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What is Reverse Thrust? | Airspace Explained

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Airspace

Have you ever wondered how reverse thrust works? I am going to explain in this video!

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Script
Twelve hours have passed, you’ve had your dry sandwich and a meal that was most likely beef or pasta served in an aluminium bowl, when you finally arrive at your destination. The plane touches down and – what is this, the engine opens up and you are pressed against your seatbelt. You know this is caused by reverse thrust – but what is reverse thrust? Does the engine spin the other way, now blowing air forward?
Nope, it does not! Today, I am going to explain to you how reverse thrust works.
Welcome to airspace explained!
Aircraft landings are absolutely fascinating, if you ask me. I myself have performed some two thousand landings and each one of them was a thrill. The transition from flight to ground roll is the art of piloting itself and the forces involved are amazing! After the plane touches down, megajoules worth of kinetic energy have to be converted into other types energy by the brakes and the reverse thrust. Planes have highly efficient carbon brakes, but that is not why you clicked this video – let’s get into the inner workings of reverse thrust.
An airliner’s jet engine has two sections, a hot section, in which the external air is first compressed, then mixed with fuel and ignited, then this air expands and drives the internal hot stream turbine, which drives a shaft that drives the compressor, sucking in more air and completing the circle. Located outside of the hot section is – you guessed it – the cold section. The drive shaft of the hot section drives the huge fan at the front of the engine, which functions just like a propeller with many blades. This increases the engines efficiency by a lot, compared to an engine which only has a hot section.
Many people think that while reverse thrust is used, the engine reverses its direction. This would be highly inefficient if not impossible, since aircraft engines often weigh multiple tons and rotate at many thousand revolutions per minute. Instead, most aircraft use some form of reverser doors that deflect the cold section air forward and outward, resulting in a decelerating force.
Some planes have pivoting door reversers, others use a sliding mechanism, but in the end, they all do the same thing – deflect the cold stream forward. On engines that do not have cold streams, such as engines of private jets, bucket type reversers are used that close into the hot stream and deflect it forward. To actuate the thrust reversers, there is a second lever on the thrust levers that the pilots can pull back in order to pull back the thrust levers beyond the normal idle position.
So, the next time you land, you will know how reverse thrust works.
But wait, there is a question – Since planes have a way of redirecting thrust forward, wouldn’t that mean that they could theoretically drive backwards on their own? Why are planes still pushed back from the gate with tractors then?
The answer is simple, reverse thrust loses efficiency the slower the plane gets, due to some physical shenanigans that would make this video too long, so just trust me on that. At a standstill, the required amount of reverse thrust would be pretty high, which would require the engine to run at high power. This is not a good idea at the gate where a lot of personnel and machinery is present, also there may be small objects left on the ground from the boarding process that may be sucked into the engine.
There you go, now you can impress your fellow passengers the next time you land with your thrust reverser knowledge.

posted by loritenor18