Air resistance is usually calculated using the drag equation. This equation calculates the force experienced by an object moving through a fluid or gas at relatively large velocity. The result is called quadratic drag. Once the drag is calculated, you have to use a formula to calculate the power needed to overcome that drag in order propel and object. Power needs are the cube of the velocity, so if it takes 10 horsepower to go 80 kph it will take 80 horsepower to go 160 kph. As you can see a doubling of speed requires the eight times the amount of power. Knowing this is essential in calculating the amount of fuel it will take to make a journey.
There are three main types of drag in aerodynamics: lift induced, parasitic, and wave. Each affects an objects ability to stay aloft as well as the power and fuel needed to keep it there.