There are 4 basic forces that act on an aircraft in flight; thrust, lift, weight and drag. Of these forces the most complex is drag. A thorough understanding of how drag affects the flight of an airplane is necessary if one is to exercise complete control over their aircraft. Drag can be broken down into 2 different types, induced and parasitic. It affects both the lift and thrust of the aircraft, and determines best glide speed as well as power required for an airplane. Drag in itself is not so difficult to understand, but as is so often the case, it is how drag interacts with the other forces that make it unique and complex.
There are four basic forces that act on an airplane in flight; thrust, lift, weight, and drag. Of these forces, it is important to take a deeper look into what drag is and how it really affects the aircraft. The total drag acting on an airplane in flight can be divided into two specific types; Induced drag and parasitic drag. Induced drag is produced by the wings and is simply a byproduct of lift. Parasitic drag is caused by moving an object through a fluid (such as air). In order to fully understand what is happening during flight and through different angles of attack, we must fully understand how drag is formed and the relationship between drag, power and airspeed.
Parasitic drag is primarily made up of form drag and skin friction, and is the easier of the two to understand. As the aircraft moves through the air, air particles nearby absorb some of the energy from the aircraft through friction. So the once relatively still air particles now are being accelerated as the aircraft passes. This transfers some of the aircrafts energy to the surrounding area. This is simply friction and specifically, skin friction. Form drag is disruption of air particles as a particular shape passes through them. Obviously an aerodynamic shape will require less energy to move through a fluid (air) than something not so aerodynamic. An example could be a sleek new Lamborghini compared to an old school Volkswagen hippy van. The Lamborghini will be more efficient and require less energy to move through the air. In the real world, parasitic drag not only comes from less aerodynamic aircraft designs, but mainly from landing gear, wing struts, antennas, or basically anything attached to the aircraft that disrupts the airflow over it. The formula for calculating parasitic drag is:
Parasitic Drag = CD * ½ p V2 * S