Not exactly sure how credible this is as it's from "howstuffworks.com" but I'll post it anyways;
"When a swept-wing travels at high speed, the airflow has little time to react and simply flows over the wing. However at lower speeds some of the
air is pushed to the side towards the wing tip. At the wing root, by the fuselage, this has little noticeable effect, but towards the tip the airflow is pushed sidewise not only by the wing, but the sidewise moving air beside it.
At the tip the airflow is moving along the wing instead of over it, a problem known as spanwise
flow."
"The lift on a wing is generated by the airflow over it from front to rear. As an increasing amount travels spanwise, the amount flowing front to rear is reduced, leading to a loss of lift. Normally this is not much of a problem, but as the plane slows for landing the tips can actually drop below the stall point even at aircraft speeds where stalls should not occur. When this happens the tip stalls first, and since the tip is swept to the rear of the center of lift, the net lift moves forward. This causes the plane to pitch up [corrected by features already discussed above], leading to more of the wing stalling, leading to more pitch up, and so on. This problem came to be known as
Sabre dance in reference to the number of North American F-86 Sabres that crashed on landing as a result."
Now it says the sweep causes the air flow to "slide" towards the tip.
I'm at a loss to see how the net force can be "tip ward", for the reasons posted earlier (in #4 I think... ) there is also a flow towards the fuselage.
I can see that both flow directions are possible but which is more pronounced, I doubt they cancel, but am sure there are features to strengthen one to balance the other...?
