Drag Equation

\[D=\frac{1}{2}\rho V^{2}AC_{D}\]

Variables

Ddrag force (N)

rho[ρ]fluid density (kg/m³)

Vvelocity relative to the fluid (m/s)

Areference area (m²)

CDdrag coefficient

Description

What is this formula?

The Drag Equation calculates the aerodynamic or hydrodynamic drag force acting on a body moving through a fluid.

It relates drag force to fluid density, relative velocity, reference area, and drag coefficient.

When to use it

Use this formula to estimate drag on aircraft, cars, rockets, drones, projectiles, underwater vehicles, or any object moving through air or liquid.

It is widely used in aerospace engineering, vehicle design, fluid mechanics, and performance analysis.

Example

An aircraft component moves through air with:

Fluid density = 1.225 kg/m³

Velocity = 80 m/s

Reference area = 2.5 m²

Drag coefficient = 0.32

Formula:

D = 0.5 × ρ × V² × A × CD

Substitution:

D = 0.5 × 1.225 × 80² × 2.5 × 0.32

D = 3136 N

Result:

Drag force = 3.14 kN

Applications

Aircraft drag estimation

Rocket and missile aerodynamics

UAV performance analysis

Vehicle aerodynamic design

Wind tunnel testing

Fluid mechanics calculations

Note

The drag coefficient is an empirical parameter that depends on body shape, surface roughness, Reynolds number, Mach number, angle of attack, and flow conditions. The equation is an engineering model and is valid when the selected drag coefficient corresponds to the actual flow regime and reference area definition.