When I thought there was higher pressure under the wing that pushed the plane up, I was happy. When I started thinking, instead, about little vacuum vortices above the wings pulling them up instead, I was suddenly much less comfortable with the whole proposition. Given the options and the limited effect on my daily life, I'm gotta go with Newton over Bernoulli on this one.
We know vacuums don't "pull" things. Instead it's air pressure elsewhere that isn't balanced by the vacuum that moves things in the direction of the vacuum.
Trial and error until we got an equation that pretty much tells us exactly what will happen for given variables.
Physics simulations where a computer helps just try out different propeller designs to see how well it works has been helping introduce all kinds of super exotic designs in the last few years cause yeah as someone who did physics; "it's all just agreed upon expected outcome from trying it."
Speak for yourself. I'm a student pilot and most of my instructors (who are either retired airline pilots or are trying to build up flight hours to qualify for an airline job) don't understand the science behind it. To be fair, understanding the science doesn't really help you fly a plane...
It is both, but the pressure one contributes more to lift. You can see this when a wing stalls, the airflow separates from the upper surface and the pressure difference is gone. The angle of a stalled wing still means air is directed downwards, but the overall lift is much smaller.