Aircraft noise levels
Glen
aircraft are lower than they used to be, and the that Concorde is noisier
than the average jet.
Anyone have more detailed numbers on different aircraft types?
How do today's jets compare to the DC8/707 era?
James Robinson
That's a bit difficult to answer, as much depends on how the noise is
measured, i.e. are they using the same measurement scale, how far away
from the aircraft are the measurements taken, and at what part of the
take-off sequence are the measurements taken, are there pure tones in
the sound spectrum? With external noise, it is easy to selectively use
measurements to prove one point or another.
Here is one approach that is used:
http://www.boeing.com/commercial/value/evphase_10.html
They look at the noise footprint for a take-off, to show that noise
exposure levels are decreasing for people living in the general area of
the airport.
The 727 would be a bit quieter than the earliest DC-8s and 707s, but not
by much. The Conway powered DC-8s were real window rattlers for those
lucky enough to feel them fly over.
Another example is at:
http://www.boeing.com/commercial/value/evquiet_9.html
You also have to recognize the source of this data, as they quote a
diesel train as 85 dBA at 200 feet, and compare it to an aircraft
measured 2 miles from the end of the runway. In the first place, a
typical diesel train is more like 70-75 dBA at 200 feet, and secondly,
the different distances make comparisons quite difficult. In any event,
you can get a general idea of the relative noise levels with exercising
a certain amount of healthy skepticism.
Here's an example of how airport noise charges are calculated. About
half way through the document there is a list of aircraft by noise
grouping, that should give you an idea of how they relatively compare.
C. Marin Faure
<na...@REMOVESPAMBLOCKsilcom.com> wrote:
> I have heard that takeoff and landing (external) noise levels generated by
> aircraft are lower than they used to be, and the that Concorde is noisier
> than the average jet.
All of that is true. Jet engines have been getting quieter with each new
generation of powerplants. The first 707s and DC-8s had pure jets, or at
best low-bypass fanjets. With the advent of high-bypass fanjets, noise
levels went down dramatically (along with emissions), and they continue to
do so. The Concord, which uses afterburners on its engines, is extremely
loud, much louder than even the first generation of commercial jet
transports. I don't know if the Concorde uses water injection during
takeoff, but if it does, that will make it louder still. I have stood
beside a runway at Heathrow with my film crew when the Concorde has taken
off directly in front of us. Even with ear protection, the noise is
extreme because you feel it inside as much as hear it. A B-52 has the
same noise characteristics, by the way.
The airframe and engine industries have been concerned about noise right
from the beginning. One of my favorite quotes is from Ed Wells,
considered to be the "best" Boeing engineer ever. In an interview in the
early 1980s, he told us that when Boeing and the engine manufacturers were
trying to reduce the takeoff noise of the 707, several nacelle and
tailpipe configurations were tried until they found one that reduced the
noise without reducing thrust. The engineers on the project were
jubilant, but Ed took another view. He said, "Some people looked at the
data and said, 'See how far we've come.' I looked at the data and said,
'See how far we have yet to go."
> Anyone have more detailed numbers on different aircraft types?
There are many ways to measure airplane noise. Airports use a footprint,
where microphones are placed at specific distances from the active
runways. The noise readings are used to calculate the desired noise
footprint, and the noise regulations at that airport are determined using
this system. The operators of any aircraft that exceed the parameters of
the noise footprint are fined each time the parameters are exceeded.
The airframe and engine manufacturers also measure noise, but again, there
are many different methods, depending on what kind of noise they're
investigating. Engine noise is not the only factor, by the way. Airframe
noise is also a significant contributor to airplane noise, particularly
during approach. The new 737, for example, as an all-new wing with a new
double-slotted flap in place of the earlier 737s' triple-slotted flap.
The double-slotted flap has reduced airframe noise considerably.
You can get specific airplane noise numbers from airport noise studies,
but you'll probably have to wade through a lot of data to find it. I
doubt the airframe and engine manufacturers would release specific data to
the general public.
C. Marin Faure
author, Flying A Floatplane
Conal Guan-Yow Ho
Faure at fau...@halcyon.com wrote on 2000-02-12 11:32 am:
> The first 707s and DC-8s had pure jets, or at
> best low-bypass fanjets. With the advent of high-bypass fanjets,
What's the difference between low-bypass and high-bypass fanjets?
