## tisdag 30 maj 2017

### Kutta Condition, Gods Finger and Secret of Flight

The New Theory Flight revealing the secret of flight (article1, article2book and website) is now backed by new computations in realistic geometry to be presented next week at the High-Lift Prediction Workshop III.

At this historic moment, let me recall the The Old Theory of Flight by Kutta-Zhukovsky presented
around 1905, which is still the accepted text book explanation of the generation of lift by an airfoil.
The Old Theory states that an airfoil is capable of generating lift because it has a sharp trailing edge, which is supposed to force potential flow without lift separating on the upper surface of the wing to instead separate at the trailing edge and then generate lift by causing a redirection of the airflow, as illustrated in this generic text book figure illustrating the Kutta condition:

The Old Theory contains two unphysical effects, which happen to balance and then miraculously give a physical result = lift. The two unphysical effects are:
1. The start is 2d potential flow without lift separating on top of the wing.
2. By making the trailing edge sharp, the flow is forced to separate at trailing edge and then give lift.
The New Theory shows that 2d flow is unphysical because real flow contains completely crucial 3d features.

To believe that real flow can be forced to separate at the trailing edge by making it sharp, is to give yourself access to the action of a God's finger of unlimited power.

In numerics you can play God and set the velocity zero wherever you want, but that is simulated virtual reality and not real physics. It is like putting a needle into a voodo doll believing it will have an effect on a real person. This is voodo-physics.

Yet, this is the text book explanation of lift. To test, ask your favourite aero-dynamicist:
1. Why do airfoils have sharp trailing edge?
2. What happens if the trailing edge is not sharp but more or less rounded?
After this experience, you will be more motivated to dig into the New Theory of Flight.

PS The book will now be updated to find an efficient publisher.