Parachute sizing and descent rate for model rockets

Choosing the right parachute size is a balance between landing safely and not drifting into the next county. Too small and the rocket lands too hard, broken fins, bent body tubes, cracked nose cones. Too large and the rocket drifts far downwind, making recovery difficult or impossible at small fields. This calculator applies standard aerodynamic drag theory (terminal velocity = √(2mg / ρC_dA)) to both parachutes and streamers, reporting landing velocity, descent time and landing kinetic energy so you can size recovery hardware to match your rocket and launch site.

Target landing velocities

Low and mid power sport rockets (under 500g): 3 to 5 m/s (10 to 15 ft/s) is ideal. Slow enough to avoid damage to fibreglass or 3D printed parts, fast enough to avoid excessive drift. High-power rockets (500g to 5kg): 4 to 6 m/s typically. Heavier rockets can tolerate slightly faster landings because mass distributes impact over a larger surface, but check your rocketry body's landing energy limits. Very heavy rockets (over 5kg): Aim for 5 to 8 m/s. Dual-deployment is standard at this weight to reduce drift from apogee.

Parachute shapes and their drag coefficients

The calculator supports five common canopy shapes, each with a published drag coefficient:

Flat circular (C_d ≈ 0.75): Simple, cheap, widely available from hobby suppliers. Comes as a flat disc of ripstop nylon or mylar with shroud lines at the edge. Inflates into a shallow bowl shape in flight. Good all-round choice for most rockets.

Hexagonal flat (C_d ≈ 0.85): Slightly more efficient than a circle due to cleaner airflow at the edges. Common in competition events.

Hemispherical / dome (C_d ≈ 1.5): Shaped into a fixed hemisphere with panels. Much higher drag per unit area, you can use a smaller chute for the same descent rate. More expensive because of the construction; popular for HPR.

Toroidal / annular (C_d ≈ 2.2): Ring-shaped with a hole in the centre. The hole creates a recirculating flow that significantly increases drag. Very stable descent, very high drag coefficient. Used on competition rockets where small diameter matters.

Cruciform / cross (C_d ≈ 0.8): Made from two overlapping rectangles forming a cross. Simple to construct, stable, common on kits.

Parachute vs streamer: when to use which

For rockets under about 60 grams, a streamer often outperforms a parachute because the parachute needed would be impractically small. Streamers also drift less in wind since their descent rate is faster (6 to 12 m/s typical), which matters for competition events held at small fields. The trade-off is harder landings. For most sport rockets and any HPR flight, use a parachute. The calculator handles both modes with appropriate drag physics for each, parachutes use canopy area, streamers use a length-width flutter model calibrated against wind tunnel data.

Dual deployment for high-altitude flights

For flights above about 600m (2000ft), dual deployment is strongly recommended. The rocket falls quickly under a small drogue parachute from apogee to a lower altitude (typically 200 to 500m AGL), then releases the full main parachute for the final descent. This drastically reduces drift, the rocket lands within 100-300m of launch instead of kilometres downwind. Size the drogue for 15 to 25 m/s descent (enough to minimise drift time) and the main for 4 to 6 m/s landing. Dual deployment requires two separate ejection charges fired by one or two altimeters.

Landing kinetic energy limits

National rocketry bodies specify maximum landing kinetic energy per section of a recovered rocket to reduce injury risk on landing. TRA and NAR typically allow up to 75 ft-lbf (about 102 J) per section at ground level for certified high-power flights. The calculator reports kinetic energy (½mv²) alongside velocity so you can confirm you're under the limit. If you're close, either use a larger chute or split a heavy rocket into multiple sections that descend independently.

Frequently asked questions

What parachute size do I need? Target 3-5 m/s landing for sport rockets, 5-8 m/s for heavy HPR. Enter your rocket mass and target velocity, the calculator returns the required canopy area.

What C_d is my parachute? Flat: 0.75. Hex: 0.85. Hemisphere: 1.5. Toroidal: 2.2. Cruciform: 0.8.

Parachute or streamer? Parachute for anything over 100g. Streamer for very light competition rockets.

How long is a good streamer? Length about 10× width, total length 8-12× body tube diameter.

Do I need dual deployment? Strongly recommended for flights above 600m (2000ft) to reduce drift and improve recovery.