I believe you also swapped the words titanium and inconel . Titanium is heat resistant enough for aircraft firewalls and components that separate the engine from the airframe, but it cannot take exhaust levels of heat for more than a few hours before developing metallurgical conditions of alpha-case and hydrogen embrittlement. Which as the name suggests, weakens the metal. I don't know about other manufacturers, but I know Boeing likes to use inconel-718 as the metal choice for exhaust ducting. I hope I don't sound like a dick correcting you, I am instead hoping to share some information and maybe make you curious enough to learn more about these kinds of metals and their applications. Cheers!
@@alphamalegold Air is not compressed in the high pressure turbine. Air is compressed in the compressor. In fact compressed air after combustion drives the High pressure turbine ( turbine blades). Titanium is not very heat esistant material and its alloys, Alpha, beta and alpha + beta are not very heat resistant. They are considered semi high temperature alloys and employed in the applications when the so called homologous temperature is about 0.5. TiAl must also be used which is of very good oxidation behaviour but again is not high temperature structural alloys. You meant nickel based super alloys which are structural alloys and employed in high pressure turbine. The "operating temperature" of the Nickel based super alloys is somehow around its melting point , sometimes higher , due to its oxidation behaviour, alumina formation, and TBC. Some
I asked this same question back in 2018 to one of the chief test pilots for the GE9x, Jon Ohman. This was his response: “The chevrons seen on the nacelles of (the GEnx and LEAP-1B) reduce noise, but with a slight drag penalty. The use of new ceramic matrix composite materials on the GE9X allows us to do some things with combuster hardware to meet our acoustic requirements without a drag penalty.”
Welp, I was 7 mins in when I started reading comments . So he was right in his theory . I think the Chevrons look cool and more futuristic, giving the plane a better look .
The 777x flew over my head at about 3000 Ft. It was descending on a right base to Boeing Field in Seattle with the power probably at idle. The only noise I heard was a very quiet swishing sound probably from airflow over the air frame and engines. It was so quiet that I was startled when I looked up and saw this really large airplane so close. BTW, the reason for the quiet treatment on the engines is for noise reduction as perceived from the ground. There are lots of noise restrictions around airports around the world particularly at big city airports where this large airplane will operate. Boeing would love to be able to gain noise exemptions for landing during "quiet periods" at some place like LHW.
You didn't hear anything because it was descending. It's already the case of most airplanes nowadays : you don't hear anything when they are descending at idle thrust.
@@noah9130 Protruding landing gears do create massive turbulence though, which should create lots of noise. I haven't done plane-spotting for a while now, and I clearly did not pay attention to the noises landing gears on inbound planes made during my last spot. Would love to do further comparisons on noise levels between outbound and inbound flights in the future.
@@paulshi5974 That's true. I live 5 miles away from an airport and when they are flying above my house at fast speed like 180 knots with their landing gear deployed, it creates a lot of noise especially when they are deploying it right above my house.
@@noah9130 Wow you can actually hear the moment landing gears deploy? I honestly don't know how to react haha. For one thing that's some perfect timing for ya, but I don't know if hearing landing gear noises every day has driven you mad or not...
My guess is that large bypass ratio makes the engine quieter. The GE9X engine has larger bypass ratio and less number of fan blades which already makes the engine quieter that renders chevron nozzle unnecessary.
@@yolo_burrito As bypass ratio (BPR) increases the overall efficiency of the engine increase which is a primary factor that yields lower TSFC for the turbofan engine. Additionally high bypass ratio engine can produce a greater amount of thrust while consuming the same amount of fuel as a lower BPR engine. Basically the additional weight added by bigger engines is negated by less fuel consumption due higher BPR. The engine doesn't need to spin as fast as it would to create the same amount of thrust at a lower BPR.
eWorkx I probably should’ve been more clear. I meant it makes the chevrons less effective not the engines. The negligible improvement of the chevrons along with larger diameter and higher BPR makes chevrons less effective.
I flew 787-8 and it was very comfortable, the cabin noise is a lot lower than in older airplanes. It was one of the best flights Ive ever made and it was a 12 hours flight!
Can’t be that it’s expensive. Would have made it uneconomical to put on the 737 Max. GE doesn’t build the nacelle. Boeing/UTC designs them, UTC builds them. This is the first thrust reverser that Boeing is fully designing and then building with Spirit. Could be the result of a closer collaboration of between GE and Boeing on propulsion integration.
Exactly, it would only add slight cost to the aircraft in general. They aren't even replaced when the engine is replaced. They're just part of the reverser doors.
Boeing usually does the engineering but, in the case of the 787, Rohr, Inc. (owned by UTC) put a decent percentage of a billion dollars into the the design and tooling for the 787 nacelles for both the GE & RR engines (at the same time they had the engineering group for the A350 nacelles working on the next floor down in the same engineering building.)
Well explained... and produced! Good audio, including non-intrusive music, voice level and great video clips. I think I've only been on one 737 with chevrons. Screaming babies on the flight cancelled out any noise reduction of the engines.
I agree, 787 takeoff was so quite. I also flew 737 Max on Southwest, very quite also. I kind of miss the loud engines at takeoff, though. My first jet flight was an Eastern Airlines B720. Such power & noise. In addition, I love the 757 takeoff power.
Some of this is down to the runway and initial climb slope. They calculate the minimum power setting needed for a location and gross weight to avoid stress on the engines and get longer life. A long runway followed by a good clearway with dense air and low fuel(short flight) can call for a very low takeoff power. The 757 was designed specifically for medium haul from difficult airports with low density air so it has extra power available. The MAX and 787 did not have this design target.
@@mytech6779: Actually, the 757 is my favorite plane as a passenger, reminds me of the B720, which was also designed for shorter runways & smaller airports--from what I have read.
I was on a flight with the 787 and then my connecting flight right after was a 777. The difference was pretty great with the 787 being much more quiet.
I've been flying airliners for over 30yrs, and I have to thank you for your proper use of terminology and clarity in explaining the subject matter. There are many TH-cam content producers that can learn from your high-level graphics and proper nomenclature.
This hurts my head. GE makes the engine not all of the composite structure around it. Just like the classic 777, Boeing designed the Nacelle. Boeing built the 777 Nacelle in Wichita. That same facility builds the 777x is now Spirit. Boeing designs the Nacelle to meet specific noise requirements. Once the requirements are met, you keep the design as simple as possible. K. I. S. S.
Chevrons are designed to enhance mixing between the different flows and not to smooth the flow. Forced mixers are only effective for lower bypass ratio engines and become too heavy on large engines and ineffective at high bypass ratios. They are typically fabricated from sheet metals and are not as expensive as you may think. Chevrons were originally intended to reduce community noise (what the people on the ground experience). The B787 Chevrons are aimed at reducing shock cell noise in flight which is caused by shock waves in the exhaust flow interacting with the shear (mixing) layer which can then propagate upstream and into the cabin. Composite fuselages are not good at attenuating noise created in this way and either you need to reduce the noise at source (disrupt the shockcells in the flow) or absorb the noise. The Chevrons on the B787 are not very good at reducing noise and increase fuel burn due to the drag on the Chevrons from the high-speed flow on the inside of the nozzle. They also change the amount of flow through the nozzle at low pressure ratios which is bad for the fan. Based on experience of Chevron design and testing, it is more effective to add sound absorbing to the fuselage than add a fuel burn penalty to the engines. So, answer 2. A competitor to Boeing doesn't have Chevrons on their nacelles for this reason. Shame really, the aerodynamics are interesting! An aerodynamicist who worked for years on Chevrons and forced mixers for an engine manufacture.
