speedbird52
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Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 6:16 am

The GE9x is dropping the sawtooth noise reduction nacelles, as they apparently have a strong impact on efficiency. Now I am wondering, could the 787 be given an extra kick by getting the same treatment? Could maybe even the 747 get a lifeline?
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AirCal737
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 6:23 am

They are removed because the GE9X need more thrust. It's an efficient design but it trades thrust for efficiency. The 779 is a bit underpowered compared to the 77W (9% lower thrust) and it can't afford to have this feature installed.
 
navjotgill45
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 7:04 am

Could you please provide the source? Cheers.
 
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OneSexyL1011
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 7:16 am

Ugh is this happening? This is one of the most recognizable features that I absolutely LOVE on the 787's and the 748's....
 
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O530CarrisPT
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 8:12 am

No. Removing the chevrons from the nacelles of the 747-8 and the 787 Dreamliner would rather make them more noisier than with them. That feature is also one of the most recognisable, as OneSexyL1011 said.
The GE9X for the Boeing 777X however, as generates less thrust than the GE90-115B of the Boeing 777-300ER, will be less noisier, thus rendering the chevrons as unnecessary. They also would compromise GE9X's fuel efficiency.
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LAX772LR
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 8:34 am

AirCal737 wrote:
The 779 is a bit underpowered compared to the 77W (9% lower thrust) and it can't afford to have this feature installed.

The 777X series doesn't *need* the trust levels of the 777LR series because it has a much larger and more efficient wing. Less trust with higher bypass = less noise = less use for chevrons.

It is not, and has never been, a question of it being able to "afford" them. The aircraft is nowhere near "underpowered."
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WIederling
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 9:04 am

Go back in time when the 787 was announced with those noise fixers.
Fans were waxing lyrical over those little teeth. at least 5% sfc. gain.
Same for "fully laminar" ( nothing more than extending laminar flow a couple %
further along the nacelle.)
Obviously that must still be the best of the best of the best solutions for mankind.
Murphy is an optimist
 
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JannEejit
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 9:09 am

Could someone explain how noise reduction is physically acheived via these chevrons please ? Thanks !
 
mjoelnir
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 9:09 am

The chevrons reduce noise, but cost some efficiency. On the 787 and 747-8 Boeing went for less noise. On the 777-8/9, I assume, Boeing needs every bit of efficiency to try to hold off the A350.
 
WIederling
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 10:19 am

JannEejit wrote:
Could someone explain how noise reduction is physically achieved via these chevrons please ? Thanks !


Mix it!
In simplistic terms you mix different speed airflows ( here environment vs Fan overspeed ) in a broken up structure.
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Nicoeddf
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 11:02 am

JannEejit wrote:
Could someone explain how noise reduction is physically acheived via these chevrons please ? Thanks !


My understanding is, that they enhance mixing of cold and hot airflow of bypass, core engine respectively. Thus reducing noise profile.
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kalvado
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 12:04 pm

JannEejit wrote:
Could someone explain how noise reduction is physically acheived via these chevrons please ? Thanks !

I may be wrong, but I was always under impression that this is a standing wave modulation with odd/even tooth count. Same approach used in magnetrons, but in opposite way.
Basically, a periodic structure is created so that nodes and antinodes correspond to period of the structure - node under tooth, antinode in between.
Then in case of even number of teeth, standing wave experiences constructive interference with itself, gets amplified and powers for example a microwave oven - or gets destructive interference in case of even teeth count, suppressing emission of frequency - which can mean noise reduction if period corresponds to peak emitted frequency.
If that is the case, I would expect some loss of efficiency with removal of teeth as more energy would get radiated as noise...
 
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Faro
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 1:33 pm

Wonder if there is more to this news item than appearances suggest...the GE9X is already heavier than its -115B predecessor despite generating less thrust...and recently had to have its variable stator vane actuators modified due to a late unforeseen design issue...and now Boeing/GE are deleting the chevrons to squeeze a little more efficiency out...is the GE9X in trouble meeting its SFC goals?...


Faro
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trex8
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 3:49 pm

Faro wrote:
Wonder if there is more to this news item than appearances suggest...the GE9X is already heavier than its -115B predecessor despite generating less thrust...and recently had to have its variable stator vane actuators modified due to a late unforeseen design issue...and now Boeing/GE are deleting the chevrons to squeeze a little more efficiency out...is the GE9X in trouble meeting its SFC goals?...


Faro

IIRC the chevrons were dropped quite early on, when first offered they were present on some early renditions of the 77X but I'm pretty sure by launch they were gone.
 
planecane
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Tue Feb 13, 2018 4:50 pm

WIederling wrote:
Go back in time when the 787 was announced with those noise fixers.
Fans were waxing lyrical over those little teeth. at least 5% sfc. gain.
Same for "fully laminar" ( nothing more than extending laminar flow a couple %
further along the nacelle.)
Obviously that must still be the best of the best of the best solutions for mankind.


