Why are the Boeing 737NG engines FLAT?
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- Опубликовано: 21 сен 2024
- Have you ever noticed that the lower part of the Boeing 737NG engines appear flat? What is the reason for this and a few more interesting details will be covered in todays video.
Enjoy!
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I’ve always preferred telling fellow passengers that sometimes we come in hard. When that happens and the engines are new, the engines bottom out on the runway and flatten a bit. A little patching, a little paint - good as new! The looks are priceless.
Oh I thought you meant you had some funky junk in your pants getting on a new plane because the engine were new
Tfw the aviation industry is just a bunch of tradies cutting corners
You probably have a pair of sunglasses and a white cane in your kit.
Scoundrel!
😎👍
🤣🤣
I was a pilot but now i am over ups and I was told that I cannot fly anymore. Well done and nobody is too old to learn new things of today. Well done and all the best to all the people learning thank you
You've compiled a wonderfully-done series, and as an engineer who worked on several of the subjects you've covered, I can attest to the in-depth accuracy of everything you present. I worked for many years in the fluid systems engineering group at AiResearch, which later became Honeywell Aerospace. As the cognizant engineer responsible for the P&W JT9D-7R4 thrust reverser for the for the A-310, I had a lot of contact with the group working on the CFM-56 dump door actuation system. Your description of the ground clearance flats on the the RH and LH engines on the Boeing 737-300 is spot on. Just how this clocking came about is an interesting yarn which occurred on the shop floor at SNECMA, who supplies the fan portion of the CFM-56. By coincidence, the circular bolt pattern that determines the clocking of the accessory drive pad relatiive to the engine mounting features was such that advancing or retarding it by an integer number of bolt holes provided the exact positions required to symmetrically position what used to be called the "belly bulge" such that it was slightly above the line you drew from the nose gear to both the R.H. and L.H. the wing tips and therefore provides the ground clearance that you so accurately described. CFM International, the consortum of Snecma and GE, realised the potential sales to be had if their engine could be fitted to the Boeing 737-300 program without a major modification and requalification, and this coincidence laid it squarely in their laps for free. I'm told that a great deal of bon vin rouge flowed that evening!
The best explanation I've heard on this subject. I was one of the engineers who designed the inlet and cowling of the 737-300 early in my career. The engine placement and cowling shape was an iterative process, but when we incorporated the CFM-56 high by-pass engines the goal was to not change the length of the landing gear which would have required a redesign of the wing, fuselage and gear, and also affected the practical aspects you mentioned about loading and servicing the airplane. Thanks for the video.
Ahhh, great to hear from. You sir! It’s an honor that you liked the video!
Does the flattened shape of the cowling has anything to do with minimizing the potential ingestion of debris of such a low engine on the runway?
I have seen these engines ever since I was old enough to start pulling things apart to see how they work. One day my parents took me to the airport to wave goodbye to a close relative leaving the country and I first saw these engines and immediately thought "gee that's a design flaw if I ever saw one". This is no doubt an economic approach that avoids having to do a complete redesign and overhaul by changing the shape of the high-pass engines. But, this would have driven maintenance costs high due to some difficulties with reaching some components which would have been stuffed in the confined space pretty good, making it sometimes difficult for people to do maintenance on the engines. Not to mention, the amount of stress on the undercarriage of the engines both from the external and internal air compression buffeting it. The shape of the geometry intakes would have also affected the bypass ratio which meant lower thrust.
While fuel efficient, the flat high by-pass engines would loose out in performance by a factor of a whopping 17% compared to a fully rounded circumference engine which would somewhat defeat the purpose of upgrading to a new high-pass engine for fuel efficiency. That 17% performance reduction may not look like much, but when you take into account, carrying tens of thousands of gallons of fuel, and thousands of 737's flying in the air every day, it's easy to realize that airliners aren't making as much profit as a result of that deficiency. In my book, that is unacceptable.
That is not to say that airliners didn't make a profit with the retrofits. Just that they won't accrue ever cent profit out of those engines. It's like taking out the engine from a Dodge Challenger SRT Hellcat and putting it into a Fiat, only to realize that you don't have enough space to put the complete engine in without sacrificing parts like twin turbo chargers which have no room to fit, reducing the overall performance of an engine that was rated to originally go 800 Horsepower.
Insofar as the clearance, cowl to ground, was not changed much, the ingestion rate of foreign objects (FOD) was not altered much. Usually this is sand, pebbles and small rocks (called clutter) on the runway and taxiways. On landing reverse roll-out with the engines in high rpm, there is an enormous amount of sand and small stone on the runway that gets sucked up. You can see the amount of damage at times. This necessitates a modest 'sanding' of the initial stage blades periodically. This can not be done too often since it puts the blades out of balance.
