Main Chutes Sizing

The formulas provided below will calculate an estimated parachute size that will result in a descent rate of about 15 feet per second. If the landing area is hard, such as packed earth or salt, a slower descent rate may be desired to prevent damage to the rocket.

Circular Parachute

$$D=39.6\times \sqrt{W\times 0.454}$$

Where:
$D$ is the diameter of the parachute in inches
$W$ is the weight of the rocket in pounds

Example of a 5 pound rocket:

$$39.6\times \sqrt{5\times 0.454}=59.7$$

Round up to a 60” circular parachute

X-Form Parachute

$$S=51.5\times \sqrt{W\times 0.454}$$

Where:
$S$ is the size of the parachute in inches
$W$ is the weight of the rocket in pounds

Example of a 5 pound rocket:

$$51.5\times \sqrt{5\times 0.454}=77.6$$

Round up to a 78” X-form parachute

A smaller parachute will result in a faster descent. A larger one a slower descent. If the ground is soft, such as grass covered, you may want to use a smaller parachute for a faster descent. A faster descent will result in less drift. If the ground is hard, like frozen earth or salt, you may want a slower descent, and therefore a larger parachute.

Submitted by: Dean A. Roth