We recently discussed planespotting and how to distinguish aircraft from one another. One defining feature of new generation Boeing jets is their serrated engine covers. Also known as chevrons, these are located on the back of the nacelle and are in place to reduce jet blast noise. Airbus has released some new aircraft since this technology was implemented by Boeing – but do you know the reason why you haven’t yet seen this on Airbus jets?
Where you’ll find these chevrons
First, let’s take a look at where these chevrons do exist. You’ll find this interesting feature on the following Boeing aircraft:
- All 787 Dreamliners, regardless of whether they are fitted with General Electric GEnx or Rolls-Royce Trent 1000 engines.
- All sizes of 737 MAX aircraft. These are CFM LEAP-1B engines.
- And the final generation of 747, the 747-8. Both the passenger and freighter variants use a similar engine as is available to the 787 – a variant of the General Electric GEnx.
In addition to acoustic liners, Boeing says that these chevrons are such effective noise suppressors that several hundred pounds of sound insulation may be eliminated from the fuselage. The reduced weight translates to greater operational efficiency for airlines.
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How the serrated edges came to be
A 2005 Boeing Frontiers article discusses this ‘new’ feature, saying the following:
“To combat the sound of jet-blast from the rear of the engine, Boeing, General Electric, and NASA developed serrated edges called chevrons for the back of the nacelle and the engine exhaust nozzle. The chevrons reduce jet blast noise by controlling the way the air mixes after passing through and around the engine.”
The fact that these serrated engine covers were developed by Airbus’ archrival Boeing would appear, on the surface, to be a strong indicator that the European planemaker is unlikely to feature it on its own jets. In this highly competitive market, having such technology would certainly provide an edge over the competitor. But is it really a case of intellectual property and patents?
Is it a patent thing?
On the one hand, it appears that Boeing is the holder of the patent for part of this design (or a variant of it). The patent, US6612106B2, is titled “Segmented mixing device having chevrons for exhaust noise reduction in jet engines” and shows that Boeing is the current assignee to this active patent – which actually expires this year. Although figures and their descriptions in the patent discuss the engine covers, it’s unclear (at least to us) if the patent applies to both the chevrons on the nacelle and the nozzle sleeve (as you will find on the 747-8 and the Quiet Technology Demonstrator image above).
Of course, this reasoning gets more unclear when you realize that certain Airbus aircraft actually do employ engines that have chevrons on the exhaust nozzles.
An interesting message thread on Stack Exchange shows a 2006 FlightGlobal article stating that the chief engineer for the Airbus A350 decided against chevrons. Apparently, the team didn’t get a noise advantage from this design. Combined with a specific fuel consumption penalty, the aircraft designers decided not to adopt them.
So, at the end of this article, we’re still left with just a little bit of uncertainty about why Airbus doesn’t have these same chevrons on its engine covers. They aren’t currently on the engine covers of Airbus jets – but maybe we’ll see them on a future Airbus aircraft.
It does seem clear, however, that the European planemaker has managed to find the same efficiencies and similar results using other technologies.
What do you think is going on here? Is it a patent issue or simply the fact that Airbus has found a way around them? Let us know your thoughts in the comments.