Sound in planes

Discussion in 'Your Questions' started by Evan, Mar 25, 2007.

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  1. Evan

    Evan Established Member

    Dec 26, 2006
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    Thought this may be a good question for NM, something to do while you visiting KUL.
    Anybody have any infomation (Searched but could not find) what the sound is inside some typical models or maybe even the frequencies that are most prominant.

    Just got me wondering, because i know i like 330's because they are quiet but some people hate them due to the different sound and almost pulseing sound you get.

    I noticed the WT+ seat o was in from LHR-SIN a week ago was rather quiet, but rather warm ! I know air con / air flow is responsible for a large amount of sound, any relationship do you think ?

    Incidently i slept 7 to 8 hours straight on that flight , could have been the quality beverages i was consuming in the BA lounge beforehand :)

    Evan
     

  2. Keith009

    Keith009 Established Member

    Mar 6, 2005
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    I noticed 330s and 340s are quiet but have a rather high pitched sound from the engines upon take off. On the whole they're more pleasant than the boeings, sound(noise?)-wise that is. Hard to beat the upper deck of a 744 though. :D
     
  3. oz_mark

    oz_mark Enthusiast

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    The A330's also have quite a pronounced drop in volume just after take-off.

    I am going to have to listen out for this as I have not noticed it. After that it will probably annoy me :)
     
  4. NM

    NM
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    There are plenty of people here finding me plenty to keep me busy, thanks very much :p
    I doubt there is much correlation between the temperature and the amount of air flow. BA just set the temp higher than most other airlines. But I think you are correct in assuming that airflow is related to sound. For example, many QF aircraft models have personal air vents over each seat , while other airlines (such as BA) do not have these vents but use larger long grills along the overhead lockers. The air flow through the restricted personal nozzles does create more noise than the same amount of air flowing through the less restrictive grills.

    Perhaps I will remember to pack my SPL meter and spectrum analyser with me for a future trip.
     
  5. Evan

    Evan Established Member

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    The BA flight was so warm i felt a little uncomfortable until a little while into the flight, and no blanket required to sleep.
    Its a pity they couldn't chill it down on entry and take off them warm it up a little later in the flight when your relaxed.

    Regardless of personal airvents or not i like fresh air. And i really notice down the back of some planes the air is really not very good, am i imagining it or is it really like that ?

    I like the A330's the most, 747's seem to be all different, also depends on the engine config, you can hear the different between GE, RR, P&W used by different airlines.

    NM, Hope your trip is good, i am home for 2 weeks after my 4 or 5 weeks of travel, arrived this morning.

    E
     
  6. NM

    NM
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    No, you are not immagining it. Aircraft used to have more fresh air intake when they allowed smoking on-board. Now that smoking is not permitted on aircraft, the operators have found they can use more recycled air and less fresh air. This requires less power for the air conditioning systems and hence less fuel burn. The downside is less fresh air for the passengers.

    Its important to note that even when cruising at 36,000 feet with an outside air temp of say -50 degrees, the air still must be cooled when its fed into the cabin. This is because the process of compressing the fresh air to get it to the cabin pressure raises the temperature of the air to above the cabin temp.
     
  7. JohnK

    JohnK Veteran Member

    Mar 22, 2005
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    That explains it. I struggle to breathe properly when I feel there isn't enough fresh air.
     
  8. I have flown on some large Airbus models that don't have individual vents for every seat - is this an Airbus standard? Poor air quality inflight is one of the few things I actually complain about; and continue to complain about; until it is rectified to my satisfaction. The FA's are usually happy to call the flight deck to see what can be done (if only to shut me up).
     
  9. Soundguy

    Soundguy Member

    Jun 15, 2006
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    The airvents could easily be redesigned to significantly lower the airflow noise; noise control doesn't even seem to have been a considered factor in the typical aircraft ventillation systems.

    But my biggest complaint about the air is that it is extremely dry - like ulta dehumidified. It is most unnatural and really dries you out. I heard the new Boeings have tackled this problem & rehumidify the air, looking forward to seeing them. They excite me more than the big Airbus monstrosity.
     
  10. SeaWolf

    SeaWolf Active Member

    Jan 24, 2007
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    I'd agree Soundguy, I always find that I dry out on planes quite quickly and need to make a fine balance in my water consumption so that I don't dry out, but don't need to be constantly getting up to go to the toilet.
    This is probably going to get harder with the new restrictions on taking liquids onto international flights. I can't just walk on with my big bottle of water anymore.
     
  11. straitman

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    If you fly a Boeing at the same speed as an Airbus the overall noise would also be quieter. Remember that the Airbus family travel approx 10% slower than the Boeing family. :cool:
     
  12. tuapekastar

    tuapekastar Established Member

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    Just on this topic, is there anything preventing one from taking an empty water bottle through security in your hand luggage, then simply filling it from a tap in the bathroom prior to boarding?
     