I saw the 777-9 takeoff from the Yuma Arizona airport while standing just outside the FBO. It's very quite, especially compared to the other jets flying in and out of there. Don't think it really needs the chevrons.
First time I flew on a 787 the takeoff engine noise inside the cabin was so low that I was worried the pilot hadn't throttled up the engines sufficiently and quickly started verifying the closest emergency exit location.
@@mytech6779 I think the 757 is what happens when the fighter design group gets bored and designs an airliner. :) Personally, though, from a sound perspective, the GE90 is my favorite engine spool sound.
As far as being surprised at the lack of sound on takeoff, this is also my experience with the geared turbofan on the C-Series (now A220.) Those things are amazingly quiet, even when sitting right beside the engine at takeoff power.
Well, I have been on a 787-8 once before, and I can definitely say it is VERY quiet in comparison with other aircraft, such as the 777 or 767, even the A350.
The mixer thing, as he pointed out, makes no sense given that it's an unmixed design. Overall the outer nacelle chevrons aren't because of mixing between core and bypass flow, it's bypass and ambient flow. My understanding is it's not about temperature so much as velocity, fast air coming out and mixing with slow surrounding air, with a shear layer, makes the noise, and chevrons help to break up that shear layer and cause quicker, thus quieter, mixing between the fast and slow air. The slower the bypass air, the less this is needed, which is why high-bypass turbofans are quieter than low-bypass or turbojets. As others point out, maybe the bypass ratio is so huge, the outlet velocity so low, that they just aren't needed. The other possibility, somewhat related to the mixer idea, is that there's some other technological solution being used instead. Maybe something secret (trade secret, not as in classified) which is why Boeing and GE haven't made the reasoning public.
787- I flew on....was by far...and I mean BY FAR the quietest ride I've ever been on. Even on take-off, I could hold a conversation at normal volume. That blew my mind.
Finally someone talked about the B777x chevrons! And tbh i got to the same conclusions but i heard(i don't remember where) that the chevrons make the engine 2% less efficient, and on a plane like B777 this would be a big problem.
I have flown on a 787, and a 777-300ER, and I have to say that the 787 was much quieter, especially during takeoff. The rumble is still there during takeoff but the scream is much less pronounced.
Myself living in the Everett area! I woukd say the 777X engines compete with the noise level of the late Gruman A6 or EA6B's as something certainly had to replace them in the otherwise noiseless northwest skies! Easily the loudest jet engine produced in decades whether it be from its sheer size or otherwise its noise is at times is undeniable! Sometimes having you look for the ghost of an aircraft seemingly right on top of you when in fact it could possibly be just spooling up infact miles away, having them be that of deceptivly and incredibly loud engines indeed!!! They have proved to be louder than I ever would have imagined them to be, especially after as you said the technology and attention put into the mitigation of noise on the 787's and 747's most recent engines! These new engines are said to be the largest ever made as so may be that of their volume level maybe the largest level in all of commercial aviation! Substantally louder than I would have anticapated by far... Perhaps noise mitagation may be something Boeing and GE are planning on addressing at a later date, I do not know? I would have to say so far it has been completely over looked for of whatever reason that maybe! I'm sure one could be left to speculate with out specifity like you were here in this here video blindly speculating of different senerios as to what may see to be of plausable reasons for the ommission of noise mitagation as your guess is as good as mine. Lack of concern perhaps after spending of the time and effort to accomplish of amazing results in such a feild to then see to loose of interest or even acknowledge of its in anyway further need? I dont know but it certainly has one scratch of their head as to what is or may be going on, for sure! I'd surely be interested in of any information you may see to gleen on the subject! My suspect is that there may just not be any information to be had. Hence the noise level of the largest jet engine ever made seeing to have of the noise level that it does just being what it is! A product of the largest jet engine in the world! What else would anyone see to expect? Rendering it a non-issue, I guess... You said that GE's design made for a quieter noise level in itself and maybe it does but from my ears experience I would further guess that of any such thing went by the way side along with the cheverons, but i have no idea as to its design other than large and loud being of the present results!
Think it depends allot of where you are sitting, I found the A350 to be more quiet, and I just got the feeling of it being cutting edge, The 777 Is so noisy it's insane, but I can live with it because the engines are so impressive, esp starting up.
Amazing to think Geoffrey De Havilland was trying similar noise reduction measures on the Avon's in the comet 4 nearly 70 years ago. They were fluted jet pipes rather than chevron on the cold section but same idea.
Having flown on a 747-8, the plane was easily the quietest I've been on. The normally loud roar on takeoff was a dull rumble and during cruise, you couldn't even hear the engines over the air conditioning. My guess is that the GE9X was "good enough" in terms of noise, and adding chevrons offered no significant noise benefit, so they cut them out for the slight drag reduction.
I flew on a 787-9 for around 5 hours. I'm not sure if it's because I don't fly often but, when the plane took off, I barely heard the engine spooling up. I took a flight a few hours after on a 777, and the engine sound was much more noticable. This was back in 2019, but I still remember it quite well.
Hi, I think you got mixed up between compressor and turbine, at 1:37 you mentioned that air go through turbine to be compressed and mixed with fuel which is wrong, air goes through compressor first to get compressed then it mixes with fuel and ignition takes place, later in the clip , at 5:35 you said “mixer sit behind the high pressure compressor” actually you meant sit behind the turbine
i flew on a Virgin Atlantic Boeing 787-9 from LHR-JFK last month, then returned on a Delta Boeing 767-400. And in 2016, a Virgin Atlantic Boeing 747-400 from LHR to MIA, and returned on the exact same plane. On takeoff, the 787 was significantly quieter than the 767 and the 747, but, the 767 and 747 brought much more excitement to me and was more fun overall. i think that chevrons are effective, but planes that dont have them are better imo, just because of how loud the roar is on takeoff
2:10 "This mixing [of distinct co-axial hot and cool airstreams] results in a turbulent flow that produces the classic roar of a turbofan. Chevrons help to smooth this mixing of hot and cool air in turn reducing engine noise ..." Way more 'splainin needed here Coby. Maybe a whole 10-minute episode on the thermal-acoustic phenomenon.
Adding chevrons on the GE9X would have reduced its thrust and Boeing didn't see the need. This is actually the reason as to why Airbus planes have no chevrons Also don't forget, the Embraer 190 has some small chevrons on its engine exhaust.
Mixers don't sit behind the high pressure compressor. They sit behind the low pressure Turbine, which is a huge difference. The Temps are high nonetheless, so i get your point. (Edit: Spelling)
Coby, You are such a handsome stud! - I really look forward to watching your videos...you do a great job of making complicated things seem simple!.. P.S. I love bears!
