Field Notes
Shear Pins, Vent Holes, and Why Dual Deploy Still Fails
How many nylon pins a 3- or 4-inch coupler actually needs, why av-bay vents are not optional, and the failure modes of dual deploy.
By Burn Wire
You can buy the right altimeter, wire a clean dual-deploy sequence, and still prang the rocket because the airframe physics were wrong. The coupler was too tight. There were no vents. There were six shear pins on a charge sized for two. Or there were zero pins, and the main came out at Mach.
This is the mechanical half of recovery reliability. Charge mass lives in the black-powder sizing guide. Bay layout lives in the avionics-bay article. Here we talk about the two cheap parts that decide whether those systems are allowed to work: nylon pins and holes.
If you only remember one pairing: pins and powder are one design. Change one, re-test the other.
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Behind the perforation
- What a shear pin is for
- Common sizes
- How many pins
- The failure mode of too many pins
- The failure mode of zero pins
- Vent holes: two different problems
- 1. Avionics-bay static ports
- 2. Chute-bay pressure
- Why dual deploy still fails when the wiring is “fine”
- Coupler fit and grease
- Ground-test the pin count
- Field checklist
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