Chinooks. Not exactly stealthy, are they?
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.
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).
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).
Avoid imitations
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,573
Received 422 Likes
on
222 Posts
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.
.I have to say I find the noise of passing 'executive' helicopters far more disturbing / irritating.
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.
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.
Chinook stealth ops!
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.
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.
Join Date: Oct 2006
Location: One Three Seven, Disco Heaven.
Age: 65
Posts: 2,538
Likes: 0
Received 34 Likes
on
17 Posts
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.
The following 4 users liked this post by Dan Gerous:
Join Date: Mar 2008
Location: Where ever the wind takes me
Posts: 65
Likes: 0
Received 2 Likes
on
1 Post
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.
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.
The following 2 users liked this post by andy148:
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 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.
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.
Have they made RAF Chinooks quieter?
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
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
The following 2 users liked this post by teeteringhead:
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.
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.
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.
I heard and saw a pair at 4.25am one morning and they too sounded remarkably quiet; that was several years ago.
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.
Whisper Mode, obviously. 
Spoiler
CH-47 quieter when loaded
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/publica...my_Helicopters
https://www.researchgate.net/publica...my_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