Is the Boeing 737MAX Really Unstable?! The 737 Engine Saga.

if you take a look at the original engines on the boing 737 and then compare them with the 737 Max ones the difference is quite impressive so why did the engines and their installation on the 737 evolve this way and is it really true that the new placement of the 737 Max engines makes the aircraft unstable stay tuned over the past few weeks I've made a lot lot of videos around the 737 Max and other developments in the industry related to it I did this because of the obvious huge interest that ca

me with the aftermath of the max 9 mid cabin door plug blowout back in January now obviously Boeing's problems with the max family started well before that but lately more and more people in my comments here on the channel seem to be repeating some misunderstandings about the max which are either misleading or just plain Falls a lot of these comments incl include mcast and the way that it works or I should say used to work and also the reasons behind it being fitted into the design in the first

place now I will eventually cover both of the max crashes in great detail over on the mentor pilot Channel but since I keep seeing references to all of those misunderstandings in the comments I also decided to make this video so let's start by having a look at how the engine installation on the 737 has evolved over its 56 plus year long career to do that we have to start with what we call the urasc version of the jet the original 77100 and also the much more common 7372 200 the original ideas be

hind both the Boeing 737 and the 727 suffered from an assumption that Boeing and also other manufacturers like Douglas for example had made in the early 1960s because they thought that an airliner especially one designed to operate into smaller airports would have to be constructed so that the fuselage would sit relatively close down to the ground this would allow baggage handlers to access the cargo holds without using special equipment and it will also allow reasonably small built-in air stair

s to be fitted both of those things would make it easier for those smaller airports to ground handle the aircraft and therefore maximize the available Network for these planes the original 737s even had a gravel kit that could be added to it to allow them to fly into non-paved runways and that's super cool now all of that might have been a great idea back in the 1960s but as a long-term strategy it turned out to be completely unnecessary this was in part thanks to the super fast expansion of air

line travel during the following decades that meant that supplying even the smallest airports with mass-produced mobile air stairs and other ground equipment really wasn't such a big problem after all and by the way this low stance of jets like the 737 isn't particularly loved by pilots either since it brings the aircraft down closer to the runway increasing the risk of tail strikes especially on the longer versions of the Jets but that trouble came later it wasn't really a factor in the origina

l 72700 and 200 who were all really nice and short and since boing Douglas and other manufacturers were introducing completely new aircraft models very quickly back then selecting design features that would make the aircraft more easily upgradeable and stretchable later wasn't n really a big priority but that was something that would later change with both the dc9 and the 737 models surviving much longer than anyone could have ever foreseen back in the 1960s and when they did it wasn't just the

pilots who disliked this low stance aircraft and engine designers weren't thrilled about it either and this brings us back to the engine evolution of the 737 family and eventually the max the original Jets flew with it then relatively new pret and Whitney J jt8 Delta and contrary to popular belief those cigar-shaped engines were not turbo Jets although they were based on the JTA Charlie which was as I have explained in a recent video I did the JTA Del was instead a low bypass turbo fan making it

much more efficient than the previous designs but still small enough in diameter to fit under these lwh hanging wings of the 77100 and 200 the engines were fitted directly underneath the wings with the front of the Eng poking out in the front and its tailpipe and reverser mechanism extended beyond the rear and because of this there were no visible pylons connecting the engines to the wings although there were obviously connections and separations between them so that was the original configurat

ion of the 737 and some people argues that this is how the 737 should have stayed as its designers originally intended and that deviating from that design was how this aircraft's problems really started but is that that really a fair assessment because the thing is this exact engine and the cell Arrangement didn't really find any imitator at least as far as I know maybe there were some older designs like the the havland comet which actually had its engines buried inside of the wing itself but be

side that I can't really think of any other aircraft with its engines centered under the wings now if I'm wrong or I've forgotten something here I'm expecting you guys to set me straight in the comments below and also subscribe while you're down there but until you correct me I think that every other successful aircraft design using Wing mounted engin actually have them poking out forward of the wing maybe not completely but at least most of the way there that also actually includes the designs

