Keeping MAX quiet - Chevrons.

[@GeeBoggs]

This man explains things beautifully to non-technical aviation enthusiasts, like me. I have learned much from his videos.

[@trishayamada807]

Robert G Gee Boggs, Jr. I very much appreciate his ability to take complicated concepts and puts them in easy to understand descriptions. It’s an excellent skill and talent. 👍🏼

[@bobbycvsixfour5258]

I like all his videos. I know a lot about Aviation and learn something new in all "MENTOUR PILOT" videos. Fun and Interesting facts. Don't forget the CREW :-)

[@tmkongen]

Yeah, been watching this guy all weekend :)

[@shannonflyer757]

I agree

[@MDE-11-84]

Yeah I agree. If it weren't for this pilots KZbin Videos I would most likely never feel safe on an international plane flight again.

[@kiwi5361]

The grounding keeps max also quiet !

MAXimum silence

[@KevinSandersMDGoHokies]

the ultimate noise abatement

[@ahmadtheaviationlover1937]

Kiwi hahaha

[@juliocamacho8354]

Sadly in 2 cases just after they hit the ground...

[@faustin289]

It makes them super fuel-efficient as well.

[@AndiYagudayevalt]

Also, the Delta 727 was so loud that when it took off from LGA that sometimes it shook the Windows, also whenever I think of a plane taking off I always remember the sound that the 727 made when it took off and flew over my house and made that turn, prolonging the noise, I freaking loved it.

[@Cardcollector-pz8hg]

Well explained as usual! As someone with an aerospace engineering degree, it is nice to hear someone who can explain these phenomena in a factual manner while making it understandable for all

[@MentourPilot]

And it’s awesome to hear that an aerospace engineer enjoys it! Great stuff!

[@bobfreestone1752]

As a former British Navy and Army Instructor Officer, I say with some authority, your instruction technique is of a very high order indeed. Thankyou.

[@69Phuket]

Easy now...! Brexit = Potential war again.. Hope i'm joking!

[@EleanorPeterson]

Yes indeed. There's an unspoken convention that airline pilots are required to speak like Petter. It inspires tremendous confidence when one's pilot doesn't sound like a stoned surfer, Beavis, or Butthead. To wit: "Yeah, like, we're, y'know, huh-huh... Cool! Dude, we were like BOOOOOM and the jet things were totally WHOA!!! So, anyhoooo, huh-huh, they cut this sorta HOLE stuff, no, I mean, like pinking shears, y'know? It was well radical 'cause... Um... OMG! I like totally screwed that up!!! Hey, everybody pose for a SELFIE!!! Yaaaaaay!!!" Ahem. Quite. Thank you for flying Elli Airways...

[@RayMelville]

@@EleanorPeterson that’s how some Southwest pilots sound like

[@ericsbuds]

it really is amazing how much aircraft noise has gone down over the years. I live very close to an international airport in Michigan and I barely notice the jumbo jets overhead these days. Great video!

[@MentourPilot]

Yes, it’s impressive. Thank you, I’m glad you liked it.

[@epleonard6350]

Max engines VERY quiet these days...

[@derahmad2831]

I barely hear them at all! 😅😅

[@faustin289]

Actually, it's all airplanes engines. They've all espoused that stealth paradigm I guess. It's been 2months that i have heard of an airplane landing or taking off lately

[@toby.maximillian]

It sounds as if they are Not even working

[@elcapitanyandel]

Very quiet 🤫😂

[@aliyusx]

Yes... And now so silent

[@paristhea]

Dear Mentour, you are really excellent, thank you so much for going to the trouble of making all these videos. You have this natural talent of being able to make complicated things easy to understand. Well done!!! I am not a pilot although I would love to be (a bit late for me now), but I am just an engineer. I did mechanical and aeronautical engineering at Glasgow University many moons ago and I was always fascinated by aircraft flying. I think the first bypass engines if I remember correctly were the so called Tay Engines developed by Rolls Royce in Scotland. I do remember our lecturer on "gas turbines" bragging about the Tay Engine and how efficient and quiet it was. I may be wrong of course, but this is what that lovely professor told us at the time. Thank you once again and please keep them coming.

