The 787 uses a variety of sound reducing mechanism including engines with characteristic chevrons:

enter image description here (Source wikimedia commons)

Would it be possible for older airplanes to also have this type of quieter engine retrofitted? I'm assuming the engines would have to be recertified of course. But do the chevrons implicate a particular type of wing or airframe that requires them to be designed in from the beginning?

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    $\begingroup$ It's more economical to design and install "hush kits" for older engines. Engines are really expensive to replace (they represent about 25% of the sticker price of a $300 million airliner), then you have to consider replacing them on a fleet of dozens of these aircraft, with each upgrade taking that plane out of the sky for weeks in addition to the cost of the engines. Hush kits are usually much cheaper and easier to install (a few days maybe), though slightly less effective than an engine designed from scratch for lower noise. $\endgroup$ – KeithS Aug 20 '15 at 4:11

The chevrons do not implicate a particular type of wing or airframe. However, the engine does need to be designed around having the chevrons, since they affect the performance as well as noise. And the engine design certainly can affect the design of the wing.

In reality, chevrons are more likely to be incorporated in an engine design from the start rather than retrofitted later. And a new engine design will probably be for a new airplane design. This could be a totally new plane like the 787. But it could also be a new derivative, like the 747-8 or the 737 MAX.

So while chevrons can be added to the engines on an existing aircraft model, it's much more likely that the aircraft model will be upgraded in other ways as well to accommodate the new engines. Adding chevrons is likely to be part of a design change large enough to justify changes to the aircraft as well.

However, these changes are not really specific to the engine having chevrons. Changes to the wing and airframe will be due to the inclusion of a new engine, not just the addition of chevrons.


Yes. This kind of engine design is independent of the wing and airframe and can be fitted on compatible aircrafts.

For example, General Electric GEnx-1B64, an engine with chevrons is fitted on Boeing 747-8, a variant of Boeing 747.

In general, the engines (especially civil airliner engines) are developed with compatibility in mind to reduce costs and increase commonality.

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    $\begingroup$ Not saying you're wrong, but the 747-8 has a new wing... $\endgroup$ – egid Aug 19 '15 at 16:41
  • $\begingroup$ To quote 747 chief project engineer Bruce Dickinson, "fundamentally, the wing's structural design is not entirely different" from that of a 747-400, though some changes were made. I understand that significant changes were made (like raked wingtips, increased span etc.), but the airfoil section and the basic structural construction remains the same. $\endgroup$ – aeroalias Aug 19 '15 at 22:57
  • $\begingroup$ The Bruce Dickinson!? That's interesting, though. I thought they'd modified the airfoil. $\endgroup$ – egid Aug 20 '15 at 0:11
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    $\begingroup$ You're also not going to see any of the older 747-400s coming back to the barn for GEnx engines anytime soon. New variants of older designs, sure; the 737MAX will have similar chevroned engine exhausts from a GE-Snecma joint venture. But engines on existing aircraft are usually only replaced if they're declared a total loss due to accident (engine fire, bird ingestion, blade-out) in which case only the destoryed engine is replaced, in turn meaning it has to be a like-for-like swap. $\endgroup$ – KeithS Aug 20 '15 at 4:23
  • $\begingroup$ @KeithS that's not entirely true. There are several major re-engine projects I can think of - the KC-135R and DC-8-7x both got CFM-56 engines late in life as refits. Turboprop upgrades have happened as well, including planes like the DC-3. $\endgroup$ – egid Aug 20 '15 at 16:02

Yes. The parts shown with the noise reducing 'chevrons' are part of an assembly called the engine cowling, which is usually manufactured by a separate manufacturer than the engine. It is reasonable to assume new engine cowlings could be designed as part of an STC upgrade. NORDAM and UTC Aerospace Systems (Goodrich) are examples of engine cowling manufacturers


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