Have you ever wondered how planes manage to slow down so fast? It’s not that they have amazing brakes, although they do have some of the most impressive disc brakes you’ll ever see, no most of the work is done by the very thing that launches them into the sky: the engines. The way they achieve this is called thrust reversal and, as the name would imply, it redirects the thrust that the engine is generating in the opposite direction, slowing the craft down rather than accelerating it. The way modern aircraft achieve this is wide and varied but one of the most common ways is demonstrated perfectly with this amazing 3D printed scale model:
The engine that the model is based off of is a General Electric GEnx-1B, an engine that’s found in the revamped Boeing 747-8 as well as Boeing’s new flagship plane the 787. Whilst this model lacks the complicated turbofan internals that its bigger brothers have (replaced by a much simpler electric motor) the rest of it is to specification, including the noise reducing chevrons at the rear and, most importantly, the thrust reversal mechanism. What’s most impressive to me is that the whole thing was printed on your run of the mill extruder based 3D printer. If you’re interested in more details about the engine itself there’s an incredible amount of detail over in the forum where the creator first posted it.
As you can see from the video when the nacelle (the jet engine’s cover) slides back a series of fins pop up, blocking the fan’s output from exiting out of the rear of the engine. At the same time a void opens up allowing the thrust to exit out towards the front of the engine. This essentially changes the engine from pulling the craft through the air to pushing back against it, reducing the aircraft’s speed. For all modern aircraft, even ones that use a turboprop rather than a fan, this is how they reduce their speed once they’ve touched down.
Many of us have likely seen jet engines doing exactly that but the view that this model gives us of the engine’s internals is just spectacular. It’s one of those things that you don’t often think about when you’re flying but without systems like these there’s no way we’d be flying craft as big as the ones we have today.