A helicopter has no wings. It has no propellers or jet turbines. Yet it manages to get off the ground with ease, thanks to its big rotor blades. But these are point up, you might say, so how do they propel it forward? The basic concept is this: As the blades spin, each blade acts like a mini airplane wing as it cuts through the air. Just like an airplane wing, it had a trailing edge, a leading edge, and a camber line. The camber line splits the rotor blade between its top and bottom edges (if the rotor blade was a hamburger, the camber line would be the meat). When an object, such as a helicopter, and the atmosphere move relative to on another, and the object (in this case the helicopter) cause the atmosphere to flow is a direction perpendicular to that flow, the force require to do this work causes and equal and opposite force that is lift.
In a helicopter, there are four factors that affect the amount of lift generated. These include density of the air, the speed of the airflow, the total area of each rotor blade, and the angle at which the rotor blade meets the air.
But how does this work? Well, the airflow meeting the leading edge of the rotor blade is forced to split over and under the object. The sudden change in direction of airflow over the rotor blade as it chops through the air causes an area of low pressure to form behind the leading edge, on the upper surface of the blade. In turn, due to the pressure gradient and the density of the airflow, the flow over the blade is accelerated down along the top of the blade. At the same time, however, the airflow forced under the blade is rapidly slowed, which causes an area of high pressure.
Since the two sections of airflow leave the trailing edge of the rotor blade with a downward momentum, this causes lift, as the downward momentum must have an equal and opposite reaction, or in simpler terms, upward momentum.
Additional lift is provided pursuant to Newton’s Third law or Motion, which states that for every action there is an equal and opposite reaction. You’ll note this is applied above, but it’s equally important here. When air that strikes the lower surface is directed immediately downward, it too, helps generate lift, and this allows the helicopter to remain airborne.
Although it may seem complicated, the basics of why a helicopter flies are fairly simple. Without lift, you’d simply have the world’s most expensive box fan on the ground, or the worlds most expensive hedge trimmer is you managed to roll the aircraft close to some hedges! Thankfully, you’ve got lift, and you can leave the ground safely and efficiently to continue on to your destination.