Fuel burn. Plannnnne and simple. The chevrons reduce noise at the expense of increased induced drag which burns more fuel. This was a calculated trade-off in that flying to airports with noise abatement procedures and cabin comfort. However, they needed a substantial fuel burn decrease for operating expenses to justify airlines to upgrade to the 777x. You can only push engine tech so far and make so many aerodynamic changes to the point where it just can't be improved enough to justify. Therefore, Boeing scrapped the pronounced chevrons to reduce drag. They still have small chevrons on the exhaust of the core but that's hidden inside.
It's much lighter than steel but much denser than aluminum. I'm sure it would be some alloy, and that makes it hard to know what its weight would be. But it wouldn't need to be super strong as a mixer, just heat resistant.
What a convenient video, cause I was just learning about mixers the moment I noticed them on base airplanes. The real curiosity came when I noticed Dassault Falcons had normal tubes when several American jets didn’t. Its crazy that sound dampening was what they are for, cause I always note how much quieter Falcons are compared to any other plane lol
As someone who lives under the approach for Paine Field and Boeing Field, where they are testing the 777x out of (you can see it take off from Boeing Field at 4:20), I've seen the 777x fly over on a few test flights as it's departing, and I gotta say, it's really quiet for it's size. It's absolutely nothing compared to the usual ups and FedEx md11s, 747s, and 757s that fly over. Those will make my house shake and wake me up at 5am when they fly out. The 777x and the 737 max, back when they were testing it, are barely audible over the usual sounds of cars and such. So they definitely figured out a way to cut down noise without chevrons.
Aviation Channel okay, and so you’re agreeing with me? CF6-80E1 vs GEnx-1B 1970’s vs 2000’s. Biggest difference relative to noise would be wide chord fan blades.
787 is so quite its my new most favourite plane, the noise so low, the lighting is futuristic, the cabin is amazing and looks brand new every time. Really the best plane for flying.
I must agree with KP Barbee. The A350 is quieter than the B87. Someday I hope to fly on the A380 and can see if that aircraft is as quiet as they say in these posts.
I flew a 787 for the first time in 2016, flying to/from Hawaii from Australia - roughly a 10 hour flight. However, I opted for the Economy Plus seats (directly behind Business class) which was forward of the main entry doors. I was incredibly impressed by the smoothness of the flight & remember a reduction in "flight noise". But it's hard to provide an objective interpretation when you're significantly forward of the wings/engines...
I live near the airport and often planes pass depending on which runway they are assigned to land. One thing I notice is, when a B787 is approaching to land the engine is a bit quieter compared to the common A320 & A330 that passes near our house.
also potentially the benefit of the chevrons is reduced as the engine size increases because of the reducing ratio of circumference vs. cross section area as the engine increases in size, so on the huge 777 engines it had more drawbacks and less benefits
I work at Boeing in Everett right next to Paine field. We have planes taking off all day and night. The only ones you really notice in the building and go to look at outside at are the Dreamlifters and the random UPS freighter 747’s and C-17’s doing touch and go’s. The 67’s 87’s 777’s and X all sound the same from a quarter mile away.
Coby I flew on an Aeromexico brand new 737 MAX before they were grounded and yes it was considerably quieter than the regular 737 NG, the whole plane experience was extraordinary, even the wifi was greate I face timed one of my sisters in Europe at 33000 ft. Out of the little fact that the MAX tends to crash frequently the plane is wonderful!!!
My first flight on a boeing a/c was on a B738M back in Dec 2021. It was significantly quieter than any other a/c I had travelled in before. Then I had travelled in a B738 in April 2022, and boy that was loud(I enjoyed it more though). So ya, Chevrons really do make a substantial difference imo.
4:40 yes there is. take the difference in drag coefficient due to the increase in AoA required due to the weight difference throughout the flight profile. Can be approximated easily in steady level flight, but there's also a benefit when climbing.
When I flew in an American Airlines 737 MAX 8 I couldn’t help but notice it was the quietest jet I’ve ever flown on! Way quieter that the older 737-800 I also flew on that trip so I think that Chevrons really do help… They also look so futuristic & cool!
Boeing, UTAS, and GE were involved in the design for the 787 nacelles, but UTAS is responsible eventually for the manufacturing and engineering of the entire nacelle system of the 787 (inlet, fan cowls, T/R and exhaust nozzle). The chevrons are located on the reverser cowling which is UTAS responsibility. If UTAS feels that the chevrons cause their components to be too heavy or cause detrimental effect to aircraft performance (ie too much fuel consumption), they collaborate with Boeing and they choose whether or not to get rid of them. For the 9x, Boeing likely took the lessons learned from the GENx and decided to go in a different direction. On top of that, if I'm not mistaken, Boeing is building them mostly in house. Boeing, while it is one of the top airframe manufacturers out there, have little experience (before the MAX) to build engine nacelles. They used to back during the days of the 757 and 737 classic (-300/-400/-500), but when they spun off part of their company in Wichita to become Spirit Aerosystems, lost most of their nacelle expertise. They recently have tried to regain that expertise by doing the manufacturing and engineering of most of the 737 MAX nacelles out in South Carolina. The cowling trailing edges are also prone to lightning strike damage and while all trailing edges are prone to this damage, it is more difficult to repair the trailing edge of chevrons because of the carbon composite laminate material and therefore introduce a new cost. Maintenance cost and aircraft down time. The 787 chevrons are mainly there to reduce noise levels and if the chevrons are not at their optimal geometry, may affect those noise levels. They can be repaired obviously to restore their function along with the strength, but again, the time and cost is the issue. The next issue, I think, is the customer support going almost entirely through UTAS. Boeing handles the initial service request from its customers, but UTAS is entirely responsible for any disposition or repair procedure, which makes things more difficult. While most customers would like something that reduces noise, unless it is a hard requirement from a governing body like the FAA, customers will NOT latch onto it if they think it'll cost them more money in the long run to operate. Next, I keep saying UTAS, but this company has gone though much change since the 787 nacelles were done. It started out as Rohr Aircraft, then it became Goodrich (when they got the 787 contract for the GE and Trent engines), then it became UTAS when they allowed UTC to buy them, then UTC spun it off and it became Collins, then it got picked up by Raytheon. UTC is an umbrella company that includes such companies as Pratt and Whitney. The change in company and its responsiveness (or sometimes lack of to Boeing) could be another reason why Boeing went in a different direction on its 9x nacelles.
As a person who worked in design at the time of the new cowling shapes being introduced, from what I heard quietly, pun intended, it was implemented to cut decibels realizing the new much larger windows on the 787 would make for a smaller insulated area. Weight is the most important thing besides strength/longevity/manufacturability/cost/serviceability... It's a balancing act. It was a fun challenge when I started in design, that if you as a designer were able to redesign a part or small assembly to shave 1 pound in two line numbers without adding any additional costs (ie It had to pay for itself in two planes) you got a 25k bonus. I only know a handful who have done it. That two planes without increasing the manufacturing cost is the challenge. So everyone who takes a big sh!t in the airport is actually doing their part to reduce global emissions.
