Parasitic drag

Parasitic drag is drag that acts on an object when the object is moving through a fluid. In the case of aerodynamic drag, the fluid is the atmosphere. Parasitic drag is a combination of form drag and skin friction drag. Parasitic drag does not result from the generation of lift on the object, and hence it is considered parasitic. Parasitic drag is drag that acts on an object when the object is moving through a fluid. In the case of aerodynamic drag, the fluid is the atmosphere. Parasitic drag is a combination of form drag and skin friction drag. Parasitic drag does not result from the generation of lift on the object, and hence it is considered parasitic. The other components of total drag, lift–induced drag, wave drag, and ram drag (see ram pressure), are separate types of drag, and are not components of parasitic drag. In flight, lift–induced drag results from the lift force that must be produced so that the craft can maintain level flight. Induced drag is greater at lower speeds where a high angle of attack is required. As speed increases, the induced drag decreases, but parasitic drag increases because the fluid is striking the object with greater force, and is moving across the object's surfaces at higher speed. As speed continues to increase into the transonic and supersonic regimes, wave drag grows in importance. Each of these drag components changes in proportion to the others based on speed. The combined overall drag curve therefore shows a minimum at some airspeed; an aircraft flying at this speed will be close to its optimal efficiency. Pilots will use this speed to maximize the gliding range in case of an engine failure. However, to maximize the gliding endurance (minimum sink), the aircraft's speed would have to be at the point of minimum drag power, which occurs at lower speeds than minimum drag. At the point of minimum drag, CD,o (drag coefficient of the aircraft when lift equals zero) is equal to CD,i (induced drag coefficient, or coefficient of drag created by lift). At the point of minimum power, CD,o is equal to one third times CD,i. This can be proven by deriving the following equations: