Celtic Kane

What is my rocket’s mass?

Usually the manufacturer of your rocket will have that type of information on their website or through a catalogue. If you’re making your own rocket, you might try asking a high school science teacher if you can use a scale. According to the Estes Catalogue, my rocket itself weighed in at 12 grams. However, you also have to take into account the weight of your engine. I assumed I’d use the biggest engine possible, which was a C engine that weighed 26.9 grams and had 12.48 grams of propellant. So how do you find the final weight that you’ll use for calculations? Take the rocket weight + engine weight – propellant weight. For me, this was 12 + 26.9 – 12.48 = 26.42 grams. For the sake of it, I rounded up to 27 grams, or .027 kilograms.

I used the equation on the math and theory page, and using a velocity of 3 m/s, a mass of .027 kilograms, and a drag coefficient of 1.5, I determined that a chute of .202 meters was needed, or 7.95 inches. Again, just for the sake of being safe I rounded up to an eight inch diameter chute.

In order for air to escape it is necessary to have a hole in the top of the parachute — I’ve heard about 10% of your surface area, but for my chute that seemed like too much. Here’s how to figure out how much you should cut out..

  • Find surface area (pi * radius2) [pi * 4.52 = 63.6 in2]
  • Take 10% of that [6.36 in2]
  • Find radius of that [6.36 = pi * r2 — solve for r -> 1.42]
  • Double radius to get diameter [2.84]

A 2.84 diameter hole just seemed like too much for me, and since this was just a fun project I went with a 1 inch diameter hole. Now that we have everything planned out, it’s time to move onto the design phase.

Next: Designing the Parachute