Bottle Rocket

Description
Participants will design, construct and launch up to two rockets made from two empty two liter plastic pop (soda) bottle which will remain aloft for a maximum period of time.

Remember, the most important part of Bottle Rockets is repetition, and an excess of about 70+ hours of launching tests is recommended (meaning, several hundred runs for maximum efficiency). Be sure to test all available options and configurations for the best rocket.

Chance is an important factor in bottle rockets. Prevailing winds, humidity, temperature, and other weather conditions can all affect rocket performance. While these factors cannot be completely mitigated or predicted, bottle rockets can be made to function in as many environments as possible through practice and testing.

Bottle

 * A standard 2L carbonated bottle of any shape or color, but cannot be modified in any way.

Active
Active recovery systems are those that deploy, like parachutes. Generally these are not allowed.

Passive
Passive recovery systems help slow the descent without changing the profile of the rocket.


 * Backsliders are the rockets that are modified so that at apogee, instead of flipping over and heading for the ground, they float back in a higher drag configuration than a nose-dive. This set includes true backsliders which actually fall vertically without tipping at all immediately after apogee and rockets that modify the aerodynamics at apogee to float. A true backslider can be made by taking your aerodynamically stable rocket and moving the CG back closer to the CP. Other ways of modifying the aerodynamics at apogee include removal of the cone or a ball, or tilting the fins for a "spin" recovery. This is a very broad category with plenty of designs to try out. A great guide to backslider construction can be found in the links below.


 * Next are the gliders. This design also has a lot of potential. The issue with gliders this year is that the most successful variations of gliders will deploy the wings at apogee and glide to the ground, which involves a change of shape which is now illegal. If you plan on building a glider you will have to have fixed wings at launch which brings up a whole new list of challenges. Two things to watch are: 1. That there is a rigid border to the wings and 2. That the covering on the wings is reasonably taut.


 * Finally, you can use one or several propellers to slow the decent. This is again something that will be quite hard this year due to the new rules. The hard parts about this design is getting the rocket to be positioned so that the propeller(s) will actually turn and hiding the propellers until apogee.

Fins
Fins usually add to the stability of the rocket, 3 or 4 work fine.

Launcher

 * Buy a launcher
 * An expensive launcher, but this one has all the bells and whistles


 * Do it yourself
 * A cheap easy launcher, not the best quality

Strategy, Balance, and Stability
The objective of this event is to get your rocket to stay up as long as possible. With the removal of parachutes in this year's rules, it is nearly impossible to predict the times for this year. My personal prediction for nationals is slightly over 30 seconds. There are 2 basic factors that will determine your time: Height, and the recovery system. Weather will also affect your flight time. Try to waterproof your rocket. In combination, these will get you the time desired. One strategy is to go all out on one of these by either having a rocket that goes almost out of sight but has a weak recovery or having a rocket with a great recovery system that doesn't go that high. This will get you some success but to get the great times you will need a good mixture.

Height- The most common misconception is that the lighter a rocket is, the higher it will go. This is not fully true. To achieve maximum height you must have stability. Maximum stability occurs when the center of gravity is ahead of the center of pressure. To find the center of gravity simply balance your rocket on a finger. The center of pressure is the point where you rocket would be balanced vertically if held in a strong wind. Achieving stability often means adding weight to the end of the nose cone. Again a good way of finding stability is by launching your rocket with different amounts of weight put in different places. My suggestion is adding a penny at a time until your height starts to decrease. This make it easy to find the optimum balance of your rocket. You will also want to have fins on your rocket, but the shape and size of the fins do not appear to have a large influence on height as long as there are even fins.



Description
Participants will design, construct and launch up to two rockets (under 200 grams each) made from two empty one liter plastic pop (soda) bottle which will remain aloft for a maximum period of time.

To build a competitive rocket there is one key... EXPERIMENT!!!! The more rockets you launch, the better idea you will get of what will work and what won't. It also helps to watch other team's rockets at competitions and see how they do. I will share some of what I have learned over the past few years, but 'there is no substitute to experimenting with your own designs!'

Note: Before you read any further you must understand that a lot of success in bottle rockets is chance, but also understand that chance favors the prepared mind.

First, lets look at the standard design for a bottle rocket:




 * A. The bottle, a standard 2L/1L bottle of any shape or color cannot be modified in any way
 * B. The nose cone, you will find it beneficial and necessary to have a cone to contain the recovery system
 * C. The recovery system, in order to get a winning time you will need a recovery system that works well and for division C, is not a parachute
 * D. The fins, fins usually add to the stability of the rocket, 3 or 4 work fine

Second, the objective of this event is to get your rocket to stay up as long as possible. With the removal of parachutes in this year's rules, it is nearly impossible to predict the times for next year. My personal prediction for nationals is slightly over 30 seconds. There are 2 basic factors that will get you time. These are height, and the recovery system. These in combination will get you the time desired. One strategy is to go all out on one of these by either having a rocket that goes almost out of sight but has a weak recovery or having a rocket with a great recovery system that doesn't go that high. This will get you some success but to get the great times you will need a good mixture.