[@vayalobo]

6 decibels (6dBA) on a logarithmic scale (the one used to plot noise levels) are by far not negligible. Great and very instructive video Mentour Pilot.

[@boblw1960]

I just wanted to say I love this site I'm 58 years old so I doubt I ever will become a pilot but I always love to learn new thing the way you explain things are so easy to understand I have learned so much about aviation because you now I wish I would have learned how to fly a plane I hope you don't mind people that are not or not wanting to be pilots I always wondered how a plane engine works and now I know I figure your never to old to learn new things I think keeping the brain active is a good thing keep up the great work you do I always look forward to anything new from you. Thank you

[@PlanesAndGames732]

5:28 VARIG, we here in Brazil miss you A LOT

[@whitemailprivilege2830]

Your hand motions really help me understand the subject matter

[@paulgracey4697]

I am old enough to remember the first flight in San Diego of the Convair 880. It had no bypass at all and four engines needing water injection both to suppress some of its sound, and add thrust at take-off. The 727 you reference was sold by Eastern Airlines as a "WhisperJet" but to its forward passengers, not to those below at take-off:) I live near a noise restricted airport, and recall another scheme that worked well to quell the noise of a then new regional aircraft, the BAE 146 which with four smallish engines (derived from a helicopter engine, I think, and thus much higher bypass than the typical JT8D found in its Douglas and Boeing competitors). The trick , I was told, was that the two engines on each wing rotated opposite to each other with some cancellation of their vortices as a result. Probably a maintenance headache keeping an equal number of each engine on hand for replacements.

[@davidmorris1879]

I love these short videos. Explained very well from a technical point of view and pilot's point of view. I have learned so much from them. Thank you very much for making them. You promoted Cambly in this video for improving English, and I find your command of English very good, as I know it is not your first language. Just one thing I have noticed on several of these videos, that makes me smile with the irony here: 1 vortex. 2 (or more) vortices (pronounced: vor-ti-sees). But no points taken away for these excellent videos! Thank you again.

[@alanhowitzer]

I love the sound of jet engines in the morning.

[@maricidevamega939]

I also love the smell of jet exhaust...am I a bit weird? Haha...

[@KaiZhao-nv5px]

No you not weird i also like the exhaust smell

[@maricidevamega939]

@@KaiZhao-nv5px Then we both are weirdos..haha

[@kerbonautics5217]

@@maricidevamega939 I love the taste of jet fuel in the morning.

[@maricidevamega939]

@@kerbonautics5217 Just like the aroma of a double shot espresso...What a kick! : )

[@janmcguire5268]

I absolutely love your explanations. You make it simple enough to understand, but still scientifically accurate. Also, your English is impeccable and your accent is charming. I wish very much that I had learned a second language as a child. Sadly, it is not a priority in most American schools. It has improved a little over time in some areas. Both my sons learned a good bit of Spanish in school, and some of the other schools around are now teaching Mandarin Chinese starting in Kindergarten. Perhaps some day American children will not be so uneducated about the rest of the world and will graduate having at least learned a little bit of a second language.

[@alejandro.shot5]

I'm becoming an airplane expert little by little thanks to your videos, thanks a lot!

[@MentourPilot]

Great! I do what I can to help you along. :)

[@pollyannapositive9192]

Same here. Iam collecting these vedio for my own flying lessons. Believe me iam going to use them as needed. In fact I am planning to enroll in pilot school.

[@makantahi3731]

some of info are not 100% sure, so be aware

[@neildahlgaard-sigsworth3819]

Late model DH Tridents used a similar technology to reduce the noise of its engines. It had what looked a bit like a fluted pastry cutter on the exhaust in order to blend cold air from outside the engines with the hot exhaust to form a cooler slower flow. This reduces the noise as the noise comes from the sheering between exhaust flow and the rest of the air. The turbo fan engines did the same by creating a zone of slower moving exhaust surrounding the hot exhaust flow, but left the mixing to nature. Please note a reduction of 3bB equates to an actual reduction of 50%.

