Bottle Rockets – B&C Bro. Nigel Pratt

Bottle Rockets Teams will design, construct, and launch rockets to stay aloft the greatest amount of time.

Event Parameters 2 rockets are prebuilt by team members (one launch per rocket) Eye Protection #5 must be worn Event Supervisor provides the launcher and water

Construction - Parameters Rockets must be made out of a 2-liter or smaller plastic carbonated beverage bottle Inside diameter of nozzle of approximately 2.2 cm Only ONE 2 liter or smaller plastic carbonated bottle will be used as the pressure vessel for each rocket

Construction - Parameters Label must be presented if removed Structural integrity of pressure vessel may not be altered. For example: Physical damage Thermal damage Chemical damage Safety check will be done

Construction – Parameters Adhesives that may be used to attach components to the pressure vessel are limited to: Tape Glue Silicone Polyurethane based Others that do not damage the structural integrity of the pressure vessel Some good ones: GOOP, PL Premium, GE Silicon

More Construction All parts must be 5 cm above the level of the bottle’s opening (nothing may break this plane)(no tethering allowed)

More Construction Rockets MUST NOT change shape or deploy ANY type of recovery system! YES!!! – no parachutes, no expanding balloons, no separating nose cones, no deploying wings, etc…..

Construction – Nose Cone Nose of the rocket must be rounded or blunt at the tip. Nothing sharp, pointed, or rigid spike regardless of material used.

Restrictions No metal may be used in the construction of the rocket. No commercial model rocket parts. No explosives, gases (except air), electronic devices, elastic, throwing, remote, chemical or pyrotechnics allowed

Competition Walk in event or sign up event Wear safety glasses Students will add water, launch, and retrieve their rockets 10 minutes to launch 1 or 2 rockets (only 1 launch per rocket) Rockets launched before time expires will be scored

Competition - Launching Rockets launched using launcher provided by the supervisor Only water/air pressure will be used for energy to the rockets Rocket will be launched at 75 psi Once rocket is pressurized, no one may touch or approach the rocket

Competition - Timing Timing begins when the rocket separates from the launcher. Timing ends when any part of the rocket touches the ground, rests on an obstruction, or goes out of sight.

Scoring Greatest time aloft of any single rocket recorded to the nearest hundredth of a second.

Scoring - Violations Tier 1 Rockets that stay intact during launch and flight Tier 2 Rockets whose parts become detached while aloft Tier 3 Rockets with construction violations not related to safety Participation Points Safety violations (including no goggles) will not launch

Tie Breaker Better score of the other rocket of the tied team’s

So, how do you build a good one? Remove the labels and clean off the glue. Use 3 fins (very slightly angled) Decide on how long you want to extend it. Always keep in mind how to cut mass!!! Go out and buy a variety of 2L bottles from DIFFERENT companies. You’ll be surprised. Use non-carbonated bottles for your extension and nose cones (tend to be thinner walls and therefore lighter.)

Build them now….while it is still warm enough to go outside and test them. Don’t wait to December!!! Check out the websites on the last slide and make sure your team knows that difference between center of gravity (CG) and the Barrowman center of pressure (CP). More on this later What you want is for the rocket to “backslide”, as in the video. Check out the websites below. To find even more info, type “Coney” + “Water Rocket” and “backslider” in your searches. Build VERY cleanly. No extra glue, smooth surfaces, no drastic transitions, etc….

Teach some real science here and make this very “hands on!” Have them… build with 3 and 4 fins have them vary the nose cone try different transition cones go out with one rocket only and try different levels of water Go out with just a bare bottle and show them what stability really means. At some point, you will launch, the rocket will almost disappear far into the sky, and then it will slowly float to the ground! CONGRATULATIONS!!!

From one website, we get “There are basically two problems to solve: making the rocket aerodynamically stable, and minimizing drag. The first thing is to make the rocket aerodynamically stable. For a rocket to fly in a stable fashion, the center of gravity (CG) must be forward of the center of pressure (CP). The CG of the rocket is easy to find: it's the point at which the rocket balances. If you were to tie a string around the rocket at its CG, it would hang from the string horizontally.

The CP is more difficult to determine. The CP is defined as the point along the rocket where, if you were to attach a pivot and then hold the rocket in the wind by that pivot, the wind forces on either side of the CP are equal, so the rocket wouldn't point either into or away from the wind: it would be "wind balanced." Adding fins to a rocket moves the CP toward the fins, since you're adding surface area. In fact, that's the main function of fins: moving the CP aft. There are a couple of methods of determining the CP of a rocket. One old standby is to make a cardboard cutout shaped like the silhouette of the rocket, and then find the cutout's balance point, or CG. This corresponds pretty closely to the CP of the rocket itself.

The other method is to calculate it, and the equations for doing so can be found in the "Handbook of Model Rocketry" mentioned above, as well as many other places. The equations are a bit hairy, but naturally there are several computer programs to help. One question remains: how far forward of the CP should the CG be? Generally it's recommended that the distance between them be 1 to 2 times the diameter of the rocket body (this is called 1 to 2 caliber stability). This is just a rule of thumb, but it's a very good one.

The second thing is to reduce drag to a minimum. At the high velocities these rockets achieve, air drag becomes a very significant force. Again, see the "Handbook of Model Rocketry" for details, but in general the fins should be thin, every surface should be as smooth as possible, the nose should be a reasonable shape (it turns out that a hemisphere isn't bad, and is usually easy to come by), and the cross-sectional area of the rocket as small as possible.

Good Websites (hint: type “water rocket” not “bottle rocket” lider.html lider.html ml ml And many many others!! Good Luck…and Happy Launching!