Height- The most common misconception is that the lighter a rocket is, the higher it will go. This is not fully true. To achieve maximum height you must have stability. Maximum stability occurs when the center of gravity is ahead of the center of pressure. To find the center of gravity simply balance your rocket on a finger. The center of pressure is the point where you rocket would be balanced vertically if held in a strong wind. Achieving stability often means adding weight to the end of the nose cone. Again a good way of finding stability is by launching your rocket with different amounts of weight put in different places. My suggestion is adding a penny at a time until your height starts to decrease. This make it easy to find the optimum balance of your rocket. You will also want to have fins on your rocket, but the shape and size of the fins does not appear to have a large influence on height as long as there are even fins.

Recovery systems- By far the most commonly used (and won with) recovery system is the parachute. This is unfortunately illegal in division C now. So, if you are in division C, skip to the new division C recovery section. This old classic can really surprise you if you happen to be lucky enough to catch an updraft. Parachutes come in all shapes and sizes and materials The most common shape of the parachute is the circle. The circular design gives you the most surface area per material. Some teams have achieved great success with a semi spherical design but this is very difficult to make. The general rule for size of the parachute is as big as your rocket design can take. I have seen some teams with a parachute diameter of 7 feet. This is a bit extreme but it is the best way go for the good time, if you can make it work. Materials range from rip stop nylon (great but expensive) to the good old cut up garbage bag. Again, try different materials and see what works for you individual design. The most common material used on more successful designs is plastic from a drop cloth. You can get this at a local hardware store.

Deployment- The hardest part of any parachute based system is getting the parachute to deploy at apogee consistently. Two mainstream solutions to this problem have been developed. First and most simple, is the passive deployment system. This design uses the fact that the rocket tips over at apogee to make the nose cone fall off. This design usually consists of a nose cone that fits very loosely and is supported by either tabs or a margarine lid. This prevents the cone from being forced too far down at take-off. This way the tipping of the rocket separates the nose cone and body. The next challenge is getting the parachute out of the nose cone. With parachutes getting increasingly larger, many teams are now using drouge chutes to pull out and open the main parachute. A drouge chute is simply a smaller parachute attached to the larger parachute. Many people also use talc powder to lubricate the parachute allowing it to leave the nose cone with less friction (it also makes a cool white cloud if you use enough). The other solution is active deployment. This involves a mechanical system that detects the apogee and pushes the parachute out of the nose cone. Most of these systems involve airspeed flaps and can be very finicky. More information on these designs can be found in the links below.

Division C Recovery- As most of you probably know, parachutes will be grounds for disqualification in division C. So, expect winning times to be greatly decreased from the 1-2 minute launches of the past. This change will limit the role of luck in the event and reward good engineering and innovation. The working definition for a parachute is anything that "fills with air." This creates a simply dichotomy of acceptable recovery systems. If a recovery system fills with air to operate, it will be considered a parachute. This bans parachutes and any other non-rigid recovery devices. The key test will be rigidity. There is a chance that streamers will be clarified legal, but it is most likely not worth testing until official word is released on the matter. Now that we have determined what isn't allowed, let's take a look at some of the options left. This is where the creativity comes in. The possibilities for a new unique deployment method are endless and chances are that some of the best designs haven't even been tried yet. A few of the systems I suggest you experiment with are backsliders, gliders, and propellers. Backsliders are the rockets that are modified so that at apogee, in stead of flipping over and heading for the ground, they float back in a higher drag configuration than a nose-dive. This set includes true backsliders which actually fall vertically without tipping at all immediately after apogee and rockets that modify the aerodynamics at apogee to float. A true backslider can be made by taking your aerodynamically stable rocket and moving the CG back closer to the CP. Other ways of modifying the aerodynamics at apogee include removal of the cone or a ball, or tilting the fins for a "spin" recovery. This is a very broad category with plenty of designs to try out. A great guide to backslider construction can be found in the links below. Next, are the gliders. This design also has a lot of potential. The most successful variations of gliders will most likely deploy the wings at apogee and glide to the ground. You will want to be very careful when designing your wings as to prevent violation of the definition of a parachute. Two things to watch are: 1. That there is a rigid border to the wings and 2. That the covering on the wings is reasonably taut. Finally, you can use one or several propellers to slow the decent. The hard parts about this design is getting the rocket to be positioned so that the propellor(s) will actually turn and hiding the propellers until apogee.

=Past Results=

Questions
What do I do about weather inconveniences?

Just launch normally, if there isn't an emergency. If there is, don't launch. Sometimes wind will alter the performance of your rocket. Rockets falling apart on account of wind are not entirely uncommon occurrences, so be careful. Don't launch when it's snowing. The temperature is below freezing point and YOUR BOTTLE ROCKET WILL NOT LAUNCH IN THESE TEMPERATURES.

How do they launch?

They pressurize the rockets, then once it's pressurized,you pull a string to launch it. At tryouts, they sometimes use bike pumps.

What if my rocket gets stuck somewhere?

You leave it! Don't risk your life to get a rocket on the roof of a 2-story building or something!

=Links=
 * Backslider Construction Information
 * Past National Event Chair's web page, includes his past national winning designs
 * This guy wrote the book on water rockets, literally!
 * Original active deployment with an airspeed flap
 * Rockets Away- simulation for testing rockets
 * A great site for rocket construction
 * Links and Concepts