A = characteristic frontal area of the body (m2)
The drag coefficient is a function of several parameters like shape of the body, Reynolds Number for the flow, Froude number, Mach Number and Roughness of the Surface.
The characteristic frontal area - A - depends on the body.
Objects drag coefficients are mostly results of experiments. The drag coefficients for some common bodies are indicated below:
|Type of Object||Drag Coefficient |
- cd -
|Laminar flat plate (Re=106)||0.001|
|Turbulent flat plate (Re=106)||0.005|
|Subsonic Transport Aircraft||0.012|
|Streamlined body||0.04||π / 4 d2|
|Airplane wing, normal position||0.05|
|Long stream-lined body||0.1|
|Bicycle - Streamlined Velomobile||0.12||5 ft2 (0.47 m2)|
|Airplane wing, stalled||0.15|
|Modern car like a Tesla model 3 or model Y||0.23|
|Toyota Prius, Tesla model S||0.24||frontal area|
|Tesla model X|
|Sports car, sloping rear||0.2 - 0.3||frontal area|
|Common car like Opel Vectra (class C)||0.29||frontal area|
|Hollow semi-sphere facing stream||0.38|
|Solid Hemisphere||0.42||π / 4 d2|
|Saloon Car, stepped rear||0.4 - 0.5||frontal area|
|Bike - Drafting behind an other cyclist||0.5||3.9 ft2 (0.36 m2)|
|Convertible, open top||0.6 - 0.7||frontal area|
|Bus||0.6 - 0.8||frontal area|
|Old Car like a T-ford||0.7 - 0.9||frontal area|
|Bike - Racing||0.88||3.9 ft2 (0.36 m2)|
|Tractor Trailed Truck||0.96||frontal area|
|Truck||0.8 - 1.0||frontal area|
|Person standing||1.0 – 1.3|
|Bike - Upright Commuter||1.1||5.5 ft2 (0.51 m2)|
|Thin Disk||1.1||π / 4 d2|
|Solid Hemisphere flow normal to flat side||1.17||π / 4 d2|
|Squared flat plate at 90 deg||1.17|
|Wires and cables||1.0 - 1.3|
|Person (upright position)||1.0 - 1.3|
|Hollow semi-cylinder opposite stream||1.2|
|Ski jumper||1.2 - 1.3|
|Hollow semi-sphere opposite stream||1.42|
|Passenger Train||1.8||frontal area|
|Motorcycle and rider||1.8||frontal area|
|Long flat plate at 90 deg||1.98|
The force required to overcome air resistance for a normal family car with drag coefficient 0.29 and frontal area 2 m2 in 90 km/h can be calculated as:
Fd = 0.29 1/2 (1.2 kg/m3) ((90 km/h) (1000 m/km) / (3600 s/h))2 (2 m2)
= 217.5 N
The work done to overcome the air resistance in one hour driving (90 km) can be calculated as
Wd = (217.5 N) (90 km) (1000 m/km)
= 19575000 (Nm, J)
The power required to overcome the air resistance when driving 90 km/h can be calculated as
Pd = (217.5 N) (90 km/h) (1000 m/km) (1/3600 h/s)
= 5436 (Nm/s, J/s, W)
= 5.4 (kW)
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
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