of earlier Jets like the Boeing 707 the Douglas dc8 and the Conair 880 even the unsuccessful dult Mercure an early European competitor to the 737 who was also using the same pret whne the engines by the way had those engines mounted on pylons under and forward of the wing and that aircraft also supported a really nice tall landing gear my point here is that the original placement of the first 737s engines was the result of a compromise which worked pretty well but only really made sense because

of the requirements at play at the time it entered Service Plus the only available engines back then still had that cigar shape of the earlier turbo Jets making them fit nicely in that original position now the reason I'm explaining all of this is because there are actually several advantages in having the engines a bit forward of the wing and also some real issues with the way that the original 737s had mounted them and I will tell you all about these and how they relate to the engine placement

of the 727 Max right after this imagine your life is like the engines of an aircraft sometimes you just need a little bit of service in order to keep it running smoothly and safely and that's where today's sponsor betterhelp comes in because whether you're feeling overwhelmed stressed or just need someone to talk to better help have what you need and will help to connect you with a licensed therapist within 48 hours from your first Contact you will then be able to talk to your therapist from th

e comfort of your own home or office like in my case and you can choose to do so either via messaging phone calls or even video sessions whatever feels best for you I have to say that I was really happy with my therapist when I tried them because she gave me clear and Direct Tools like taking dedicated time off for friends and rewarding myself with reaching certain bite-sized targets to avoid procrastination this really helped improve my productivity which I hope that you guys have noticed but a

lso my general well-being through a better work life balance signing up with better help is super easy you just fill in a short questionnaire and then they will assign the therapist for you and if you want to try this out for yourself then use the link here in the description below which is betterhelp.com Menor now that will give you an exclusive 10% off your first month of therapy and I highly recommend it thank you better help now let's continue so what were the problems with the original engi

ne setup of the Jurassic 737s well let's start with an easy one aircraft noise if you are standing on the ground near an airport and an aircraft passes overhead soon after takeoff most of the noise that you hear comes from the exhaust in the back of the engines but what if you are inside of the aircraft well with most Jets the fact that the engine sits further forward means that the wing blocks The View and therefore also the noise from those exhaust at least for most of the passengers but in th

e 7272 200 whose engines are also much noiser than modern variants are anyone sitting in the back half of the cabin will also have a front seat view of those exhausts making it for a a lot more noisy experience the exhausts also caused a second issue which I'm sure has annoyed a lot of ground Crews over the decades if you look at pictures of some of these older 737s you might see that they seem to have smudged fuselages just behind the wing these smudges are basically suit from exhaust gases whi

ch are directed towards the fuselage when the bucket trust reverses are deployed definitely not ideal given how much work it takes to actually clean them finally another reason why aircraft designers put engin forward of the wing even when they have room to put them underneath has to do with something called the area Rule now I have explained this in previous videos in some detail but the gist of it is that when an aircraft Fly Fast close to the speed of sound they produce less drag if the cross

section of the whole aircraft doesn't vary abruptly from the front to the rear so when you have something that increases the cross-section of the aircraft like a wing for example it is better to not also align the engines with the wing because they would then increase the cross-section even more right there and therefore also cause more wave drag there are more reasons both aerodynamic and possibly also structural ones why putting the engines forward of the Wing makes a lot more sense I can just

think of just the fact that you separated a little bit more from the wing in case of an engan fire and boing Engineers obviously knew about those two which is again why the 707 had this layout already back in the 19 1950s but for the 737 there simply wasn't room to fit both new pylons and those cigar engines under the wing it was just that simple but that fact just had to change when more efficient higher bypass engines like the cfm56 became available back in the 1970s boing who first engineere

d their way to retrofit cfm56 is onto its 707 soon realized that they could do the same with the 737 and by doing so make it much more efficient like most other high bypass turbo fans the cfm56 is larger in diameter than other earlier engines and that might seem like a problem at first but those engines are also shorter from front to rear so Boeing and CFM figured out a way to fit this engine under the wings of the 727 classic which was the generation that followed the Jurassic 737s well when I

say under the wing that's a bit debatable because even these engines are almost completely forward of the wing and obviously their bigger diameter means that they have to be higher partially in front of the wing as well but this wasn't enough as you can see in these photos Boeing and CFM had to get more creative than that and actually make changes to the engines themselves in order to get them to fit previous versions of the cfm56 powering re-engine Boeing 707s and KC 135 tankers for example all

