There's so many wrong explanations of why planes fly, and we went through them.
It's not equal-time-to-the-end-of-the-wing, and it's not pushes-flow-down-so-goes-up.
It's a good time to do some critical thinking, though:
1) We observe that planes can fly upside down. Does the theory under evaluation explain this?
2) It's hard to take off behind another plane that's just taken off. Why?
You remember? Action requires opposite and equal reaction?
Plane is (mostly) not a rocket and so to be able to fly it has to act on something and the only something up there is air. If the plane is being lifted it means a bunch of air needs to be pushed/dragged down.
Helicopter is a better way to visualize it.
Now, in a plane, once that air is pushed/dragged down it immediately starts doing funky things like vortices and so on, but at least initially the air is being pushed/dragged down.
I write "pushed/dragged down" because the air is deflected on both sides of the wing. On the low pressure side of the wing (hopefully for most people this is the upper side) it is being deflected by creating low pressure in a laminar flow. If that laminar low pressure flow state is lost and instead we get turbulences, those turbulences are really bad at inducing the air to go down. We say that "it has stalled".
EDIT:
The only way for something to stay up is to push off something. When you stay on the ground you push off the ground but when you are up there you have to push something else even to just stay at an altitude.
Wings, turbines, rocket engines, propellers, barn doors, these are just different ways to accomplish the same task -- push air (and very infrequently some other material) downwards.
A plane is different from a rocket in that the material is mostly air (and very tiny amount of fuel) and main mechanism of pushing it are wings and air breathing engines/turbines.
Some planes can have so much power that their main pushing mechanism is engine exhaust and additional air sped up by the turbine.
But most planes have engines that do not produce anywhere near what is needed to stay up this way. These planes use the engines to push (mostly) forward (there is slight downwards vector due to engine exhaust being in line with the plane body but AoA positive). These planes rely on air stream being deflected downwards as seen by the plane to be economical.
First of all, rockets are no exception. Just throwing things backwards will make the object fall to the ground, no matter how hard it pushes.
It is indeed the air that pushes the wing up, but you have to ask yourself why the wing would need to be shaped in a certain way if it's merely deflection. If it was that, you could just have flat boards at an angle and be done with it.
Vorticity has to come into the explanation, and explains both the points further up.
Rockets are easiest understood by concervation of momentum. In the case of a rocket, this is for the combined momentum of the rocket and the spent fuel/exhaust. The rocket "trows" the exhaust backward with a momentum exactly opposite to the momentum gained by the rocket.
A wing or the propellar. They accelerate the aircraft by "throwing" air in some direction, with a momentum per unit of timemass equal to the acceleration they cause. (In order to maintain their altitude, this acceleration must counteract the "gravitational acceleration", g of 9.81m/s^2)
This all follows from Newton's laws, where "Force" is the time derivative of momentum F=(dp/dt)=ma => a=(dp/dt)/m. With conservation of momentum for the aircraft + air, one gets:
(dp_aircraft/dt) + (dp_air/dt) = m_aircraft * -9.81 m/s^2
If dp_aircraft/dt = 0 (level flight), then: dp_air/dt = -m_aircraft * 9.81 m/s^2
In other words, lift is generated by accelerating air in the opposite direction of the lift.
Airodynamic theory, including Bernoulli and Navier-Stokes equations only serve to explain _how_ the wings accelerate the air down.
A sideways rocket would... fall to the ground. Just like anything that doesn't have a way to oppose gravity.
> Airodynamic theory, including Bernoulli and Navier-Stokes equations only serve to explain _how_ the wings accelerate the air down.
But those are the very point of this discussion. Does the force, enough to hold up the entire aircraft, come from essentially pinging tiny tennis balls off the wing, or does it perhaps come from a complex interaction of the air with the wing, involving ideas of boundary layer separation?
Well, a helicopter pointing it's rotor horizontally also falls down. Why do you assume that the rocket should point horizontally? (Technically, of course, rockets _can_ and _do_ point horizontally, after going fast enough to maintain orbit.)
> But those are the very point of this discussion. Does the force, enough to hold up the entire aircraft, come from essentially pinging tiny tennis balls off the wing, or does it perhaps come from a complex interaction of the air with the wing, involving ideas of boundary layer separation?
There are multiple factors at play. Deflection of air downwards is a side effect of those factors that creates lift.
From your previous post:
> It is indeed the air that pushes the wing up, but you have to ask yourself why the wing would need to be shaped in a certain way if it's merely deflection. If it was that, you could just have flat boards at an angle and be done with it.
Creating lift can be done perfectly well by a flat board. The wings are shaped as they are to minimize the drag/lift ratio at the speeds and angles of attack the wings will operate under. And for that all the complexity of the airodynamics and air/wing interactions come into play.
You're right that it's not "merely deflection", but the reason you give here is not conclusive.
PS: I've tried replying to you by email so we can coordinate our efforts, but I don't seem to have been able to deduce your email from your profile. If you want to contact me, my email is in my profile.
Update: A second attempt may have succeeded.
You can certainly have symmetrical (vis-a-vis the horizontal plane) wings.
ETA: here some more info: https://aviation.stackexchange.com/questions/39146/how-do-sy...
https://aviation.stackexchange.com/questions/14283/how-do-pa...
The special shape is just an optimization, ie. cambered wings are more efficient/stall at higher angles of attack.
Yes, it is. It cannot be any other way; momentum is always conserved. You need to get that 9.81m/s^2 acceleration from somewhere!
To answer your two questions:
1) A simple wing is basically a teardrop shaped fairing around a flat plate - not unlike a rudder. Like a rudder, it can redirect the flow in either direction, depending on the angle it meets the air. (In fact, most aircraft struggle to fly upside down - if they're not aerobatic they tend to have wings that are like fairings around curved plates, to more efficiently redirect air in a single direction.)
2) The aircraft in front of you has just imparted a ton of downward momentum to the air. Compared to flight through clean still air, you're on an elevator that's going down.
One notable wake turbulence incident was in 2006 at Boeing Field in Seattle where a Cessna 172 and Boeing 747 were both on final approach for parallel runways. The Cessna 172 got flipped almost upside down and recovered 150 feet over the terrain: https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?E...
For a plane flying straight up you have (usually) two things happening:
1. It is trading kinetic energy for potential energy.
2. They have so much power that their engines can literally lift the entire plane.
These planes do not fly. They just use the air to keep the right direction but do not get meaningful lift when going straight up in a straight line.
You can have aircraft with engines powerful enough that they can overcome gravity with thrust alone so can fly upward indefinitely but their wings will still be generating lift, even if they are travelling vertically and it's not useful for overcoming gravity.
"Lift is the force that directly opposes the weight of an airplane and holds the airplane in the air."
https://www.grc.nasa.gov/www/k-12/airplane/lift1.html#:~:tex....
Since gravitation always points down (BY DEFINITION), "the force that DIRECTLY OPPOSES IT" can only point up.
I hope you don't plan to dispute NASA on what is lift.
"Lift acts through the center of pressure of the object and is directed perpendicular to the flow direction."
And:
"Lift is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid: no motion, no lift. It makes no difference whether the object moves through a static fluid, or the fluid moves past a static solid object. Lift acts perpendicular to the motion. Drag acts in the direction opposed to the motion."
So I'm not wrong, even according to the page you cite.