[Wee Weasley Welshman]

ZA714 flew over my house about seven minutes ago at what I estimate to be 200ft and 90kts. His mate flew in formation 10 seconds behind and to the left.

I was at the British shooting show last weekend and bought my first digital night scope which I was out playing with in the dark. I had a cracking view. Thing is for a pair of CH47's they were really quiet. It's a calm evening in wide open countryside but I only heard them about 30 seconds before they flew right over. Which seems unlikely! I have actually flown in Chinooks a couple of times in the 1990's. Tonight there was no wokka wokka audible from ten miles away...

Have they got different rotor blades or something these days?

it was pretty dark with a 30% moon and a misty night air and they were bloody low.


WWW



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[teeteringhead]

Or maybe your hearing is not what it was!!

[ETOPS]

was at the British shooting show last weekend

There's a clue :ok:​​​​​​​

[Video Mixdown]

ZA714 flew over my house about seven minutes ago at what I estimate to be 200ft and 90kts. His mate flew in formation 10 seconds behind and to the left.
I was at the British shooting show last weekend and bought my first digital night scope which I was out playing with in the dark. I had a cracking view. Thing is for a pair of CH47's they were really quiet. It's a calm evening in wide open countryside but I only heard them about 30 seconds before they flew right over. Which seems unlikely! I have actually flown in Chinooks a couple of times in the 1990's. Tonight there was no wokka wokka audible from ten miles away...
Have they got different rotor blades or something these days?
it was pretty dark with a 30% moon and a misty night air and they were bloody low.

They flew over my town and sounded pretty normal to me. Because of the unusual hour I looked them up on ADSB and it seems both rotary and fast jet were doing some night flying.

[chevvron]

See also 'Chinooks; Not exactly stealthy are they?' on this thread last posting 19 Feb 2024.
I heard and saw a pair at 4.25am one morning and they too sounded remarkably quiet; that was several years ago.

[beardy]

I was under the impression that variations in rotor noise were a function of speed and blade loading. I too heard them last night and yes they were less noisy than usual.

[Lonewolf_50]

Whisper Mode, obviously. :p
(For those who are not rotary wing aviators, see the movie Blue Thunder).



[Semreh]

I don't know how significant it is (the difference is about 5 dB at an airspeed of 130 knots), but CH-47s are quieter when loaded up.

https://www.researchgate.net/publication/235097773_Operational_Noise_Data_for_CH-47D_and_AH-64_Army_Helicopters

Except at the highest speeds, sound variation with speed is not a large factor. In terms of sound variation with load, the CH-47D actually made less sound during level flight at full load than it did lightly loaded, although the sound did increase with load during takeoff and landing. As with other aircraft, the CH-47D makes more sound during landing than it does during level flight or takeoff

[76fan]

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.
Yesterday afternoon I thought a nearby neighbour was using very noisy garden machinery until I realized the noise was constant and gradually getting louder. It was a considerable time before I at last saw a light helicopter flying directly towards me and as it passed overhead it looked like a Bell 206 LongRanger. A check on Flightradar 24 showed it to be G-RAZE, apparently a Bell 407 which was doing an clockwise trip around London and passed overhead at about 1500ft AGL and 130kts. It was by far the noisiest helicopter I have ever heard yet the LongRanger was such a smooth quiet aircraft albeit some15-20kts slower. I guess outside noise considerations come pretty low on the manufacturer's list.

(There is a short YouTube video of the same aircraft overflying Farnborough a year ago so I guess it's not just me)

Bell 407 Helicopter G-RAZE Flying over Farnborough - YouTube

[Dan Gerous]

We regularly get S-76 helicopters flying over us, G-ROON being a frequent visitor, but they never appear on ADSB. Talking of noise, on the odd occasion we get the HM Coastguard helicopters over this way and they are noisy, but I bet to anyone awaiting rescue it must sound like angels singing.

[Chock Puller]

The US Army conducted some tests to determine acoustic characteristics for the Chinook at several military bases.

https://www.chinook-helicopter.com/Technical_Reports/Operational_Noise_Data_for_UH-60A_and_CH-47C_Army_Helicopters.pdf

[Wee Weasley Welshman]

I can't help suspect they were modified in some way to be quiet. It was a still night and my hearing and eyes were attuned to the shooting conditions.

I felt and smelled the downwash. I would estimate I had 20 seconds notice of their overflight.

