I just realize that there is no sound-reduction chevron on the GE9X on the 777X.
Do anyone know why? Maybe it was proven useless, unnecessary or something?
Chevron on GEnx (787):

Cre: Tinhte.vn

Non-chevron GE9X (777X):

Cre: Wikipedia

They carry a fuel burn hit and Boeing removed it later in the development of the 777X as they found a better solution in the nozzle design that probably didn’t carry the fuel burn penalty.

I heard that it may eventually be removed on new 787 engines. Not sure if this will come to fruition but maybe during a substantial pip it would be modified.

ikolkyo wrote:

They carry a fuel burn hit and Boeing removed it later in the development of the 777X as they found a better solution in the nozzle design that probably didn’t carry the fuel burn penalty.

Antaras wrote:

Do anyone know why?

Because they're already obsolete tech.

Advances in design allowed GE to get similar noise reduction without the (minuscule, but still present) inefficiency caused by the chevrons, so there's no point in having them.

LAX772LR wrote:

Antaras wrote:

Do anyone know why?

Because they're already obsolete tech.

Advances in design allowed GE to get similar noise reduction without the (minuscule, but still present) inefficiency caused by the chevrons, so there's no point in having them.

I don't think it's fair to call them "obsolete". Chevrons still work, in principle. GE simply found a different way to comply with regulations at a lower fuel burn penalty compared to the chevrons. If noise regulations keep getting stricter, we could easily see the chevrons return to future engines.

It's like saying winglets are obsolete because some new aircraft don't feature them (e. g. original 777, MC-21) or use raked wingtips. It's just that certain wings and missions benefit more from them than others, and each aircraft has different constraints (e. g. gate size). Yet adding wingtip devices (almost) always improves aerodynamics, just like chevrons (almost) always reduce noise. Sometimes the trade-off makes sense and sometimes it doesn't.

In any case I think they're fugly so I for one am glad they have advanced past them...

mxaxai wrote:

LAX772LR wrote:

Because they're already obsolete tech.

I don't think it's fair to call them "obsolete". Chevrons still work, in principle.

No one's claiming that they don't work.
While they're still functional, they're obsolete in the sense that they're no longer optimal technology for ongoing application.

8Tracks, CDs, and cassettes can still retain sound recordings just fine... would you argue that it's unfair to call them obsolete, on account that they "still work?"

Too bad, I really like how they look, mostly because they are different, and distinctive.

744SPX wrote:

In any case I think they're fugly so I for one am glad they have advanced past them...

Each to their own, I quite like them and they help distinguish aircraft type.

bergkampsticket wrote:

744SPX wrote:

In any case I think they're fugly so I for one am glad they have advanced past them...

Each to their own, I quite like them and they help distinguish aircraft type.

At least it was the best way for you to differentiate a MAX and a NG.

LAX772LR wrote:

mxaxai wrote:

LAX772LR wrote:

Because they're already obsolete tech.

I don't think it's fair to call them "obsolete". Chevrons still work, in principle.

No one's claiming that they don't work.
While they're still functional, they're obsolete in the sense that they're no longer optimal technology for ongoing application.
"

Are we sure that some other technology was introduced?

As I recall, the chevrons were dropped about the time the thrust requirement and fan size were frozen.

I suspect the GE9X was able to meet noise targets organically as the larger diameter and reduced thrust combined just simply doesn’t need further treatment. Just as the GTF and LEAP A & C don’t need them to meet target.

Due to smaller diameter and therefore higher velocities, the LEAP B needs them to reduce noise footprint to be competitive with the larger diameter twins. Even then, I understood it beats regulations pretty easily.

The 787 probably doesn’t need them to meet ground noise targets. And perhaps some day they will get removed. It could also be the rear cabin may become unacceptably noisy if removed, hence it was designed from the start with them, and may require tweaking insulation to offset? Doubtful but weirder things have happened. It could just be Boeing trying to leverage a patent to encourage regulatory agents to further reduce further requirements that would provide additional value to Boeing as the patent holder.

