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I know that for turbofan engines there will be Gyroscopic effects while pitching, rolling and yawing maneuvre. But if the aircraft is cruising at an altitude or is simply idling on the ground, what would be the torque loads acting on the aircraft because of the rotation of fan blades? and what would be the direction of the moment if there's any?

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  • $\begingroup$ Remember most turbofan aircraft have an even number of engines, so that with a 2-engine aircraft, each spins the opposite way, and with a 4 engines 2 spin each way. $\endgroup$
    – Rory Alsop
    Commented May 15, 2022 at 16:08
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    $\begingroup$ They don't counter rotate. All of the engines on any turbofan will spin the same direction. The only "handing" that goes on is during the build-up to accommodate left side or right side plumbing connections. $\endgroup$
    – John K
    Commented May 15, 2022 at 20:14

2 Answers 2

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There is no net torque on turbofan engines

According to Newtonian physics, in order for the engine to transfer a torque onto the aircraft, it must impart some angular momentum (in the opposite direction) onto the air particles. More simply, the engine must make the exhaust gases swirl in one direction for it to transfer a torque onto the aircraft in the other direction.

However, the exhaust guide vanes exist precisely to prevent this - they ensure that the exhaust gases exit with as little angular momentum as possible. This is desirable since the EGV's are actually converting that angular momentum into linear momentum, producing some additional thrust in the process.

GEnx rear view image

Image source. In this image of a GEnx, you can see the stator assembly for both the core exhaust and fan exhaust

Propeller driven aircraft do not have a stator assembly as such, and so air ends up exiting in a swirling motion, and hence the torque.

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  • $\begingroup$ I can only read "gyroscopic" in the question. The questioner knows that there are gyroscopic effects while manoeuvring and would like to know if it exist also during stationary phases, like cruising or idling... as simple as that. $\endgroup$
    – sophit
    Commented Feb 25, 2023 at 2:02
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    $\begingroup$ I agree anyway that the question is not clear as well as the OP-self answer. $\endgroup$
    – sophit
    Commented Feb 25, 2023 at 2:13
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If we are considering only one engine for analysis then yes there will be torque load which can be calculated using right hand rule which will depend on rotation of fan blades. During manoeuvre, there will be gyroscopic loads acting on the engine caused due to torque.

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    $\begingroup$ Are you going to accept your answer? $\endgroup$ Commented Jun 29, 2022 at 15:12

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