Question: Reverse Thrust

Hello !
So I am a real avgeek and I have a good knowledge of aviation but unfortunately I still don‘t understand how the reverse thrust works. So I do know that the air is pushed in the other direction and this stops the plane but why does the engine creates thrust while it‘s reversed ?
Found this YT-video about it

Ok so my main question is: Why does the engine creates thrust while it’s reversed ? Does it spin in another direction?

So it‘s a bit embarrassing for me to ask this as I really know many things but yeah still have to learn a bit 😆

Thanks ✈️

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It’s still spinning in the same direction per say it just diverts the thrust opposing forward motion.

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Ok, but why is it spinning faster then ?

@DeerCrusher we need you here ;)

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I don’t have the correct vocabulary but

Only the part in the exterior reverses, the central part with compressors and fuel injection stills produces trust.

I know in Geneva for example only IDLE reverses are authorised and it somehow works.

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I removed the part on the gulfstream because I just learn different styles of reversers exist.

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So here’s the thing

Thrust reverser works by ceasing the cold duct with actuated internal annular flaps (most commonly used, 2 types, all on wing mounted engines) or external exhaust redirection mechanisms (used on most rear-mounted engines) to redirect cold flow (fan thrust) to the reverse direction (i.e. front of the aircraft) for increased drag (opposite force) thereby decelerating the aircraft quick enough before it runs out of RWY.

The reason the engines are throttled up when TR is deployed is because it is very inefficient for the engine to run in such way at low throttle. While hot flow from the engine is still pushing the aircraft forward, the fan thrust is nevertheless force blocked and had to immediately turn into an opposite direction therefore some energy must be wasted at the stagnation point right at those internal flaps and be converted into heat and sound, resulting the forced-forward airflow less momentum and force. That’s why You also hear loud wind noises when TR is deployed.

Yes I know that only exterior part with the cold air is responsible for the reverse thrust but why the engine creates thrust, the engines spin faster ?

IDLE thrust (no advanced throttle) still creates power. So whether you add thrust or not when reversing you still produce power.

@nincombop said it all

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Well that’s what I found wierd. Here in LSGG, charts forbid the uses of anything above reverse idle unless you really need them because of noise restrictions

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Some airports need that for NB purpose, but they are either expecting incoming aircraft to be lightly loaded (below MLW) or they have a very long runway. When an aircraft is considered below MLW, its approach speed will be slightly lower compared to that of the highly loaded counterparts, therefore at touchdown they can solely rely on brakes and full spoilers without the need of TR.

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To simplify this in a few words:

Reverse thrust only means “redirecting the flow of air produced by the engine”. The pictures that @Q-ENAN posted are perfect to seeing how this occurs.

The general misconception is the fact that people think that the engine reverses the rotation of the fan blades. Not true.

This simply means that doors on the engine are opening and “barriers” within the bypass section of the engine deploy, which in turn cause the air sucked in by the engine to exit in a fashion other than normal.

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