Recovery System Basics: Parachutes, Ejection Charges, and Safe Landings

Why Recovery Is the Most Important System

A rocket that flies perfectly but crashes on landing is a failed flight. In the American Rocketry Challenge, teams are scored on altitude accuracy and egg survival — both depend entirely on a reliable recovery system. A parachute that fails to deploy cleanly or a shock cord that snaps under ejection force can end a season of careful design work.

This guide covers the fundamentals every student needs before their first competition flight.

How Ejection-Based Recovery Works

Most model and mid-power rockets use a motor-ejection recovery system. Here is the sequence:

1. The motor burns out and the delay grain ignites
2. The motor's built-in delay grain burns for a set number of seconds
3. The ejection charge fires, pressurizing the body tube
4. The nose cone separates, pulling out the recovery wadding, shock cord, and parachute
5. The parachute inflates and the rocket descends at a controlled rate

Each step in this chain must work reliably. A single failure point — tangled shroud lines, insufficient wadding, a friction-fit nose cone that is too tight — and the rocket comes down ballistic.

Sizing Your Parachute

Parachute diameter determines descent rate. Too small and the rocket (and its egg payload) hits the ground too hard. Too large and the rocket drifts far from the launch pad, potentially landing in trees or crossing range boundaries.

The descent rate formula is straightforward:

Descent rate = sqrt((2 × weight) / (air density × drag coefficient × canopy area))

For a typical ARC rocket weighing 400-600 grams, a 45-60 cm diameter parachute produces a descent rate of 4-6 meters per second — fast enough to limit drift but slow enough to protect the egg.

Buy or sew multiple sizes and test them. Real-world descent rates vary from calculated values due to canopy shape, porosity, and packing method.

Ground-Testing Your Ejection System

Never fly an untested recovery system. Before your first flight, perform ground ejection tests:

1. Pack your recovery system exactly as you would for flight
2. Remove the motor and insert a small ejection charge (black powder) in the motor mount
3. Run an ignition wire to a safe distance (at least 5 meters)
4. Fire the charge and observe: did the nose cone separate cleanly? Did the parachute deploy fully?

Run this test at least three times. If the nose cone does not separate every time, reduce friction fit or increase the charge slightly. If the parachute does not unfurl, review your packing technique — the most common issue is shroud lines tangled around the canopy.

Packing Technique

How you fold and pack the parachute matters as much as the parachute itself.

Our recommended method for competition reliability:

1. Lay the parachute flat and untangle all shroud lines
2. Fold the canopy in half, then in thirds, creating a narrow strip
3. Z-fold the strip so it fits the body tube diameter
4. Wrap the shroud lines loosely around the folded canopy — do not cinch them tight
5. Place recovery wadding between the ejection charge and the parachute
6. Insert the packed assembly gently — do not force it

Practice this packing method until you can do it consistently in under two minutes. On competition day, muscle memory matters.

Shock Cord Selection

The shock cord connects the nose cone to the body tube after separation. It must absorb the ejection force without snapping or allowing the nose cone to fly completely free.

For ARC-class rockets, use elastic shock cord (flat rubber or tubular nylon) at least 2-3 times the body tube length. Attach it securely to both the nose cone and a bulkhead or motor mount anchor point. Test the attachment by pulling firmly — if it fails on the ground, it will fail in the air.

Checklist Before Every Flight

• Wadding in place and sufficient
• Parachute packed with lines untangled
• Nose cone friction fit tested (firm but separates with hand pressure)
• Shock cord attached at both ends
• Motor and recovery setup are compatible with your simulated flight profile
• Ejection charge is live

Recovery is not glamorous, but it is the system that brings everything else home safely. Treat it with the same rigor you give to fin design and motor selection.