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grimey
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Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 8:16 pm

I was standing out my back garden a few minutes ago when a Atlas Air B747-400 passed overhead at 39,000 feet. I thought I could hear a little sound in the air like jet engines but I cant think that you could hear an aircraft at cruise. Would sound go through the air at that altitude since it wouldn't be as dense?

By the way I live 7 miles away from DUB and I think I would have known if it was another aircraft landing / taking off.

Grimey
 
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scbriml
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 8:21 pm

Yes, planes at cruise are easily audible on the ground.
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Rj111
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 8:36 pm

Remember it takes about 30s for the noise to get from the plane to your ear at that height.
 
cobra27
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 8:51 pm

Quoting scbriml (Reply 1):
Yes, planes at cruise are easily audible on the ground.

Nope, it happened a lot of times, that I didn' t hear anything. And especially if it is a bizjet a 45000 feet
 
PlymSpotter
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 8:53 pm

Smaller aircraft and those without jets cannot be heard as easily. For example a Dash 8 at 20,000ft+ is barely audible, whilst a 747-400 at 40,000ft is still quite clearly heard as a low drone overhead.


Dan  
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MYT332
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 8:57 pm

Of course you can. Here we have a regular passenger airliner in flight which is heard seemingly rather loudly down on the ground.

http://www.youtube.com/watch?v=oMOyeuDKAlg
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brilondon
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 8:57 pm

It would also depend on the wind and humidity to be able to have the noise come down from above. There are also other noises canceling out the sound.
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gokmengs
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 9:04 pm

Quoting MYT332 (Reply 5):

LOL! Awesome. Thanks for the link. get ready for the correction/captain obvious squad 
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grimey
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 9:07 pm

Quoting MYT332 (Reply 5):

I seen that video before, I think I read somewhere that the woman on the boat is the captains wife. There was very little outside noise around me earlier that must be why I was able to hear the B744 fly over, usually there would be cars driving around or other planes flying around coming in and out of DUB

Grimey
 
timz
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 9:45 pm

Here in Oakland we often hear 747s overhead around FL300 en route LAX to the Orient-- no sensitive ears needed. You'd think they'd be at least as loud climbing out of 2000 ft altitude, 30000 horizontal feet away, but seems like they're not?
 
cf6ppe
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 10:51 pm

Although I live near a major airport, just last week when I picked up our newspaper about 6am, I heard a big transport overhead. When I got to a clearing in the trees, I watched it for a half minute or so - maybe 3 to 5 miles across the sky before local trucks/cars drowned out the cruising aircraft.

In the early '50's from home we used to watch the overhead aluminum overcast - i.e., B-36 bombers with the six big PW R4360 28 cylinder recips - droning away on its mission from Carswell AFB to a North Dakota AFB or on its return mission to Carswell. By the part of the mission we could see overhead, I think that the J47 jet defuelers had been shut down. Regardless, they were the biggest things that we had ever seen in the sky. Anyway, it was pretty easy to see and hear the big airplane in the quiet and cloudless farm country.

Oh' those memories....
 
MSPNWA
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 11:07 pm

If you're in an area without a lot of ambient noise (e.g. not in the middle of a city), it's not difficult to hear an airplane at cruise (or even descent) as long as its close to overhead. I'd say that, during the day, a plane within 10-15 horizontal miles of your location should be audible at cruise. The interesting part is trying to compare the sound you're hearing with the location and type of airplane you can see in the air, when you're able to do both. There's a huge difference between a 747 or 777 directly overhead versus an A320 or CRJ a little ways off. Engine types matter too. An old, noisy JT-8 on an MD will make quite a racket compared to a larger, newer turbofan on a 737.

Sometimes I'll be outside and immediately get a few tingles when I first hear a widebody I didn't know was coming. The distinct low rumble produced by large turbofans is impressive. You can just hear the power. But what's even more fun is being outside at nighttime. When I'm stargazing, it's amazing how much easier it is to hear an airplane, since the ambient noise is so low. My guess is that you can hear an airplane from double the distance compared to the daytime. A 747 rumble can be heard for minutes.
 
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 11:22 pm

80 miles out from SeaTac and guessing 6 miles away on horozontal axis we seldom can hear commercial airlines over ambient noise, a freeway about two miles away.
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PlymSpotter
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 11:23 pm

Quoting MSPNWA (Reply 11):
But what's even more fun is being outside at nighttime. When I'm stargazing, it's amazing how much easier it is to hear an airplane, since the ambient noise is so low. My guess is that you can hear an airplane from double the distance compared to the daytime. A 747 rumble can be heard for minutes.