Okcflyer wrote:

Are we sure that some other technology was introduced?

It was a redesign of the nozzle and later nacelle, which gave them the results they wanted without the penalty.

Thus, not so much new tech, as the chevrons being unnecessary tech.

Trent XWB didn't need chevrons to meet/exceed noise requirements either...

744SPX wrote:

Trent XWB didn't need chevrons to meet/exceed noise requirements either...

Nor the Trent 7000 ...

IIRC in the early days the chevron nozzles were meant to be temperature sensitive and be made of some material that would "morph" when the engine would run at full power and with some hotter gas stream to affect the exhaust airflow and noise somehow. That concept got abandoned early on.

LAX772LR wrote:

Antaras wrote:

Do anyone know why?

Because they're already obsolete tech.

Advances in design allowed GE to get similar noise reduction without the (minuscule, but still present) inefficiency caused by the chevrons, so there's no point in having them.

Safran not GE are responsible for the nacelle.

Okcflyer wrote:

744SPX wrote:

Trent XWB didn't need chevrons to meet/exceed noise requirements either...

Nor the Trent 7000 ...

I would've assumed that there are patents like this one: https://patents.google.com/patent/US6360528B1/en that keep Airbus from using them. But it could also be that Airbus focused on other methods to reduce noise and meet regulations. Chevrons, like winglets, need a lot of fine-tuning to get a good balance of added weight, cost and fuel flow for a certain noise reduction.

With the Trent 7000 (and also the max and neo), Airbus / Boeing could claim that these are new variants of an older model and thus don't need to meet the recent stricter regulations. Nevertheless, several airports charge fees based on noise and reduced engine noise has other benefits like thinner cabin insulation. It's great for marketing as well.

Noshow wrote:

IIRC in the early days the chevron nozzles were meant to be temperature sensitive and be made of some material that would "morph" when the engine would run at full power and with some hotter gas stream to affect the exhaust airflow and noise somehow. That concept got abandoned early on.

Indeed, shape memory alloys were looked at: https://iopscience.iop.org/article/10.1 ... 15020/meta

mxaxai wrote:

Okcflyer wrote:

744SPX wrote:

Trent XWB didn't need chevrons to meet/exceed noise requirements either...

Nor the Trent 7000 ...

I would've assumed that there are patents like this one: https://patents.google.com/patent/US6360528B1/en that keep Airbus from using them. But it could also be that Airbus focused on other methods to reduce noise and meet regulations. Chevrons, like winglets, need a lot of fine-tuning to get a good balance of added weight, cost and fuel flow for a certain noise reduction.

With the Trent 7000 (and also the max and neo), Airbus / Boeing could claim that these are new variants of an older model and thus don't need to meet the recent stricter regulations. Nevertheless, several airports charge fees based on noise and reduced engine noise has other benefits like thinner cabin insulation. It's great for marketing as well.

Noshow wrote:

IIRC in the early days the chevron nozzles were meant to be temperature sensitive and be made of some material that would "morph" when the engine would run at full power and with some hotter gas stream to affect the exhaust airflow and noise somehow. That concept got abandoned early on.

Indeed, shape memory alloys were looked at: https://iopscience.iop.org/article/10.1 ... 15020/meta

There is chevron on GE CF6 installed on Embraer E-jets, Bombardier CRJs, as well as CFM56 on Airbus A321.

So I guess, Boeing copyrights this but only on the engines' container, but GE can bring this anywhere?

speaking of fuel burn I wonder what fuel burn figures they are seeing on the 777-9 during this test phase

Can someone also explain why the -9x has a much larger silvered leading edge on the nacelle than the -90? Sorry if I'm not using the right terminology, bit of a tech noob here.

aerokiwi wrote:

Can someone also explain why the -9x has a much larger silvered leading edge on the nacelle than the -90? Sorry if I'm not using the right terminology, bit of a tech noob here.

