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When the turboprop engine is active, the propeller shaft rotates and causes the propeller to rotate as well, which in turn generates thrust. The propeller shaft rotates because of the torque (or twisting moment) created by the turbines of the engine and then which is conveyed to the propeller shaft. My question is that if I am trying to conduct a FEA analysis for the mount at which this engine is attached, should I also apply this torque on it or not? I was thinking that I shouldn't apply any kind of torque at this engine mount since I don't think that engine itself is rotating at all because of any twisting moment, but it is recommended that the torque should always be taken into account while conducting such analysis. Moreover, I believe that there exists some bearings somewhere inside the engine which makes the engine mount to not take any kind of torque generated by the engine.

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  • $\begingroup$ The simplest rotation machine is the house fan, does its stand move while the fan is at its top speed? However, if the base is too small to handle the drag it created, the fan will be falling forward. This observation tells us a fact - the engine mount (base) has nothing to do with the torque but the thrust it causes. $\endgroup$
    – r13
    Sep 3 at 15:06
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    $\begingroup$ @r13 the fan base is always made with enough mass. Just hold one in your hand and see if there is a reaction. If not try it with an electric drill with a big bit and see if your wrists notice a reaction force when you jam the bit… $\endgroup$
    – Solar Mike
    Sep 3 at 15:10
  • $\begingroup$ @SolarMike You confuse me with mass while I was talking torque. Will a handheld cooling fan rotate on my hand? We feel differently though. $\endgroup$
    – r13
    Sep 3 at 15:20
  • $\begingroup$ @r13 the mass and torque are linked… or don’t you get that? If the fan base does not have enough mass or the mass is not sufficiently distant then the fan will be unstable. Put a drill bit in a drill and clamp the drill bit in a vice. Take good hold of the drill and pull the trigger. Done it often to test if the motor develops full power. Note the reaction force. $\endgroup$
    – Solar Mike
    Sep 3 at 19:40
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    $\begingroup$ @PhilSweet Sorry, but this is a perfectly straightforward question about dynamics and in fact every trainee pilot (not just aircraft designers) is taught the answer - for the good reason that not knowing the answer is a good way to crash the aircraft when taking off! $\endgroup$
    – alephzero
    Sep 4 at 10:59
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For every action there is an equal, but opposite, reaction.

Never found a case that this is not true.

Torque reaction on the P51 even caused uneven tire wear: https://www.aopa.org/news-and-media/all-news/2007/august/pilot/north-american-aviation-p-51d-mustang

So, if you open the bonnet or hood of a car and run the engine with it in neutral, then blip the throttle you will see the engine try to rotate in the opposite direction to that which it runs. Yet another example and it’s not connected to the output…

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  • $\begingroup$ The Newton's third law always holds. The problem is I couldn't understand if there physical connection between the turbines (or propeller shaft) and the engine casing (to which the mount is attached). If there is no physical connection, then I couldn't think of any reason why the engine casing or the mount will also be experiencing the torque or twisting moment. Moreover, I don't know the torque (if) experienced by the engine casing and mount would be equal to what the propeller shaft or turbine is experiencing. $\endgroup$ Sep 3 at 14:19
  • $\begingroup$ @RameezUlHaq Since the engine housing does not rotate there must be no net torque on the engine. We know the engine applies torque to the propeller. So where do you suppose the counter-torque is, which makes it zero net? Now, to my untrained eye I wouldn't have thought that torque was significant, but maybe it is.... $\endgroup$
    – user253751
    Sep 3 at 16:15
  • $\begingroup$ The torque (which balances the drag of the prop blades going around the circle) is transmitted to the prop by the turbine. Specifically the rotating parts of it.The reaction force would be in the turbine stator blades. $\endgroup$
    – Pete W
    Sep 3 at 17:38
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    $\begingroup$ A turbine consists of rotors and stators, doesn't it? I'd expect there to be torque on the stators $\endgroup$
    – user253751
    Sep 3 at 19:06
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    $\begingroup$ @RameezUlHaq "doesn't matter if the torque is on the stator or rotor". It totally matters. The shaft is isolated by bearings. It can't exert a torque on the mounts, That is what the bearings are for - so it can't. Shaft torque does not get transmitted to the mounts, but stator torque and gearbox frame torque does. Gearbox torque should be about 15 times as big as stator torque - perhaps in the opposite direction. $\endgroup$
    – Phil Sweet
    Sep 4 at 9:43
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Yes, indeed it creates a reaction torque equal and in opposite direction in the frame of the airplane. All the engine mounts have diagonal braces designed to transfer the propeller's torque to the wing or mount.

