Wing Shapes
Aussie Flying,
If a symmetrical wing is generating lift, there IS a difference between the upper and lower surfaces, at least from the perspective of the oncoming air. The reason is that a lifting symmetric airfoil will be at a non-zero angle of attack. This means that the air will meet the wing at a point slightly below the front. As a result, the air that travels over the top surface will 'see' a different shape than the air that travels under the bottom surface does.
Think of it this way. Any roughly flat body will generate some lift if it is at a positive angle of attack relative to the oncoming flow. Having a good airfoil shape only makes the generation of lift more efficient, it is not a requirement. The bottom line is lower pressure on the top than on the bottom. However you achieve that, you will get lift.
banktoturn