Mon Jun 5 03:36:35 2023 GMT
What's A "Water Rocket"?
Frequently Asked Questions
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).
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:
Using a little algebra we can rearrange this into other forms:
To calculate Velocity for a given weight(R) and diameter:
or to calculate the area to provide a given descent velocity for a given weight(R):
Use this spreadsheet to calculate the proper size for your parachute.
Now build the parachute:
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
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