[@johnferguson7235]

I live about 1 km from an airport. The US Navy has an offshore missile and bombing range just off the coast. Sometimes, if their F-18 Super Hornets are low on fuel returning from practice, they will land at our local airport for refueling. They use the afterburners on their engines to takeoff. THE NOISE IS STUPENDOUS. The sounds echo around the local hills and it feels like it will knock the glass out of the windows of our house.

[@cliffordnelson8454]

Be happy the US Navy is not still using F-4. They would make the F--18's sound quiet.

[@benbraceletspurple9108]

This is due to supersonic wind speeds causing a air-based supersonic boom, along with an actual sonic boom once in a while.

[@GrasshopperWithoutGrass]

@@benbraceletspurple9108 supersonic wind

[@sunshine7453]

There is a lot more than just simple noise. I could not believe that it is linked to efficiency. I have learned a lot from you. Thank you.

[@WDFJR16345]

I’m not a flyer but find these videos excellent! Keep up the great work!

[@doenjangstew4438]

As I am a small country east asian, I want to learn English from you captain. Thank you for sharing. I want to be like your English fluency.

[@SpyGeorgilis]

Nice couch cushions, but they belong to a First Officer couch... you need to find some Captain cushions!

[@MentourPilot]

Hahaha!

[@craig47j]

Lol🤣

[@MrJdsenior]

Good eyes.

[@masteryoda1966]

Hahaha😂

[@kdawg3484]

Great video as always. Even though the answer to the initial question was obvious, I appreciate how you always walk us through the history and considerations underlying these design choices. It keeps the video information-dense, and I'm always surprised at how much I've learned by the end of each one. Keep up the good work.

[@Quasihamster]

On a more basic level, these chevrons seem to work a lot like a suppressor on a gun: They release some particles of air into the open earlier than others instead of all at the same time, thereby reducing the noise.

[@ZE0XE0]

Silencers work by slowing the velocity of the expanding high pressure gas.

[@Xxfireman024xX]

ZE0XE0 yeah, therefore not allowing the gasses to escape all in one uncontrolled explosion, but rather in a more controlled and quieter release of gas

[@Quasihamster]

Yes, that's what I mean by "on a more basic level". The gun suppressor achieves it in a different way, but it still slows down the gas release.

[@slaughtergang518]

awesome !

[@justincase5272]

No. They, too, work by phase cancellation. Put simply, they drag out the sharp report over several cycles of the report's frequency. A properly designed silencer critically dampens the acoustic of the report. A plastic bottle overdampens it, capturing all the gasses and allowing them to escape slowly. The oil filter silencer kits do the same thing - overdampen. The chevrons on the engine create vortices which interrupt the rapid boundary layer "ripping" that occurs when the rapid exhaust gases meet the slower-moving surrounding air.

[@mrhoffame]

Love all these videos. When you really pay attention and learn the complexity of these incredible machine I think watching an jet fly by and not think twice about it is kind of a crime lol AMAZING MACHINES!!

[@CallmeDaBreeze1971]

I have been curious about those "Chevrons" (I call them scallops) ever since we got our new 747-8's. I work on the ramp for UPS at SDF. Thank you for that explanation.

[@rodneylloydroberts]

Just a general comment. I enjoy your videos very much. 1st you standard of presentation, succinct and to the point, not diverting from the subject good time management. So many videos that have the potential to be interesting are spoilt by waffle. 2nd content, I am not a pilot but has been close to military aviation for a looong time. The content is so good, it enhances my understanding of what is happening on the flight deck and the airframe++. In the past I have spent time on the flight deck, if only I knew as much then as I do now. Thank you.

[@aSnAdEr_79]

Your videos are perfect Captain.

[@GeeBoggs]

Another clearly explained engineering/physics concept. This man is amazing.

[@stephenevelyn1571]

Your videos are really great. Thanks for producing them

[@Shineto147]

Hey, I just gotta say... I love seeing these videos helping us follow pilots. Really!!! props bro.

