Heli noise footprint
Thread Starter
Senis Semper Fidelis
Joined: Feb 2001
Posts: 1,288
Likes: 0
From: Lancashire U K
Heli noise footprint
Hi Rotorheads,
In the area that I operate from we are blessed, to be able to see a lot of o/head traffic covering nearly every Heli that op in the UK, so far as my little test have turned out the 109 Power and the 500D have by far he greater footprint of any that I see, in fact the 109 Power seems to be the outright winner, its noise signature and prop beat can be heard on average for at least 10 miles, by comparison the Twin squirrels hardly ever put out a prop beat but a very noisy gearbox , that seem to anounce itself at about 6/7 miles, The Gazelles again have hardly any prop noise but that high pitched gearbox noise but only announce themselves at about 2 miles, now my little observations are only done by using local knowledge of land, and being able to recognise the Helis involved, my question is< are there any limitations to noise footprint( apart from the Noise regs in Dbls) and do other people find particular Helis noisy as well, and, is the prop beat avoidable, by easing back a little on the power ?
In the area that I operate from we are blessed, to be able to see a lot of o/head traffic covering nearly every Heli that op in the UK, so far as my little test have turned out the 109 Power and the 500D have by far he greater footprint of any that I see, in fact the 109 Power seems to be the outright winner, its noise signature and prop beat can be heard on average for at least 10 miles, by comparison the Twin squirrels hardly ever put out a prop beat but a very noisy gearbox , that seem to anounce itself at about 6/7 miles, The Gazelles again have hardly any prop noise but that high pitched gearbox noise but only announce themselves at about 2 miles, now my little observations are only done by using local knowledge of land, and being able to recognise the Helis involved, my question is< are there any limitations to noise footprint( apart from the Noise regs in Dbls) and do other people find particular Helis noisy as well, and, is the prop beat avoidable, by easing back a little on the power ?
Iconoclast
Joined: Sep 2000
Posts: 2,132
Likes: 0
From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
In the early 1970s Hughes helicopter was given a contract by DARPA (Defense Research Agency). They were to develop a silent helicopter. They started out by designing a dynamometer that would be capable of simulating the loads generated by the main rotor, the tail rotor and the engine. They placed a model 500 on the dynamometer and ran it as a normal helicopter. They took sound readings on several hundred points to see how the mechanical sounds were transmitted through the structure and broadcast to the surrounding environment. They also took sound readings of the engine, the main and tail rotors and the respective elements of the drive train. They then hooked the 500 up to the dynamometer and removed the main rotor. This was followed by the tail rotor being removed and the main rotor being reinstalled. This test was followed up by the engine being disconnected from the drive train and connected to the dynamometer. Once all of the sound generating points and the broadcast points (vibrating skins) were identified and quantified they went about installing insulation, a muffler on the engine, a five blade main rotor and an X tail rotor and placed the helicopter on the dynamometer and re-ran the tests modifying as they went along to decrease sound generation. When they were satisfied they flew the helicopter and it could fly 4-500 feet overhead and all you could hear was a muffled whoosh. Most of us at Hughes felt that this for some special ops in Vietnam. The helicopter was shipped out and we never saw it again.
Guest
Posts: n/a
Haven't head many powers , surprised at the 500 though always thought they were pretty quiet. To me the all time most annoying noise is a 407 going full bore , thankfully the ones flying over the falls seldom approach VNE but when I hear em ferrying people to Toronto I have a good 10 minutes warning of their approach. ( must be about 30 miles at VNE ).
Iconoclast
Joined: Sep 2000
Posts: 2,132
Likes: 0
From: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
When I lived in Tehran back in 1975-76 my apartment was situated very high on a hill about ten to twelve miles from Mehrabad the main airport. There was a difference in about 2-3000 feet in elevation between my apartment and the airport. We were on the main flight path between the Shahs’ flight and the palace. Any time a 205 or a 206 lifted off more than fifty feet and started heading for the palace you could hear it coming. It absolutely amazes me that they didn’t lose more of these helicopters during the Vietnam conflict because of the telegraphing of the helicopters’ rotor noise. The CH-47 is just as bad.
Joined: Apr 2001
Posts: 64
Likes: 0
From: Hartford, Connecticut, USA
Has anyone else noticed the schreeching noise from the 365s? I have actually only heard one, the schreeching sounded louder than the rotors and engine. is this the fenestron or what? thanks in advance.
Joined: Aug 1999
Aviation Qualifications: ATP+Mil
Posts: 4,411
Likes: 83
From: Gold Coast, Australia
On the subject of the 365C and it's fenestron, try living next to a hangar full of them 
The first 365N for the Vic PAW is now test flying, and sounds more like a lawn mower on steroids, but it's a delight after the deafening shriek of the C model.
On the original question, there is an ICAO noise compliance that has to be met for C of R, and this is now being used to limit movements for some helicopter types in Helipad planning and approval. Before it was canned by the current State Gummint, the proposed (and approved by the previous political incumbents) Sydney Heliport at Darling Harbour was limited in movements based on noise factors, with an Agusta A109 landing having a factor equivalent to nearly three JetRanger landings. And charged accordingly!!
The first 365N for the Vic PAW is now test flying, and sounds more like a lawn mower on steroids, but it's a delight after the deafening shriek of the C model.On the original question, there is an ICAO noise compliance that has to be met for C of R, and this is now being used to limit movements for some helicopter types in Helipad planning and approval. Before it was canned by the current State Gummint, the proposed (and approved by the previous political incumbents) Sydney Heliport at Darling Harbour was limited in movements based on noise factors, with an Agusta A109 landing having a factor equivalent to nearly three JetRanger landings. And charged accordingly!!
Thread Starter
Senis Semper Fidelis
Joined: Feb 2001
Posts: 1,288
Likes: 0
From: Lancashire U K
Good Morning Lu,
Just recently(last three days) our daily UK newspapers have made reference to super silent or stealth Helicopters being using in Bin Liner country. Possibly a development from your 500 story!
Just recently(last three days) our daily UK newspapers have made reference to super silent or stealth Helicopters being using in Bin Liner country. Possibly a development from your 500 story!