The movement of the accessories to the 'cheeks' and the resultant flat bottom was all done for ground clearance. While ingestion was one issue, the other was roll clearance.
Sadly.. 737max loves the ground more than other siblings..
A little suicidal, hates himself.
that was a dumb thing to say.
let`s just say ... it a lazy plane !
Snap! After those 737's get back in the air, my specific line of work will be overwhelmed with overalls from the existing tried and true CF6-80, GE90, LEAP and GenX models keeping everone afloat.
What u mean
why am i watching this channel over and over again
I use to tell people it is a sign of hard landings - the wings flexing and the engine casing hitting the runway :-)
This video is very relevant in the face of the recent troubles with the 737 max. I saw on a separate video that the larger engine required a different placement that altered the aerodynamics of the aircraft, requiring an automated system to be installed to detect possible stalls. That system is what made the Ethiopian airlines plane crash, as the sensors detected wrong data (possible stall) and forced the plane into a dive.
It's so much stupider than that. The "system" was just software called MCAS that took control of the elevators to push the nose down in the unlikely but technically possible event of approaching a stall out at the edge of what's possible for the 737. Pilots are already familiar with the edges of the older 737's flight envelope, but the MAX's changes to the engines restricted this flight envelope a little bit to no longer be capable of flying with this unlikely combination of attitude and airspeed. Well, normally you'd have to re-train pilots on the new model if it makes significant changes like this, but that's expensive and could limit the number of customers who would choose Boeing's MAX for their fleet upgrades over Airbus's equivalent that had already been on the market for a bit. So Boeing took advantage of their very comfortable relationship with the FAA to push ahead by writing this MCAS software and not requiring any retraining. They didn't even require that pilots watch their informational video about MCAS, so there were quite a few pilots who were only familiar with the very basics of what it does, not the particulars of how and why. That was Boeing's first major mistake.
Their second major mistake with designing MCAS was that it only used input from a single sensor to determine the plane's pitch, a sensor that's usually only very helpful to have (not critical) and is notoriously prone to failure. If this sensor failed at the wrong time in flight, it could trigger the MCAS to cause a hard nose down push in an attempt to avoid a stall that it mistakenly thought was about to happen.
Well, the sensor failed, and MCAS kicked in, and the pilots weren't familiar enough with the MCAS to quickly recognize what was happening or eventually disable the connection between the MCAS software and the elevator. So at a point where going hard nose down was dangerous that's exactlt what MCAS did anyway, and the pilots struggled for a while to wrestle with the plane to keep the nose safely up against the MCAS that insisted they were stalling. That plane crashed, and everyone died. Then Boeing made their third major mistake.
Instead of immediately grounding the whole MAX fleet across all customers until the MCAS issue could be fixed on all the planes, Boeing figured they could do the updates pretty quickly before the same slightly odd set of events happened again to a second plane. Well, that was criminally reckless, and it didn't work out. A second MAX forced itself into the ground despite pilots fighting it the whole way, and again everyone died.
@@BlahVideosBlahBlah Very nice writeup! Probably the most succinct description to what happened to the MAX I've seen.
@@BlahVideosBlahBlah couldn't they just make the landing gear longer
@Kids coding World i think they did that only
@@pugothing That's doable, but landing gear is built to be one of the strongest, most rugged systems on a plane. It's already a pretty significant weight eating into fuel efficiency, and when you make it taller its weight goes up very quickly. For an extreme example, if you doubled the height of the landing gear it would easily triple the system's total weight, or worse. As the plane sits further from the ground the airstairs also have to get longer, heavier, and more difficult to handle. Maintenance is a bit more efficient on planes lower to the ground, too. The overall purchase price and operating price just goes up so much with longer landing gear that it's very worthwhile to pursue other solutions whenever possible.
Short note: the JT8D engines on the original 737s are still considered turbo-fans, just “low bypass”. A turbojet engine should be all core, no bypass (ie JT4). Love the channel, I learn a lot from your videos!
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Was kinda fun to learn that after understanding turbojets, that basically no aircraft uses pure turbojets. Even fighter jets apparently.
I've flown commercially (helos and fixed wing) and am a retired airline dispatcher. Yet... I still learn things from you!
I enjoy your friendly style and solid knowledge.
Thanks.
KutWrite You should then watch enslaved by no media videos on how efficient the engines have actually become (free energy air engines) also watch JonesSenoj channel on how the commercial airlines are practically running on no fuel at all.. no room for fuel in the wings like theyve told us... Brilliant to watch I am sure you will enjoy watching them both!!
you should already *know it all*
I miss seeing those old JT-8D clamshell thrust reversers close up on landing. It was so cool as a kid sitting in the window seat.