Actually my dad helped design the engine and he said that they don’t have chevrons because the nozzle is a whole different design from like the 787 or 737 max
I am a baggage handler for southwest airlines and I can say the difference in noise between the 737s and the 737 max is astounding. I can hear a normal 737 from 20 gates away at DEN with hearing protection in, but if I am talking with my coworkers that max will deffinately sneak up on you. I'll admit I've left a max waiting on the j-line once or twice while discussing the turn plan with my crew
My only experience is with the 787 so it's difficult to say, and that plane is significantly quieter than anything, bar the a350 (which doesn't have the chevrons). I need to try the 747-8i to give you a definitive answer:)
I got to fly on a 747-8i with Lufthansa in 2016 from Frankfurt to Washington. The trip to Frankfurt was on a 747-400, and I could definitely hear the difference between the two planes!
John Ohman (GE test pilot for the GE9x) confirmed to me on Twitter several years ago that the use of “the use of new ceramic matrix composite materials on the GE9X allows us to do some things with combuster hardware to meet our acoustic requirements without a drag penalty.” I’m think theory three is actually correct.
Although I'm an Airbus fan, the 787 with Chevrons was the quietest plane I've flown on. Amazingly, I was also surprised how quiet the A380 was given 4 engines, but also the most comfortable by a country mile. As someone who flies (ahem...flew) every couple of weeks, I never thought I'd say I'm missing flying ATM.🤦♂️
FYI - Hey Coby, Titanium burns. The super nickel alloys are resistant to the high temperatures of a jet engine because they are resistant to creep - they keep their shape in high temperatures. Titanium is used on the cold side - the air intake fan....
I had flown on “The Max” several times before the FAA grounded it. The Max is much quieter. However, that could also be a function of the acoustics inside the longer cabin and that it is a newer plane with a different resonance owing to the composite materials used in manufacturing the plane.
Having flown on both, I feel the inside cabin noise is less on the Airbus A350s than the Boeing B787s. These are both quieter than all the other wide and narrow body jets I've travelled on.
The use of a mixer is the most likely reason why they're ditching chevrons. I've worked around the GE Passport 20 engines on the Global 7500 jets and I always admire the design and how those beautiful mixers look whenever I'm walking behind the aircrafts or when the thrust reverser assembly is taken off from the engines. The GE Passport 20 is the first civilian aircraft engine to use CMCs, the material has been previously used in only military engines,..
Coby, just a quick note. Even some APU's use those corrugated mixers but they are made of inconel, Hasteloy X or W, or Waspaloy to handle the heat in the exhaust stream. Titanium just wouldn't hold up.
Did I accidentally swap the words "compressor" and "turbine"? You bet! Always remember to proofread, folks :)
how DARE you make such a mistake! You should be have you channel banned! lol 😂
I believe you also swapped the words titanium and inconel . Titanium is heat resistant enough for aircraft firewalls and components that separate the engine from the airframe, but it cannot take exhaust levels of heat for more than a few hours before developing metallurgical conditions of alpha-case and hydrogen embrittlement. Which as the name suggests, weakens the metal. I don't know about other manufacturers, but I know Boeing likes to use inconel-718 as the metal choice for exhaust ducting.
I hope I don't sound like a dick correcting you, I am instead hoping to share some information and maybe make you curious enough to learn more about these kinds of metals and their applications. Cheers!
rolls royce new engine with blue fan blades???
Alcino Vilela Belluzzo Filho this joke will be outdated in a few months once it’s flying again.
@@alphamalegold Air is not compressed in the high pressure turbine. Air is compressed in the compressor. In fact compressed air after combustion drives the High pressure turbine ( turbine blades).
Titanium is not very heat esistant material and its alloys, Alpha, beta and alpha + beta are not very heat resistant. They are considered semi high temperature alloys and employed in the applications when the so called homologous temperature is about 0.5. TiAl must also be used which is of very good oxidation behaviour but again is not high temperature structural alloys.
You meant nickel based super alloys which are structural alloys and employed in high pressure turbine. The "operating temperature" of the Nickel based super alloys is somehow around its melting point , sometimes higher , due to its oxidation behaviour, alumina formation, and TBC.
Some
I asked this same question back in 2018 to one of the chief test pilots for the GE9x, Jon Ohman. This was his response: “The chevrons seen on the nacelles of (the GEnx and LEAP-1B) reduce noise, but with a slight drag penalty. The use of new ceramic matrix composite materials on the GE9X allows us to do some things with combuster hardware to meet our acoustic requirements without a drag penalty.”
With that answer, I think a mixture of theory two and three is the correct answer to the question posed in the video.
Thanks. Saved me 10 minutes of my life.
Thanks bro!
Welp, I was 7 mins in when I started reading comments .
So he was right in his theory .
I think the Chevrons look cool and more futuristic, giving the plane a better look .
But the chevrons do look pretty sexy though
Coby, you need to make a flight review channel. It can be called Coby Complanes :D
Haha love this, the last review he made was pretty complain-ey
That’s actually such a good name
Hahaha love it. Got any ideas for a potential flight sim channel as well??
@@cobyexplanes How about Coby Re-Planes xD (like replays, or reviews) sorry it's not my mothertongue haha
First review on a 747-8 to FRA plz
@@Lukatz Ive actually been thinking of doing that - I really want to fly on the -8 before they're all retired
Engines with chevrons looks so cool.
Yea they really do
Oppie
Agreeable
I know. when I see other engines now they look boring and outdated
My question is…. When did DreamLand get wi-fi access?
The 777x flew over my head at about 3000 Ft. It was descending on a right base to Boeing Field in Seattle with the power probably at idle. The only noise I heard was a very quiet swishing sound probably from airflow over the air frame and engines. It was so quiet that I was startled when I looked up and saw this really large airplane so close. BTW, the reason for the quiet treatment on the engines is for noise reduction as perceived from the ground. There are lots of noise restrictions around airports around the world particularly at big city airports where this large airplane will operate. Boeing would love to be able to gain noise exemptions for landing during "quiet periods" at some place like LHW.
I am really wondering if Boeing wanted a 777X or an A380neo/747X
You didn't hear anything because it was descending. It's already the case of most airplanes nowadays : you don't hear anything when they are descending at idle thrust.
@@noah9130 Protruding landing gears do create massive turbulence though, which should create lots of noise. I haven't done plane-spotting for a while now, and I clearly did not pay attention to the noises landing gears on inbound planes made during my last spot. Would love to do further comparisons on noise levels between outbound and inbound flights in the future.
@@paulshi5974 That's true. I live 5 miles away from an airport and when they are flying above my house at fast speed like 180 knots with their landing gear deployed, it creates a lot of noise especially when they are deploying it right above my house.
@@noah9130 Wow you can actually hear the moment landing gears deploy? I honestly don't know how to react haha. For one thing that's some perfect timing for ya, but I don't know if hearing landing gear noises every day has driven you mad or not...
