The question is "why planes fly".
There are only a few things to understand:
(1) There are no pulling forces in explaining how a plane flies.
Unfortunately much of the models and mathematics developed came before the atomic theory of matter was finally accepted (thanks to Einstein) and developed. As a crude approximation fluid equations seemed to answer most questions and deliver reasonable results.
This has continued to this date. Aerodynamics is a series of approximations and cludges. Mixtures of different mathematical models (which sort of work .. mostly) and empirical results (such as certain aerofoils are better than others for a particular flight regime).
However misconceptions continue to this day .. such as:
(a) The Coanda effect. This is a symptom of something else that is more fundamental, not a thing in itself. It has no contribution to flight whatsoever (despite what NASA says).
(b) Low pressure "pulls" something up (see NASA site for this explanation ... they should know better). Air does not suck. It has no attactive force whatsoever (well I suppose there is a little gravity or some interactions between oxygen atoms and the metal of the wing .. sod all of anything).
(2) You can explain everything by understanding 2 things:
(a) Air is full of molecules, each with mass and speed and there are a lot of them.
(b) Each molecule is moving, but at different speeds and different directions.
Therefore, air exert a force in all directions, up, down, sideways, at an angle.
A wing (or barn door) when stationary has all the forces balanced. Gravity pulling down, air pressure pushing up, air pressure pushing down. What we call pressure is simply the sum of all the forces of all the air molecules bouncing off the wing. Straight foward Newton.
When we start moving and the wing (or barn door) is angled up, we start bouncing off the air molecules, pushing a lot of them down. The net transfer creates a force upwards (lift).
We also push some molecules forward (remember they are coming in from all directions and at different speed, i.e. different momentums). This is what we call induced drag. Because the wing is angled we can't help pushing some of them forward rather than down, thus wasting energy.
What happens above the wing is a little more subtle. The air is pushing down at all times by molecules (M for short) hitting the wing. But remember, not all air M travel at the same speed (it actually follows a normal distribution). The average speed of an air molecule (at 0C and sea level is about 1600 km/hour. However some are far faster, some are slower, some are virtually stationary.
The wing is angled, as it moves forward the molecules have further to travel to hit the top of it (a simple diagram will show this, basically the surface moves away from it) and hence bounce off it and exert a force downwards. The fastest ones will hit quickly (which is why there is still air there) the slowest will take longer, so overall there is less air there and hence less momentum transfer (=force) at the beginning of the upper part of the wing. At sub sonic speeds and a reasonable sized wing most of the molecules will eventually hit the wing, exerting a force downwards (some will miss it entirely).
So we have a pushing upwards from below, but less of a push downwards from above (particularly at the beginning of the wing).
Sum up the forces .. and a plane flies if you go fast enough.
This explains why the majority of the lift comes from the beginning of the wing (or barn door), there are more net upward forces (upwards + less downwards).
Next post(s):
- Why there are wingtip vortices, why wingtips have less lift, why vortices have nothing to do with loss of lift or drag.
- Why temperature is important to describe why there is less l/d drag issues at height (= why can we go faster the higher we go).
- Why does air flows (= sum total movements of air M) seem to curve.