[@somfanheller]

I feel that you forgot a really important aspect of the chevron design. Noice frequency and how humans perceive different frequencies. This in turns is affected by surface area. The noise from the engines are produced when high-velocity air hits slower velocity air and the air molecules "rub" against each other. The surface area is important with regards to sound pitch and frequencies. Whit the old engines there was a smaller surface area between the two airflows (engine exhaust gas and ambient air) compared to modern high bypass engines. In an effort to reduce the noise frequencies from engine exhaust they are increasing the surface area of the exhaust gas exit and ambient air by adding chevrons. The total surface area of the fan air and ambient air contact area can be increased without increasing the diameter of the fan air outlet by using chevrons. By doing this the manufacturer is able to lower the pitch of the sound produces. Since humans perceive high pitch noise as louder/more annoying a lower pitch is preferred. If you look at the outflow valve on the B737 you can see the same design. Older models will have a straight edge opening while newer models will have a tooth-like design (chevrons), this was done to lower the pitch levels of the air rushing out from the valve to reduce high pitch noise levels in the aft cabin/galley.

[@MentourPilot]

Great info Sören!

[@flav6350]

Dear Captain, thank you for this informative video. I wanted to mention that 6 dB means 4 times smaller noise power, which is actually huge !

[@drkjk]

The irony of using the B-727 example is that years ago Eastern Airlines marketed their 727s as "WhisperJets" touting how quiet they were.

[@stevefrandsen]

Thanks! I wondered why 787 engines were serrated on the back and now I know.

[@AgnostosGnostos]

The 737 Max is nowadays is the most silent airplanes ever produced.

[@elcapitanyandel]

I agree with you. Don’t hear them at all!

[@stanburton6224]

And the most fuel efficient, they dont burn a drop of fuel....

[@tiagodagostini]

They are also more invisible than the F35

[@austindarrenor]

Great stuff. I've always loved flying. When I was four years old I flew on an SAS DC-7 from LAX to CPH, still have vivid memories of the flight. If I had a time machine the first thing I would do is go back and take a cross-country flight on a TWA Super Connie.

[@DeshWitus]

7:00 Kloten! :-D on the left Side you see our Village, Buchs ;-)

[@HenriqueCarneiroM]

Just had this topic in my technical knowledge class at my CPL course, excellent video!

[@rEdf196]

I remember in the 70’s to early 80’s seeing the first generation 707 and DC8 planes with engines that had a rocketlike daisy shaped thrust nozzle in an attempt at suppressing noise in the 1950’s to 60’s.

[@MentourPilot]

Ahh Yes, Hush-kits

[@adriangroeneveld9341]

Nozzle suppressors. Made a big difference on the turbojets of the old jets e.g. B707.

[@shajiaviator]

You are a perfect educator !!!! Hats off Captain

[@terryboyer1342]

I like the roar of turbojets! Helps me sleep better.

[@jamesmiller113]

it's when they suddenly go quiet that we should be worried...

[@inactivefatimahgianna245]

Saaaaame

[@markholbrook7482]

Great video. Brilliantly explained. I thought it was to limit or control cracking at the rear of the engine, so obviously I was wrong. Take a look at the supporting end of the drum on modern concrete wagon. Strengthening plate has a wavy edge to reduce risk of cracking where welded to the drum. Difference is that on an engine this shape isn't overlapping another structural element.

[@conned]

LEAP..takes forever to start n stabilize...must protect thermal..new technology..we gain some...we lose some... Good stuff Capt Mentour.

[@wildzach]

AW AV in my opinion, the LEAP is only loss and no gain.

[@jacksonstandley555]

At LAX I saw a 787-9 fly over on landing, the thing was whisper quiet. When we start up our 1971 Beechcraft Bonanza A36, it make more noise than a 100 ton beast. I reckon the chevrons make the engines look better than any other engine type in the world. My favourite engines are the GeNx engines, love them!

[@will2see]

2:54 -Now, that looks batter!

