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If an airplane with two propellers has both propellers with the same rotation direction (say, both the propellers rotate counter-clockwise as seen from nose to the tail), will be the four left-turning tendencies still be generated?

Airplane with two propellers

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Yes, for the most part.

  • Definitely P-factor will still exist and provide a yaw torque in the expected direction. This is why twin-engined aircraft have a "critical engine".

  • Engine torque will still produce a roll torque in the expected direction.

  • Gyroscopic precession will still produce a yaw torque in the expected direction when the aircraft pitches.

  • The yaw torque from the spiralling slipsteam interacting with the vertical fin-- which is normally quite significant in conventional single-engine aircraft-- is the one effect that may be be greatly reduced in a twin-engine airplane of the usual configuration, since the fin is not located in a strong part of the circulation behind either prop.

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  • $\begingroup$ Do you have a link how a proper way to calculate the tendencies? My intuition also said that there should be also tendencies. $\endgroup$ – AirCraft Lover Nov 9 at 3:10
  • $\begingroup$ @AircraftLover-- no I don't $\endgroup$ – quiet flyer Nov 9 at 13:03
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No, because they turn on different axis which does not coincide with the longitudinal axis of the airplane. Having two propellers turning the same way on the same axis, it would enforce the effect.

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    $\begingroup$ How does the separation of the axes make the torque disappear? This seems to contradict classical mechanics. $\endgroup$ – AEhere supports Monica Jan 24 at 14:52
  • $\begingroup$ As the engines rotate clockwise seen from a pilot view (or anti-clockwise from the nose to the tail view), when the engine 2 rotate, will it not hil the vertical stabilizer which will make turn-left tendency? $\endgroup$ – AirCraft Lover Jan 25 at 1:50
  • $\begingroup$ As long as my deduction comes from observation and not from a mechanical engineer degree, both engines outflow will hit the vertical stabilizers one on each side of the longitudinal axis, having not the torque applied to one of the axis won't let the airplane turn, in my humble opinion, one or both the engines running, since the torque they would apply is not on the longitudinal axis of the plane. $\endgroup$ – Max Lombardi Jan 28 at 9:01
  • $\begingroup$ Seems that I have missed this discussion. I apologize. $\endgroup$ – AirCraft Lover Mar 1 at 2:49
  • $\begingroup$ As I said, if both the propeller are rotating counter-clockwise (seen from nose to the tail), then in my opinion, propeller 2 will generate wind spiral, which it will still hit the vertical stabilizer, then make the airplane forced to turn left. $\endgroup$ – AirCraft Lover Mar 1 at 2:53

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