  13. SeaWolf

    SeaWolf Active Member

    Jan 24, 2007
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    You know what, that's an excellent idea. The only catch is that it might attract unwanted attention from security thinking you're somehow trying to get around the rules, or questions on arrival as to how the liquids got through departure, but still, certainly worth a try.
     
  14. Dave Noble

    Dave Noble Senior Member

    Oct 10, 2005
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    My understanding was that , as per UK, the issue relates to what liquids can be taken through security, not what can be taken on the plane , so no reason for them to be concerned

    Dave
     
  15. Keith009

    Keith009 Established Member

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    Cool... Hm I know nothing about the technical intricacies of aviation unfortunately. So this thread is definitely interesting.
     
  16. oz_mark

    oz_mark Enthusiast

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    ..but would they be as quiet as an Airbus? I have never heard that the interior noise of a plane was so dependant on the speed of the plane.
     
  17. NM

    NM
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    The presence or otherwise of personal air vents has nothing to do with the amount of fresh air in-flow to the cabin.
     
  18. Evan

    Evan Established Member

    Dec 26, 2006
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    About cruise speed,
    A330 is about 860-865kms/hr
    B777 is about 895-900kms/hr

    So a little difference but not all that much as 10%, most modern jets are similar to above.

    E
     
  19. Ritzy

    Ritzy Newbie

    Mar 25, 2007
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    #19 Ritzy, Mar 27, 2007
    Last edited: Mar 27, 2007
    Hi Everyone

    Noises in most aircraft are due to a number of things

    1. Some Aircraft have Hydraulic pumps in the wheel well (Where the wheels are stowed after take off) which causes a bit of noise as these are powerfull pumps delivering approx 3000 psi to move various flight controls

    2. Airconditioning Packs : These are located in the belly of the aircraft and they make a lot of noise due to the Air cycle machines and compressors and the amount of airflow through them

    3. There maybe other things like Whether it is a twin engined aircraft or a 4 engine aircraft which determines How far are the engines located from the airframe. Having said that every engine has vibration limits which are strictly adhered to.

    4. The Noise would be maximum at take off and landing as these are two phases of flight where maximum engine power is used (Some of u may have noticed that as the engines are started the PA system / Music volume is automatically increased.

    5. Airbus and Boeing have a variety of options when it comes to fitting out engines, Some engines buzz at a higg freuency some dont but ALL of them have to confirm with noise regulations both in and out of the aircraft

    6. Regarding flying faster or slower. Passenger jets very rarely fly at their maximum intended speeds. Ar Cruise the pilots have their Autopilots on to maintain a certain speed and the engine thrust is adjusted accordingly and its an automatic process.

    Some other points

    The airflow for the airconditioning system is fed from the Engines in air, Now the aircraft has to be pressurized to maintain sea level pressure therfore there are severe restrictions as to How much air can be let out and at what altitude to maintain a comfortable pressure in the aircraft so the question of "More fresh air" does not arise. The air is carefully let out by devices call pressurization valves which are basically openings in the airframe (mostly visible on the aft end) To overcome stale air aircrafts have something call recirculation fans (depending on the aircraft) this sucks the air from the cabin (which comes form the airconditioning packs) and blows it back into the cabin. All of the airconditioning components have very high quality filters which are regularly changed.

    Someone mentioned at the back of the aircraft it is diffciult to get fresh air (I do not know any technical reason for it)


    I hope I havent complicated things and everybody finds this post usefull, Please feel free to ask anything technical about aircrafts:confused:

    Cheers

    Sunny

    (Now to find a card which gives me an excellent limit)
     
  20. NM

    NM
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    This is not quite correct. The aircraft is not pressurised to maintain sealevel pressure. At cruise, the pressure inside the cabin of a modern airliners will be the equivalent of between 6,000 feet and 9,000 feet. One of the benefits of the 787 noted by Boeing is the ability to operate with a 6000 foot cabin pressure, however airlines choose to reduce the cabin pressure to closer to the 8000 feet commonly used by most airliners now. Larger changes in cabin pressure pose more stress on the aircraft and require more regular maintenance. The process of pressurising and depressurising the cabin affects the life of the hull.

    Not all air the flows into the cabin is fresh air. A proportion of the air that is fed into the cabin is recycled from the existing cabin air. Some fresh air is required to replace that which is exhausted via the pressurisation values. In the past when smoking was permitted onboard aircraft, less of the cabin air was recycled and more was fresh. However, the process of pressurising the fresh outside air and cooling it to cabin temperature requires more energy the recycling the existing air. So many operators have reduced the amount of fresh air and increased the amount of recycled air that is fed back into the cabin via the cabin environmental conditioning system.

    Naturally the recycled air is passed through filters and cooled again by the air-conditioning system before being fad back in.
     
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