GE90

[Cre: Wikimedia]

GE9X

[Cre: Aviation Week]

Maybe the reason is in their sizes. The 9X is noticeably bigger than its brother 90, so because of some technical reasons the small "silvered leading edge" on GE90 is somehow should be thicker on the GE9X????
Or maybe Boeing and/or GE just want that silver ring to be thicker for no technical reasons ????

P/s: I think they are grey, not silver


EDIT: note that on the GE9X, the fan is much deeper from the engine "mouth".

aerokiwi wrote:

Can someone also explain why the -9x has a much larger silvered leading edge on the nacelle than the -90? Sorry if I'm not using the right terminology, bit of a tech noob here.

Probably for laminar flow reasons. Or maybe they just think it's pretty.

Antaras wrote:

mxaxai wrote:

Okcflyer wrote:

Nor the Trent 7000 ...

I would've assumed that there are patents like this one: https://patents.google.com/patent/US6360528B1/en that keep Airbus from using them. But it could also be that Airbus focused on other methods to reduce noise and meet regulations. Chevrons, like winglets, need a lot of fine-tuning to get a good balance of added weight, cost and fuel flow for a certain noise reduction.

With the Trent 7000 (and also the max and neo), Airbus / Boeing could claim that these are new variants of an older model and thus don't need to meet the recent stricter regulations. Nevertheless, several airports charge fees based on noise and reduced engine noise has other benefits like thinner cabin insulation. It's great for marketing as well.

Noshow wrote:

IIRC in the early days the chevron nozzles were meant to be temperature sensitive and be made of some material that would "morph" when the engine would run at full power and with some hotter gas stream to affect the exhaust airflow and noise somehow. That concept got abandoned early on.

Indeed, shape memory alloys were looked at: https://iopscience.iop.org/article/10.1 ... 15020/meta

There is chevron on GE CF6 installed on Embraer E-jets, Bombardier CRJs, as well as CFM56 on Airbus A321.

So I guess, Boeing copyrights this but only on the engines' container, but GE can bring this anywhere?

Those are not CF6s

Those chevrons are on the mix between core and the bypass. Essentially the exhaust nozzle. It becomes a pain as some of our A321s has them and we had to do a engineering order to remove them as we could not mix engines. I think on some of the smaller regional aircraft with the CF34 you can mix willy nilly with no issue but I’m not sure.

On the 787 the chevrons are on the translating sleeve of the TR. we get a lot of lightning strike discharge damage to them....

aerokiwi wrote:

Can someone also explain why the -9x has a much larger silvered leading edge on the nacelle than the -90? Sorry if I'm not using the right terminology, bit of a tech noob here.

I´ve been wondering the same for some time already. It´s not only on the GE9X.
It´s also on all engine types for the 787.
But no Airbus type has it.
I personally find it very ugly, it makes the engine look fat and cartoonish
But there must be a good reason for it

AFAIK it's required for optimum laminar flow over the nacelle. The surfaces must be superclean and smooth. This is why on the 787 the customer cannot paint the engine pods. The surface needed for laminar flow would be ruined just by the paint layer. So you have to select the pod in a color you like from the factory catalogue. That's it.

Noshow wrote:

AFAIK it's required for optimum laminar flow over the nacelle. The surfaces must be superclean and smooth. This is why on the 787 the customer cannot paint the engine pods. The surface needed for laminar flow would be ruined just by the paint layer. So you have to select the pod in a color you like from the factory catalogue. That's it.

But Virgin Atlantic, Qatar Airways, Air Canada, Air Kenya, Avianca, Royal Jordanian, just to name a few, have the engine pods painted in the same colors as their liveries. Sheer luck that the color was available in the catalogue? Or did they accept a small performance loss in order to have a better looking plane?
And what about RR Trent XWB or Trent 7000? They are as modern as the GEnX and GE9X but don´t use neither the Chevron nor the big metal lip

Actually, a lot of the CF6-80's also have the silvered/grey leading edge as well. Qantas 744ER's for example. It looks good on the CF6's

Those 787-engine pods mentioned are not painted but factory made in these colors. The material itself is colored, there is no customer applied paint layer on the super smooth surface.