Comment by p_l
2 years ago
Because the explanation in school misses something like 90% of the detail replacing it with zero-explanation magical thinking.
For example, yes, the air above the wing moves faster than the air below the wing, and it's related to shape of the airfoil.
However, it has nothing to do with magical "air has longer to travel".
It starts with how combining flows at the trailing edge of the airflow create a vortex which induces an opposite vortex around the wing, which is a bit counter-intuitive (but it has nothing on why swept wings work, which can be summarised for practical aircraft design purposes of "because if we calculate at an angle we get better values and reality is crying in the corner")
> It starts with how combining flows at the trailing edge of the airflow create a vortex which induces an opposite vortex around the wing,
Wait, I was under the impression this Cutta circulation was a computational simplification and the "real" reason were the pressure differences as explained in this submission. What am I missing?
Essentially the work in the article shows the harder to grok, but still half of the whole equation, with only one small mention of an effect that points to the wider environment. Essentially, this is a more close-in view of the airfoil without consideration of the wider flow around.
One comment already mentioned how position of flaps could have visible effect on pressure sensors in front of the plane, and this is slightly mentioned in how the pressure created by front of the air foil has an impact on air "at a distance" from the airfoil.
The vortices created around the airfoil result in significant change of flows, which especially at low speeds provides big chunk of the pressure changes necessary for the creation of lift, with the effect IIRC getting lower as you go faster, with transsonic regime breaking it - because that's when the resulting speeds go beyond speed of sound at given pressure in the air, which in very simplified way means that air can't move towards front of aircraft anymore in those areas, breaking all sorts of flows you depend on at lower speeds.
The whole air has longer to travel thing is obviously hand waving a lot of different properties that are all combining to get better efficiencies. For example, don't forget the coanda effect and its contributions to the shape of a wing. Luckily we can always just return to the navier-stokes equations to help us out.
Growing up I got the "air has longer to travel on the top of the wing than the bottom" explanation, and it always smelled like BS. This is the first explanation of flight aerodynamics that really made sense to me — incredible article as always from this author.