--
Conal Ho
Graduate Student
Dept. of Anthropology
University of California, Santa Cruz
C. Marin Faure
<con...@cats.ucsc.edu> wrote:
> in article faurecm-1202...@blv-pm406-ip74.nwnexus.net, C. Marin
> Faure at fau...@halcyon.com wrote on 2000-02-12 11:32 am:
>
> > The first 707s and DC-8s had pure jets, or at
> > best low-bypass fanjets. With the advent of high-bypass fanjets,
>
>
> What's the difference between low-bypass and high-bypass fanjets?
Fanjets drive a large fan in front of the engine (the part you can see
turning). This fan, much like a propeller, produces thrust. So the total
thrust of the engine is the thrust from the fan plus the thrust from the
turbine engine itself. Some of the air off the fan is sent into the
engine, and the fan works as sort of the first stage of compression. The
rest of the air from the fan simply flows back through ducts alongside the
turbine housing and out the rear of the nacelle. The first fans were not
that large, and only a relatively small portion of the air off the fan
flowed back around the engine. This is a "low bypass" fanjet. As
turbines became more powerful and efficient, they could power larger fans,
and more air could be taken from the fan as pure thrust instead of being
sent into the engine. These are "high-bypass" fanjets. If you look at a
777 engine, for example, the fan, the dramtically large front end, is
actually MUCH larger in diameter than the turbine itself, which is behind
the fan inside the nacelle. Remove the fan and the C-ducts (the ducts
that direct the fan air back around the turbine casing) from a 777 engine,
and it's actually not all that large.
Incidentally, on most of the newest engines, the thrust reversers are
actually redirecting the air from the fan, not the exaust from the
turbine.
Conal Guan-Yow Ho
Faure at fau...@halcyon.com wrote on 2000-02-12 6:45 pm:
> In article <B4CB050E.10A41%con...@cats.ucsc.edu>, Conal Guan-Yow Ho
> <con...@cats.ucsc.edu> wrote:
>
>> in article faurecm-1202...@blv-pm406-ip74.nwnexus.net, C. Marin
>> Faure at fau...@halcyon.com wrote on 2000-02-12 11:32 am:
>>
>>> The first 707s and DC-8s had pure jets, or at
>>> best low-bypass fanjets. With the advent of high-bypass fanjets,
>>
>>
>> What's the difference between low-bypass and high-bypass fanjets?
>
> Fanjets drive a large fan in front of the engine (the part you can see
> turning). This fan, much like a propeller, produces thrust. So the total
Thanks for the explanation. It's much clearer now. :)
C
JF Mezei
> > turning). This fan, much like a propeller, produces thrust. So the total
For a high-bypass engine, when you look at the thrust generated by the non-jet
portion, does the heating and slight compression of the ducted fan contribute
significantly to the thrust or is that just a very marginal thing ?
ITRADE
C. Marin Faure <fau...@halcyon.com> wrote in article
<faurecm-1202...@blv-pm401-ip61.nwnexus.net>...
> In article <B4CB050E.10A41%con...@cats.ucsc.edu>, Conal Guan-Yow SNIP
> sent into the engine. These are "high-bypass" fanjets. If you look at a
> 777 engine, for example, the fan, the dramtically large front end, is
> actually MUCH larger in diameter than the turbine itself, which is behind
> the fan inside the nacelle. Remove the fan and the C-ducts (the ducts
> that direct the fan air back around the turbine casing) from a 777
engine,
> and it's actually not all that large.
>
Hell, from what I had seen, the entire diameter of one of those 777 engine
housings was about the diameter of the fuselage of a 737. BIG!
Rich
larry white
too... they`re humongous!!
Jens Lüke
"C. Marin Faure" schrieb:
> There are many ways to measure airplane noise. Airports use a footprint,
> where microphones are placed at specific distances from the active
> runways. The noise readings are used to calculate the desired noise
> footprint, and the noise regulations at that airport are determined using
> this system. The operators of any aircraft that exceed the parameters of
> the noise footprint are fined each time the parameters are exceeded.
In connection with the plans to extend Frankfurt airport (FRA), plans have
(re)surfaced to determine the airport charges for each aircraft according to the
noise actually produced during each individual landing and take-off at FRA. This
way, not only the type of aircraft and engines would factor into the airport
charges, but also the individual efforts of the crew to reduce noise by
maintaining the least noise producing flight path within the corridor assigned
to the aircraft.
The article in the German daily newspaper "Frankfurter Rundschau" I am referring
to states that this approach has been discussed before, but was not supported by
the German government, since it doesn't comply with current standard
international procedures. However, since the noise problem is the main obstacle
towards extending FRA, they are obviously willing to give this new approach
serious consideration now.
It will be interesting to see if this policy will actually be implemented.
Jens