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I stumbled upon a wikimedia picture and I saw something that I have not seen before: a CFM56 with a toothed engine exhaust. Can someone explain to me what engine variant that is?

enter image description here Source Author: Konstantin Nikiforov CC-BY-SA-3.0

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    $\begingroup$ Interesting picture. Welcome to Av.SE! $\endgroup$ – Ralph J Feb 2 at 23:59
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    $\begingroup$ Usually the "teeth" are meant to reduce noise levels, up to a couple dB. $\endgroup$ – Pheric Feb 3 at 0:29
  • $\begingroup$ That is a very special add-on. I guess you learn something new every day. $\endgroup$ – Miyo Hazuki Feb 3 at 0:57
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    $\begingroup$ related: aviation.stackexchange.com/q/19440/1467 $\endgroup$ – Federico Feb 3 at 7:00
  • $\begingroup$ I almost didn't upvote this question because your rep was at "172", hehe :) $\endgroup$ – Jeff Bridgman Feb 7 at 18:56
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The “toothed” exhaust are called Chevrons and they reduce noise. They are an option on CFM56 equipped A321 aircraft.

Wikipedia CFM International CFM56

”GE and Snecma also tested the effectiveness of chevrons on reducing jet noise. After examining configurations in the wind tunnel, CFMI chose to flight-test chevrons built into the core exhaust nozzle. The chevrons reduced jet noise by 1.3 perceived loudness decibels during takeoff conditions, and are now offered as an option with the CFM56 for the Airbus A321”

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So far my suspicion is that this is the /p option in "CFM International CFM56-5B3/P" as found when I looked up VP-BWN (the aircraft in your picture). The useful chart at Wikipedia, as linked by @Mike-Sowsun, does not list the /P option, which would of course complicate the chart. I wonder how many of these minor options are available? Not like I'm in the market.

More Info: Airliners.net was excited about this roughly ten years ago, but the links to explanations have gone dry. So I was happy to see that one intrepid commenter there had done the right thing and produced a quote from the linked material, which I will reproduce here:

As stated in the article : http://www.airbus.com/store/mm_repos...dia_object_file_FAST37_p19_p22.pdf

The "noise package" is now standard on the A321 and an option on the other models. The reason behind this is that the A321 (heavy weight version) doesn't comply with the new stage 4 noise limits in effect for all new aircraft, certified after 1 January 2007. In fact this is the present noise standard, although legally not valid for the present A320 generation of aircraft, all certified before 1 januari 2007. All other sub types of the A320 series are at or below the stage 4 noise standard and don't need the chevrons, but can be delivered as an option with this "noise package", to become even more silent.

Also stated in the article is the fact that the FADEC needs some tweaking to produce the same thrust level, so there must be a loss in efficiency somewhere. Because this is an Airbus brochure, nothing is said about the actual loss in SFC.

Here's a similar explanation (again, without specific model number) from a 2002 GE press release:

All CFM-powered A320 family aircraft meet current FAR Stage III noise requirements with significant margin. These engines also meet the CAEP 5 recommendations, except for the CFM56-5B-powered A321. However, CFM and Airbus have defined an acoustic package to ensure this aircraft will operate well within proposed limits. CFM is conducting development testing on engine and nacelle treatments that will reduce the cumulative noise signature at least 10 EPNdB (effective perceived noise in decibels) below Stage III levels.

The new technology includes three-dimensional aerodynamic designed outlet guide vanes; a core chevron nozzle; and improved reverser and inlet linings on the nacelle. Flight tests on the A321 are scheduled for later this year, followed by certification and entry into service in early 2003.

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    $\begingroup$ Thanks for the detailed explanation. $\endgroup$ – Miyo Hazuki Feb 3 at 10:53
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    $\begingroup$ You can see chevrons on B-787 engines too. $\endgroup$ – Anthony X Feb 3 at 15:28

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