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I've noticed that the engines on the A320 make a very a distinct sound on takeoff. Is there something about the CFM-56 series that causes this?

This noise can be heard in this video.

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  • $\begingroup$ If it were the CFM56, the 737 would do the same thing. A320's can also use IAE engines. Is there a video of what you are talking about? $\endgroup$ – fooot May 1 '15 at 17:54
  • $\begingroup$ youtube.com/watch?v=2m9l-nDd1fw $\endgroup$ – Madhav Sudarshan May 1 '15 at 18:14
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    $\begingroup$ That's an IAE V2500 engine. $\endgroup$ – JulianHzg May 1 '15 at 18:24
  • $\begingroup$ What is it that causes the noise? $\endgroup$ – Madhav Sudarshan May 1 '15 at 18:26
  • $\begingroup$ Are you asking about the buzz or the whine, or something else? Here is a CFM56 to compare to. $\endgroup$ – fooot May 1 '15 at 18:31
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The whining noise is generated by the rotating components in the engine. At takeoff power for an engine of that size, the fan is rotating at about 5200 rpm. This is about 86 times per second. There are also 22 blades on the fan at the front of the engine. This means a given point sees a fan blade pass about 1900 times per second. Each fan blade changes the pressure as it passes, resulting in a tone of about 2kHz. This is the whine that you hear. At takeoff the tips of the fan blades are going supersonic, each one creating a shockwave.

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    $\begingroup$ Excellent answer. The dominant sound from a turbojet is the the roar of the engine exhaust which can exceed 160 decibels. At high power outputs a mechanical whine from the rapidly rotating fan becomes audible, the shrill 2 - 3 Khz whine that you hear at close range when a jet is taking off under full power. If you've heard an older turbojet without a fan e.g. the B-52G P&W J57 engine you will be struck by strikingly different audio signature. $\endgroup$ – user28563 Jan 26 '18 at 23:33
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Unfortunately I am unable to watch your video at the moment so I can't say for sure that this is the noise you are hearing, but you have commented that the noise is a whine and not engine buzz. The A320 series is known for having a distinct whine, essentially caused by the pressure equalisation vents for the fuel tanks, which are open to the external airflow.

As Lufthansa describe here, the effect is the same as when you blow over the mouth of a bottle. Lufthansa are retrofitting vortex generators on their A320s in order to reduce this whine.

Some more interesting reading on this issue is here and here.

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  • $\begingroup$ I've asked an extremely similar question here, and I'm pretty sure the OP was NOT talking about these vents. The sound I recognize from the two linked videos is tightly linked to the engine rotation, and doesn't vary much with airspeed. $\endgroup$ – Daniel Griscom Nov 30 '15 at 21:36
  • $\begingroup$ I upvoted your well written and relevant post. But the "Airbus whine" is more of a howl and distinct from the characteristic mechanical whine of most turbofan engines. It's worth noting though that we need to distinguish similar sounds that can arise from multiple related causes. $\endgroup$ – user28563 Jan 26 '18 at 23:40
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All high bypass jet engines make this roaring noise due to the blade tips of the first N1 stage (The first fan blades you can see from your seat). At take off this noise is generated by the blades tips which are rotating at 75-95% of maximum power, nearing or exceeding the speed of sound. This creates a MILD continuous sonic shock waves (supersonic bang) sounding like a motorbike. The loudness of the bang depends on the size. A fighter jet aircraft which has a much bigger airframe than that of a fan blade would sound like a small bomb explosion. Technology can reduce the loudness of the roaring but not eliminate it. I've got three videos of Pratt & Witney, IAE and CFM engines on take off but can't attach them here (Don't know how to). They have different high pitch whistling but the same roaring.

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  • $\begingroup$ Point to this one, as the other answers talk about "whine", and the most prominent sound in the example video is definitely not a whine, but more like an air compressor running at high rpm, matching well with the described source in this answer. $\endgroup$ – Jpe61 Jan 1 at 17:47

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