[@malghawazi]

My job involves a lot of traveling by air.. thanks to you, I now know what is going on up there in the cockpit and also feel a lot safer knowing the redundant systems that most planes have 😘

[@ahmadz251]

Congratulations on 250k Captain 😍😍👍👍

[@MentourPilot]

Thank you!!

[@eloisebrynlee]

Congratulations!

[@gungadinn]

The thrust reversers on the newer GE and CFM engines use an acoustic sound suppression method called two degree of freedom. There are two layers of honeycomb core separated by a perforated skin to create different size chambers that deaden different wave lengths of sound. If you look at a few of the pictures of the A380 thrust reverser parts that blew off a Qantas A380, you can see the two layers and cell diameters of core used.

[@igoralc]

5:33 Varig, Varig, Varig!

[@davidrigoni8231]

Nice explanation What caught my attention was the camera angle on that jet taking off at the beginning . Looked like it was going straight vertical. All under seat carry on can now be found at the rear of the aircraft

[@Lloyd2605]

great work mate

[@maureenbarnes7496]

I once watched a couple of F104s take off together ... holymoly, the noise!

[@neilharper6317]

Very nice and comprehensive podcast, Mentour Pilot. I did have a fantastic time just watching this!

[@MentourPilot]

That makes me happy to hear!

[@liesdamnlies3372]

I've been on a 737-MAX, and when I realized I was getting on one, I was fucking giddy. The cabin is seriously amazing... ...and so are the engines. It's really cool to hear this huge difference in sound between these and the previous generation.

[@mikoto7693]

Lol, I’m ground crew and when on my first day I realised that we were preparing one to be ready to receive passengers and fly back out, I was profoundly glad that I was just there for when it’s on the ground and don’t have to be anywhere near it when it flies although it was re certified.

[@durranydesigns2752]

Thanks, for the insight. It was truly informative and interesting.

[@MentourPilot]

Great! I’m so happy you liked it

[@gazza6262]

I love how there's absolutely no lag when they leave the ground ! Awesome

[@marmaille59]

Chevrons and vortexs, feeling in Stargate :-P

[@tgrules565]

That's why I love camping at Download Festival. The campsite is right near East Midlands Airport runway. Early morning rush is a great wake-up call!

[@turbofanlover]

Excellent vid, sir.

[@ksbear2]

Just flew on a Max-8 last week for the first time. Amazingly quiet in the cabin.

[@vedantbrahmbhatt848]

Great work sir !!

[@beegood9395]

Great video. Very educational. Very experienced pilot. Good work.

[@richardshiggins704]

MAX is now very quiet .

[@Uncle-Duncan-Shack]

Good video, it reminded me of how to make a crude silencer for a pistol or rifle barrel. Tie a bunch of grass around the end, creates vortices that muffle the sound due sudden change in pressure at the hot end. The grass of course also absorbs energy in that area, acoustic and heat. The grass normally catches fire but that's ok if you're expecting it.

[@nmsh92]

Thank you, Mr Mentour! No more words needed.. 😁

[@MentourPilot]

Thank YOU for watching!

[@nmsh92]

Mentour Pilot well... It'll be hard to get rid of me 😉

[@RonDicken1971]

This is fascinating. I had no idea about jet bypass engines, and I find this very interesting. It's very cool that someone had the idea for this, and it turned out to be so interesting.

[@lyianx]

before even watching this video "or are they there to look cool" I already know the answer is, no. Airospace designers don't design things just for looks.. ever. Everything has a purpose, regardless of how it looks :P Airline designers especially. I don't see air carriers giving two shits about how 'cool' the plane looks. They only care about how many people they can cram into it, and how much money they can make flying it. If something exists on it to make it more efficient, they will use it.

[@rikjanssens8971]

I love aircraft noise!

[@tituslim4648]

great and informative video as always !

[@viccabrales3091]

Amazing comprehensive explanation. Great content Cpt! Blessings from Florida USA.

