Have you ever seen a helicopter fly? Have you noticed a tiny propeller on the back of the tail? Is it for stability? Turning? Steering? As it turns out, it is all of those things combined. The main job that the tiny rotor must complete is to cancel out the torque created by the main rotor. Torque is the rotational force put on an object. For example, a common action that we do everyday is removing the cap from a bottle by twisting the cap. The force put on the bottle and the cap is torque. In order for a helicopter to fly, the top blades must spin at high revolutions per minute. In order to do so, the engine of a helicopter produces mass amounts of torque. Now, think back to the bottle. Imagine a very heavy substance is in the bottle. Now, try twisting the cap off without holding the bottle. See? The cap is stuck to the bottle and whenever you twist, the whole bottle moves. So how does that relate to the helicopter? The rotors are like the cap and the main body of the helicopter is the bottle. As the motor attempts to spin the rotors, the entire body of the helicopter gets dragged along, spinning in the same direction as the motor, but the opposite direction of the rotor by Newton’s third law. This is because there is nothing holding the body of the helicopter in place, in contrast to the transmission and drive shaft of a car. So, to cancel out this rotational force, an additional smaller rotor is placed on the rear wing of a helicopter. This rotor is positioned vertically, so the torque put out by itself does not affect the horizontal steering of the helicopter. The thrust put out cancelled the torque put out by the main rotors.