Originally Posted by
Bendo
The point of it is that the laminar flow accross the back of the spoon causes the water to deflect , the same way as the wing causes downwash at the trailing edge. Newton's Third will have it that every action has an equal and opposite reaction.... and so the spoon deflects the water, and the water pushes the spoon.
Similarly, the wing forces the airflow downwards... and the downwash pushes the wing up.
Do it again - I think you'll find the water
pulls the spoon, as indeed the pressure reduction of the airflow travelling over the upper convex surface
sucks or pulls the wing upwards.
The other similar demo using flow over the top surface only, is the one where you hold a piece of paper at the near corners so that it droops away from you and blow gently (laminar flow) over its curved upper surface.
Does a carb type venturi need
downwash at the trailing edge to produce suction? Of course not - after the
waisting of the tube it reverts to same old tube.
Regards,
rts