Topic of the Day: Drag: Types, causes and effects
Induced drag is due simply to the development of lift. Induced drag is higher with low speed, maneuvering flight. Induced drag varies as the square of lift.
Airplane configurations designed to operate at high lift coefficients (sailplanes, transports) demand a high aspect ratio wing to minimize induced drag
Parasite drag is drag that is not associated with the production of lift. It is composed of form drag, friction drag and interference drag
Form drag, also known as pressure drag or profile drag, is caused by airflow separation from a surface and the low pressure wake that is created by that separation. It is primarily dependent upon the shape of the object. Form drag is reduced by streamlining. Since turbulent airflow adheres to the surface better than laminar flow, maintaining turbulent airflow on an airfoil will greatly reduce form drag with only a small increase in friction.
Due to viscosity, a retarding force called friction drag is created in the boundary layer. Turbulent flow creates more friction drag than laminar flow. Friction drag is usually small per unit area, but since the boundary layer covers the entire surface of the airplane, friction drag can become significant in larger airplanes. Rough surfaces increase the thickness of the boundary layer and create greater skin friction. Friction drag can be reduced by smoothing the exposed surfaces of the airplane through painting, cleaning, waxing or polishing.
Interference drag is generated by the mixing of streamlines between components. An example is the air flowing around the fuselage mixing with air flowing around an external fuel tank. We know the drag of the fuselage and the drag of the fuel tank individually. The total drag after we attach the fuel tank will be greater than the sum of the fuselage and the fuel tank separately. Roughly 5 to 10 percent of the total drag on an airplane can be attributed to interference drag. Interference drag can be minimized by proper fairing and filleting, which allows the streamlines to meet gradually rather than abruptly.