Have you ever heard what they sound like in silence? It’s a weird squeaky noise and then a loud *CLANG* that you can feel.
It's been a while, but yeah, I have.
I much prefer the window seat, haha!
LOL! It took 8 MINUTES to explain the reason why the housing of the engine is flat is so there is more ground clearance. Well nobody can accuse you of not being thorough lol! Seriously though I’ve watched a number of your videos and you have a talent for explaining information regarding Aircrafts that’s easy to understand for beginners. As always I hope you’re doing absolutely fantastic!
Hi! Great video! Maybe it’s been said in a previous comment but the JT8D is not a turbojet, it is a low-bypass turbofan. The JT3C, the JT4A, and the JT8A, which are similar in size are turbojets but they were not used on the 737-100 and -200. With the classic and NG models, the engine was switched to different variants of the CFM56, which is a high-bypass turbofan.
Yes. Exactly.
This is a great video, I just want to correct one small item. Even military aircraft rarely use jets anymore. Most use low bypass turbofans (5-15%) with afterburners. The last jet used by the U.S. military was the A-6 Intruder. Good day!
I love watching this stuff I’m a GSE Mechanic(ground support equipment) and I’m fascinated with the planes. I’m
Always looking at them and talking to the aircraft technicians learning about them. I want to go back to school and get a degree to work on them I’m already certified in diesel/gas and auto Collision repair.
Thank you so much for sharing this info. As an AA flight attendant, I always wandered about this specific issue with the engines and other things on Boeing aircraft-now I know why. Keep up the good work.!!!
Uri You should watch enslaved by no media videos on how efficient the engines have actually become (free energy air engines) also watch JonesSenoj channel on how the commercial airlines are practically running on no fuel at all.. no room for fuel in the wings like theyve told us... Brilliant to watch I am sure you will enjoy watching them both!!
Hi Mentour. Your podcast has been fantastic as always. Extremely saddening to here that the flat bottom engines won't be seen in a few years. one of my favourite features on the B737.
I started working at Schiphol this year, mostly loading and unloading 737-700 and 737-800 and I see all these things I have questions about. But you already answer all of them!
Hey mentour pilot..greetings from India..hope ua doing great...Iam an aerospace engineer and I make it a point to watch Ya videos...I love it..what I like the most about your videos Is that you give importance to small details with such a relaxed and positive vibes..you are like a cool zen of materialism...love your vids..keep doing what you love 😍
I always wondered why the plane was so low and why the engine was flat! Thank you for answering!
I've wondered about that flat aspect of the engines for decades, never expecting that I would hear someone give the reason! Thank you.
Urban VIII
Just about everyone who is even vaguely interested in commercial aviation knew this already, especially in the wake of the 737 max issues.
@@WhiskeyGulf71 Well, I didn't, and I didn't know who to ask.
Moving the engine pylons forward wasn't just for CG and ground clearance, but it also improves area-rule drag at higher speeds. It becomes significant around mach .75, which is about where you want the 737 to cruise.
Oh great. Don't tell me we have a Flat Engine Society now too :D
It's called the Subaru Owners Club.
I say this with as much respect for another man as possible my dude, you looking good af in flight attire
... and now when we have two 737-Max down in five months, this is time to reiterate that work-around is not a substitute to something designed perfectly as a whole. Modifications/Additions led towards change of center of gravity which was accommodated through shifting engines a bit forward on the wings and this changed aerodynamics and introduced a tendency for "always climb" which was corrected through MCAS... so far MCAS has "Corrected" this on two occasions when actually correction was not required and results were catastrophic.
this is what happens when you (quietly) introduce a new critical system that functions and relies on just ONE sensor. when that malfunctions, pilots don't even know how to address the issue because they have no clue of its existence. the plane came with a new 2 hour manual of which a pilot could complete anywhere in the world on their smart phone or tablet and has no mention of MCAS at all. for pilots, the plane has a mind of its own, only nobody knew until it was to late. its a terrifying thought to imagine looking out the window as I personally love to do myself, only to see you plummeting to the ground, and to feel the angel of decent, you would instantly without a shadow of doubt know something is horribly wrong!
I feel for the victims of those two flights!
Now i can die in peace . . This always stucked in my mind . Love from Dubai.stay blessed
Please dont, continue to be awesome instead! Glad I could straighten out your question mark!
I'm an AME and I love watching these videos to learn a little something new every time.
This certainly answers one of the burning questions of my life.
You'd think the flat bottom would also be beneficial in the event of a water landing. If the pilot can keep the wings fairly level when hitting the water, the bottom of the engines should act like skis to keep the wings up until the speed drops enough.
