STRUCTURAL ANALYSIS

Recovery Loads

Opening shock calculation and recovery harness sizing for safe deployment.

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01

Load Events

EventTypical G-LoadDuration
Drogue deployment5-15 g0.1-0.5 s
Main (from drogue)10-30 g0.1-0.3 s
Main (no drogue)20-70 g0.1-0.3 s
Opening shock2-6× steady dragInstantaneous

Main Without Drogue

Deploying the main parachute directly at apogee creates massive opening shock. Always use a drogue for high-power rockets.
02

Opening Shock

Dynamic Pressure Method
Fopening=Cx×q×(CD×S)chuteF_{opening} = C_x \times q \times (C_D \times S)_{chute}
Canopy TypeShock Factor (Cx)
Solid canopy1.5-2.0
Annular/toroidal1.2-1.5
Ribbon/ring slot1.0-1.2
03

Shock Cord Sizing

Minimum Strength
Rating=Fopening×SFRating = F_{opening} \times SF

Safety Factor

3-5×

Recommended

Cord Length

2-3×

Rocket length per section

MaterialStrength/WeightStretchHeat Resistance
Nylon tubularGood15-25%Moderate
Kevlar flatExcellent2-4%Excellent
Kevlar tubularExcellent2-4%Excellent
Spectra/DyneemaExcellent3-5%Poor (melts)
Some stretch is desirable to absorb shock. Pure Kevlar with no stretch can damage attachment points.
04

Hardware Selection

All hardware in the recovery chain must exceed the opening shock load:

ComponentSizing Rule
Quick linksRating ≥ shock cord rating
SwivelsRating ≥ shock cord rating
U-bolts
Eye boltsRating ≥ 2× cord (stress concentration)
Bulkheads

SOURCES

References

Academic Papers

NASA & Technical Reports

Textbooks

  • Parachute Recovery Systems Design Manual — Knacke, T.W. (1992)

    Comprehensive reference for parachute design and opening shock

Community Resources

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