Model rockets are reusable. You’ll need a new engine, but the rocket can go again and again. However, that’s only possible if you get the rocket back in good condition. It needs to have a safe and secure landing, and that all depends on the parachute. Hobbyists often ask, “What size parachute do I need for my model rocket?” And we have an answer for you.
The Design
Rocketeers can use parachutes on almost any size model rocket. The parachute controls the model’s descent speed more accurately and brings the model down more slowly than any other recovery method. The best parachute designs are strong, thin, soft, and flexible.
Thin plastic sheets work well for smaller model rockets. This material folds up tightly and fits inside the small-diameter body tubes. Hobbyists can get creative with the design and type of materials they use for their parachutes.
Some have used plastic drop cloths, dry cleaning bags, gift wrapping plastic, or trash bags. Test the material by tearing it in both directions to see which side is stronger than the other.
The Drag Coefficient
Some parachute shapes are more efficient than others, and that has a lot to do with the drag coefficient. The drag coefficient is a dimensionless number that tells rocketeers how efficient a parachute is at creating drag.
Drag is the force that counteracts gravity as the rocket comes down. Test out the parachute on weights with the same mass as your rocket. Record the time it takes the weights to land with the parachute attached. The more drag a parachute creates, the safer the landing will be for your rocket.
The Standard Sizes
The size of the parachute you choose depends on the size of the rocket. Rockets that are 12 inches and shorter should use an 8-inch chute.
- Rockets 12 to 18 inches tall need a 12-inch parachute.
- Rockets 18 to 24 inches tall need a 12- or 18-inch parachute.
- Rockets 24 inches and taller need an 18- to 24-inch parachute.
These are the simple rules of thumb for standard sports rockets. When selecting a model rocket launch kit, it might come with a proper size parachute for the rocket size.
The Rocket Durability
Lastly, you need to factor in the durability of the rocket. Unfortunately, this is not a question anyone can answer directly. Unless you drop the rocket onto the ground hard until something breaks off, you won’t know its durability.
But it’s still a question we need to answer. You’ll need to choose between the average descent speeds: slow or fast. For a slow descent, assume your rocket can survive a fall to the ground without breaking from a height of two feet. A fast descent would be a fall from a height of three feet.
At AC Supply, we want to help all our hobbyists and rocketeers land their models safely. And choosing the right size parachute for model rockets will always be part of the equation.