Pretty sure the engines are getting ripped off in any type of water landing, nice thought though.
The left engine did get ripped off though.
If you're landing a plane like that in water, keeping the wings up is the least of your problems.
@@raymondjackson6069 sully told me it was easy..
I don’t think the engine mounts would resist taking the whole weight of the aircraft on them...
PS: Not to mention the enormous forces involved...
I asked this question of a pilot as I was boarding this plane about the flat bottom to the fan cowlings and he said that he had no idea why. Made me feel really good about the flight seein’ as how all he apparently knows how to do is press buttons and push/pull/turn a yoke!
But now you know! 😂
Its no reason for a pilot to know about it😉
JT8D is a low-bypass turboFAN engine, not a turboJET engine. The later model engines are high-bypass turbofans.
true - Boeing used pure turbojet engines for civilian airplanes only on early 707s.
Of course, with early turbofans, low bypass did not contribute much power - but they were a lot less noisy than Caravelles or Comets.
Yep, surprised by this mistake - there's never been a turbojet on a 737.
the 707 used the PW jt3D low bypass turbofan. the militar 707 plane uses PW TF33 also low bypass turbofan.
According to English language wikipedia, first 707-120 used P&W JT3C turbojet engines - this is obviously a mistake: JT3C, as well as successors, was a turboFAN version of the J57 family.
So your objection is correct.
Yes. And all fighter jets today are using turbo fan engines. Just as Any airliner. Fighters are not using turbojets as mentioned in the video.
i wanted to know that for sooooo long tbh
Great! I hope you liked the explanation!
Same
I thought it was because they use female fork lift drivers!!!
iRx Destiny same
Me too and thank you for this!
I like it when you make the videos less than 10 minutes. Easier to watch and enjoyable.
Your videos are fascinating. I knew very little about aircraft design and operation, but always wanted to know more. Thanks!
Excellent to hear that you like them! Have a great day!
This makes great sense to me. Thank you for the information. ✈️
turbofan sounds like an additional turbo charger to a conventional jet engine
@@fidelcatsro6948 they so so so loud
And your head is flat, apparently.
Hello 👋 I love 💕 I’m sorry 😐 I wasn’t even mad 😠 you didn’t have much oops 🙊 I love ❤️ this game I was so off this to love 💕 was my first night in Iowa the morning I love ❤️ love 💕 I was one ☝️ now I’m a little tired 😴 is my love 😍 was my last time for you haha 😆 was a good morning how’s your day going good day I love ya ya know bye 👋 day and I was thinking 🤔 you know valentine would we we have a valentine gnome
I work with both the 737 and the a320 family and I've always wondered this. Very informative, thanks for the great video!
I am not a pilot but love these videos, thank you so much!
The JT8D is a turbofan not a turbojet. It is a much lower bypass ratio (less air going around the engine) than the CFM56.
That doesnt answer the question
and ....
@@karteix 40 inches fan diameter for the initial JT8D vs 61 inches fan diameter in the CFM56
So the CFM engine is significantly closer to the ground
@@brk932 agree!!
Wiki is wrong?
I am a new student to a 14 cfr part 147 amt school in Portland, Oregon, but have military experience on rotary wing aircraft. I am there to assist in my learning of fixed wing commercial and general private aircraft. Thanks for the education, sir.
I found the video informative but I thought they could extend the fuselage without changing the center of gravity: one fuselage extension in front of the wings, and one behind them. And I had thought they were unable to lengthen the landing gear for a round engine inlet due to dimensional constraints of the wheel well as defined by the frame.
Video: talks about 737s
Duration: Boeing 7:57
Haha true.
my name is classified that’s not how coincidence works...
I am brazilian pilot and like your videos so much. tnks!
It needs to be inflated to the correct pressure. thats why it's flat.
So it's a Patriot's football
Lets pray it should stay there forever ......
Jason Molenaar American football makes no sense
Lol
Peter, I want to tell you how much I love your channel!!! I am not a pilot, nor involved in aviation outside of being a commercial passenger. I'm not sure you have discussed this on a previous video, but I wonder if you could explain the difference between wing-mounted and rear-mounted jet engines. Are there different experiences for pilots? Advantages/disadvantages? I'm that curious guy that learned of Skill-Set from you and enjoying it very much. Keep up the good work!!!!!
The flattened lower lip's increased ground clearance also helps with ingestion of runway debris, whether chunks of ice, gravel, etc. The suction ahead of the turbofan engine at take-off power is strong enough to actually pull chunks of concrete or asphalt out of a cracked runway in addition to other runway debris. By moving the lower lip up even just a few inches decreases the engine's proclivity to pull debris off the surface. Also, the flattened cross section (by moving the accessories) of the larger-diameter turbofan engine allows for more ground clearance should a tire/tires blow on on one side.