Absoloutely right. I live in South west England and often go to bed very late; 4-5am sometimes if I've been stuck into work, and from my bed I can hear the dull rumble of aircraft heading East at cruise towards FRA, CDG, ZRH etc... even with the windows shut. It's not a noise which double glazing seems to keep out. It's only annoying because curiosity gets the better of me sometimes and I have to log on to RadarVirtual to find out what it was and where it was heading to. 


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daninafryingpan
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 11:50 pm

Quoting brilondon (Reply 6):
t would also depend on the wind and humidity to be able to have the noise come down from above.

I was thinking this too. I live a quarter mile from the nearest main road and on clear dry days the road noise is minimal whereas an overcast damp day the road noise would be very very loud. It was the same for my old workplace where there was a railway line a short distance away.

Aircraft at cruise can be heard quite loudly where I live in the Northwest of Northern Ireland as it seems to be a busy route for Transatlantic traffic to take and the low rumble can be heard quite often as they pass overhead.
 
timz
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RE: Can You Hear An Aircraft At Cruise?

Mon Jun 14, 2010 11:56 pm

Quoting MSPNWA (Reply 11):
I'd say that, during the day, a plane within 10-15 horizontal miles of your location should be audible at cruise.

But if it's 10-15 horizontal miles away, climbing out of 2000 ft altitude, you won't hear it-- right?
 
brilondon
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RE: Can You Hear An Aircraft At Cruise?

Tue Jun 15, 2010 1:24 am

Quoting MYT332 (Reply 5):
Of course you can. Here we have a regular passenger airliner in flight which is heard seemingly rather loudly down on the ground.

http://www.youtube.com/watch?v=oMOyeuDKAlg


Oh yeah, well that was neat. I forgot about that video. So yes you can hear airplanes at altitude on the ground.   
Rush forever Closer To My Heart
 
Fly2HMO
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RE: Can You Hear An Aircraft At Cruise?

Tue Jun 15, 2010 1:37 am

As has been said already, of course you can hear them, in the right conditions. I find that in the midst of a city I rarely hear them, but out in an open field or an isolated area you can hear most planes from the moment they're just before overhead of you to when they are 3/4 of the way to reaching the horizon. I find 747s to be the loudest. 777s with GE-90s are quiet but do make a pretty unique drone when cruising overhead. And you can hear the buzz of Dash 8s from pretty far away as well, since they cruise much lower.

[Edited 2010-06-14 18:39:05]
 
MSPNWA
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RE: Can You Hear An Aircraft At Cruise?

Tue Jun 15, 2010 1:51 am

Quoting timz (Reply 15):

But if it's 10-15 horizontal miles away, climbing out of 2000 ft altitude, you won't hear it-- right?

Yeah, you can be just a few miles away and not hear it climb out. Science can be strange.
 
Arrow
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RE: Can You Hear An Aircraft At Cruise?

Tue Jun 15, 2010 3:22 pm

I do a lot of hiking in an area about 200 km east of Vancouver -- on the major east-west flyway. In both directions, aircraft are at cruise, and they are plainly audible. Terrain is mountainous with valleys at 4000 ft, peaks up to 8500 feet. Often jet traffic is the only noise you hear on those trails.

One one hike, I watched a Martin Mars water bomber cruise through the valley almost at eye level. He couldn't have been more than 8000 ft, if that. I had no trouble hearing him.
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DocLightning
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RE: Can You Hear An Aircraft At Cruise?

Tue Jun 15, 2010 8:45 pm

Quoting MYT332 (Reply 5):
Of course you can. Here we have a regular passenger airliner in flight which is heard seemingly rather loudly down on the ground.

That is *NOT* a regular passenger airliner.

I have noticed that it's hard to hear aircraft cruising over SFO (for example, the flights out of LAX to Asia, or the UAL flight from ORD to HNL which passes directly over the city on the great circle route). But if I'm in Aspen at 7-10,000 feet visiting my brother, then I can hear them much more clearly.

That makes sense, of course. Decreasing my distance to the engines by 25-33% is going to make them louder.
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KELPkid
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RE: Can You Hear An Aircraft At Cruise?

