måndag 24 september 2012

Pilots Fooled by Federal Aviation Administration

Let us now check out how the generation of lift of a wing is presented in Pilots Handbook of Aeronautical Knowledge by Federal Aviation Adminstration. We read in Chapter 3 Principles of Flight:
  • The formulation of lift has historically been the adaptation over the past few centuries of basic physical laws. These laws, although seemingly applicable to all aspects of lift, do not answer how lift is formulated. In fact, one must consider the many airfoils that are symmetrical, yet produce significant lift.
This is not a very promising start. The next step is a digression into the Magnus effect of a rotating cylinder:
  • In 1852, the German physicist and chemist, Heinrich Gustav Magnus (1802–1870), made experimental studies of the aerodynamic forces on spinning spheres and cylinders. (The effect had already been mentioned by Newton in 1672, apparently in regard to spheres or tennis balls). These experiments led to the discovery of the Magnus Effect, which helps explain the theory of lift.
  • To summarize the Magnus effect, an airfoil with a positive AOA develops air circulation about the upper surface of the wing. Its sharp trailing edge forces the rear stagnation point to be aft of the trailing edge, while the front stagnation point falls below the leading edge. [Figure 3-4]

We see here an attempt to explain the Kutta-Zhukovsky circulation theory, which is unphysical by asking the incoming flow to change direction. This is sensed by FAA feeling that prospective pilot will not be convinced, and so seeks to enhance the message by: 
  • A half-century after Newton formulated his laws, Daniel Bernoulli, a Swiss mathematician, explained how the pressure of a moving fluid (liquid or gas) varies with its speed of motion. Bernoulli’s Principle states that as the velocity of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases. This principle explains what happens to air passing over the curved top of the airplane wing. 
This time it is not circulation but instead Bernoulli with lower pressure above supported by a picture illustrating the Venturi effect:

FAA thus hints at the "Venturi" effect, which however is identified by NASA as Incorrect Lift Theory #3.

The discussion is then rounded off by:
  • Since air is recognized as a body and it is accepted that it must follow the above laws, one can begin to see how and why an airplane wing develops lift. As the wing moves through the air, the flow of air across the curved top surface increases in velocity creating a low-pressure area. 
  • Although Newton, Magnus, Bernoulli, and hundreds of other early scientists who studied the physical laws of the universe did not have the sophisticated laboratories available today, they provided great insight to the contemporary viewpoint of how lift is created. 
We see again how a governmental agency struggles with the sad fact that there is no convincing theory of lift offered by aerodynamicists to be taught to pilots. 

The New Theory of Flight presented on The Secret of Flight is the first scientific explanation of the generation of lift of a wing, and as such it both describes real physics and is possible to understand, by both prospective pilots and air passengers.

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