had their accessory gearbox fitted directly below below the engine but for the 727 classic that gearbox was instead moved to the side to enable those engines to have that odd flatten bottom chip monk appearance it was actually a real engineering feat to make those inlets that shape and not to have the air intake being greatly affected and on top of that the fan diameter was also reduced a bit from the original this actually reduced the engin efficiency slightly because it meant that the engines

could have had a higher bypass ratio but but even so the 737 classic family was much more efficient than the Jurassic which explains its Commercial Success the Jurassic 737 had done pretty well with sales of around 1,125 7700s and 200 series aircraft produced but the classic series thanks to their hugely more efficient cfm56 engines and also a bit of airline industry growth to be honest accounted for almost 2,000 aircraft in total but even though though it was that successful in 1993 less than

a decade after the classic entered service Boeing announced that they would still replace it with the 77 NG or next Generation boing did this because the Airbus A320 had then entered service and was now stealing away key Boeing customers like United Airlines I have explained before that Boeing initially planned to replace the 727 classic with the open fan 7 j7 but slow engine development got in the way of that happening with the NG boing knew that they could still eek out a little bit more effic

iency from the 737 model with more structural and other improvements but as for the engines they were still going to use the cfm56 with just some minor tweaks most of those tweaks were internal involving a more compact engine core changes to the combustors and a digital control system but on top of that the fan was also changed its diameter went up by an inch or around 2 and 1/2 cm and the number number of fan blades was reduced with each fan blade instead becoming wider these changes made the 7

7 NG around 8% more efficient than the 727 classic and allowed it to be competitive with the then all new Airbus A320 interestingly many a32s also have CFM 56s but those engines have a different fan 7.3 in or 18.5 CM bigger than the one on the 727 NG the Airbus fan also has more blades similar to that original engine design now as I have explained in a much older video over on the mentor pilot Channel this difference in the fan size and layout is why the Airbus and the boing cfm56 engine sound s

o different especially during takeoff the Airbus has a higher pitched and decisively whining sound due to the higher tip speed while the 727 NG's engines make a deeper growling noise now despite the internal and fan differences between the engines of the 727 classic and the NG their placement and the cells didn't change that much at least not externally but of course that isn't really true when it comes to the 737 Max the next and likely final version of the 73 when Boeing launched the max they

knew they would need to get even more creative in order to get the even bigger CFM leap engines to fit because obviously these engin had an even bigger diameter and Boeing took quite some time to try to figure out how big of an engine fan they could actually get away with when they had made up their mind the fan of the CFM leap 1 Bravo was 69.4 in or 1 76.3 cm which is actually a little bit crazy because that meant that it isn't just bigger than the 737 NG engine it is actually 0.9 in or 2.3 CM

bigger than the cfm56 of the Legacy Airbus A320 so how did Boeing do that then well the change that you'll probably have heard the most about is that boing moved the engine even more forward and upward than they had done previously but actually the first thing that boing did was to increase the length of the nose gear strs by 6 to 8 in or 15 to 20 cm now that might sound a little bit odd but it makes more sense when you consider how much further forward the engines are from the main landing gear

after that had been done especially for the longer 737 Max 10 boing also installed a very clever telescoping link or Shrink link mechanism into it this allowed the main gear to get taller when it was extended but still fit into the same wheel well Bay when it was retracted now that change had less to do with the engines of the max 10 and more to do with the fact that it's nearly as long as some boing 707 which makes those pilot headaches regarding tail strikes a bit more serious that telescopin

g landing gear makes the max 10 gear 9.5 in or 24 cm longer when it really matters and to be clear the max 10 is not the first aircraft to have such telescoping or shrinking gear many military jets and some wide bodies also have a similar mechanism for space saving reasons including the Concord so boing did not reinvent the wheel here now going back to the engines and their Nels you can easily tell them apart from all the 737 installations because of those Chevrons in the back of the engines des

