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‫Here you have the top view of the chopper, let's assume that the center of mass is located directly

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‫underneath the rotational axis of the rotor.

3
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‫I actually don't know if that's the case in real chopper designs, but let's assume that it's here.

4
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‫You can see the rotation of velocity of the main rotor and the main body of the chopper.

5
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‫And you can also see how the tail generates a talk about the center of mass that counteracts the rotation

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‫of the main body.

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‫And so if we assume no extra disturbances, then the magnitude of the talk that the rotor is experiencing

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‫equals the magnitude of the talk that the helicopter is experiencing.

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‫Because, remember, talks of the rotor and the helicopter are opposite in direction, but they are

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‫equal in magnitude.

11
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‫That means that the tail has to create the talk with the same magnitude that the helicopter is experiencing,

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‫but opposite in direction.

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‫And it makes sense, right?

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‫If the body of the helicopter experiences a talk like this, then the tail, in order to keep the body

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‫steady, needs to generate a talk in this direction and it has to be equal in magnitude.

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‫Therefore, the magnitude of the talk that the tail generates equals the magnitude of the talk that

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‫the helicopter experiences and the magnitude of the talk that the tail generates can be written like

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‫this in terms of the force that the tail generates times the distance to the center of mass.

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‫And you can also write it down like this.

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‫And this is the tail talk here.

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‫And so if you want to compute the force that the tail needs to generate to counteract this helicopter

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‫talk, then you very simply rewrite this equation like this.

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‫The magnitude of the force equals, remember, the talk of the tail was equal to the talk that the helicopter

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‫experienced.

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‫Their magnitudes were equal.

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‫Therefore, you have the magnitude of the talk of the helicopter divided by the distance the sea.

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‫And that force would be, of course, in Newtons, that is if we don't assume any other disturbances.

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‫And so that's the force that the tail needs to generate to keep the chopper rotational at rest.

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‫We usually use the absolute value signs to indicate that we are talking about the magnitude of the vector.

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‫So when we have a vector and we put absolute value signs here, then that means that we are talking

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‫about the magnitude of the vector.

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‫And now you know why in the drone Morash one and three rotate counterclockwise and motors two and four

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‫rotate clockwise.

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‫Because what would happen if all propellers rotate it, for example, counterclockwise?

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‫If all propellers rotated counterclockwise, then it would make the drone itself spin clockwise.