In order to be as efficient as possible, aerodynamics plays a major role in designed and constructing a horizontal axis wind turbine, or HAWT. Aerodynamics is the science and study of the properties of moving air, and the behaviour of objects in an air flow. In order to maximize the amount of power, while keeping cost in mind, one must consider the number of blades needed, and the shape they must be. Modern wind turbines use a blade shape known as airfoils, which are specifically designed for use on rotors. This shape does not use the concept of drag, but instead uses life to harness the wind’s energy. The airfoils operate with forces that are perpendicular to the direction of the air flow, which makes them more efficient than a blade that uses the concept of drag to harness energy. When the edge of the blade is angled slightly out of the direction of the wind, the air moves faster on the upper side of the airfoil, which creates a low pressure that lifts the airfoil upwards (Wind Turbine Aerodynamics,Turbinesinfo.com). One can use Bernoulli’s law to explain how faster flow of air creates lower pressure. Simply put, Bernoulli’s law states that, where P is the static pressure, p is the fluid density, v is the velocity of fluid flow, and h is the height about a reference surface (Bernoulli's Law, scienceworld.wolfram.com). When the velocity increases, the static pressure must decrease in order to maintain the constant. However, a turbine blade can never reach 100% efficiency. A German physicist in 1919, by the name of Albert Betz, demonstrated that if a blade is too efficient it is not able to turn. He proved that a blade efficiency of 59% is the theoretical maximum. This came to be known as Betz’s Law. The most common commercial turbines operate at approximately 40% efficiency. Reaching the theoretical limit of 59% can be done in many ways, although it becomes increasingly difficult as the blade size increases (Wind Power, Aeronautics.nasa.gov).