My guess is that large bypass ratio makes the engine quieter. The GE9X engine has larger bypass ratio and less number of fan blades which already makes the engine quieter that renders chevron nozzle unnecessary.
This makes waaaaaay more sense.
Exactly this was my guess as well.
I was thinking the bypass and larger diameter also make them less effective.
@@yolo_burrito As bypass ratio (BPR) increases the overall efficiency of the engine increase which is a primary factor that yields lower TSFC for the turbofan engine. Additionally high bypass ratio engine can produce a greater amount of thrust while consuming the same amount of fuel as a lower BPR engine. Basically the additional weight added by bigger engines is negated by less fuel consumption due higher BPR. The engine doesn't need to spin as fast as it would to create the same amount of thrust at a lower BPR.
eWorkx I probably should’ve been more clear. I meant it makes the chevrons less effective not the engines. The negligible improvement of the chevrons along with larger diameter and higher BPR makes chevrons less effective.
I flew 787-8 and it was very comfortable, the cabin noise is a lot lower than in older airplanes. It was one of the best flights Ive ever made and it was a 12 hours flight!
787 without Chevrons will look way less beautiful
I couldn’t even imagine...
No duh. Its not even a 787 then
Chengyou Jiang the chevrons do look pretty cool, the 747-8 GEnX engines even cooler with the exhaust scalloped as well
If there was a plane with the face of an A350, and the wings and engines of a 787, that would be amazing, with the APU outlet of a 777.
I don’t think so. Looks cooler with the chevrons, yes. Still a beauty airplane.
Can’t be that it’s expensive. Would have made it uneconomical to put on the 737 Max. GE doesn’t build the nacelle. Boeing/UTC designs them, UTC builds them. This is the first thrust reverser that Boeing is fully designing and then building with Spirit. Could be the result of a closer collaboration of between GE and Boeing on propulsion integration.
Exactly, it would only add slight cost to the aircraft in general. They aren't even replaced when the engine is replaced. They're just part of the reverser doors.
Boeing usually does the engineering but, in the case of the 787, Rohr, Inc. (owned by UTC) put a decent percentage of a billion dollars into the the design and tooling for the 787 nacelles for both the GE & RR engines (at the same time they had the engineering group for the A350 nacelles working on the next floor down in the same engineering building.)
Well explained... and produced! Good audio, including non-intrusive music, voice level and great video clips.
I think I've only been on one 737 with chevrons. Screaming babies on the flight cancelled out any noise reduction of the engines.
Glad you enjoyed :)
I agree, 787 takeoff was so quite. I also flew 737 Max on Southwest, very quite also. I kind of miss the loud engines at takeoff, though. My first jet flight was an Eastern Airlines B720. Such power & noise. In addition, I love the 757 takeoff power.
Some of this is down to the runway and initial climb slope. They calculate the minimum power setting needed for a location and gross weight to avoid stress on the engines and get longer life. A long runway followed by a good clearway with dense air and low fuel(short flight) can call for a very low takeoff power. The 757 was designed specifically for medium haul from difficult airports with low density air so it has extra power available. The MAX and 787 did not have this design target.
@@mytech6779: Actually, the 757 is my favorite plane as a passenger, reminds me of the B720, which was also designed for shorter runways & smaller airports--from what I have read.
I was on a flight with the 787 and then my connecting flight right after was a 777. The difference was pretty great with the 787 being much more quiet.
Yes I have flown onboard the b787 the engines aren't noisy during take off and landing
Same with 737 max
Much quieter than a350
I have also flown on a 787, it was a Boeing 787-9 and it is not that loud during takeoff and landing
alaska airlines 001 I was on an a350 and 787 back to back and 787 was much quieter during takeoff
@@AntonLoves737 are you sure which airlines
Always a pleasure watching your videos. I've flown the 787-8 and 78-9 and I must admit it is a very "silent" aircraft.
I've been on both the 747-400 and 747-8I, I can clearly hear the difference in cabin noise induced by the engines.
But how much of the difference is the chevrons itself vs the fact the GENx is 20 years newer?
CF6 vs GEnx. Not a fair comparison regardless of chevrons.
The difference is because of the difference between difference in bypass ratios of those 2 engines rather then chevrons.
Agree. The fair comparison would be the B787 vs the A350 or A330neo.
@@youngtimer964 could be rolls royce or pratt & whitney engines too than the ge cf6
I've been flying airliners for over 30yrs, and I have to thank you for your proper use of terminology and clarity in explaining the subject matter. There are many TH-cam content producers that can learn from your high-level graphics and proper nomenclature.
This hurts my head. GE makes the engine not all of the composite structure around it. Just like the classic 777, Boeing designed the Nacelle. Boeing built the 777 Nacelle in Wichita.
That same facility builds the 777x is now Spirit. Boeing designs the Nacelle to meet specific noise requirements. Once the requirements are met, you keep the design as simple as possible. K. I. S. S.
Chevrons are designed to enhance mixing between the different flows and not to smooth the flow. Forced mixers are only effective for lower bypass ratio engines and become too heavy on large engines and ineffective at high bypass ratios. They are typically fabricated from sheet metals and are not as expensive as you may think. Chevrons were originally intended to reduce community noise (what the people on the ground experience). The B787 Chevrons are aimed at reducing shock cell noise in flight which is caused by shock waves in the exhaust flow interacting with the shear (mixing) layer which can then propagate upstream and into the cabin. Composite fuselages are not good at attenuating noise created in this way and either you need to reduce the noise at source (disrupt the shockcells in the flow) or absorb the noise. The Chevrons on the B787 are not very good at reducing noise and increase fuel burn due to the drag on the Chevrons from the high-speed flow on the inside of the nozzle. They also change the amount of flow through the nozzle at low pressure ratios which is bad for the fan. Based on experience of Chevron design and testing, it is more effective to add sound absorbing to the fuselage than add a fuel burn penalty to the engines. So, answer 2. A competitor to Boeing doesn't have Chevrons on their nacelles for this reason. Shame really, the aerodynamics are interesting!
An aerodynamicist who worked for years on Chevrons and forced mixers for an engine manufacture.
I saw the 777-9 takeoff from the Yuma Arizona airport while standing just outside the FBO. It's very quite, especially compared to the other jets flying in and out of there. Don't think it really needs the chevrons.
Excellent video. Thanks for taking the time to film and edit it and of course for positing it for our benefit. Keep up the good work! -Migs
First time I flew on a 787 the takeoff engine noise inside the cabin was so low that I was worried the pilot hadn't throttled up the engines sufficiently and quickly started verifying the closest emergency exit location.
The engine sound at full throttle reminded me of the sound of a vacuum cleaner.
clrd4tkf the same thing happened to me except i got out of my seat and started opening up the cabin door screaming “we are all going to die!!!”
I like the 757 at takeoff, you hear and feel that power, like a race car.
@@mytech6779 I think the 757 is what happens when the fighter design group gets bored and designs an airliner. :) Personally, though, from a sound perspective, the GE90 is my favorite engine spool sound.
As far as being surprised at the lack of sound on takeoff, this is also my experience with the geared turbofan on the C-Series (now A220.) Those things are amazingly quiet, even when sitting right beside the engine at takeoff power.
