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In aerodynamics, the zero-lift drag coefficient is a dimensionless parameter which relates an aircraft's zero-lift drag force to its size, speed, and flying altitude. Mathematically, zero-lift drag coefficient is defined as , where is the total drag coefficient for a given power, speed, and altitude, and is the lift-induced drag coefficient at ...
One method for estimating the zero-lift drag coefficient of an aircraft is the equivalent skin-friction method. For a well designed aircraft, zero-lift drag (or parasite drag) is mostly made up of skin friction drag plus a small percentage of pressure drag caused by flow separation.
C D0 is known as the parasitic drag coefficient and it is the base drag coefficient at zero lift. C Di is known as the induced drag coefficient and it is produced by the body lift. C D = C D 0 + C D i { C D 0 = ( C D ) C L = 0 C D i {\displaystyle C_{D}=C_{D0}+C_{Di}{\begin{cases}C_{D0}=(C_{D})_{C_{L}=0}\\C_{Di}\end{cases}}}
Zero-lift axis. A typical lift coefficient curve. A cambered aerofoil generates no lift when it is moving parallel to an axis called the zero-lift axis (or the zero-lift line .) When the angle of attack on an aerofoil is measured relative to the zero-lift axis it is true to say the lift coefficient is zero when the angle of attack is zero. [1]
For example, the NACA 65 4-415, has the minimum pressure placed at 50% of the chord, has a maximum thickness of 15% of the chord, design lift coefficient of 0.4 and maintains laminar flow for lift coefficients between 0 and 0.8.
In fluid dynamics, the lift coefficient (C L) is a dimensionless quantity that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity and an associated reference area.
At angles of attack above the stall, lift is significantly reduced, though it does not drop to zero. The maximum lift that can be achieved before stall, in terms of the lift coefficient, is generally less than 1.5 for single-element airfoils and can be more than 3.0 for airfoils with high-lift slotted flaps and leading-edge devices deployed.
The drag coefficient of a sphere can be determined for the general case of a laminar flow with Reynolds numbers less than using the following formula: C D = 24 R e + 4 R e + 0.4 ; R e < 2 ⋅ 10 5 {\displaystyle C_{D}={\frac {24}{Re}}+{\frac {4}{\sqrt {Re}}}+0.4~{\text{;}}~~~~~Re<2\cdot 10^{5}}
The average modern automobile achieves a drag coefficient of between 0.25 and 0.3. Sport utility vehicles (SUVs), with their typically boxy shapes, typically achieve a Cd =0.35–0.45. The drag coefficient of a vehicle is affected by the shape of body of the vehicle.
is the overall drag coefficient , C D 0 {\displaystyle C_ {D_ {0}}\;} is the zero-lift drag coefficient , C L {\displaystyle C_ {L}\;} is the aircraft lift coefficient , π {\displaystyle \pi \;} is the circumference-to-diameter ratio of a circle, e 0 {\displaystyle e_ {0}\;} is the Oswald efficiency number.