It is immediately noticeable in a helicoper with a disabled rudder propeller and will cause imminent danger of crash because it causes the copter to spin.

I am a private pilot and especially in single-engine airplanes like Cessna 182 the torque of the propeller causes significant loss of authority on the yoke and has to be dealt with. We need to control the roll and yaw (rotation of the plane on the horizontal plane about the Z-axis) it causes with the ailerons combined with the rudder. Thi procedure is different for each airplane and the pilot must follow the manufacturer's instructions. Here is a link to torque reaction.

source

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torque reaction

Edit

after some comments I googled specifically jet engines' torque. and summing up the statement the answer is yes they do create torque.

unless in exceptional cases like in vertical lifiting Harrier fighter jet were there is no stream of air at take off to counter the torqu they have added a fan on the front, turning the opposite direction of the jet engine with revrse torque to cancel the engine torque.

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    $\begingroup$ The question is about a turboprop. Totally different. The conrods create all the engine mount torque in an ICE. Jets don't have those. Residual torque in jet mounts is optional. It is a design choice. An alternative is to accept swirl in the jet exhaust. The real issue here is the gearbox arrangement, which the OP hasn't described. $\endgroup$
    – Phil Sweet
    Sep 4 at 0:45
  • $\begingroup$ @PhilSweet What you say is true in theory, but the only "jet engine" design I know where all the mechanical torque is reacted by aerodynamic torque and none appears at the engine mounts is this one, designed a few thousand years ago: en.wikipedia.org/wiki/Aeolipile. The gearbox is irrelevant, except for semantic arguments about which side the boundary between the "engine" and "airframe" it is on. $\endgroup$
    – alephzero
    Sep 4 at 17:43
  • $\begingroup$ @alephzero The gearbox is relevant. More than 90 percent of the mounting torque will be due to the reduction gears. There aren't any options here. A 15:1 gearbox is going to put 14 times the input torque onto the mounts no matter how you do it. $\endgroup$
    – Phil Sweet
    Sep 4 at 19:35
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The engine mount (connection) is responsible for the maximum horizontal force on the plane including the effect of the thrust, and its weight.

enter image description here

ADD:

The pictures below show how the engine is attached (mounted) to the pylon, which is attached to the wing. The simple connections (19a & 19b) make me hesitate to think they can resist the torque (rotated about the axis of travel). Or maybe the torque is rather small.

enter image description here enter image description here

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  • $\begingroup$ So where is the torque reaction on your diagram? Or not sure where it goes :) $\endgroup$
    – Solar Mike
    Sep 3 at 20:01
  • $\begingroup$ I don't know the engine, but after a few readings, it goes like the gas pushes the pistons, which moves the crankcase that connects and rotates the flywheel in a CW or CCW direction to produce the torque in the shaft housing/transmission. The engine will experience torque if the rotation is suddenly reversed, as the designed rotation can either be CW or CCW. $\endgroup$
    – r13
    Sep 3 at 20:17
  • $\begingroup$ There is no reaction in the engine for the torque it produced. The ultimate reaction is, for cars, at the contact of the tire and the road, for an airplane in the air, it is the thrust. $\endgroup$
    – r13
    Sep 3 at 20:24
  • $\begingroup$ @r13, I want to agree with what you are saying since I believe the same. But in reality and according to some other experts, there is some torque production at the engine casing itself which makes the engine mount to experience a reaction torque. Doesn't make sense near me as well, but apparently this is true somehow lol $\endgroup$ Sep 3 at 20:51
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    $\begingroup$ @r13 You show a picture of a turboprop (which is what the OP asked about) and then talk about "pistons" in a comment. Turboprops don't have pistons! $\endgroup$
    – alephzero
    Sep 4 at 17:46

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