Answer
Placing the propeller at the tail maximizes the distance between the applied force and the axis of rotation, which maximizes the resulting torque and makes it easier to rotate the helicopter clockwise or counterclockwise.
Work Step by Step
The torque is proportional to the distance between the point where the force is applied and the axis of rotation.
The propeller rotating in a vertical plane can apply a force to the helicopter to rotate the helicopter in the horizontal plane clockwise or counterclockwise. For a given force created by the propeller, the resulting torque will be greater if the distance from the axis of rotation is greater.
Placing the propeller at the tail maximizes the distance between the applied force and the axis of rotation, which maximizes the resulting torque and makes it easier to rotate the helicopter clockwise or counterclockwise.
