If you are to ask a group of pilots what makes a plane fly you are going to get caught in a really long heated discussion. One of the reasons why FSX require such a powerful computer to run is that it stimulates the forces acting on the plane as accurately as the flight model it is programmed with is capable of doing. If you thought that FSX was just a game, you will be surprised.
Flight simulator 10 uses a very complex mathematical models to simulate how plane flies through the air, something that only really mathematicians and flight engineers might be interested in. However understanding why a plane can fly is not really as important as being able to control these forces in flight.
The best way to imagine how these forces act on a plane is to imagine what happens when a plane flies low over the ground. As the plane passes the long gr[censored] underneath it gets flattened but as the plane moves away the gr[censored] stands up again. If you are unfortunate enough to be behind a plane you could know that a great deal of wind gets kicked up towards you.
As an air plane moves throughout the air, it moves a m[censored] of air downwards. Some air m[censored] also moves at the top but let’s ignore this for the moment. It is the air that is being pushed down that is keeping the plane up in the air. It is very similar to when you are swimming in a pool, the more water you can move downwards the better you will be able to float.
Similarly as a plane moves through the air that downward force it creates is enough to overcome gravity and thus it flies. It is because the downward force is greater than gravity they creates this overall positive lift which keeps you afloat.
An air plane needs to generate lift in order to fly and it can do this using two main methods. The first real method is to displace air molecules downwards by moving through the air very fast. On the other hand a plane to move slower through the air. But as it moves slower the volume of air it displaces gets larger. At the end of the day how fast your air plane moves through the air and how much m[censored] it is able to displace, determines the flight characteristics of your plane.