igned to reduce noise the nelas themselves also have a less pronounced flat bottom but it it's still there and it's visible if you look closely the engine Inlet is also different with a one piece lip skin that has a laminer flow profile in order to reduce its drag but did this engine and its installation more forward and higher up actually make the 727 Max unstable well let's try and put this into some perspective first of all while it is true that the engines were moved forward a bit the placem

ent of these and the 727 NGS engines doesn't differ as much as you might think if you compare the front edges of the engines of these Jets against the cabin windows you'll see what I mean now what is more relevant here is that the leap 1 Bravo engines on the max are heavier mainly because of their larger overall diameter making each indine about 850 lb or 386 kilos heavy than the engin they are replacing this extra weight can affect the stability of an aircraft that's true but not negatively as

I've explained in many of my videos an aircraft is like a seesaw or a teeter board with a fulcrum or pivot point being the center of gravity on the wing in nearly all Jets except maybe some military ones the center of gravity is positioned well forward of the center of lift and then there is an opposite vertical Force at the tail balancing the system out this is part partly what produces the stability of an aircraft and crucially if we move this center of gravity further forward we make the airc

raft more stable not less so since the engines of the 737 Max are heavier and are positioned very slightly more forward of where the previous engines were they actually make the whole thing more stable in theory now I should mention that we don't want the center of gravity to move too far forward because then we would need more downforce from the horizontal stabilizer to balance the system out which is less efficient but as I said the effect of the engines isn't as dramatic as some suggest no in

stead it's actually the size of the engines that causes the behavior of the 737 Max to change slightly compared to previous 737s you see at lower speeds and higher angles of attack their size and shape actually causes some lift to be created so in these very specific situations despite their weight these new engines actually generate a slight pitch up tendency not a pitch down one these were the changes in the plan's behavior that Boeing needed to address in order to keep the differences between

the 737 NG and the 737 Max to an absolute minimum and meet the regulatory requirements for longitudinal stability and constant stick Force per G so my point here is that these design changes had very little to do with how aerodynamically stable the boing 737 Max is it is and has always been a stable aircraft from that perspective and it's not more prone to store than any other earlier variant was the only thing that would differ is that at those very specific High angles of attack at low speed

the feeling in the control Yol for the pilots would have been slightly lighter than on other types which wasn't ideal but far from dangerous in fact you can actually hear what the system was supposed to do in its name maneuvering characteristics augumentation system meaning a System created to augment the maneuvering characteristics of the aircraft not keep keeping it from stalling or making it more stable all aircraft have to behave in a very constant and specific way throughout their handling

envelope and since these new engines change that slightly this system was implemented to buff that change out and bring it into full Regulatory Compliance so once and for all mcast was not implemented to fix any dangerous flaw in the 77 Max flying characteristics it was just implemented as a way to make it behave more similar to the older 737s and beh in a fully linear way to keep the authorities happy this is actually perfectly showed in the way that any issues with the speed trim system and th

erefore also the mcast is dealt with nowadays after the upgrades if any issue whatsoever is encountered with the system it is simply Switched Off and inhibited for the remainder of the flight and that's something that would never be done if the system was actually needed for the safe handling of the aircraft no instead it was the implementation of the mcast system into the design that was the issue not the aircraft itself and after those horrific crashes it has now been thoroughly fixed but back

again to the engines in the immediate future Boeing has some very different Nel related issues to deal with involving the engines and the ice system this will likely include a redesign of the Nel due to potential issues with how the Carbon Composites in the Nels are affected by the use of the engine anti I system and hopefully Boeing will have a solution to that problem within a year or so but until then we Pilots have been given specific procedures that we need to follow in order to deal with

it specifically making sure that the anti anti system doesn't get overheated but what do you think is it time for boing to start working on a brand new aircraft and leave the 737 behind I will be discussing this and a lot of other things together with my patrons in my next Zoom hangout and I would love for you to also take part and if you want to use the link that is somewhere here on the screen or in the video description below to sign up also as my final point please go over and give some supp

ort to my fellow Aviation YouTuber Stefan Drury who is going through some tough times right now he creates some truly great Aviation content that I hope that you've all checked out before and if you haven't definitely go and do so now I will link to his latest video here on the screen and in the description have an absolutely fantastic day and I'll see you next time bye-bye