Cruise flight indicates that total lift and weight of aircraft cancel and thrust forces generated cancels with total drag forces. However, I am looking closely at the nacelle instead of the whole aircraft. Would the strut that connects the nacelle to the wing still experience reaction forces during cruise flight? Since engine thrust generated is greater than engine drag and lift on the engine is larger than weight of engine it sounds like even during cruise there needs to be a reaction at the strut to fix the engine to the wing, unless I am misunderstanding something.
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$\begingroup$ Related: How does the load transfer from a prop to the airframe? $\endgroup$– user14897Commented Oct 20, 2021 at 14:55
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$\begingroup$ Related: How are engines mounted onto wings?. Indeed forces need to be transferred from the engine to the wing, the pylon strut needs to bear these forces, for each force there is an equal opposite reaction. The nacelle is neutral, it just hangs from the pylon. $\endgroup$– minsCommented Oct 20, 2021 at 15:05
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1$\begingroup$ Welcome to the site! Your choice of username is somewhat limiting. $\endgroup$– GdDCommented Oct 20, 2021 at 16:16
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$\begingroup$ It's OK, @GdD, we'll let him ask about other things, too. ;) $\endgroup$– FreeManCommented Oct 21, 2021 at 21:25
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Yes. The structure that joins the engine mount to the wing, nacelle, pylon, or whatever, has to transfer all of the forces being produced by the engine and propeller or fan, and their mass, to the wing box, and these forces are certainly present in cruise flight.
So you have the thrust of the propeller/fan applying a tension load forward pulling the airplane along, the torque reaction from the prop applying a rotation load trying to twist the nacelle, the weight of the engine and prop trying to bend the nacelle downward from gravity and G loads (where are there all the time unless the plane pitches over into zero G flight), and gyro precession loads from the propeller/fan trying to bend the nacelle to the side or up and down when the airplane yaws and pitches, and they would all be present to one degree or another during cruise flight.
You could eliminate the thrust and torque reaction loads by reducing power to remove those forces, but you can't do much to remove propeller/fan precession loads or gravity related loads while in flight.
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$\begingroup$ "The nacelle structure that joins the engine mount to the wing has to transfer all of the forces", rather the pylon strut. $\endgroup$– minsCommented Oct 21, 2021 at 12:03
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$\begingroup$ Actually wing mounted jet engines aren't "nacelles" anyway. You have an engine, the cowl, and the pylon. A nacelle is normally a pod that fairs the engine into the wing and provides a structural base to attach the engine mount. A pylon is not a strut or a nacelle. Anyway, I tried to use a catch-all phrase, but made some changes to be more catch all. $\endgroup$– John KCommented Oct 21, 2021 at 12:21
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$\begingroup$ The inlet, the duct for the fan flow, the reverser, the exhaust and the associated cowls make the nacelle. Here is the nacelle manual for CFM56-5 engines on the A320. $\endgroup$– minsCommented Oct 21, 2021 at 15:58
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1$\begingroup$ Ok fair enough. We didn't call them nacelles on the CRJ program. $\endgroup$– John KCommented Oct 21, 2021 at 16:22