Hi Coby, just flew in a 737 Max-9 from Iceland to Seattle. It was the quietest and smoothest flight I can recall ever having.
I flew on a 787-9 and the noise reduction was extremely significant. Made the whole trip more relaxed. Easily the quietest plane I have ever flown on.
Thanks for your concern about sound quality and pronunciation, this makes it easy for a non-native English speaker to understand. Good job.
Its possible that the ge9x exhaust outlet, with its almost rounded octagonal shape, does the same thing as the chevrons for less drag penalty.
No u are wrong
Nope
Well, I have been on a 787-8 once before, and I can definitely say it is VERY quiet in comparison with other aircraft, such as the 777 or 767, even the A350.
The mixer thing, as he pointed out, makes no sense given that it's an unmixed design. Overall the outer nacelle chevrons aren't because of mixing between core and bypass flow, it's bypass and ambient flow. My understanding is it's not about temperature so much as velocity, fast air coming out and mixing with slow surrounding air, with a shear layer, makes the noise, and chevrons help to break up that shear layer and cause quicker, thus quieter, mixing between the fast and slow air. The slower the bypass air, the less this is needed, which is why high-bypass turbofans are quieter than low-bypass or turbojets. As others point out, maybe the bypass ratio is so huge, the outlet velocity so low, that they just aren't needed. The other possibility, somewhat related to the mixer idea, is that there's some other technological solution being used instead. Maybe something secret (trade secret, not as in classified) which is why Boeing and GE haven't made the reasoning public.
787- I flew on....was by far...and I mean BY FAR the quietest ride I've ever been on. Even on take-off, I could hold a conversation at normal volume. That blew my mind.
Finally someone talked about the B777x chevrons! And tbh i got to the same conclusions but i heard(i don't remember where) that the chevrons make the engine 2% less efficient, and on a plane like B777 this would be a big problem.
Nice .. I like the Chevrons :) wish they werw continued in the 777x too
No one:
Literally no one:
Coby: let me explane
Bad pun...
@@classicjoker2008 If you're saying bad pun for the "explane" that's literally what this channel is called
C-
You tried.
I did not know that I need to know about chevrons until this video :D
Lame meme.
I have flown on a 787, and a 777-300ER, and I have to say that the 787 was much quieter, especially during takeoff. The rumble is still there during takeoff but the scream is much less pronounced.
This question is always in my mind. Thank you for explaining this!
You mean his theories
@@tripleceven no, i always thought why ge9x doesn't have cheverons
@@alaybey9771 you said thank you for explaining this like what he said was factual. He clearly said they were theories.
@@tripleceven well, this is some sort of explanation
@@alaybey9771 i see
Flew round trip on Air Canada, YVR to Incheon/Seoul in 2017, and those 787-9 were VERY quiet and comfortable in Premium Economy. Fantastic flights!!
If you look at the GEnX on the 747-8, the primary exhaust is also scalloped
Myself living in the Everett area! I woukd say the 777X engines compete with the noise level of the late Gruman A6 or EA6B's as something certainly had to replace them in the otherwise noiseless northwest skies! Easily the loudest jet engine produced in decades whether it be from its sheer size or otherwise its noise is at times is undeniable! Sometimes having you look for the ghost of an aircraft seemingly right on top of you when in fact it could possibly be just spooling up infact miles away, having them be that of deceptivly and incredibly loud engines indeed!!! They have proved to be louder than I ever would have imagined them to be, especially after as you said the technology and attention put into the mitigation of noise on the 787's and 747's most recent engines! These new engines are said to be the largest ever made as so may be that of their volume level maybe the largest level in all of commercial aviation! Substantally louder than I would have anticapated by far... Perhaps noise mitagation may be something Boeing and GE are planning on addressing at a later date, I do not know? I would have to say so far it has been completely over looked for of whatever reason that maybe! I'm sure one could be left to speculate with out specifity like you were here in this here video blindly speculating of different senerios as to what may see to be of plausable reasons for the ommission of noise mitagation as your guess is as good as mine. Lack of concern perhaps after spending of the time and effort to accomplish of amazing results in such a feild to then see to loose of interest or even acknowledge of its in anyway further need? I dont know but it certainly has one scratch of their head as to what is or may be going on, for sure! I'd surely be interested in of any information you may see to gleen on the subject! My suspect is that there may just not be any information to be had. Hence the noise level of the largest jet engine ever made seeing to have of the noise level that it does just being what it is! A product of the largest jet engine in the world! What else would anyone see to expect? Rendering it a non-issue, I guess... You said that GE's design made for a quieter noise level in itself and maybe it does but from my ears experience I would further guess that of any such thing went by the way side along with the cheverons, but i have no idea as to its design other than large and loud being of the present results!
Chevrons? I call them Shark teeth. !:- )
Bio mimicry
I do agree
And rightly so!
I flew on both A350 and B787, both times sat near the trailing edge of the wing. The 787 was definitely quieter. But I like the A350 better..
Think it depends allot of where you are sitting, I found the A350 to be more quiet, and I just got the feeling of it being cutting edge, The 777 Is so noisy it's insane, but I can live with it because the engines are so impressive, esp starting up.
The mixer sits where...?
Glad someone else heard that
@@batz910 I guess it's easy to mix up(no pun intended) compressor and turbine. But still they do very different tasks!
... somewhere in the cabinet under the kitchen sink.
01:32 is also pretty bad :’)
@@HermesBird11 Why? Seemed pretty accurate to me.
Amazing to think Geoffrey De Havilland was trying similar noise reduction measures on the Avon's in the comet 4 nearly 70 years ago.
They were fluted jet pipes rather than chevron on the cold section but same idea.
Having flown on a 747-8, the plane was easily the quietest I've been on. The normally loud roar on takeoff was a dull rumble and during cruise, you couldn't even hear the engines over the air conditioning. My guess is that the GE9X was "good enough" in terms of noise, and adding chevrons offered no significant noise benefit, so they cut them out for the slight drag reduction.
You should try flying on an A380 or A350 bro
Great video coby, very professional and so NOT ANNOYING like many TH-cam folks! I’m in!
Before I clicked on this video, I thought the answer could be stated in 30 seconds. But you did a great (9 minute) job of explane'in the reasons 👍
It's not as simple of an answer as I originally thought. Before doing research for this video I thought it'd be 4 minutes tops but alas
I flew on a 787-9 for around 5 hours. I'm not sure if it's because I don't fly often but, when the plane took off, I barely heard the engine spooling up. I took a flight a few hours after on a 777, and the engine sound was much more noticable. This was back in 2019, but I still remember it quite well.
Boeing jets aren’t the only planes with Chevrons. The Embraer 170-195 have hot section chevrons and so do some CFM equipped A320 series aircraft.
Right. The Boeing ones are the only ones with the more distinctive chevrons on the nacelles, though.
That is wrong but very close
Learn something every day. I always thought they were just decorative. Thanks.
