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During the landing reverse thrust of an aircraft engine is seen that the compressor fan rotates in opposite direction to counter the aircraft's forward motion if I'm right So, my question here is "does the engine stops its rotation(clockwise) and than starts to rotate it in opposite direction(anti-clockwise) So, as to perform the reverse thrust operation?

In a nutshell my question is does the engine stops midair to perform the reverse thrust operation! C-17 GLOBEMASTER PERFORMING REVERSE THRUST

Scramble shravan
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2 Answers2

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During the landing reverse thrust of an aircraft engine is seen that the compressor fan rotates in opposite direction

This is wrong

Reverse thrust does not reverse the rotation of the fan/compressor/turbine.

Reverse thrust "simply" redirect the airflow coming out of the turbine in the reverse direction (well, almost, as we'll see in a moment) w.r.t. the usual one.

In the image you posted, the thrust reversers are deployed, and you can see them circled here:

enter image description here

The airflow is the coming out not from the back of the engine, but from the sides, slightly directed forward. The thrust (i.e. the force that the airflow is imposing on the aircraft) is directed backwards, while normally is directed forwards, it is then reversed.

This is nicely illustrated in this image (source)

enter image description here

NOTE: there are different typologies of thrust reversers, this is only one of them, but none of them require spinning the engine in the opposite direction.

Federico
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  • Thankyou for making me right..and it was a good information indeed. – Scramble shravan Mar 15 '18 at 15:47
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    Not illustrated: The fan airflow (deep blue) is much larger than the turbine airflow (red), and as much as 90% of thrust comes from the fan airflow. Thus, in reverse mode, the "red" continues to be forward thrust, but there's not enough of it to make a difference. The red is more turbine exhaust than intentional thrust on a high-bypass. The fan does "all" the work. – Harper - Reinstate Monica Mar 15 '18 at 18:43
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When you put your car in reverse gear, does the engine first stop and then start spinning in the opposite direction? No. The engine still keeps on spinning in the same direction, it's some extra gears that cause the output to be in the other direction

Similarly, Reverse thrust is merely a deflection of thrust from the rear to the front. It is done using mechanical levers and gates that redirect the flow of thrust to the opposite direction.

If reversal of turbine's rotation was hypothetically required, the resultant reverse thrust would be produced too late and negligible to be of any use. You can't stop a turbine from a massive RPM to nothing within a few seconds, and then spool it up again in the other direction.

Hanky Panky
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    Turbine working in opposite direction won't work at all. Shapes of all rotor and stator blades are optimised for so-called forward airflow, temperature gradients and pressure gradients at every stage. The least bad thing that can happen when you try to reverse the rotation is complete stall of the turbine stages. Similarly, inversing the crank rotation of 4 stroke engine will produce no power output at all. On the other hand, 2 stroke engines can run both directions. – Crowley Mar 15 '18 at 18:34