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3 Answers

Momentum of thrust

Asked by: 972 views , ,
General Aviation

Dear Aviators, 

In a symmetric rotating multi engine aircraft, Though there is a difference in momentum of thrust produced by each engine, why there is no effect of it while both engines are operative?

Thanks in advance

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3 Answers

  1. Best Answer

    Skyfox on Mar 16, 2016

    I’m not entirely sure what you mean by symmetric rotating multi engine aircraft. If you mean counter-rotating where the left engine is rotating clockwise and the right engine is rotating counterclockwise, if they’re set to the exact same power settings (throttle & prop RPM) then they should be producing the same thrust output and therefore have symmetric/equal thrust. If you mean a multi engine aircraft where both engines are rotating the same direction (usually clockwise), the right engine will have a slightly higher amount of thrust because of asymmetric thrust on the props causing the greater thrust on the descending blades of the right prop having a greater arm from the center of gravity as compared the more inboard descending blades on the left engine which are closer to the center of gravity. In that case, at cruising speed and power settings the effect of asymmetric thrust is greatly minimized as compared to slow flight at high power settings.

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  2. srishan on Mar 16, 2016

    Thank you for your answer .
    I mean to say both propeller rotating on same direction say clockwise..
    Is there any special mechanism build in to minimise the assymetric thrust ?
    while flying not able feel the assymetric thrust, so I just want to make sure whether the assymetric thrust is minimal or its been reduced with mechanism.
    Theoritcally I understood that there should be a assymetric thrust as the right down going propeller is further away from cg as compare to left side..

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  3. Skyfox on Apr 11, 2016

    There could be any number of corrections engineered into the aircraft such as a very slight upward angle on the left side engine to give it slightly higher asymmetric thrust on its inboard descending blade to counteract the thrust produced by the right engine’s outboard descending blade. Or the rudder could be positioned with a very shallow angle to the left to cause more yaw to the right to counteract asymmetric thrust (which would be unnecessary if the airplane is designed with rudder trim). It really varies from one manufacturer to the next, so check the POH of the particular airplane to see if it describes any built-in correction factors.

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