torsdag 2 augusti 2012

Text Book Theory of Flight: Kermode 2006

We continue our overview of current text book theory of flight, now inspecting Mechanics of Flight by A. C. Kermode, 11th edition 2006 (1st edition 1972), with my comments in parenthesis.

From Preface to 11th edition by R. H. Barnard and D. R. Philpott:
  • The late A. C. Kermode was a high-ranking Royal Air Force officer responsible for training. He also had a vast accumulation of practice aeronautical experience, both in the air and on the ground. It is this direct knowledge that provided the strength and authority of this book. (Suggests that the theory is weak.)
From Chapter 1 Mechanics:
  • The flight of an airplane provide glorious examples of the principles of mechanics. (What principles? Glorious?)
From Chapter 3 Aerofoils - subsonic speeds:
  • An interesting way of thinking about the airflow over wings is the theory of circulation. The fact that the air is speeded over the upper surface, and slowed down on the under surface of a wing, can be considered as a circulation round the wing superimposed upon the general sped of airflow (this does not mean that particles of air actually travel around the wing). This circulation is , in effect, the cause of lift. But this is not all. When the wing starts to move, or when the lift is increased, the wing sheds and leaved behind a vortex rotating in the opposite direction to the circulation round the wing -- sometimes called the starting vortex -- so there is a complete system of vortices, round the wing (then the wing-tip vortices) and finally the starting vortex. The engineer power keeps renewing the circulation round the wing.  (Kermode struggles to make sense of circulation theory: "this does not mean that particles of air actually travel around the wing": circulation without circulation. )  
  • This is not just theory; the flow over the wing can clearly be seen in experiments, while the starting vortex is easily demonstrated by starting to move a model wing, or even one's hand, through water. (Misleading experiment: The vortices seen by moving a hand trough water do not explain the creation of lift of a wing).

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