Hi, I think you got mixed up between compressor and turbine, at 1:37 you mentioned that air go through turbine to be compressed and mixed with fuel which is wrong, air goes through compressor first to get compressed then it mixes with fuel and ignition takes place, later in the clip , at 5:35 you said “mixer sit behind the high pressure compressor” actually you meant sit behind the turbine
i was going to say the same!, it was not the turbine, it was the low and high compressor
Yep you're right, this is why you always ned to proofread your work! lol
i flew on a Virgin Atlantic Boeing 787-9 from LHR-JFK last month, then returned on a Delta Boeing 767-400. And in 2016, a Virgin Atlantic Boeing 747-400 from LHR to MIA, and returned on the exact same plane. On takeoff, the 787 was significantly quieter than the 767 and the 747, but, the 767 and 747 brought much more excitement to me and was more fun overall. i think that chevrons are effective, but planes that dont have them are better imo, just because of how loud the roar is on takeoff
Yes 789 I was on was really quiet was disappointing because I love jet noise!!
2:10 "This mixing [of distinct co-axial hot and cool airstreams] results in a turbulent flow that produces the classic roar of a turbofan. Chevrons help to smooth this mixing of hot and cool air in turn reducing engine noise ..."
Way more 'splainin needed here Coby. Maybe a whole 10-minute episode on the thermal-acoustic phenomenon.
Adding chevrons on the GE9X would have reduced its thrust and Boeing didn't see the need. This is actually the reason as to why Airbus planes have no chevrons
Also don't forget, the Embraer 190 has some small chevrons on its engine exhaust.
I've seen chevrons on the Antonov 124
@@aarondynamics1311 yeah that too
Actually some A320s with CFM engines have chevrons (it's hard to see but they do).
Mixers don't sit behind the high pressure compressor. They sit behind the low pressure Turbine, which is a huge difference. The Temps are high nonetheless, so i get your point. (Edit: Spelling)
Coby, You are such a handsome stud! - I really look forward to watching your videos...you do a great job of making complicated things seem simple!.. P.S. I love bears!
Fuel burn. Plannnnne and simple. The chevrons reduce noise at the expense of increased induced drag which burns more fuel. This was a calculated trade-off in that flying to airports with noise abatement procedures and cabin comfort. However, they needed a substantial fuel burn decrease for operating expenses to justify airlines to upgrade to the 777x. You can only push engine tech so far and make so many aerodynamic changes to the point where it just can't be improved enough to justify. Therefore, Boeing scrapped the pronounced chevrons to reduce drag. They still have small chevrons on the exhaust of the core but that's hidden inside.
Does this engine have a greater bypass ratio? If so, perhaps the resulting change in ratio between hot and cold flows creates less turbulence-noise.
I've always wondered about that serrated engine design, glad to have stumbled on this 👍
5:38 "..not only are these materials heavy and expensive.." - isn't titanium actually quite light, considering its strength?
It's much lighter than steel but much denser than aluminum. I'm sure it would be some alloy, and that makes it hard to know what its weight would be. But it wouldn't need to be super strong as a mixer, just heat resistant.
@@CodeKujo Exactly. And it's gonna be thick, too.
1:49. Coby, the source says Safran, but the video is from Pratt and Whitney.
r..emember the old 707's they had something at the engine exhaust, that looked suspiciously like these "new" 'mixers'!
No those are the reverse thrusters
737max I was on was not only the quietest I've been on, but the noise it produces was also far less "annoying". it is one heck of a plane
I have been on the Qantas Dreamliner, and you can barely hear the engines when inside the plane
What a convenient video, cause I was just learning about mixers the moment I noticed them on base airplanes. The real curiosity came when I noticed Dassault Falcons had normal tubes when several American jets didn’t. Its crazy that sound dampening was what they are for, cause I always note how much quieter Falcons are compared to any other plane lol
Good question
- Shrek
As someone who lives under the approach for Paine Field and Boeing Field, where they are testing the 777x out of (you can see it take off from Boeing Field at 4:20), I've seen the 777x fly over on a few test flights as it's departing, and I gotta say, it's really quiet for it's size. It's absolutely nothing compared to the usual ups and FedEx md11s, 747s, and 757s that fly over. Those will make my house shake and wake me up at 5am when they fly out. The 777x and the 737 max, back when they were testing it, are barely audible over the usual sounds of cars and such. So they definitely figured out a way to cut down noise without chevrons.
I've been on the 787-8 before, and it's much quieter than the A330.
nah then
Generational difference in engines, my friend
Well d'oh!
That's like saying B737-800 is more efficient than B727. Obviously.
@@youngtimer964 GE CF6 to GEnx
Aviation Channel okay, and so you’re agreeing with me? CF6-80E1 vs GEnx-1B 1970’s vs 2000’s. Biggest difference relative to noise would be wide chord fan blades.
787 is so quite its my new most favourite plane, the noise so low, the lighting is futuristic, the cabin is amazing and looks brand new every time. Really the best plane for flying.
*quiet
I must agree with KP Barbee. The A350 is quieter than the B87.
Someday I hope to fly on the A380 and can see if that aircraft is as quiet as they say in these posts.
Simple it doesn’t need one for noise reduction
Right
I flew on a Virgin Atlantic 787-9 overnight. I had never been able to sleep on a flight until then! Really made a difference
First 787 flight I took was on a Virgin 787-9 - I think I slept like 6 hours straight it was awesome
Pretty surprised you say that chevrons are on their way out. They wer introduced just 13 years ago,that is surprisingly young.
I flew a 787 for the first time in 2016, flying to/from Hawaii from Australia - roughly a 10 hour flight. However, I opted for the Economy Plus seats (directly behind Business class) which was forward of the main entry doors. I was incredibly impressed by the smoothness of the flight & remember a reduction in "flight noise". But it's hard to provide an objective interpretation when you're significantly forward of the wings/engines...
787 was definitely a lot quitter compared to 777!! N much more peaceful
I live near the airport and often planes pass depending on which runway they are assigned to land. One thing I notice is, when a B787 is approaching to land the engine is a bit quieter compared to the common A320 & A330 that passes near our house.
They design for noise at takeoff thrust, that is where you will get the real difference.
also potentially the benefit of the chevrons is reduced as the engine size increases because of the reducing ratio of circumference vs. cross section area as the engine increases in size, so on the huge 777 engines it had more drawbacks and less benefits
I work at Boeing in Everett right next to Paine field. We have planes taking off all day and night. The only ones you really notice in the building and go to look at outside at are the Dreamlifters and the random UPS freighter 747’s and C-17’s doing touch and go’s. The 67’s 87’s 777’s and X all sound the same from a quarter mile away.
I wish I had an airplane joke! 😅
Just found this channel and instantly subbed! Can't wait for what's more in store ✈
Welcome aboard :)
Coby Explanes Thank you Captain! 👨🏻✈️
I appreciate the theories, you could have just included the T word in the title.
Coby I flew on an Aeromexico brand new 737 MAX before they were grounded and yes it was considerably quieter than the regular 737 NG, the whole plane experience was extraordinary, even the wifi was greate I face timed one of my sisters in Europe at 33000 ft. Out of the little fact that the MAX tends to crash frequently the plane is wonderful!!!
