Drag Force Calculator Formula
Understand the math behind the drag force calculator. Each variable explained with a worked example.
Formulas Used
Drag Force (D)
drag_force = cd * 0.5 * air_density * pow(velocity, 2) * ref_areaPower Required to Overcome Drag
drag_kw = cd * 0.5 * air_density * pow(velocity, 2) * ref_area * velocity / 1000Variables
| Variable | Description | Default |
|---|---|---|
cd | Drag Coefficient (CD) | 0.03 |
air_density | Air Density (rho)(kg/m³) | 1.225 |
velocity | Velocity (V)(m/s) | 80 |
ref_area | Reference Area (S)(m²) | 25 |
How It Works
Aerodynamic Drag Force
Drag is the resistive force opposing an object moving through a fluid. It depends on the shape (captured by CD), the flight condition, and the size of the body.
Formula
D = CD × 0.5 × rho × V² × S
The power needed to sustain flight against this drag is P = D × V. Minimizing drag is a central goal in aerospace and automotive design because it directly reduces fuel burn.
Worked Example
An aircraft wing with CD = 0.03, area 25 m², flying at 80 m/s in sea-level air.
- 01Dynamic pressure q = 0.5 × 1.225 × 80² = 3920 Pa
- 02Drag = 0.03 × 3920 × 25 = 2940 N
- 03Power = 2940 × 80 / 1000 = 235.2 kW
Frequently Asked Questions
What is a typical drag coefficient for a passenger aircraft?
A modern airliner has a total drag coefficient around 0.02-0.04 in cruise. A streamlined car is about 0.25-0.35, while a flat plate perpendicular to flow is about 1.2.
Does drag increase linearly with speed?
No. Drag increases with the square of velocity, and the power required increases with the cube of velocity. Doubling your speed quadruples the drag force.
What is the difference between parasitic and induced drag?
Parasitic drag comes from skin friction and pressure differences on the body. Induced drag is a consequence of generating lift and is proportional to CL squared. Total drag is the sum of both.
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