Yes I've wondered for a long time... why the flat bottoms on these engines ?! Thank you for this explanation. BTW... the 757 always remind me of a beautiful long-legged lady. Cheers !
Cool! It always reminds me of a bird of prey. I think the 757 is one of the most beautiful aircraft out there.
Mentour Pilot Yes!! Like a falcon- The talon-like gear in combination with the slightly down sloped nose cone... This is the first time I have heard another say this. My father was an engineer on the 757 with Eastern Airlines in the 80s (when they still needed engineers). This was how he taught me to recognize her.
Mentour Pilot extremely fantastic video, extremely fantastic explanation... Well done great pilot!!!!!!
Thank you! Im so happy you liked it!
Really nice summary of the new engine design and of turbofan vs jet engine. It seems to explain that; turbo-prop engines are turbofan engines geared to a propeller and not jet engines geared to a propeller; but not sure about that? I love the sound of a turbo-prop engine. Something about them, sounds right.
It is amazing the amount of technology that is applied so that Rhonda can visit her great-aunt Elanor in Kansas City.
Dorothy went to Kansas just by clicking her ruby slippers together. Plus she was on LSD.
LardGreystoke Dorthy never left LA...
Whynot Whynot junhnj
When I was a kid I thought that the bottom of aircraft engine had hit the ground.
Hahaha my son once asked me the same thing:-)
Actually it was the Toilet Rupturing all the Tarmac ! Have yo not seen the skid Marks Bro ! That's why Shit Hits the Fan Blades Dude Hee Hee! Some body has to Clean up the Mess!1
The engines were initially round and ground to the flat bottom shape during landing.
It it flat so it doesn't hit the ground :D
kids are so stupid!
To be more specific, on the original CFM56 engines, the engine accessory drive systems were located on the bottom of the engine. in order to keep the larger fan of the CFM56 for the 737-300/400/400 models, engineers at the then-GE/SNECMA consortium moved the accessory drive systems away from the bottom of the engine and Boeing designed an engine nacelle that could give proper ground clearance. Note on the 737 MAX models, the newer main wheel design allowed a more "round" engine nacelle for the CFM LEAP-1B engine.
Can you talk about Reverse Thrust, I love sitting next to the window and see the reverse thrust vents open and the engine rev up when they land. And how it works, I notice, some pilots use it but not that much, they close it right away, is that to save fuel??? or to lessen stress on the engine mounts?
Hi! No, some airports are very noise sensitive and if the reversers are not needed for landing distance reduction or brake cooling, we just open them in case they would be needed but we do not spool the engines up. That is all to save on noise.
Thank you. I didn't know that!
That is why we are here to learn...
Another reason I've heard is to prevent the reverse thrust from kicking FOD up in front of the engines - which are under power and gulping large volumes of air at that point. I've also heard this is why aircraft usually get a push out from the terminal instead of using their reverse thrusters - they'd kick stones and stuff at the terminal windows.
Of course, this is all hearsay - I'm so far from expert, I can see the curvature of the universe. :-D
aussiebloke609 Any area with aircrafts on it, is checked very often for FOD.
The long and infamous FOD walks...
when i was young, (at that time, i didnt know that much about planes) i sed to recognize the 737 by its engines, the long 737-200 and the flat 737
the Jurassic ones were easy to distinguish, even by the sound.
yeah the sound how can i forget that i still remember the first time i flew in the 200, the best prt of that engine is the reverse thrust a love how it closes.
Same, in Indonesia and east Timor, all airlines used B737, mainly the -200adv or the -300/-400. I always wondered why their engines looks weird compared to the rounded engines on A300 or MD-80.
I loved the olds TAN Sahsa 737 landing in the old tegucigalpa toncontin.. great memories
Omg Jurassic 😂
I have always wondered why that part of the engine is flat. Thanks for the lesson. By the way, you look sharp in that uniform, Captain!
What about doing a video on the split scimitar winglets vs standard winglets for the 737
Thanks for the very detailed explanation. I kind of like how the Jurassic 737’s have Engines that stretch to all the way behind the wings.
It was spectacular watching the thrust reversers deploy on the -200s though!
Andre Wunjo yes, definitely spectacular seeing it deploy!
And LOUD! the air buffetted off the rear fuselage and you could feel the vibration! Which is also why you often saw soot on the fuselage aft of the wings. You don't with the non-JT8D models.
Andre Wunjo they were sure loud!!! Really big shame we don’t see these old 737s that often anymore.
