This old chestnut again. Found in my son's library book:



Why is the fast moving air moving faster?
Why does it have to meet up with the same slow-moving air it separated from?
Why does a paper airplane fly?

It amazes me that one of the defining achievements of the 20th century, indeed of all time, is explained so incorrectly so often.

Oh no, I wanted to delete this topic but can't. Even I don't want to read it again.

Oh well; as I understand it it is mostly deflection and redirection. The deflection, I suppose, is actually higher pressure air.

How is the explanation in the kid's book wrong?

The air moves faster on the top of the wing so the plane can fly and meets up with the other air at the end of the wing just cause.

The simple explanation is Bernoulis principle. A wind tunnel also shows what the air is doing. The speed of the air creates different pressure and by this lift can be created. That is one theory and there are others that disagree. Windsurfers need to remeber that the rules of aerodynamics and airflow change when a body goes supersonic. The shock waves cause additional chop to build up on the water and the downforce created by compression waves forces your feet further into the footstraps. A loud scream, higher in pitch to a sonic boom, is emitted from the windsurfers mouth when they gybe at these speeds. Naturally, all this information is classified because of the untold damage it would cause the kiting industry if they knew our secret.

Note: No kiters were injured during the composition of this dribble.

It's definitely wrong to say the split stream has to meet up at the exact same point at the exit.
But I can't see where the book says this.
However, it is correct to say the air flow over the top is faster than the flow over the bottom, (and I'm sure this does create lift), I think because it is more compressed it is forced to move faster.
I'm not sure what happens when angle of attack is increased though, surely at some point the compression on top and bottom flows equalises, and flow rates do the same????
Lift then must be due to deflection?

I find it hilarious that they used that old (and wrong) explanation, but then went and showed a symmetrical airfoil. With zero angle of attack.

But why, daddy, how does the air know which side to go faster over?


It's almost as if you have to go through the rite of passage of learning that explanation, then learning that it's wrong.

Gosh. It's Santa Claus all over again.

^^ what do you mean he flies only on angle of attack, not just an airfoil shape?

I believe the air travels over the top of the wing faster because it has to travel further due to the curve on top . Also with the angle of attack this creates lower pressure on top of the wing , effectively sucking the wing upwards . This also happens on a windsurf sail. So I believe. That's why the old VW Beetles over a certain speed try to start flying.