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This video's topic covers How Lift is Created. When we talk about Lift we re talking about the useful force that is developed by an airfoil as air passes around it. It's the force that opposes weight and allows things to fly. But where does it actually come from? There are a few theories that seek to explain that.

Bernoulli's Principle: this was named after David Bernoulli who studied fluid dynamics back in the early 1700's. He discovered that as liquid moved through a narrow space, it increased in velocity and decreased in pressure. Airflow acts just like liquids at the speeds we're worried about and shares these characteristics. This effect is known as the "Venturi Effect." If you note the lower half of the tube, you can start to see how the Venturi effect applies to an airfoil. An airfoil's camber or curvature causes airflow to accelerate over the upper surface much like it accelerated in Venturi tube. The airflow travels faster on top of the airfoil resulting in a lower pressure when compared to the lower surface. Keep in mind that variations in angle of attack can cause this to have more or less of an effect. With a pressure differential present, there is the natural tendency for equilibrium to be met. This results in an upwards forces acting on the airfoil known as "Lift."

Newton's 3rd Law of Motion: this theory states that for every action there is an equal and opposite reaction. This explanation is based on the idea that an airfoil, acting at an angle to the wind pushes the air down and the airfoil up. Some call this the "inclined plane method of lift" because any object can do it. When applied to an airfoil it works much like any other object where when the airflow impacts the angle surface it is directed downwards and the action reaction is that the airfoil is lifted up.

Both theories are accurate in showing how Lift can be produced. However, neither seem to hold all the answers by themselves. For instance, although the action/reaction theory logically explains lift, it cannot explain why or how a blade stalls with too much angle of attack. And some claim that Bernoulli's principle cannot explain why an asymmetric airfoil can still produce Lift when inverted in the case of fixed wing aircraft. So while neither fully explain lift, it is commonly accepted that both theories in conjunction offer the best explanation.

That wraps up how lift is created. If you're just getting started and want more information, pictures, and more explanations, I'd recommend reading the Rotorcraft Flying Handbook http://amzn.to/2ifPlnZ. If you've already got a basic understanding, and want to further your professional helicopter education with advanced helicopter concepts, I'd recommend reading Cyclic and Collective, by Shawn Coyle http://amzn.to/2ifQGLx.

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