I found the A350 even quieter than the 787 to be honest.
This is the question I was asking myself. Thank you.
My first flight on a boeing a/c was on a B738M back in Dec 2021. It was significantly quieter than any other a/c I had travelled in before. Then I had travelled in a B738 in April 2022, and boy that was loud(I enjoyed it more though). So ya, Chevrons really do make a substantial difference imo.
Coby is always getting hotter. Love the cub beard😍
He's flippin’ adorable. Glad to see a perception that aligns with mine.
4:40 yes there is. take the difference in drag coefficient due to the increase in AoA required due to the weight difference throughout the flight profile. Can be approximated easily in steady level flight, but there's also a benefit when climbing.
When I flew in an American Airlines 737 MAX 8 I couldn’t help but notice it was the quietest jet I’ve ever flown on! Way quieter that the older 737-800 I also flew on that trip so I think that Chevrons really do help… They also look so futuristic & cool!
I'm impressed! Very nice work. Thanks.
Boeing, UTAS, and GE were involved in the design for the 787 nacelles, but UTAS is responsible eventually for the manufacturing and engineering of the entire nacelle system of the 787 (inlet, fan cowls, T/R and exhaust nozzle). The chevrons are located on the reverser cowling which is UTAS responsibility. If UTAS feels that the chevrons cause their components to be too heavy or cause detrimental effect to aircraft performance (ie too much fuel consumption), they collaborate with Boeing and they choose whether or not to get rid of them. For the 9x, Boeing likely took the lessons learned from the GENx and decided to go in a different direction. On top of that, if I'm not mistaken, Boeing is building them mostly in house. Boeing, while it is one of the top airframe manufacturers out there, have little experience (before the MAX) to build engine nacelles. They used to back during the days of the 757 and 737 classic (-300/-400/-500), but when they spun off part of their company in Wichita to become Spirit Aerosystems, lost most of their nacelle expertise. They recently have tried to regain that expertise by doing the manufacturing and engineering of most of the 737 MAX nacelles out in South Carolina.
The cowling trailing edges are also prone to lightning strike damage and while all trailing edges are prone to this damage, it is more difficult to repair the trailing edge of chevrons because of the carbon composite laminate material and therefore introduce a new cost. Maintenance cost and aircraft down time. The 787 chevrons are mainly there to reduce noise levels and if the chevrons are not at their optimal geometry, may affect those noise levels. They can be repaired obviously to restore their function along with the strength, but again, the time and cost is the issue. The next issue, I think, is the customer support going almost entirely through UTAS. Boeing handles the initial service request from its customers, but UTAS is entirely responsible for any disposition or repair procedure, which makes things more difficult. While most customers would like something that reduces noise, unless it is a hard requirement from a governing body like the FAA, customers will NOT latch onto it if they think it'll cost them more money in the long run to operate.
Next, I keep saying UTAS, but this company has gone though much change since the 787 nacelles were done. It started out as Rohr Aircraft, then it became Goodrich (when they got the 787 contract for the GE and Trent engines), then it became UTAS when they allowed UTC to buy them, then UTC spun it off and it became Collins, then it got picked up by Raytheon. UTC is an umbrella company that includes such companies as Pratt and Whitney. The change in company and its responsiveness (or sometimes lack of to Boeing) could be another reason why Boeing went in a different direction on its 9x nacelles.
As a person who worked in design at the time of the new cowling shapes being introduced, from what I heard quietly, pun intended, it was implemented to cut decibels realizing the new much larger windows on the 787 would make for a smaller insulated area.
Weight is the most important thing besides strength/longevity/manufacturability/cost/serviceability... It's a balancing act. It was a fun challenge when I started in design, that if you as a designer were able to redesign a part or small assembly to shave 1 pound in two line numbers without adding any additional costs (ie It had to pay for itself in two planes) you got a 25k bonus. I only know a handful who have done it. That two planes without increasing the manufacturing cost is the challenge.
So everyone who takes a big sh!t in the airport is actually doing their part to reduce global emissions.
I found the 787 quieter but more impressive to me was the smooth ride due to the flexibility of the composite wings.
Actually my dad helped design the engine and he said that they don’t have chevrons because the nozzle is a whole different design from like the 787 or 737 max
@@InForTheLonghaul because that is how far technology has come ;)
I am a baggage handler for southwest airlines and I can say the difference in noise between the 737s and the 737 max is astounding. I can hear a normal 737 from 20 gates away at DEN with hearing protection in, but if I am talking with my coworkers that max will deffinately sneak up on you. I'll admit I've left a max waiting on the j-line once or twice while discussing the turn plan with my crew
My only experience is with the 787 so it's difficult to say, and that plane is significantly quieter than anything, bar the a350 (which doesn't have the chevrons). I need to try the 747-8i to give you a definitive answer:)
I got to fly on a 747-8i with Lufthansa in 2016 from Frankfurt to Washington. The trip to Frankfurt was on a 747-400, and I could definitely hear the difference between the two planes!
John Ohman (GE test pilot for the GE9x) confirmed to me on Twitter several years ago that the use of “the use of new ceramic matrix composite materials on the GE9X allows us to do some things with combuster hardware to meet our acoustic requirements without a drag penalty.”
I’m think theory three is actually correct.
Although I'm an Airbus fan, the 787 with Chevrons was the quietest plane I've flown on. Amazingly, I was also surprised how quiet the A380 was given 4 engines, but also the most comfortable by a country mile. As someone who flies (ahem...flew) every couple of weeks, I never thought I'd say I'm missing flying ATM.🤦♂️
FYI - Hey Coby, Titanium burns. The super nickel alloys are resistant to the high temperatures of a jet engine because they are resistant to creep - they keep their shape in high temperatures. Titanium is used on the cold side - the air intake fan....
I had flown on “The Max” several times before the FAA grounded it. The Max is much quieter. However, that could also be a function of the acoustics inside the longer cabin and that it is a newer plane with a different resonance owing to the composite materials used in manufacturing the plane.
Having flown on both, I feel the inside cabin noise is less on the Airbus A350s than the Boeing B787s. These are both quieter than all the other wide and narrow body jets I've travelled on.
I agree, but the absolutely quietest is the A380! Probably because it’s the most modern 4 engine plane.
Chevrons reduces radar crosssection therefore it’s too stealthy and towers can’t see the plane 🥷
Before Boeing, it’s the Embraer E series first use chevron’s to commercial flight. But it’s Boeing who first use chevron for wide body jets.
The use of a mixer is the most likely reason why they're ditching chevrons. I've worked around the GE Passport 20 engines on the Global 7500 jets and I always admire the design and how those beautiful mixers look whenever I'm walking behind the aircrafts or when the thrust reverser assembly is taken off from the engines. The GE Passport 20 is the first civilian aircraft engine to use CMCs, the material has been previously used in only military engines,..
Coby, just a quick note. Even some APU's use those corrugated mixers but they are made of inconel, Hasteloy X or W, or Waspaloy to handle the heat in the exhaust stream.
Titanium just wouldn't hold up.