‫Here you have the top view of the chopper, let's assume that the center of mass is located directly
‫underneath the rotational axis of the rotor.
‫I actually don't know if that's the case in real chopper designs, but let's assume that it's here.
‫You can see the rotation of velocity of the main rotor and the main body of the chopper.
‫And you can also see how the tail generates a talk about the center of mass that counteracts the rotation
‫of the main body.
‫And so if we assume no extra disturbances, then the magnitude of the talk that the rotor is experiencing
‫equals the magnitude of the talk that the helicopter is experiencing.
‫Because, remember, talks of the rotor and the helicopter are opposite in direction, but they are
‫equal in magnitude.
‫That means that the tail has to create the talk with the same magnitude that the helicopter is experiencing,
‫but opposite in direction.
‫And it makes sense, right?
‫If the body of the helicopter experiences a talk like this, then the tail, in order to keep the body
‫steady, needs to generate a talk in this direction and it has to be equal in magnitude.
‫Therefore, the magnitude of the talk that the tail generates equals the magnitude of the talk that
‫the helicopter experiences and the magnitude of the talk that the tail generates can be written like
‫this in terms of the force that the tail generates times the distance to the center of mass.
‫And you can also write it down like this.
‫And this is the tail talk here.
‫And so if you want to compute the force that the tail needs to generate to counteract this helicopter
‫talk, then you very simply rewrite this equation like this.
‫The magnitude of the force equals, remember, the talk of the tail was equal to the talk that the helicopter
‫experienced.
‫Their magnitudes were equal.
‫Therefore, you have the magnitude of the talk of the helicopter divided by the distance the sea.
‫And that force would be, of course, in Newtons, that is if we don't assume any other disturbances.
‫And so that's the force that the tail needs to generate to keep the chopper rotational at rest.
‫We usually use the absolute value signs to indicate that we are talking about the magnitude of the vector.
‫So when we have a vector and we put absolute value signs here, then that means that we are talking
‫about the magnitude of the vector.
‫And now you know why in the drone Morash one and three rotate counterclockwise and motors two and four
‫rotate clockwise.
‫Because what would happen if all propellers rotate it, for example, counterclockwise?
‫If all propellers rotated counterclockwise, then it would make the drone itself spin clockwise.