The real details of how an object generates lift are very complex and do not lend themselves to simplification.
And therein lies the problem. The explanation used in flight schools must be sufficiently simple to enable the typical student pilot to understand it, but the simplification process inevitably reduces its accuracy.
In the past I spent quite a few years running a ground school which provided theoretical knowledge training for PPL and ATPL students. The vast majority of them would have dropped out of the course if I and my instructors had attempted to explain lift in term of Navier-Stokes, Prandtl, Blasius or Euler. This level is OK for an engineering degree course in which something like six months might be devoted to the subject, but in a typical pilot training course, be it PPL or ATPL, the time devoted to this subject is usually less than 1 hour. Having used a single 50 minute lesson to deal with the subject of flow through convergent-divergent ducts, one student who had recently completed an aeronautical engineering degree said, “well that’s six months of thermodynamics dealt with in less than 1 hour. My lesson had obviously involved a lot of simplification, but the majority of the students had understood the essentials of the subject.
A symmetrical aerofoil at zero AoA creates no lift, but it does create drag.
Explain how this drag is generated. Please keep it in relation to Bernoulli's theorem.
Ah now, do you really want the small red coat or are you just checking out the shop assistants?
Explanation 1 (loosely based on Bernoulli)
Bernoulli’s Theorem is based upon the assumption that the total energy of the air will be constant at all points along the flow. For this to be true there must be no energy added and no energy lost due to factors such as friction. In reality some energy is lost due to friction, so Bernoulli cannot provide the whole explanation. This lost energy is of course the “Friction Drag”.
The air which strikes the leading edge of the wing at the stagnation point is brought to rest, so all of its dynamic pressure is converted into static pressure. This increased static pressure exerts a rearward force which opposes the forward motion of the wing. Air slightly above and slightly below the stagnation point is not brought to rest, but its velocity is reduce, so some of its dynamic pressure is converted into static pressure. This adds to the rearward force opposing the forward motion of the wing. This sequence of reducing deceleration continues as the distance above and below the stagnation point increase. The overall effect of all of this is an area of increased static pressure acting in a rearward direction on the leading edge.
As the air flows past the leading edge its velocity gradually increases, so some of the static pressure is converted into dynamic pressure. It may be tempting to imagine that the sum of this static pressure plus dynamic pressure acting on the rearward facing surfaces of the wing would provide a forward force which would be equal and opposite to the rearward force on the leading edge. But this is not the case for two reasons:
1. As discussed earlier friction causes the air stream to lose energy, so the total pressure over the rearward facing surfaces is less than that over the forward facing surfaces.
2. Although static pressure acts in all directions, dynamic pressure acts only in the direction of flow (the downstream direction). So the dynamic pressure does not tend to push the wing forward.
The overall effect of all of this is that the changes in velocity and pressure which are caused by the movement of the wing through the air, exert a rearward force on the wing. This together with the friction force is the zero-lift drag.
Explanation 2 (Based on the awareness principle)
Air molecules are inherently lazy, so they really do not like to be disturbed by things flying through them.
When they become aware of an approaching aircraft they bunch-up together to produce an area of increased static pressure. This increased static pressure opposes the forward motion of the aircraft. This is the zero-lift drag.
Both of the above explanations are of course simple but inaccurate.