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| About
Hydroflite |
A Brief
History of Hydroflite Water Rocket Development
It all started with a red water rocket and a red and white pump from Park Plastic made in Linden New Jersey. Hours of fun were had by filling the rocket with the little funnel, pumping until you couldn't get any more bubbles to go in and pulling the trigger. The rocket would shoot up in a spray of water that would soak all observers. The toy would come out off and on over the years until my first year at college. I had one in the swimming pool and was playing Trident submarine missile launch.. If you launch too deep, the water resistance prevents a good launch. Too shallow, and it is just like regular. There was a depth just right that really improved the launch. The water resistance on the canted fins caused a very rapid spin on the rocket which gave it unbelievable stability. The rocket ended up on top of the five story apartment building. I have not seen those water rockets in the stores lately. There are many other kinds made in China available now, but they just don't work the same. Pressure vessel selection Shortly after starting work as a rocket scientist, I thought it would be fun to design a larger version of that old red water rocket. As mentioned on the About Hydroflite page, I looked at using a Trident C4 first stage case as the pressure vessel. The calculations showed that the rocket would fly over 1.5 miles up! That Kevlar fiber really holds the pressure. You just can't go up to the rocket manufacturer and ask for a spare rocket motor case for private launching purposes so I was never able to verify those calculations. I looked at other options including commercial pipe or custom aluminum. As most newly graduated engineers are, I was low on funds and rich in ideas. I had to find a cheaper pressure vessel. The year was 1981 and 2 liter soda pop bottles were relatively new. I called a bottling company and asked where they got their bottles. I was referred to the manufacturer where I obtained some technical information. The bottles are proof tested to 170 psi. That is plenty of pressure for a magnificent launch. First launch attempt The first attempt at a launch was, to say the least, less than spectacular. I took the bottle cap and drilled a hole to accept a tire valve. I removed the valve stem so the water and air could come out. With the bottle half filled with water, I attached this modified bottle cap and pumped it up with a foot pump. The launch was simply turning to bottle upside down and (ungracefully) detaching it from the pump. Water sprayed everywhere but without enough thrust to overcome gravity. I let go of the bottle and it just dropped to the ground and sprayed water everywhere. Many attempts later, I could hold the thrusting rocket to just the point where it started to tug upwards and then let go. It would spin out of control after a second of hovering. I needed more thrust which meant larger throat area. But how could I pressurize the bottle? I came upon the brilliant idea of putting the valve stem back into the tire valve and pressurizing like before. Only this time, I could detach the bottle from the pump and carry the pressurized rocket to the launch point. The rather brilliant release was simply turning the bottle upside down and unscrewing the cap. What a mess! The cap shot down (never to be seen again) and the bottle shot up. The first launch at last. There had to be a better way. First launch stand The little red toy rocket had a seal mechanism of a sponge like disk that the bottom of the rocket pressed onto. I thought I could do the same with the 2 liter bottle. I went to the hardware store and started assembling a launcher out of 1/2 inch galvanized pipe. They had all the threaded pipes, T's and plugs I needed. I brought the first launcher home and cut out a sponge for the seal. There was no hold down mechanism so I needed an assistant. My wife became a reluctant lab assistant. I told her to hold the bottle down and let go when I told her. As I pumped, the water started leaking through the sponge. The faster I pumped, the faster the water came out. I couldn't get it up to launch pressure. (Of course, I blamed the lab assistant for the failure to launch.) We traded places. The pressure started to build and the water came through the sponge. (If only she would pump faster!) This was not working. I switched gasket materials to a cut up bicycle inner tube with a little more success. (Notice the great cost of the materials.) Everything was fine when you could hold the bottle level. If you got off by just a little bit, the water would spray out. Once again, there had to be a better way. Release mechanisms The lab assistant really gets drenched with the manual release technique. All of the early 2 liter bottles had a carrying lip near the top of the bottle. This became the natural external holding feature of the rocket. I found that a chain link was the right size to slip over the carrying lip. I connected two chain links with nylon twine and looped it beneath the launcher. With just the right length of twine, you could compress the rubber tire tube and slip the chain lengths over the lip. Releasing was a simple matter of flipping the chain links off of the lip with your thumbs. Drenching was assured and unless you got both chain links to come off at exactly the same time, the chain links and twine went flying with the rocket. I used up my entire chain I lost so many release mechanisms. Next I tried bent wire (coat hanger) to latch over the lip. Finally, a remote launch was possible by attaching a string to the top of the wire. This worked exactly once until the coat hanger unbent and dug into the plastic lip. I designed forks, pull pins, catch mechanisms, cams, and many other things trying to get a good seal as well as be able to release the bottle. Then I noticed that a 1/2 inch sprinkler pipe fit almost exactly inside the bottle. An o-ring seal of sufficient tightness would not only seal the water and air, but it would also hold the bottle down until enough pressure was reached for liftoff. Eureka!! A quick modification and an o-ring groove cut with a rat tail file and we had a launcher. A couple of variants With the secret of holding and sealing now understood, the only thing left was to hold the o-ring post upright during launch. One early design used welded pipe and sheet metal to hold the o-ring post. That was quite a bit of work for the launcher and could not be manufactured in your kitchen. We gravitated to a PVC version of the original design and sold a few. I made one special launcher for the neighborhood kids that allowed two pumps to pressurize the bottle. The kids were pumping away on one end and I was on the other end. That made them think they were pumping when they were really just compressing the same air over and over again. (Unless you see bubbles coming up, there is no more air being put in the bottle. I changed the design from a "T" configuration to a "W" configuration for a more stable variation. That was more expensive to build. The design finally settled down to the current "E" configuration which is a compromise between economy and stability. |
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