Nolinor out of Quebec used a -100 out of YKZ to fly cargo to the arctic every day until just last year. Houses less than 1km away. Departure was every morning at 0600. They were not popular. LOL
If you can ever visit YMX Montreal Mirabel you can enjoy Nolinor 737-100s and Convair 580s and suddenly it's 1972 again.
I'm thinking clearance. I've wondered for TWO DECADES. I am finally going to find out!!!! Thank you!!
Love your videos... but the JT8D is not a turbojet, but rather a low-bypass turbofan (with 2 fan stages) :)
Oh well, almost anyway. :)
Correct, the JT8D is a turbofan. But, it is a low-bypass turbofan, with a smaller diameter fan than later, high-bypass turbofan engines. Once it is in a nacelle, the JT8D does not look too much bigger around than a turbojet of the same power.
Mark Holm the JT8D was (.96:1) : yeah, low :O when the engine went into service in '63 was a welcome guest bolted 3x to the 727-100. now here was a beautiful lady, fast, good range and could crack plaster and bust dishes with the best of them. the engine was a mod from the J52, which was a turbojet.
As an A&P school graduate I enjoy your vids immensely. I would like an over view of the electrical system on the new Boeing 787 all electrical aircraft and especially the AC variable frequency generators.TX!
D. G. Probably just call Boeing. You’re an A&P so they’ll probably tell where to find it all.
George Doughty
Ll.
. To .
Amazing way of explaining the technology behind.... just great
Wait, the PW JT8D is a low-bypass turbofan at 0.96 to 1 ratio, not a turbojet. It does look like a turbojet but it really isn't.
Yes, I have found that out now. I should have researched it a bit closer. It actually has s tiny bit of bypass
Mentour Pilot what is this ratio of bypass you guys are talking about? Is it at a certain point in this ratio that makes the clear definition between when a engine on an airplane is a turbojet and when another is a turbo fan? Because when I look at the diagram.... They both still look similar. They have tons of fan blades in a cylindrical casing..... Maybe an episode on that and the new geared turbofan ?
Kevin Lee in the low bypass engine the majority of the thrust comes from hot gases exiting the compressor, in the high bypass engine most of the thrust comes from the large fan at the front (which is driven by the compressor).
arthur staal is that what makes up the ratio they mention above? Haha. Is everyone who follows this channel so current and responsive? I just got an answer to another question I asked following the thread on a video.... I'm impressed at the turn around time with responses around here. Had this anything to do with airlines and OTP?
Kevin Lee (bypass ratio) = (cold fan air) / (hot compressor air).
To give an example, if a fan moves 10 times the air of the compressor you get BPR=10/1 (a bypass ratio of 10).
Ps. The aviation community is very passionate in general, so maybe that's why everyone is happy to explain stuff 😁
Excellent and well detailed information, thank you.
Thank you! I’m glad you liked it!
List of Jet engine types I know:
Turbojet (includes the JT4A)
Low-bypass Turbofan (includes the JT8D)
High-bypass Turbofan (includes the CFM56)
Ultra-high-bypass Turbofan (might include the PW1000G)
Turboprop (Includes the P&W PT6)
I really do miss the sound of the JT8D engines. They were loud and crackly. But they left a lot of smoke behind it.
jimmycrackcorn90745 Made them easy to follow across the sky, just like the F4 Phantom.
You sound like you may have a Hot Rod heart...liking all the smoke and having it loud. Nothing wrong with that except Boeing and other aircraft makers spend a lot of money trying to quite these babies down.
Those JT8Ds will rattle windows like a fighter, incredibly distinctive sound when spooling up too. I flew on a number of MD-80s and 737-200s back in the 80s and 90s, very familiar with their sound, just as the CFM-56 has its distinctive "howl" when spooling down.
hmmmmmmm inefficiency
He explained it well. Earned a sub.
Thank you! I’m so glad you liked it!
agreed subbed as well.
Walking off a recent flight, I just noticed the engine shape. I actually wondered why they were shaped that way. I accidentally came across this video. Thanks for answering that question!
it shouldn't take eight minutes to say 'because the engine is larger in circumference'
Hahaha
I am a retired Aerospace Engineer and worked for a reputable turbine design and manufacturing company. I was told that this flatten design was also modified to mitigate the induced sand into the inlet from the runway being to low and also to modify inlet flow.
Loved this topic. I’d always figured it was for ground clearance but didn’t notice that the pylons had been raised and extended as well. I tried googling this question before and many of the answers were absurd. Ha.
I do have another question I haven’t been able to find an answer to though, and that is, what is the purpose of the small horizontal strakes found on the inboard side of the engine nacelles on some (or all) models? I’m sure it’s aerodynamic, but wonder why it’s needed.
