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Old 30th January 2013, 05:57 PM   #81
Checkmite
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Originally Posted by Biscuit View Post
It just occurred to me that "unknown jet noises" are just jet noises from an unknown location. They are still caused by jets.

Well, not necessarily. "Jet-like" noises might be a better description; from given distances, many things from vacuum cleaners to leaf-blowers to furnaces can make a similiar sound. That's what makes the mystery so difficult to solve - if only jets made that noise, then we could confidently pin the noise to jets no matter how far away the airport was. I've certainly heard many noises that I instantly identify as jet planes doing things that jet planes do; what sets this noise apart is that it doesn't sound like a jet plane doing things that jet planes do.

This looks like it might possibly have some pertinence to the discussion.
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Old 30th January 2013, 09:35 PM   #82
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Originally Posted by Dancing David View Post
I am assuming most of the noise comes from the rear of the engine, not the front. So a cartoid distribution from the rear, therefore on take off the planes engine are tilted downwards, and again I don't normally here engines noises, but flight paths vary.

If you look here you will see that on take off alot of the noise comes from fan exhaust and jet exhaust
http://www.nasa.gov/centers/glenn/about/fs03grc.html
If the noise comes from the rear of the engines (which makes sense), then it makes sense that if this is the cause of the noise I hear, I would hear it on takeoff (when the plane is flying directly away from my house).

I still don't think this explains it though, as I have a hard time believing that a plane receding into the distance would make a approximately constant noise for 10 minutes.
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Old 30th January 2013, 10:09 PM   #83
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Originally Posted by Aardvark422 View Post
I grew up 10-15 miles away from Norton Air Force Base in Southern California. We heard similar engine noises.
And the lunch whistle from the Santa Fe rail yard, too, I'll bet.
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Old 30th January 2013, 10:25 PM   #84
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Originally Posted by TjW View Post
And the lunch whistle from the Santa Fe rail yard, too, I'll bet.
Not quite, I lived south of the base, but did hear the trains through the canyon behind my house.
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Old 9th February 2013, 11:05 PM   #85
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Last night I had an interesting observation. While I was in bed, I heard noises that sounded similar (but not the same) to what I've been talking about. When I opened my window to listen, I didn't hear the same sound; what I heard was a whooshing sound sort of like constant wind which was softer then the sound with the window closed. I don't know the source of the whooshing sound--yesterday the area was hit with a big snowstorm so it could have been wind (although it didn't seem like there was a lot of wind) or it could have been the noise of distant snow plows (which were roaming the streets at the time).

There was a sharp contrast between the noise heard from inside and outside so much that when I cracked the window and put my ear near the crack I heard the noise as whooshing; if I put my ear a foot or two above the crack I heard the sound as roaring.

It is possible that this phenomenon can be responsible for some of the jet noises I hear, but not all of them. Last time I heard the jet noises I opened the window but the sound stayed the same.

It appears that a sound entering my house through the closed windows or walls can be radically changed.
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Old 10th February 2013, 01:04 AM   #86
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Sounds can be made to appear quite different just by turning your head. I know I've been kept awake at night by noises that were too loud for me to sleep, until I rolled over and the sounds became inaudible.

When I first noticed that as a kid, it was really weird. Now I just accept it as the way my world works.
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Old 12th February 2013, 10:28 AM   #87
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Maintenance engine runs.

Did someone already mention engine runs for maintenance. That could last for 10 minutes at high noise levels. Take-offs only last about 1 to 2 minutes at high thrust. The planes quickly climb away, at 250 KIAS to 10,000 feet, then accelerate to 300 to 320 KIAS and are gone.

Engine runs last for as long as they need to trim the engine for maintenance. Many maintenance facilities have hush houses so they can run engines as needed anytime and avoid excessive noise. They can move a plane to the hush house and run engines with less noise. Engines can be take off and run for maintenance too. Lots of noise.

http://atomictoasters.com/wp-content...terburnert.jpg
http://www.airlinebuzz.com/chickenwo...8_AB_stand.jpg
http://www.airport-suppliers.com/sup...obal_Aviation/
http://www.vitallinkinc.com/hush_houses.html

A 10 minute maintenance run would not be unusual. They would be at a high power setting.
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Old 13th February 2013, 11:25 AM   #88
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Originally Posted by beachnut View Post
Did someone already mention engine runs for maintenance. That could last for 10 minutes at high noise levels. Take-offs only last about 1 to 2 minutes at high thrust. The planes quickly climb away, at 250 KIAS to 10,000 feet, then accelerate to 300 to 320 KIAS and are gone.

Engine runs last for as long as they need to trim the engine for maintenance. Many maintenance facilities have hush houses so they can run engines as needed anytime and avoid excessive noise. They can move a plane to the hush house and run engines with less noise. Engines can be take off and run for maintenance too. Lots of noise.

http://atomictoasters.com/wp-content...terburnert.jpg
http://www.airlinebuzz.com/chickenwo...8_AB_stand.jpg
http://www.airport-suppliers.com/sup...obal_Aviation/
http://www.vitallinkinc.com/hush_houses.html

A 10 minute maintenance run would not be unusual. They would be at a high power setting.
The engine test explanation has already been offered, and seems like the best explanation to me.
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