[@PilotJuanCarlos]

Great video, will be great to see a detailed video with the differences between a B737NG and the B737NG SFP

[@MentourPilot]

Good idea

[@andrewtrainor8220]

Mentour love your videos, I work at Safran Aerospace Composites (50-50 partner with GE for the LEAP Engine). I work in the US plant that builds the Fan Blades and Fan Cases, there is a lot of very impressive engineering going into these planes

[@MentourPilot]

Ahh, cool!

[@brucedenning7127]

I appreciate your very comprehensive explanation of the chevrons and other topics. Keep it up!

[@deen9405]

Really learnt more here than in class..

[@MentourPilot]

Hahaha! Great, this is just an overview though

[@user-tt2fh8nf1o]

skool is dum!

[@arturoolvera2604]

This is a great explanation, also gives a bit of insight into the complex balancing act that is aircraft design and aeronautical engineering.

[@user-ky6vw5up9m]

Hey, Mentour , Your cushions are runway-end threshold marking stripes ! (Nicknamed the piano keys)

[@titan9259]

Thnx captain for learning about my planes!

[@SVAyouTube]

Thanks!

[@Jayme501]

How could people dislike this video? It’s educational. It’s not subjective, biased or controversial

[@elcapitanyandel]

Max 8 is the most silent plane today!

[@kicikici5]

Great plane, great pillows and great video.Thank you 🤗

[@mitondo6123]

This is how the wings of owls enable them to fly with virtually no sound.

[@jeremybosman4018]

Congratulations on a quarter of a million subscribers! Great video as always.

[@rogernevez5187]

1:06 Is this an operational takeoff or a high performance one for demonstration purposes? The climb rate seems very aggressive ...

[@shuntsam2]

Boeing pilots' demonstration of the then new MAX8 possibly at Oshkosh 2016 Air show.

[@boeing787aa6]

Great video, Captain! Very informative! Figured it had something to do with the vortexes from the engines.

[@MentourPilot]

Great! I’m glad you liked it!

[@craigkdillon]

Very interesting, and very well explained. BTW..where did you get the name "Mentour", What does it mean? Why do you use it??

[@qtheplatypus]

Craig Dillon I think it is a pun on “Mentor” a trusted advisor.

[@alex2143]

? the Platypus Also, touring means traveling, which is fitting since aviation is in the travel industry. So it’s like a double pun.

[@belmanikanovic5982]

I’m so happy I’m from California because I know English as if it’s my first language and it can help me in the aviation career

[@MentourPilot]

That is a good thing.

[@retepaskab]

6 dB is about quarter the noise energy, that is much. I wonder if that is at full power, or also at approach (approaches are noisier on the ground - airplane is slow and close to ground).

[@MentourPilot]

That’s at takeoff thrust.

[@TheOmega13a]

My dad said back in the 70s when he worked for SRI (Stanford Research Institute), he did research into how to reduce jet noise. He told me years before the 787 that chevrons can reduce engine noise. It surprised him that it took so long for there be jet aircraft designed that have chevrons like that.

[@yottaforce]

AFAIK the primary reason for the high bypass ratio is fuel economy. You get a higher impulse for the same energy.

[@MentourPilot]

Of course, but now the topic was noise. :)

[@Adam-mb1jn]

Always wondered what these were. Amazing video

[@mugilana5601]

Captain your the best. I am your beloved student from India.

[@MentourPilot]

Thank you!

[@ElectroRail]

Great video as always Mentour! Keep up the good work!

[@maheshbhatia8033]

Mentor hi... in the recent announcement from tim clark president of Emirates airlines said there might be no Windows in the future aircrafts or virtual Windows like in their business class of Boeing 777 thus to decrease the weight of the aircraft. What's your say on it or make up an video on it... Thanks

[@vidalroland]

Great explanation ! They treated the problem at the source.

[@danielhamdan3853]

Thanks captain !

[@MentourPilot]

You are more than welcome!

[@brandonlee0115]

I just flew from ich to hkg on an a330 good to see a mentour video right after a flight

[@WatDaMattaForYou]

The chevrons would look like rockets if they would paint flames along the edges.