STRUCTURAL ANALYSIS

Ejection System

Black powder charge sizing and shear pin design for reliable deployment.

Black Powder Sizing

Design pressure for reliable separation:

Rocket Type	Design Pressure
Model rockets	5-10 psi
High-power rockets	10-15 psi

Simplified Formula

m_{BP} \approx 0.006 \times D^2 \times L

Where D = diameter (inches), L = chamber length (inches), result in grams.

Ground Testing

Always ground test ejection charges before flight. Start with calculated amount and adjust based on actual separation force.

Shear pins prevent premature separation while allowing controlled ejection:

Number of Pins

n_{pins} = \frac{F_{sep}}{F_{shear} \times 0.75}

Use a safety factor of 0.7-0.8 (not > 1.0) to ensure pins break reliably. Minimum 2 pins to prevent pivoting.

Prevent ascent pressurization that could cause premature separation:

1% Rule

A_{vent} \approx 0.01 \times A_{cross}

Typical: 1/8" to 1/4" hole per bay. See the Vent Sizing page for detailed calculations.

SOURCES

How To Size Ejection Charge — HARA
Step-by-step black powder sizing guide
Black Powder Sizing — Rocket Lab Delta
BP charge calculation methodology
Shear Pin/Screw Calculations — Feretich
Detailed shear pin strength analysis
Shear Pin Design — Rocket Lab Delta
Practical shear pin selection guide
Shear Pin Calculations — Leederville Rocketry
Alternative approach to shear pin sizing

Put this methodology into practice with the interactive calculator.