There are many different factors that help to determine the flight capabilities of model rockets. For a model rocket to be considered stable it must be able to resist the drag coefficient in order to reach its maximum altitude while in flight. If a model rocket is unstable there is the chance of serious injury occurring. You should always find out roughly how stable your model will be before launching it.

There are a few different ways that you can do this. One method involves using the center of gravity and center of pressure. There are a few things you will need to gather to be able to figure these. You will need some scissors, a pencil, a ruler, some string and a piece of cardboard. The first step will be to locate your rocket’s center of gravity. The center of gravity is the specific point that your rocket rotates around.

To find this you will need to tie the string around the middle of the rocket. You can then begin to move the string back and forth until you find the point at which it is able to balance horizontally. Once you find this point you should make a note of it. Next you will find the center of pressure. This is the point on the rocket that is affected the most by air pressure or drag. Take the piece of cardboard and trace the profile of the rocket on it. Cut the profile out and balance it on the edge of the ruler. This will give you the rough center of pressure.

Mark the balance point on the cardboard profile and you will then be able to make any adjustments necessary. The next step is to try a string test out on the model rocket itself. Tie the string around the center of gravity and then you can swing the model around in circles making certain not to let it go. If you have properly found the CG then the rocket will point into the direction you are swinging it rather than having a wobbling motion.

By roughly calculating the CG and CP in this method you can then begin to adjust your rocket design to lessen or change these values for a longer, shorter, higher or lower flight time or path. For those that have a love of high mathematics, there is a way to calculate the CP much more accurately called the Barrowman Method. This method involves a great deal of computations but this can be offset by finding spreadsheet templates online that are free and will calculate the CP for you with just a few inputs on your part.
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You do not need to be a scientist to be able to make a bottle rocket, but you need to approach it like one, in the sense that you need to have the right tools and materials in place.

First gather all the necessary material you will need to construct a bottle rocket. These include a bottle of course. Any will do, but a 1 liter size soda bottle is preferable.

You will also need a bottle of rubber cement, paint thinner (1 can), a roll of masking tape, a hose clamp (1 inch) and a manila folder.

You should also have the following: a couple of 2in nails, two pieces of wood one measuring 2×4x12, and another 6×1/2×18; four sheets of balsa wood (6×4); five wood screws, an inch long.

An electric junction box, a 3″ thin steel (about 1/8″ diameter); a 12″ string, a copper tubing 12″ long, and a test tube stopper. In this project the size has to be 4 with an opening in the middle.

As for the tools, prepare a compass, drill scissors, sand paper, hammer, marker angle, air compressor, jigsaw, and a screwdriver. The size will vary according to the wood screw you selected.

To build the bottle rocket, begin by washing and drying the soda bottle. Use the paint thinner to eliminate all the glue, and take off the labels as well.

Take the balsa wood, and use the market to highlight a 5×3 shape (right triangle). Use the jigsaw to cut out the shape, and apply the sand paper to smoothen the edges. These will serve as the fins of your rocket.

Stick the fins onto the bottle with the rubber cement. Make certain that they are equidistant from each other. The masking tape will be used for straightening out the fins.

Take the compass and make a 4″ circle. Use the scissor to slice a line from the outer circle to the center. Fold it into a funnel shape. Glue it, and add some tape. Put it at the top of your bottle, and you have its nose setup. Leave the glue overnight and then you can remove the tape.

Making the launching pad for the bottle rocket is easy. Take the 2×4 wood and cut it in half. Lay them so that each is approximately 18 inches separate from each other, Get the 18 inch wood and put it on the 2×4 so that both sides are resting on it. Use the screwdriver to drive a wood screw into the 18in board. Repeat the process on the other side, and the platform is complete.

Next take the junction box and inert a screw so that the junction box is connected to the platform. Drill a hole into the box so that the test tube stopper can fit in. Put the stopper in there. Place the copper tubing into the stopper. Connect the air compressor with the tubing using the hose clamp.

Get the wire and shape it into a horseshoe. Secure the string at the center of the horseshoe, and put inside the electrical box. Drill a hole in each 2×4 wood piece, and the platform for the bottle rocket is finished.

Take the launch pad outside, and hammer a couple of nails into the base so it is attached to the ground. Pour 20 ounces of water into the bottle, put a pin in its neck, set the air compressor to 45 psi. Pull the string and watch your bottle rocket fly.
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One of the core ideas behind the concept of improving balance with stability exercises is that aging is not the only culprit when it comes to your deteriorating sense of balance. I believe that a big share of the blame lies in the fact that as we get older, we use our sense of balance less. This disuse then allows that sense to diminish the same way the strength of a muscle diminishes if you don’t use it.

This concept is actually good news. Why? If aging is the only reason your sense of balance is decaying, then there’s nothing you can do about it. But if disuse is also a primary cause, then that means you can do something about it.

An article from Biomechanics magazine recently reinforced my point, perhaps you’ll find it interesting and motivating. The article related that astronauts, after living in space on the space station for a while, display poor balance when they come back to Earth. Let’s think about this. You don’t see many astronauts over the age of 65. In fact, it’s probably safe to say that most of them are under 50. Yet, these relatively young men and women experience balance impairments after a few months in space. This means that their poor balance is not caused by old age.

Have you guessed what caused their poor balance yet? Disuse! There’s no gravity in space, so you can’t really fall since you’re floating around. This means that your brain doesn’t need to use it’s sense of balance. After spending several months without using their balance, these young astronauts return to Earth to find that their sense of balance is poor.

What they experience is really an accelerated version of the process that happens from the age of 60 to 80 as we move less and less, thus using our balance less and less. Your balance deteriorates much more slowly and over a longer period of time, but the result is the same.

So there you have it. Poor balance is at least partly caused by not using that sense. Naturally, the solution to the problem is to use your balance more by doing balance exercises. That or you can move to outer space.
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