Hi everybody, welcome to Mentour, here's another video podcast as always I hope you are doing absolutely fantastic so today on the podcast, Why is the engine on the 737 flat at the bottom? Stay tuned. Right everybody, so why is it that the 737NG has engines that look like they're a little bit flat at the bottom? Well, in order to understand this we really need to go back in time We need to go back into the history, when the 737 family was born. So back in the 1960s Boeing engineers were looking into creating an aircraft type that would be easy to use Easy for ground personnel to both board and to load with bags, and they were using something called Bulk loading, which means that they Were basically taking the baggage and throwing it into the hole; they weren't using containers like to do on more modern aircraft, okay? Now in order to do that efficiently, they wanted to have an aircraft that was fairly low-down to the ground so they created The 737 to be just that to be low-down to the ground, easy to handle, and that was not a problem because at The time they were using turbojet engines. Now, they were using an engine type called JT8D and that engine essentially looks like a cigar and the reason that it's so much smaller than the current engines that you see is Because a turbojet engine uses the core engine action, the hot gases that's being expulsed at The back of the engine to create thrust. Okay, that's how jet engines used to be run and you also see them in a lot of fighter jets today Now, the 737-100 and -200, the ones that We refer to as the Jurassic 737 models, they kept this engine but as the decades was moving forward into the late 70s and beginning 80s We were sort of seeing the advent of the turbofan engine now the turbofan engine works very differently Than the turbojet engine. The turbofan engine uses the Hot air gases that goes through the turbines to drive a big fan at the front of the engine. Now, that big fan Is what's creating most of the thrust so it's the bypass ratio as in the, air that's passing By the core of the engine that is cause-- that giving most of the thrust and that Also has the benefit of damping the sound so they're much more efficient fuel-efficient and Quieter than the turbojet engines so The Boeing engineers wanted to fit the new CFM56 engines, the new Turbojet, -sorry the turbofan engines onto the 737 model, but here they encountered a problem. So since they originally Wanted the aircraft to be that low-down to the ground if you wanted to put a turbofan engine onto that same Airframe the turbofan engine is much bigger; it has a much bigger diameter Than than the the turbojet engine did. Okay so They faced that problem. They, also faced an additional problem of since they wanted to redesign the 737 they also wanted to be able to fit more passengers and the only way to do that is by stretching the airframe so the 737-300 and -400 and -500 actually they were continuously being stretched, okay now When you stretch an aircraft the center of gravity is going to change, okay? and I'm going to do a separate episode about center of gravity and why you're not allowed to sit where you want later on, but When they did this, they also needed to solve the problem with this change of center of gravity, and the way that they Did that was that they redesigned the engine pylons, those are the things that's actually holding the engines to the wings so they Moved the engines from being under the wings to being ahead of the wings By doing that they could actually lift the engines a little bit from the ground, and By redesigning the engine lip, the engine intake, okay, to being a little bit more flat at the bottom they could also gain a couple of precious Centimeters from the ground so by essentially moving it forward they were solving the problem with the center of gravity Because that actually balanced the aircraft out, and it could also lift it to get it away From the ground so the engines are not flat alright the engines obviously is completely circular they're round Because the fan is round but the lip is a bit flattened and That helps when, we are for example doing crosswind landing so in a crosswind landing you might come in with A slight bank angle into the landing. Now, what you really really don't Want is for the engine to be so close to the ground that it is a risk of hitting the ground So it is crucial That the engine inlet is as far away as possible from the ground, okay? Another redesign that you might have seen on the 737NG And the classic actually, is that they have kind of like a chipmunk Sight to the engine. That's because another thing that We did or that Boeing engineers did in order to gain extra ground clearance is they moved the accessory gearbox and the fuel pumps from being Located under the engines to the side of the engines and that's why you see that kind of little chipmunk shape to the Right so, by doing this they now Have achieved more ground clearance they could fit the more efficient, quieter Turbofan engines to the 737 family but they didn't have to redesign the landing gear the only thing they Did was they strengthened it a little bit because the aircraft and the airframe was now heavier but They didn't have to extend it they, on the 757 they actually Did extend it but that's a different model so up until the newer 737NG's the New generation 737, we have kept more or less the same ground clearance and we have enabled them to be easier to handle, to be easier to Load than for example the airbus 320 family, which is much higher than the 737 is Now, from from the 737NG, now we're going into the 737 MAX family; the 737 MAX family will have Increased the the landing gear height slightly, okay, so that's to enable the leap engines to be fitted Which is an even more efficient turbofan engine so from the 737 MAX family and up, we will not see this iconic Flattened shape of the engines from the 737 family anymore Guys, I hope you liked that explanation and continue to send in more questions about all things that you want explained And also make sure that you get the mentor aviation app There's more and more people that are joining, by the day, you will find some links here in the description of this video inside of the app You'll be able to watch videos you can get collections and see how to for example do a full set up or an emergency evacuation Of the 737 and also you can chat with other users other People that might be in training from different parts of the world and You can chat with me, so get in there register yourself, enable push notifications and Just tag @mentour if you, want to speak to me directly Have an absolutely fantastic day wherever you are and i'll see you next time