It's a long answer but here goes. When the flaps are in their landing position (flaps 40), the flow around the nacelle is nearly vertical (pure crossflow) due to the upwash. This flow separates off the nacelle in a very weak vortex. When this vortex encounters the adverse pressure gradient on the wing it bursts and causes the wing to separate and stall. The chine or fence on the inboard side of the nacelle causes the flow to separate in a very strong vortex. This vortex can negotiate the wing adverse pressure gradient much better. The height and position of the chine are tailored to produce the desired stall speeds and pitch characteristics. As a young aerodynamicist who worked on the 737-300 I was there. Admittedly it was a fair amount of trial and error but it worked. Now, in order for the wind tunnel model to have the same stall characteristics as the full size airplane required a trick. Sorry, not divulging that one!
Doug Ball Thanks so much for the detailed answer! Makes sense now. It had always made me curious. Thanks again. You were just the person to know!
Doug Ball A year or so ago I actually asked a friend who’d piloted 737s for several years.... and he had no idea. Ha. So thanks again. That little feature is more critical than I’d have imagined.
Doug Ball Thanks! Without you, I never would have known.
I'm trying to think of any recent passenger / commercial aircraft that has the engines under wing rather than being mounted forward on the pylon. Can't remember any
"Chipmunk"! Love it... :-)
i loved that cartoon back in the 90s
Randomly found your channel. As an avation fan, love this stuff! keep up the good work.
When you say that fighter jets of today use a turbojet engine that is incorrect. Most, not all, fighter jets of today use a low bypass turbofan engine, the f100-PW-220 has 25% bypass, this is about the same for most turbofan engines with augmenters. When the engine has bypass they have augmenters, turbojet engine has an afterburner.
Absolutely correct, I was relying on a less detailed source for that. The 737-200 engine was also, actually, a low-bypass turbo fan engine.
Thank you for observing.
He was comparing it during the era of the early 737s.
New subscriber from Taiwan. Thank you so much for these interesting and well-explained videos!
Great! Thank YOU for supporting!
737 front looks like friend fish
Ray Chang u
sexy girls
I love learning from your channel. I used to be a fearful flyer and even stopped flying sometime in 2017. Recently I have a health issue which prevented me from flying, but hopefully soon I can resume. I wish you were my pilot. Maybe someday!
Aye aye captain!
Thanks for the great info which I was always afraid to ask...
Mentour Pilot: Why doesn't the engine behind you have the scroll in the centre, or does the paint just wear off from dust in the air?
Yes, it has worn off, needs to be re-painted.
Well explained!
I used to be a plannish hammer operator at Rohr Ind. in Chula Vista....we made the engine cowlings and pylons fore a lot of engines. I didn't working on the small parts, but I HATED working on the nose lips and access doors, as they required 2 people to maneuver the part around.
Video about the 737 that is Flying Pencil long I mean 7:57 minutes long.
For extra ground clearance
Exact and usualy the gear box was at the engine bottom and so moved on the engine side to allow this flat!!
There was me thinking it was an optical illusion caused by refraction of light through a more dense region of air.. Thanks! Very informative video.
Why does the Boeing 737 not have landing gear doors for the main landing wheels? You can see the two wheels from the outside when they are retracted. Other aircrafts stow their main landing gears in enclosed compartments.
That video is coming up.
Kevin P the 737 was originally a short haul aircraft. Because there would be so many takeoff and landing cycles, the designers decided to leave the doors off. Cheaper, less complex, lighter, etc.
Faster description:
Because they can touch the ground, if they will be not flat.
The 737 is Peter Dinklage of Boeing. It has short legs (undercarriage); but, New turbo-fan engines reduce ground clearance...!
Great explanation as usual! :)
Thank you! I am glad you liked it!
Mentour, why did that engine at he beginning not have a spiral? I thought it was almost mandatory
Hi! It had been worn down due to wear and tear. They might re-paint it during the next engine revision.
Mentour Pilot thanks for letting me know.
You are more than welcome
Thanks for the reply! I was wondering that too, and glad someone else had already asked.
I always liked them engines on the earlier 737s streamlined looking and blended into the wings, as always some interesting information from you Petter
Kind of what I figured.
Yup
Kind of?
A pilot in a hotel room - a match made in ‘heaven’.
During L/G extension/retraction, brakes are applied to counter the gyroscopic effect produced by spinning wheels..
This system is available on all modern aircraft with L/G doors too and it's known as In-Flight Braking.
Engines aren't flat, just the housing.
Dark Sigma watch the full video
I didn't listen to all. These stupid titles to get you to watch is just a big turn off. "Why are engine nacelles flat?" would have been a great title and his first remarks did say engines flat? My dumb answer for a dumb title Aristotle.
