Everything about Parasitic Drag totally explained
Parasitic drag (also called
parasite drag) is
drag caused by moving a solid object through a fluid. Parasitic drag is made up of many components, the most prominent being
form drag.
Skin friction and
interference drag are also major components of parasitic drag.
In aviation,
induced drag tends to be greater at lower speeds because a high
angle of attack is required to maintain lift, creating more drag. However, as speed increases the induced drag becomes much less, but parasitic drag increases because the fluid is flowing faster around protruding objects increasing friction or drag. At even higher speeds in the
transonic,
wave drag enters the picture. Each of these forms of drag 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 at or close to its optimal efficiency. Pilots will use this speed to maximize endurance (minimum fuel consumption), or maximise
gliding range in the event of an engine failure.
Form drag
Form drag,
profile drag, or
pressure drag, arises because of the
form of the object. The general size and shape of the body is the most important factor in form drag - bodies with a larger apparent cross-section will have a higher drag than thinner bodies. Sleek designs, or designs that are
streamlined and change cross-sectional area gradually are also critical for achieving minimum form drag. In some cases, cooling systems can be a serious source of drag, and
Evaporative cooling was developed to remedy that. Form drag follows the
drag equation, meaning that it rises with the square of speed, and thus becomes more important for high speed aircraft.
Profile Drag (Pxp): depends on the longitudinal section of the body. A diligent choice of body profile is more than essential for low
drag coefficient.
Streamlines should be continuous and
separation of the boundary layer with its attendant
vortices should be avoided.
Interference drag
Interference drag arises from
vortices. Whenever two surfaces meet at a sharp angle on an airplane, the airflow has a tendency to form a vortex. Accelerating the air into this vortex causes drag on the plane, and the resulting low pressure area behind the plane also contributes. Thus, the primary method of reducing interference drag is eliminating sharp angles by adding
fairings which smooth out any sharp angles on the aircraft by forming
fillets. Interference drag is also created by closely spaced parallel surfaces such as the
wings of a
biplane or
triplane, or the facing surfaces of an external load (such as an external fuel tank or weapon) and the
fuselage or wing. As with other components of parasitic drag, interference drag follows the
drag equation and rises with the square of the
velocity.
Skin friction
BLA would become wet if sprayed with water flowing in the wind. As with other components of parasitic drag, skin friction follows the
drag equation and rises with the square of the
velocity.
Skin friction is caused by
viscous drag in the
boundary layer around the object. The boundary layer at the front of the object is usually laminar and relatively thin, but becomes turbulent and thicker towards the rear. The position of the transition point depends on the
Reynolds number of the object.
Further Information
Get more info on 'Parasitic Drag'.
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