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Aircraft vs a lever
G'day all.
I recently saw someone say that an outer engine on a 4-engine aircraft will yaw the aircraft more compared to a smaller two-engine aircraft using one engine. They compared it to a lever in that it's easier to turn the fulcrum the further away you are from it. Is this all correct? Is this an accurate comparison? |
Sort of, except the fulcrum would be the non-moving pivot point for the lever. In the case of an airborne aircraft, the fulcrum will be the center of gravity. In general, yes, the further away from CG (the longer the lever arm is from the fulcrum point), the more yawing force.
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Originally Posted by 340drvr
(Post 11567079)
Sort of, except the fulcrum would be the non-moving pivot point for the lever. In the case of an airborne aircraft, the fulcrum will be the center of gravity. In general, yes, the further away from CG (the longer the lever arm is from the fulcrum point), the more yawing force.
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OK, sure, other various factors could result in a significant difference in yaw moment between, say, a 777 losing engine #2 vs a BAE 146 Avro losing engine #4.
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The torque or moment of force is simply the product of the force value by the arm length with which the force makes the object pivot around its center of gravity. That torque is the intensity of the "pivotal action".
The arm length is supposed to be measured on a line passing by the CG and perpendicular to the line holding the force and its application point. If the engine is reasonably abeam the center of gravity, you can approximate this arm length with the distance between the CG and the engine. So the effect of the torque will be higher if the distance CG-engine increases or if the thrust of the engine is higher. You will then also need a higher torque to counteract the engine torque and control the yaw motion of your aircraft, either by increasing the size of the tail fin or by putting that fin further aft. |
Or by increasing the effectiveness of the rudder. EG DC10 and B777 double hinged rudders.
( I know the reason on the 10 is the shorter fin) |
The torque or moment of force is simply the product of the force value by the arm length with which the force makes the object pivot around its center of gravity. That torque is the intensity of the "pivotal action". The arm length is supposed to be measured on a line passing by the CG and perpendicular to the line holding the force and its application point. If the engine is reasonably abeam the center of gravity, you can approximate this arm length with the distance between the CG and the engine. So the effect of the torque will be higher if the distance CG-engine increases or if the thrust of the engine is higher. You will then also need a higher torque to counteract the engine torque and control the yaw motion of your aircraft, either by increasing the size of the tail fin or by putting that fin further aft. |
Thank you all for your contributions and explanations. I understand now :)
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