Science2.0 tells How Airplanes Fly - The Real Story:
- Wings are simple and straightforward devices, yet misconceptions abound on how they work, and many people carry wrong perceptions on their lift-creating mechanism. The 'equal transit time' fallacy being the most prominent misconception in this area.
- The physics of flight is well understood and straightforward. Airplanes and earth gravitationally attract each other. Newton's laws of motion tell us that to defy gravity and keep the airplane and earth at constant separation requires exchange of momentum between both bodies. This exchange of momentum is realized by the wings of the airplane directing air to earth, and earth reversing this airstream back up.
- That's it folks. Circulating air. That is how an airplanes fly, how helicopters fly, and how birds fly.
- The wings of the airplane divert up-moving air down. A large portion of this diverted air is located above the airplane. How do the airplane wings manage to divert all this air from far above?
- This is because air consists of erratically moving molecules that tend to spread over the full volume available. When the air in the layer just above the wing is pushed down, it allows the air molecules above this layer to get in. As a result higher air layers get accelerated down. This creates room for air molecules in still higher layers to move in, and so on.
- All of this pulling in of air molecules causes the pressure to become lower above the wing. This is nothing more than a direct manifestation of Newton's laws of motion applied to the accelerated air.
- It is referred to as Bernoulli's principle: the downward acceleration of the air circulating above the wing generates lift.
- This picture of air circulation as the direct cause of lift dates back more than a century. At that time, the German mathematician Martin Wilhelm Kutta and the Russian scientist Nikolai Zhukovsky independently developed the mathematics of circulating flows that allows us to predict the lift of wings.
- But you don't need this particular shape to keep you in the air. An upside-down airfoil works as well, and so does a tilted barn door. All of these create circulation by diverting air in a downward direction. Perhaps the cleanest manner to generate a backspin air flow is a rotating cylinder. And yes, these make a viable, albeit inefficient and impractical, wing design.