Bruh😒🙄
Franklin Parnell stfu
Realy?
Great video once again Petter!
Thank you RS, its always great to hear from you!
RS Aviation
I believe that the inlet for the 737 classic was mostly round. The NG inlet was noticeably flatter on the bottom. Another reason for this design change had to do with Air Florida Flight 90. Under certain conditions, wet snow could be sucked into the engine during the takeoff run. The classic was too far along to incorporate the inlet design change. So, it ended up on the NG. The NG also incorporated a different pylon fairing and a wing similar to the 757 wing.
0:15 why is there no swirl painted on the spinner?
Not every engine has a swirl. Not every engine blade is tilted 5 degrees from the normal. Not everything is the same in this world
@@Deezorz just wondered y not to use some improved safety standards
@@nativeafroeurasian old materials?
If the ground crew can’t hear the engine when it’s on and where it’s white it’s is bringer to prevent ground crew to get sucked in but it still happens DONT search it
@Mentour I've really enjoyed watching your channel the last few days. I've always loved flying and the science behind it. I do have a question to contribute, and if this has already been asked and addressed, I apologize. My question is have any commercial airline pilots gone on to work for NASA, or other Space research organizations to either, pilot a shuttle, or some other form of space travel research. I would really be interested to hear your insight on this. Have a great day!
Thats a great question! I don't think that many have since most NASA astronauts have come from the US navy or airforce but it is possible.
I live in Daytona Beach FL, so I'm really close to Embry Riddle. and of course we have the cape a few hours away. plus my father was in the Air force as a navigator. So I've known quite a few people in various roles.
I believe Thomas Pesquet was flying for AirFrance before he joined the European Astronaut Corps.
Johannes Næsset Hillestad Yup! He was an A320 first officer at Air France before becoming an astronaut.
No, but it has happened the opposite way. A few Shuttle Commanders and pilots now work for Southwest Airlines once they left NASA. One of the more notable ones was Hoot Gibson (now retired from SWA). It probably has a lot to do with SWA having a domicile at KHOU which is close to Johnson Space Center (and the fact that it’s a great company).
I have recently found your videos on RUclips. Fascinating facts. Thank you so much for taking the time to explain these features and facts. I will be passing a link to my 7 year old grandson who is seriously into aviation and recently flew with EasyJet and asked the captain to explain reverse thrust. I note that you have already put out a video on that subject. Now he can ask you, instead of me. Seriously, a wonderful website. Thank you.
The JT-8D is a low bypass fan engine. Really all fighter engines are low bypass fans as well...
IE Turbofan., not turbojet as described early in the video
Correct. Beat me to it. :)
Brian Crawford No, that’s not what he said.
Banshee365 same engine as the dc9
Willem Heitlager And 727
I always wondered that, great explanation thx.
Thank you for supporting the channel!
You say it right , the 737 is a design from the 60s , and this explains all the problems ✈️💥
I think it’s b’coz the Gear box was moved from down to the sides of the engines
Nice explanation. The only thing you didn’t mention was foreign object entrainment. I had always heard this was the primary reason for the flat inlet lip since the inlet would be much closer to the ground and more likely to suck in things left on the ramp, taxiway or runway. I would have thought with a nose high attitude in the landing flare that hitting the front of the engine would be less likely even in a crosswind landing than the middle or back of the engine or even the wing tip. Besides I thought it was not common practice for airliners to perform side slip landings which would place one wing lower and closer to the ground?
True! It was actually in one of my takes but got edited out.
You're correct about the ground clearance being the reason for the flatness, but you're wrong as to why. The 737 wasn't built low to the ground for baggage loading sake. It was built low because it's design intent was to be a commuter aircraft that can land on small and unimproved runways. The 737 is the only non-military jumbo jet that can land on a dirt runway. The flatness was incorporated into the design because the runways might not be as wide and they didn't want the engines to hit anything. At the time I worked for Boeing, the 737 engines were $5 million dollars a piece. That's an expensive mistake if you land on a small runway and hit a sign or something. Interesting note, the 737 can be spec'd with built in stairs as well.
I have another question
Why boeing 737 family doesn't ave landing gear doors?
Coming up!
Mentour Pilot please hit us with your explanation asap, thnx
donny bb he's really responsive, you'll see there's no need to rush him.
Kevin Lee i know that's why I put asap( as soon as possible) so i may not sound pushy, but dying to know hahahaha, coz i assume boeing want to save money kind of thing (cut unnecessary cost) by not giving the landing gears a proper cover, and the drag effects if there's any versus with cover like Airbus
Because it doesn't.........