The scientific principle of how an airfoil creates lift so simple, that Its unimaginable why the scientists completely missed the point, for more then a 100 years. Not only this, they also went about chasing the most absurd and unrelated scientific ideas to explain airfoil lift. Some of these ideas are nothing short of being hilarious the way they are presented as possible explanations. The following is the simpler version of the zone-theory of lift, please read on …
We definitely perceive flight as a fantasy since there’s nothing visible, and the mere sight of a huge metallic air frame structure leaving the ground definitely bedazzles the mind. There’s a natural tendency to perceive it as something surreal, and very very complicated. Whereas, on the contrary its not. But only if we keep the facts in mind, avoid having a wind-tunnel vision 🙂 and think logically.
No concept of science has been a greater source of misguidance in flight aerodynamics then the Bernoulli’s principle. As already mentioned in a post, even Albert Einstein failed to explain airfoil lift, because he made the wrong assumptions and used the Bernoulli’s equation. Failure was inevitable. Another concept presented to explain airfoil lift is the angle-of-attack (or AoA). Let me make it very clear; an airfoil needs no such angle; it produces lift at zero AoA.
Airfoil Lift Generation Action
Something wonderful happens when an airfoil (aircraft or bird) starts to move in air. The process of generation of lift by the airfoil is as follows. When the aircraft moves a Subduction Zone is created in the air mass near the leading edge. The Deflector physically pushes the air in the Subduction Zone away from the leading edge in different directions. Of particular importance is the repulsion of air upwards above the zero-slope line, or point C in figure above. In doing so it creates rectangular-slot shaped opening in the air mass for the rest of the wing to move in with least resistance.
Thereafter as the airfoil further penetrates past the zero-slope edge into the Subduction-Zone, its Inductor now starts to further rarefy the air over itself, creating the Induction-Zone of less than atmospheric pressure. This happens exactly as predicted by the Salman Effect. The wing experiences an upward force due to relatively higher atmospheric pressure underneath, as shown in above figure.
The constant recession of the Inductor Surface to create a pressure drop is analogous to the rotating vane of a rotary vacuum pump. The difference is that the vane of the rotary pump rotates in the cavity to create the vacuum or low pressure behind it, whereas the wing moves linearly forward in the imaginary conduit, reducing the pressure behind it as shown in above figure. The action in both cases is to expand and compress the air behind and ahead of it, respectively. So far so good? Yes, but wait … there’s still some mystery to be solved ahead, as mentioned in the thermodynamics and energy conversion involved in this forced expansion by the inductor of the airfoil.
Approximation of an enclosed transient conduit by the finite transit time of air-mass to refill the void:
The mass of air in the Induction-Zone certainly experiences expansion and negative work similar to a mass of gas in an enclosed cylinder fitted with a receding piston. But no such container boundaries are present in the atmosphere.
So how is such expansion even possible in open atmosphere over the wing, and generate low pressure? The answer is that air at normal atmospheric pressure surrounding an immediately created induction zone takes a finite time to rush in and replenish this void, as in blue region of p<1atm, in above figure. This doesn’t happen all of a sudden in zero time. Due to the delay, there exists an invisible transient boundary of the shape of the wing around the void, for the time period taken by the atmosphere to creep back into.
Therefore, air in the Induction-Zone constantly undergoes expansion within the invisible bounds of the imaginary conduit, until surrounding air refills the Induction-Zone.
That’s the mystery of Lift which has baffled scientists, laid bare right before your very own eyes 🙂
Its that simple folks 🙂 … but people went about wild goose chase in wind tunnels, and now computational fluid dynamics CFD, all the time completely missing the point that its the wing that moves like the vane of a vacuum pump, constantly creating and carrying its own low pressure zone, and stays aloft. There’s just no flow of any kind involved in creation of lift.
Read the ebook if you’re interested to learn more, there’s plenty to learn … 🙂
If the same airfoil wing is at rest the air exerts same pressure over and under it. Even if we cause the air to move from leading edge towards the trailing edge, no difference in pressure is created since the air is moving uniformly around the airfoil, hence no lift is generated. This is a very easily observable phenomenon in propeller aircraft. Such aircraft rev up the engines to the maximum, at the start of takeoff and create large flows of air above and below the wings, but they never fly. They have to start rolling and gain takeoff speed termed V1, before they can rotate and get airborne.
What happens to the air in front of the airfoil shown in red ? The ebook provides more details on this plus many other related flight dynamics topics, e.g., flaps, stall, angle of attack, etc.