What REALLY Happens Inside a Jet Engine at Takeoff?

Subscribe to the channel for more machine knowledge:    / @ironlogicyoutube   Most people, if asked how a jet engine works, would say something like: it sucks in air, burns fuel, and blows the hot gas out the back, and the reaction pushes the aircraft forward. That is correct. It is also the least useful way to think about what is happening inside one. The more accurate mental model is this: a jet engine is a machine for converting chemical energy into a very specific kind of kinetic energy — the acceleration of a large mass of air rearward. Newton's third law does the rest. The faster you can accelerate more air rearward, the more forward thrust you produce. That single objective — accelerate as much air as possible, as fast as possible, as efficiently as possible — explains every design decision in a modern turbofan engine. And the word turbofan is important here, because it reveals the part of a modern jet engine that most people do not fully account for. When you look at a jet engine from the front — that enormous disc of blades — you are not looking at the core of the engine. You are looking at the fan. And on a modern high-bypass turbofan like the GE90, the fan is doing approximately 75 to 80 percent of the total thrust work entirely on its own, without any combustion, simply by accelerating a massive volume of air around the outside of the engine core. The combustion core — the part that actually burns fuel — is responsible for only around 20 to 25 percent of the total thrust. It exists primarily to drive the fan through the turbine shaft, not to generate thrust directly through exhaust. This means that when you hear a jet engine, the overwhelming majority of what you are hearing — the massive volume of air moving — is unburned bypass air being accelerated by a fan driven by a shaft connected to a turbine driven by combustion. The exhaust you see at the back is a relatively small fraction of what is actually being moved. Understanding this changes how you see everything that follows.