We spent a lot of time and energy building our Black Knight water rockets, and we didn't want to see them be destroyed in one flight. After several attempts at using a parachute and failing we decided that we needed a different kind of recovery system. So I went on the Internet and did some research. On Robert Youens water rocket page I discovered the Coney. The Coney uses a unique kind of recovery system. This rocket, instead of coming down straight, like you would expect, it comes down sideways. Why is this? This happens because the center of gravity is below the center of area. I thought that if I made a long skinny rocket this would move the center of gravity back behind the center of area because the fins are heavier than the rest of the rocket. This was a bad assumption, although it did work once, but I think that was luck. I found a more reliable way of moving the center of gravity back behind the center of area was to add weights to the fins in the form of quarters. The first time I tried this I added too many quarters (4) and the rocket was unstable. So I took off two of the quarters and it worked beautifully. My Dad also made a computer model to calculate the center of area. The math was a little bit beyond me so I can't explain exactly how it worked. We calculated the center of gravity by balancing the rocket horizontally on a knife blade. The center of gravity is the point at which the rocket balanced. If the center of gravity was behind the center of area we knew we had a backslider. Another way to calculate the center of area would be to make a cardboard cutout of the rocket and balance this on a ruler. The center of area would be the point at which the cardboard cutout balanced.

Here is a picture of my first backslider. It is made from four one liter smart one water bottles. We taped a crushable nose cone to the rocket, which was another smart one bottle. We added a crushable nose-cone so all our hard work wouldn't get destroyed.

My first backslider water rocket

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Me standing next to our Black Knight rocket

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Coney

Rocket Stability A Detailed Analysis

Backglider videos

Movies/galleries

In this picture you can see the rocket on its' decent. This rocket is my first backslider.

Black Knight, backgliding to earth

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This is a picture of my dad and I standing next to our water rocket, with an Este's space shuttle sitting on the top of the rocket. The space shuttle caused the rocket to be unstable. As a result the rocket went about 50 feet, and then tumbled back to earth. Although it wasn't a complete success it still looked cool.

Black Knight with Shuttle

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This is what happens to a water rocket that does not backslide. As you can see in the photo below the nose pretty much got destroyed.

Crunched nose-cone

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Here is a picture of my first backslider. It is made from four one liter smart one water bottles. We taped a crushable nose cone to the rocket, which was another smart one bottle. We added a crushable nose-cone so all our hard work wouldn't get destroyed.

Me holding Black Knight

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Last weekend we launch off our black knight water rocket. The first time we launched it it kind of backslid. When it hit the nose-cone was damage. We put the rocket on the launcher and popped the nose-cone out. When we launched the rocket again we added weight to the fins. This moved the center of gravity back below the cent of pressure. When we launched the rocket again it backslid.

Today we pressure tested our water rocket. We pumped it up to about 100 P.S.I. It held for about 20 seconds, and then the top half of the rocket flew off while the bottom half stayed on the launcher. The bottle between the part of the rocket that launched off and the part that stayed on the launch pad got torn apart. We are not sure why that particular bottle failed instead of another bottle, but we are going to need to build a new rocket. This time I think we will make it out of two sections of plastic mailing tube, and use the tops of a 1 liter 7-up bottle as the nozzle and nose-cone of the rocket.

Blown up on Lauch Pad

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Last weekend we launched our latest Black Night water rocket with a reduced nozzle. We experimented using less water and discovered that for bigger rockets with small nozzles using less water makes the rocket go higher. We used about 1 liter of water and got about 500 feet. Maybe higher! On our last launch our rocket went so high that we lost it on a house. The rocket was in the air for about 25 seconds. That's a long time, espcialy for a rocket using a backslider recovery system! We got some cool video of the launch, below the rocket. Check it out by clicking on the link below.