WWW

[Evalu8ter]

Nothing modified - the blades are the same. Boeing were trying to progress the composite ACRB (Advanced Chinook Rotor Blade) as part of the Block II CH-47F upgrade, and that may have different noise characteristics as they featured swept tips (to smooth airflow separation - they are similar in concept to the blades proposed for the RAH-66 IIRC). However, despite showing promising improvements in lift, it vibrated badly and has, last I heard, been shelved for now. Many moons ago at Odiham we were instructed to slow down to less than 120kts inside the MATZ to be 'good neighbours' as it reduced noise (albeit at the 'cost' of us being airborne longer…). AT 90kts, it's broadly min power speed so neither engine nor rotor/transmission system are under high loading, and at low level the footprint is appreciably smaller. Careful planning and the use of wind and topography can yield some very interesting results, and you can get surprisingly close sometimes (especially at 50ft) before you're heard - and as MGD noted earlier, reflected noise can also help to confuse an opponent.

[treadigraph]

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.
Four miles away would have been rather more audible and I would probably have seen them! During lockdown when there was virtually no traffic about and it really was quiet up on the common I could hear a Lynx following the Thames heli lane. In the right conditions, noise can reach sensitive ears a long way...

[DogTailRed2]

Just watched a Chinook going downhill at quite a rate of nots with a load slung under the rear of the aircraft.
Does the chinook have multiple load points underneath? Always thought they picked stuff up in the middle.

[PPRuNeUser0211]

Just watched a Chinook going downhill at quite a rate of nots with a load slung under the rear of the aircraft.
Does the chinook have multiple load points underneath? Always thought they picked stuff up in the middle.
3 hooks iirc, different points to allow for different CG combinations and attaching more than one load at a time I guess

[Thud_and_Blunder]

RAF PR image (https://www.raf.mod.uk/index.cfm/_api/asset/image/?filePath=/raf-beta/assets/Image/1117CA7E-8010-42F2-B160DC523FE10397-ODI-20190802-536-078.jpg)

Every RAF Chinook trainee aircrew - pilots and loadies - had to qualify on triple-USLs prior to finishing the OCU course. A favourite exercise was with the RA 105mm light gun, where you land to pick up the gun crew then lift to the hover and pick up the ammunition, the 1-tonne LR and the gun. I was surprised to learn that in the US Army at the time I was operating on type (1989-1997), carrying USLs was considered an advanced skill that was covered after pilots had started Sqn service; don't know if that was true.

[chinook240]

RAF PR image (https://www.raf.mod.uk/index.cfm/_api/asset/image/?filePath=/raf-beta/assets/Image/1117CA7E-8010-42F2-B160DC523FE10397-ODI-20190802-536-078.jpg)

Every RAF Chinook trainee aircrew - pilots and loadies - had to qualify on triple-USLs prior to finishing the OCU course. A favourite exercise was with the RA 105mm light gun, where you land to pick up the gun crew then lift to the hover and pick up the ammunition, the 1-tonne LR and the gun. I was surprised to learn that in the US Army at the time I was operating on type (1989-1997), carrying USLs was considered an advanced skill that was covered after pilots had started Sqn service; don't know if that was true.

T&B, I think you are correct, during GW1 we met US Army CH47 crews based in Italy that weren’t “sling load qualified” although it did make us wonder what they did if they didn’t trash haul like us!

[minigundiplomat]

T&B, I think you are correct, during GW1 we met US Army CH47 crews based in Italy that weren’t “sling load qualified” although it did make us wonder what they did if they didn’t trash haul like us!

They saved themselves from what seemed like an eternity dragging an underslung minidigger across West Falkland at 40kts in a 50Kt headwind.

[Mogwi]

They saved themselves from what seemed like an eternity dragging an underslung minidigger across West Falkland at 40kts in a 50Kt headwind.

Hmm, that would take an eternity! 😊

Mog

[Thud_and_Blunder]

Which is why we sat and played uckers remained at MPA fulfilling other important tasks on such days :E - the standby RADAR for the W Falkland sites was a particular pain.

Conversely, with an average wind we could lift off from W Falkland with a full ISO underneath at the same time as a Sea King lifted from North Arm (E Falkland, SW of the airfield) and be half-way through shutdown checks having deposited the load in the appropriate place before the SQ arrived in the hover at MPA.

[JohnDixson]

T&B-glad you brought up that sling training anomaly. Example: in 1963 all pilots being trained got sling training in the basic course ( H-19s or H-34s ).
In 1977-8 we trained the trainers at Ft Rucker ( the new Instructor Pilots for the UH-60 ) in slings. However on a trip down there over a year or two later, they had moved that training to the units. Maybe some senior IP can pass along the thinking associated with that move??