How to make a water rocket fly high?

zeo2396 · Apr 9, 2011

I did a bottle rocket yesterday (2 liter bottle). I made 4 fins and the end of the fins touch the ground instead of the bottle's opening. I also equip my rocket with a parachute (hide under the nose cone). In addition, I added a modeling clay to my nosecone too! When I tested it, my teacher said I should fill a rocket 3/4 with water and pump to 100 psi. I did as he said and my rocket fly short and twisty. My teacher said that I did something wrong with my rocket because it lost the balance when it fly. I have no idea what can I add to my rocket to make it fly straight up (not twisty) and high in the sky.

1. Do you think my rocket fly twisty because of 4 fins? I think I should made 3 instead of 4. Also, what is the good material to make rocket's fins (carton, or paper..)? Should I stick the fins at the half of the bottle or near the bottle opening to keep it easily to stand?
2. I add clay to my nose cone to make it heavier and easier to release the parachute under it. I didn't stick my nosecone to the rocket body but it didn't drop out when it fly to release the parachute. What can I do make my nosecone drop out when it reach the maximum height. My parachute didn't come out, is it because the way i fold it is wrong!

3. What amount of water do you think I should add to my 2 liter bottle rocket? (1/4 or 2/4 or 3/4) and what is the best "psi" should I pump to?

4. Should I make my rocket heavy or light (specially is the nosecone)?

I hope you answer my question and give me some of your great ideas to make my rocket fly high and straight and to active the parachute easily!

Thank you very much!:shy:

Here are my rocket's pictures:

1.Full view

Handmade model rocket of cardboard tube body with blue and yellow sections, red cone nose, and four green fins, standing on a wooden floor in front of a black backpack.

2. Fins touch the ground instead of the bottle's opening:

Photo of a homemade water rocket with four green cardboard fins and a yellow body, standing on a wooden floor, with the bottle's threaded neck and white collar visible between the fins.

3.When the nosecone come off the rocket, the parachute release:

Homemade water rocket made from a blue cardboard tube with a taped top, green and yellow cardboard fins, and a red and clear plastic cap, with a black plastic bag parachute and white cord on a wooden floor.

4. 4 Fins:

Homemade water bottle rocket with four green cardboard fins attached around a clear plastic bottle, held up by a hand with a string tied to its side.

cjl · Apr 9, 2011

It sounds like your rocket was unstable. For stability, you need a sufficient amount of fin area (4 is better than 3 in this regard, and larger fins are also better), and you also need the center of gravity to be far enough forward. The noseweight helps with this (though too much weight in the nose will hinder altitude, since you're making the rocket heavier). The fins should be as far back as possible, and in the free airstream (not just behind the main bottle). Another key is for the fins to be stiff and solidly attached. If they can just flap around in the airstream, they won't do much to aid stability.

As for pressure and quantity of water? 100PSI and 3/4 full should be pretty good to get close to max altitude, but for test flights, I would go with 40PSI and around half full. That way you can see what's happening a bit better, and it won't have as much energy if something goes wrong. Then, once you get it working, you can ramp up to the 100psi 3/4 full flight.

Do you have any pictures of your design?

zeo2396 · Apr 10, 2011

cjl said:

It sounds like your rocket was unstable. For stability, you need a sufficient amount of fin area (4 is better than 3 in this regard, and larger fins are also better), and you also need the center of gravity to be far enough forward. The noseweight helps with this (though too much weight in the nose will hinder altitude, since you're making the rocket heavier). The fins should be as far back as possible, and in the free airstream (not just behind the main bottle). Another key is for the fins to be stiff and solidly attached. If they can just flap around in the airstream, they won't do much to aid stability.

As for pressure and quantity of water? 100PSI and 3/4 full should be pretty good to get close to max altitude, but for test flights, I would go with 40PSI and around half full. That way you can see what's happening a bit better, and it won't have as much energy if something goes wrong. Then, once you get it working, you can ramp up to the 100psi 3/4 full flight.

Do you have any pictures of your design?

Here are my rocket's pictures:

1.Full view

Homemade model rocket made from a blue cardboard tube with a red paper nose cone, green fins and a yellow wrapped section, standing on a wooden floor in front of a black backpack.

2. Fins touch the ground instead of the bottle's opening:

Photo of a homemade water rocket on a wooden floor, showing bright green cardboard fins splayed out around a yellow body tube with the bottle's plastic neck and cap visible beneath it, with the fins extending below the nozzle.

3.When the nosecone come off the rocket, the parachute release:

Homemade model rocket made from a blue cardboard tube with green and yellow paper fins, a red nosecone, and a black plastic bag parachute tied with white string on a wooden floor.

4. 4 Fins:

Photo of a homemade water rocket on a bottle, with four green cardboard fins taped around the base and a white string tied to the side, held by a hand.

Do you know how to stabilize my rocket?

cjl · Apr 10, 2011

Your fin area and placement looks fine - I think the problem is the attachment. Fins which can flop around freely provide almost no stabilization. You should really find some way of attaching them more securely. That should probably fix your stabilization problems.

How to make a water rocket fly high?

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