Knowing Newtonian physics doesn't mean we understand all things that move.
The point about "not understanding" flight is that, if we truly understood it, we could design the optimal aircraft from first principles before it ever entered a wind tunnel. Instead, we work based on incrementally improving tribal knowledge of what has worked in the past and try to make something similar to fit our desired flight envelope.
Compared to something like rocket science where the entire craft can be built on a computer and we'll know exactly how much cargo we can get to the moon without even turning a single screw, we don't understand flight.
The point about "not understanding" flight is that, if we truly understood it, we could design the optimal aircraft from first principles before it ever entered a wind tunnel. Instead, we work based on incrementally improving tribal knowledge of what has worked in the past and try to make something similar to fit our desired flight envelope.
Compared to something like rocket science where the entire craft can be built on a computer and we'll know exactly how much cargo we can get to the moon without even turning a single screw, we don't understand flight.