METHODOLOGY

Drag Calculation

Component-based drag coefficient prediction from subsonic through hypersonic flight regimes.

Total Drag Coefficient

The total drag coefficient is the sum of individual component contributions:

C_{D_{total}} = C_{D_{friction}} + C_{D_{pressure}} + C_{D_{base}} + C_{D_{wave}} + C_{D_{fin}}

1. Skin Friction Drag

Caused by viscous shearing stresses in the boundary layer. The skin friction coefficient depends on Reynolds number and flow regime (laminar or turbulent).

SUBSONIC

~45%

of total drag

SUPERSONIC

~35%

of total drag

HYPERSONIC

~25%

of total drag

Skin friction coefficient calculation:

C_{D_{friction}} = C_f \cdot \frac{S_{wet}}{S_{ref}}

Laminar (Blasius):

C_f = \frac{1.328}{\sqrt{Re}}

Turbulent (Prandtl):

C_f = \frac{0.074}{Re^{0.2}}

Reynolds Number:

Re = \frac{\rho V L}{\mu}

Where $\rho$ = density, $V$ = velocity, $L$ = characteristic length, $\mu$ = dynamic viscosity

2. Pressure/Form Drag

Caused by the rocket pushing aside air. Primarily determined by nose cone shape.

NOSE TYPE	SUBSONIC CD	NOTES
Ogive	0.02 - 0.04	Best all-around
Conical	0.03 - 0.05	Simple to manufacture
Parabolic	0.02 - 0.03	Good subsonic
Von Karman	0.02 - 0.03	Optimal subsonic
Haack (LD-Haack)	0.01 - 0.02	Minimum drag

3. Base Drag

Caused by the low-pressure wake behind the rocket. Base drag is inversely proportional to skin friction drag.

Powered flight:

C_{D_{base}} \approx \frac{0.029}{\sqrt{C_{D_{friction}}}}

Coasting flight (subsonic):

C_{D_{base}} \approx 0.12 + 0.13 M^2

4. Wave Drag

Significant only at supersonic speeds (M > 0.8). Caused by shock waves forming around the rocket.

TRANSONIC RANGE

0.8 < M < 1.2

Drag rises sharply

PEAK DRAG

M = 1.0 - 1.1

Maximum wave drag

Wave drag depends on nose cone fineness ratio and can be minimized with area ruling (Sears-Haack body).

5. Fin Drag

Each fin set contributes profile drag, induced drag, and interference drag.

C_{D_{fin}} = C_{D_{profile}} + C_{D_{induced}} + C_{D_{interference}}

Fin profile drag:

C_{D_{profile}} \approx 2 \cdot C_f \cdot \left(1 + 2\frac{t}{c}\right) \cdot \frac{S_{fin}}{S_{ref}}

Where $t/c$ is the thickness-to-chord ratio

Atmospheric Model

We use the US Standard Atmosphere 1976 model for density and temperature calculations.

def atmosphere(altitude_m):
    if altitude_m < 11000:
        T = 288.15 - 0.0065 * altitude_m
        p = 101325 * (T / 288.15) ** 5.2561
    else:
        T = 216.65
        p = 22632 * exp(-0.00015769 * (altitude_m - 11000))

    rho = p / (287.05 * T)
    return T, p, rho

Try the Calculator

Enter your rocket geometry and see the component-based drag breakdown.

Open Drag Calculator

SOURCES

References

Academic Papers

Drag Coefficient Prediction — Braeunig, R.A.
Comprehensive methodology for component-based drag calculation across all Mach regimes (via Internet Archive)
Development of an Open Source Model Rocket Simulation Software — Niskanen, S.
OpenRocket thesis with detailed drag modeling methodology

NASA & Technical Reports

NACA Reports on Nose Cone Drag
Historical wind tunnel data on nose cone pressure distribution and drag

Textbooks

Fluid-Dynamic Drag — Hoerner, S.F. (1965)
The foundational reference for aerodynamic drag, covering theory and experimental data