© 2011 - 2020 Sphero Inc. All rights reserved. littleBits, littleBits logo, Bits, "Make Something That Does Something," bitLab, "Snap The Internet To Anything", and “Making Changemakers” are trademarks of Sphero Inc. Q: How do I make and attach a parachute to the rocket?A: A 10-20 inch diameter parachute made from a plastic garbage bag works well for a 2-liter plastic bottle rocket weighing about 1/4 pound (4 ounces). I'll present instructions for manufacturing the parachute below, but first lets talk about some design decisions you need to make. There are a few factors you may want to consider before designing your parachute: These factors are important to your design because they effect how fast you'll want the rocket to descend under parachute, and how far down-range it will go before returning to the ground. For most of us there is limited space for our recovery area (the park, or your backyard). An example: Your rocket is going to go 200 ft in the air (by simulator estimate), it weighs 3.8 onces, and the wind is blowing at 6 miles per hour. If you have a 30 inch parachute on your rocket it will descend at 2.3 feet per second. The wind is 8.8 feet per second. Your rocket will travel 765 feet down-range before landing. Do you have a field 800 feet wide? If you reduce the size of the parachute to 8 inches it will descend at 8.8 feet per second. Then the rocket will land 200 feet down-range from apogee. So, how do I calculate the right size? The behavior of a circular parachute is governed by the drag it produces when pulled through the air. The resistance force due to drag is: Where: Using a little algebra we can rearrange this into other forms: To calculate Velocity for a given weight(R) and diameter: Now build the parachute: You'll need: Step-by-step:
NOTE: you may also cut off 1-1.5 inches of the point to form a 2-3 inch hole in the center of the parachute canopy. A hole in the center stabilizes a parachute so that it descends without wandering. for more information see: Paul Grosse: NSA - Nose Separates at Apogee Wikipedia: Drag (back) How does the parachute deploy on a model rocket?The streamers/parachutes get deployed by the rocket engine. The engine has a stage that moves the rocket up, and when that stage is used up, a second stage ignites that blasts a small charge back up the rocket tube, in the direction of the nose-cone. This pushes the stuff in the rocket out.
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