As far as I remember, the chevrons were never said to improve efficiency. They were always said to slightly reduce efficiency from an aerodynamic standpoint but reduce noise. I think it was stated that it would be less efficient for the airframe to have the extra weight to reduce the noise to the same level without the chevrons.

When they dropped them from the 777X, boeing made statements that improvements to other means of noise reduction rendered the chevrons unnecessary and not worth the efficiency penalty.

They are on the 737 MAX as well.
 
LH707330
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Wed Feb 14, 2018 5:09 am

I've read that the chevrons cost about a quarter percentage in fuel burn. As far as how they work, think first of the core and bypass flow basically as cylinders of faster-moving air coming out the back of the engine. As these faster-moving airstreams mix with the ambient air, they mix in a somewhat chaotic manner, which creates that familiar rumble that us avgeeks love. Now, when you cut chevrons into the end of the cylinder, the higher-pressure air in the outlet escapes slightly laterally, and the mixing occurs in a more predictable manner. The downside is that the lateral movement robs some propulsive efficiency.

As to why the newer designs don't have chevrons? The volume of the jet noise scales at roughly the eighth power of the jet velocity, so a tiny increase in bypass ratio and FPR reduction yields a huge gain, thus obviating the need on the 350 and 77x. The 380, meanwhile, went with oversize fans for the thrust level, which meant that they retained propulsive efficiency, but lost overall due to the weight of a bigger fan and cowl.
 
WIederling
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Wed Feb 14, 2018 11:58 am

planecane wrote:
As far as I remember, the chevrons were never said to improve efficiency. They were always said to slightly reduce efficiency from an aerodynamic standpoint but reduce noise.


Amusing to go back in time:
search.php?keywords=chevron+787&terms=all&author=&t=0&fid[]=3&sc=1&sf=all&sr=posts&sk=t&sd=a&st=0&ch=300&t=0&submit=Search
viewtopic.php?f=3&t=434505&p=5769007&hilit=chevron+787#p5769007
....

A trendy must have at the time. :-)
And strong connotations that Airbus can't use it for patent reasons and that is an obvious drag for Airbus! :-)))
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Faro
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Wed Feb 14, 2018 12:20 pm

WIederling wrote:
planecane wrote:
As far as I remember, the chevrons were never said to improve efficiency. They were always said to slightly reduce efficiency from an aerodynamic standpoint but reduce noise.


Amusing to go back in time:
search.php?keywords=chevron+787&terms=all&author=&t=0&fid[]=3&sc=1&sf=all&sr=posts&sk=t&sd=a&st=0&ch=300&t=0&submit=Search
viewtopic.php?f=3&t=434505&p=5769007&hilit=chevron+787#p5769007
....

A trendy must have at the time. :-)
And strong connotations that Airbus can't use it for patent reasons and that is an obvious drag for Airbus! :-)))



I believe Airbus use a slightly different 'chevron'...one that is zig-zaggy and not curvilinear...on the hot, core exhaust of CFM engines installed on A321's...like Embraer on the core exhaust of E175/195's too...


Faro
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WIederling
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Wed Feb 14, 2018 12:31 pm

Faro wrote:
I believe Airbus use a slightly different 'chevron'...one that is zig-zaggy and not curvilinear...on the hot, core exhaust of CFM engines installed on A321's...like Embraer on the core exhaust of E175/195's too...

Mixers on the hot core are a regular feature. .. and in diverse forms.
Remember the early convoluted thingies in times back when ..
Murphy is an optimist
 
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Faro
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Thu Feb 15, 2018 9:33 am

WIederling wrote:
Faro wrote:
I believe Airbus use a slightly different 'chevron'...one that is zig-zaggy and not curvilinear...on the hot, core exhaust of CFM engines installed on A321's...like Embraer on the core exhaust of E175/195's too...

Mixers on the hot core are a regular feature. .. and in diverse forms.
Remember the early convoluted thingies in times back when ..



So mixers are not subject to patent protection whereas chevrons are...or have been previously patented by Airbus/Embraer for their designs...such mixers do not figure on any Boeing engine core exhaust nozzle...this is the logical conclusion...is it correct?...

Out of curiousity, who would hold the patent on the 787/748 nacelle chevrons, Boeing or General Electric?...


Faro
The chalice not my son
 
WIederling
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Re: Could the 747-8 and 787 be made more efficient by removing the sawtooth nacelles?

Thu Feb 15, 2018 12:47 pm

Faro wrote:
So mixers are not subject to patent protection whereas chevrons are...or have been previously patented by Airbus/Embraer for their designs...such mixers do not figure on any Boeing engine core exhaust nozzle...this is the logical conclusion...is it correct?...

Out of curiousity, who would hold the patent on the 787/748 nacelle chevrons, Boeing or General Electric?...


probably Boeing.
I'd question the validity of such a patent. IMU it would not survive litigation. ( same domain as the Basler Winglet patent:
too much prior art around. )

Hmm:
GE: https://patents.google.com/patent/US6360528
AB: https://patents.google.com/patent/US7469529

a sceptic:
https://nintil.com/2015/12/31/you-didnt ... s-edition/
Murphy is an optimist

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