ORIGINAL: mitchell170
>> Why does the wing being "tilted" away from "level" make any difference in the lift being generated compared to the other wing ?
How does the wing know that it is on the low side so it can produce more lift ? <<
Some of my old physics here, and don't even think about asking "how old".
The lift generated by a wing with no dihedral is purely vertical in straight and level flight. The lift generated by a dihedral wing has both a vertical and a horizontal component in straight and level flight. Think of it like this..........draw a horizontal line representing a wing and then a vertical arrow from the wing. As you tilt the wing (add dihedral) the arrow now tilts slightly toward the fuselage. Because the arrow is now tilted the amount of pure vertical lift is reduced. The plane flies straight because the other wing has just the opposite horizontal component, and they balance each other.
Now, picture the right wing rolled to the right in a shallow turn. When the bank angle is equal to the dihedral angle the right wing is now completely horizontal, and it's "arrow" now points straight up. More lift. At the same time the effective bank angle of the left wing is now the dihedral angle PLUS the bank angle, and it's arrow now has even MORE horizontal component. Less lift.
As a result the natural tendancey of the plane will be to roll back to the left (level) since the right wing is producing more lift than the left. When it gets back to level the lift is now the same for each wing and it tends to want to STAY level.
With a straight wing, no dihedral, the horizontal component of each side is going to be equal at any given bank angle and the plane will tend to remain banked even if you neutralize the controls. The rudder complicates things and makes the above a bit of over simplification, but if you play with the drawings and the arrows you'll see what is happening.
Bob
I understand what you're saying here. However, even though the now horizontal wing (right wing in right bank) wants to create more lift vertically, the opposite wing (left wing) wants to create more lift horizontally, in the direction of the bank. Regardless of bank angle, there is still the same amount of air passing under and over the wings; they do not know if they are horizontal or not. (There's a post like this in the aerodynamics forum, and its debated there, too.)
I'm a mechanical engineering student. I haven't taken fluid dynamics yet (next semester
), but I believe that the dihedral issue is more based on simple mechanics.
Imagine, for an exaggerated example, that the dihedral was 90 degrees, so that when the plane is flying level, the wings are each at a 45 degree angle. If you bank to the right so that the right wing is now horizontal (45 degree bank right) you will have an unbalanced wing with the weight of the plane completely at the end. Gravity will pull down on the plane, until the force is balanced on the left side by the left wing generating some vertical lift.
Now imagine the same plane with no dihedral in a 45 degree bank. Gravity will have a much harder time 'righting' the plane because there is vertical lift being generated by the left wing, and less vertical lift being generated by the right wing.
Unfortunately I haven't flown a model plane yet! This theory would be proved if the dihedral had less self-righting characteristics at higher speeds, which means that as the lift force of the wings increases (in the direction perpendicular to the surface of the wing), the effect of gravity becomes negligible. If you could fly really, really fast in a plane with dihedral, it should have almost no self-righting characteristics at all (if my postulate was correct).