Tue Jun 15, 2010 9:41 pm

I miss the good ol' days...all those 707's, DC-8's, DC-9's, (non-hushkitted) 727's, and 737-200's flying over the ELP and EWM vortacs, and yes, you could hear them down at ground level easily   Military aircraft are easy to hear at ground level, too...
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soon7x7
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RE: Can You Hear An Aircraft At Cruise?

Wed Jun 16, 2010 12:38 am

Here on Long Island at sea level you can clearly hear them and also the converse is true...sort of...While flying a sailplane out east at 5,000 feet I could clearly hear the horn of the Long Island railroad train below. I was in a Scwheizer 2-32 and is not as quiet as a Grob or other comparable ship.
 
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KPDX
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RE: Can You Hear An Aircraft At Cruise?

Wed Jun 16, 2010 1:59 am

Heres a nice (and cool) example:

AN-225 at cruising alt http://www.youtube.com/watch?v=twkaRK74vqQ
 
access-air
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RE: Can You Hear An Aircraft At Cruise?

Fri Jul 09, 2010 8:18 pm

Quoting MSPNWA (Reply 11):
But what's even more fun is being outside at nighttime. When I'm stargazing, it's amazing how much easier it is to hear an airplane, since the ambient noise is so low.

I too have noticed that at night or early in the morning you can hear lots of things that during the heat of the day you dont seem to...
You also have to remember that the engines are not the only thing ona plane that makes the noise....
Ever have an airliner land over top of you and after its passed you can hear the swirling sounds if air from the wingtip vortex? Imagine that noise amped up to cruise speed on a plane...in addition to the engine noise...

Ive noticed that the only two loud airplanes that I can really hear overhead any more are an MD-80 and a 777.....It seems that the shockwave created by the 777s wings is sharper or something...

Prop planes especially at night are interesting to hear...
For a long time every Monday thru Thursday between 110am-120am a turboprop plane would fly over enroute supposedly from Chicago going West. Sometimes upon hearing itd, I quickly go outside to see if...I had thought that it was a Metroliner II, just by the sound of the Garrett turboprops....Well, I was close as my investigations would reveal that it was actually a cargo carrier flying an MU-2 flying from Midway over to Des Moines.....This was consistant since I first noticed this in 1992 until just recently...I dont ever hear it anymore..Perhaps the company has gone out of business.....
At cruise I can usually tell the difference between a Garrett TP and a PT6.....but of course actually seeing the plane, especially if its daytime helps... 

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bri2k1
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RE: Can You Hear An Aircraft At Cruise?

Sat Jul 10, 2010 2:56 pm

The exhaust noise from the engines, much like the wake vortices from the wingtips, propagates in a somewhat conical shape from the rear of each engine. Wind can affect the speed and direction that it propagates, too, and the winds at the surface are almost always different from winds at cruise and even climb altitudes. All these things combine to make the time you actually hear the sound different from what you might expect based on seeing the aircraft.

Quoting timz (Reply 15):
But if it's 10-15 horizontal miles away, climbing out of 2000 ft altitude, you won't hear it-- right?

I can't agree with that. You would always hear it, if the conditions were right. I don't know where you could be in Oakland at any time of day or night that you couldn't hear the traffic noise from at least 2 or 3 freeways. My guess is that ambient noise is just obscuring the noise from the jets. I've been in quiet areas, like Syracuse NY early in the morning, about 10 miles from the airport and can clearly hear the compressor stages first, followed by the exhaust noise, even on relatively quiet RJs as they climb out.
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timz
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RE: Can You Hear An Aircraft At Cruise?

Sat Jul 10, 2010 9:23 pm

Quoting bri2k1 (Reply 25):
Quoting timz (Reply 15):
But if it's 10-15 horizontal miles away, climbing out of 2000 ft altitude, you won't hear it-- right?

You would always hear it, if the conditions were right.

So you think if conditions are right you can stand on Telegraph Hill in San Francisco and hear departures from SFO and OAK as they leave the ground, if not before?

(Looks like the west end of DEN rwy 25 is just under 15 statute miles from the I-25/I-70 interchange. Think there's a chance?)

[Edited 2010-07-10 14:29:46]
 
bri2k1
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RE: Can You Hear An Aircraft At Cruise?

Sat Jul 10, 2010 11:29 pm

Quoting timz (Reply 26):

Yes, absolutely. It's just propagation of sound waves. Just because you haven't been able to hear them doesn't mean they're not making sound. ANR headsets work by creating sound waves equal and opposite to those in the environment; the traffic, waves in the bay, wind, etc. is creating a cacophony of random sounds, some of which are cancelling the sound waves from those takeoffs just like what happens inside those headsets.
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timz
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RE: Can You Hear An Aircraft At Cruise?

