How Helicopters Fly
You can begin to understand how a helicopter flies by thinking about the abilities displayed in the previous section. Let's walk through the different abilities and see how they affect the design and the controls of a helicopter.
Imagine that we would like to create a machine that can simply fly straight upward. Let's not even worry about getting back down for the moment -- up is all that matters. If you are going to provide the upward force with a wing, then the wing has to be in motion in order to create lift. Wings create lift by deflecting air downward and benefiting from the equal and opposite reaction that results (see How Airplanes Work for details -- the article contains a complete explanation of how wings produce lift).
A rotary motion is the easiest way to keep a wing in continuous motion. So you can mount two or more wings on a central shaft and spin the shaft, much like the blades on a ceiling fan. The rotating wings of a helicopter are shaped just like the airfoils of an airplane wing, but generally the wings on a helicopter's rotor are narrow and thin because they must spin so quickly. The helicopter's rotating wing assembly is normally called the main rotor. If you give the main rotor wings a slight angle of attack on the shaft and spin the shaft, the wings start to develop lift.
In order to spin the shaft with enough force to lift a human being and the vehicle, you need an engine of some sort. Reciprocating gasoline engines and gas turbine engines are the most common types. The engine's driveshaft can connect through a transmission to the main rotor shaft. This arrangement works really well until the moment the vehicle leaves the ground. At that moment, there is nothing to keep the engine (and therefore the body of the vehicle) from spinning just like the main rotor does. So, in the absence of anything to stop it, the body will spin in an opposite direction to the main rotor. To keep the body from spinning, you need to apply a force to it.
The usual way to provide a force to the body of the vehicle is to attach another set of rotating wings to a long boom. These wings are known as the tail rotor. The tail rotor produces thrust just like an airplane's propeller does. By producing thrust in a sideways direction, counteracting the engine's desire to spin the body, the tail rotor keeps the body of the helicopter from spinning. Normally, the tail rotor is driven by a long drive shaft that runs from the main rotor's transmission back through the tail boom to a small transmission at the tail rotor.
What you end up with is a vehicle that looks something like this:
The helicopter shown in the previous videos has all of the parts labeled in the diagram above.
In order to actually control the machine, both the main rotor and the tail rotor need to be adjustable. The following two sections explain how the adjustability works.
