Water rocket tips...plz help?

Question

i have to do a water rocket project for technology class and i was wondering if you had any tips or advice to give (on the design of the fins, how much water to put in the rocket, etc)...websites/ links would be helpful too...also, if you have built a water rocket before could you give me some of your experiences? thanks =D

Answer 1

I have built water rockets using a soda bottle. Glue a tennis ball to the top of the bottle as a nose. This both acts as landing gear and enhances stability.

Use PVC pipe that extends all the way into the bottle, sealed with an O ring at the bottom. This gives a substantial boost to the altitude, because the rocket is reacting against the tube during launch. Use a car tyre pump to pump it up to about 80psi for launch.

My rocket went up about 100 feet, and it was a blast! Use a long enough piece of string so you don't get soaked when it Launches or injured if it blows up during pressurization. I purchased a heavy duty pump from an outfit called Bigfoot Stilt. It worked much better than a pump from the auto parts store.

Answer 2

The most efficient water load is a half-full bottle. That gives you a large reaction mass while allowing a large volume of compressed air. Since the air provides the energy and the water provides the thrust, you get the best performance that way.

In terms of fin size, since you're going to be dealing with a slow rocket with chaotic thrust you'll want quite large fins. There is a way you can test the rocket without having to actually launch it; this technique is modified from testing procedures for black-powder model rockets.

What you need to do is insert a balloon into the bottle neck and fill it up to about half the size of a full load of water. s***w on the cap to hold the balloon and water in about the place they'll be when the rocket is launched. That will give a good approximation of the balance of the rocket in flight.

Take a long piece of twine, say 8 or 10 feet long, and tie it in a loop around the rocket body. Slide the loop so it goes around the centre of gravity, probably near the middle of the balloon. You'll be in the right place when the rocket stays horizontal while being hung from the string. Tape the loop into place.

To test the stability, take the rocket outside where there is plenty of room, and start to swing it around your head in a circle. If the rocket flies correctly, with the nose forward, you're fine. If it flies backward, you definitely need larger fins; the rocket is unstable.

Answer 3

I had success building a water rocket out of two small16 oz mountain dew bottles. The bottles were mounted end to end so as to extend the lengt of the rocket. A cone was shaped and  cut from a plastic report cover and the fins(2) were made from paper covered foam board. We had 45 minutes to construct the rocket

The object of our competition was distance so rockets were launched on a ballistic trajectory (see video).  Rocket balance is key as you want a nose heavy rocket (think lawn dart but not too heavy).  A rule of thumb for balance point is 1 to 1.5  body diameters in front of the leading edge of the fins.   If the rocket is tail heavy it will be unstable so you either have to remove some weight from the rear by removing fin area or add weight to the nose. (Excess weight reduces performance)  A trick we did to minimize overall  weight necessary on the nose was to lenghen the rocket which allowed less weight in the nose to have more effect in balancing the rocket. (The longer length acts like a lever)

It was mentioned that you can swing test you rocket which is a valid means of testing. However we didn't have string or a water balloon in our contest supplies. So we tried tossing the rocket(empty no water) a few times by hand on the grass. We found the rocket was a little tail heavy and cut off a three inch length from the rear of the fins. (The results are seen in the video )  Launch was done using 6oz of water @ 60 psi   for a distance of over 400 feet.

Answer 4

u should fill it half way ora little bit higher also if you buy dry ice you have to watch it you want enough to make alot of pressure to shoot off but not enought to blow it up so have the people that you buy it from will cut it for you cut it 3" to 4" if that doesnt work then look on google