Sat Jul 10, 2010 11:49 pm

Quoting bri2k1 (Reply 27):
Just because you haven't been able to hear them doesn't mean they're not making sound.

Yes, we agree they're making noise-- just not enough noise to be audible 15 horizontal miles away (unless conditions are right, which they roughly never are).

Can you hear DEN tower on your scanner from 15 miles away, so you can tell when an aircraft is departing from a runway you've chosen? Is it usually clear enough you can see the aircraft just after takeoff? If so, pick a spot 15 miles from the end of a runway and try it.

(Next question to wonder about: how much difference does it make whether you're in line with the runway or 15 miles left/right of it.)
 
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DocLightning
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RE: Can You Hear An Aircraft At Cruise?

Sun Jul 11, 2010 1:58 am

Quoting MSPNWA (Reply 11):
An old, noisy JT-8 on an MD will make quite a racket compared to a larger, newer turbofan on a 737.

Back in the '80's, living anywhere within 50 miles of DTW was a noisy prospect with all the DC-9's and 727's around.
-Doc Lightning-

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hangarrat
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RE: Can You Hear An Aircraft At Cruise?

Sun Jul 11, 2010 4:12 am

Quoting DocLightning (Reply 29):

I think that's a safe statement for any major airport.

When I was a kid, I lived about seven miles off the end of the 9s at PHL, and when the weather was bad, the air was humid and the wind was blowing toward my house, the takeoffs and reverse thrust on landing would keep me up at night.

That was back when USAir was sitll using BAC One-elevens and I'm sure a lot of the cargo operators were using low-bypass DC-8s and unhushed 727s.

I can still remember the way the storm windows would rattle.
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DocLightning
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RE: Can You Hear An Aircraft At Cruise?

Sun Jul 11, 2010 5:25 am

Quoting HangarRat (Reply 30):

I can still remember the way the storm windows would rattle.

An aircraft going over used to sound like thunder. Today it sounds like a light hum.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
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dxing
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RE: Can You Hear An Aircraft At Cruise?

Sun Jul 11, 2010 9:50 am

Quoting MYT332 (Reply 5):
Of course you can. Here we have a regular passenger airliner in flight which is heard seemingly rather loudly down on the ground.

Sure that's not just one of those phantom trains passing by??   

Whether or not you are going to hear it is totally dependent on three things, whether there is a major wind shift between you and the aircraft, ambient noise, and your hearing.
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access-air
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RE: Can You Hear An Aircraft At Cruise?

Wed Jul 14, 2010 4:09 pm

Quoting HangarRat (Reply 30):
When I was a kid, I lived about seven miles off the end of the 9s at PHL, and when the weather was bad, the air was humid and the wind was blowing toward my house, the takeoffs and reverse thrust on landing would keep me up at night.

That was back when USAir was sitll using BAC One-elevens and I'm sure a lot of the cargo operators were using low-bypass DC-8s and unhushed 727s.

I can still remember the way the storm windows would rattle.

Something that I would have loved!!!!!!!!!!!!!!!!!!!!!
Especially those BACs!!!!!

Access-Air
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vikkyvik
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RE: Can You Hear An Aircraft At Cruise?

Wed Jul 14, 2010 6:45 pm

Quoting Access-Air (Reply 24):
Ever have an airliner land over top of you and after its passed you can hear the swirling sounds if air from the wingtip vortex? Imagine that noise amped up to cruise speed on a plane...in addition to the engine noise...

Wingtip vortices are actually probably stronger at landing than at cruise. Their strength (and your related induced drag) is a function of the lift coefficient you're generating. At landing, since you're at slower speeds, your Cl will be higher, and vortices stronger (due to flaps, your wing area will also be higher, which would reduce the strength of the vortices, but I doubt that cancels out the increased Cl).

That said, at high speeds, the noise from the air friction will be louder.

Quoting Access-Air (Reply 24):
Ive noticed that the only two loud airplanes that I can really hear overhead any more are an MD-80 and a 777.....It seems that the shockwave created by the 777s wings is sharper or something...

I don't think you should be able to hear the shockwave from the local supersonic flow over the wings, as the shock would terminate at whatever distance from the wing the supersonic flow terminates.
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