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Apr 26, 2010, 07:45 AM
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Jet Nautilus, Static Dive Concept/Experiments

The Jet Nautilus is a dynamic diving submarine resembling the Disney Nautilus from the 1954 movie 20,000 Leagues Under the Sea. The primary development criteria of the JetNautilus was that a simple propulsion/control system based on bilge pumps could be developed and incorporated into a model RC submarine every bit as responsive as the more complicated traditional systems with servos, dive planes, rudders and props. The system has been tested in both a 7 foot and 4 foot model. Early working renditions of the concept have evolved over time with various improvements. The current working version (3) incorporates DVVT ( dual voltage variable thrust).

At one time I had developed a gas operated static dive system. And while the system worked very well it proved to be impractical for the typical environment encountered in southeast Georgia, namely piss poor water clarity in the majority of ponds and lakes.
Once the sub went under it was difficult to judge the operating depth without being able to see it.

The operating depth of the dynamic diver however could be roughly gauged by the angle of the dive and the length of time using the down control. Release of the down control would level the sub and as long as forward was applied it would tend to travel in a horizontal plane underwater. There are actually two means to induce dynamic diving. One is to increase the surface speed (unique hydrodynamics of the Goff design, discussed elsewhere) and in the current version this is accomplished by applying 24 V to the forward thrusters. The other is to use a pump or thruster to direct the front of the sub down and in combination with forward movement the sub will go under

But as a matter of curiosity I was wondering if I could extend the basic development principal (simplicity of operation and low-cost) to a static system using a bilge pump.

Here is the concept; water can be pumped into an airtight chamber, compressing the air and adding weight to the Nautilus. With an 1100 rule bilge pump at 24 V it will introduce almost 2 1/4 pounds of water into a 2 L plastic soda jug. Since the two litter soda bottle is about half filled I know the pressure (provided by the bilge pump) is about 1 atmosphere or 14 psi. What's great about this system is that when the water is released the compressed air in the soda bottle simply returns to normal volume at ambient 14 psi (0 relative). There is no need to replenish the gas. Also when the pump can no longer fill the chamber it just runs. So you can't stall it or short it out. So once the sub goes under just release the control. The water would be released through either a valve or small hole. Since you want the sub to come up anyway a small hole (lowest point of the WTC) would mean that eventually the sub would become positively buoyant (a control valve could be used as well).

Assuming 2 1/4 pounds is enough to sink the sub the next problem would be finding two litters of volume within the sub. And while I'm sure it's there it's just not in a convenient shape.

If 2 L of space could not be found the other solution would be to find a pump with greater pressure. If this could work with just a bilge pump it would be a relatively inexpensive modification. A high pressure pump might cost a little more. Anyhow that's the concept.

To test the concept I used a spare Hull and the following video shows the basic concept. The sub sinks. The tail end of the sub is filled with foam so it floats. However in this test set up a high point of the bottle had water and the low air. They should be reversed and it is in the second video.

The next video shows the same test except the bottle is reversed so that the low point always has water. The sub sinks and then returns. The pump fills the bottle, compresses the air, the sub sinks, the bilge pump is disconnected and the compressed air pushes the water back through the bilge pump and the sub surfaces.

The next series of tests would incorporate a one-way valve from the bilge pump to the bottle and then a small orifice to slowly release the water. In this way the sub will remain submerged for a fixed amount of time. But the video shows the principal at least.

The next phase of this experiment is to either find an inexpensive pump with greater PSI capability or to modify an existing bilge pump. Since I had a few spare pumps I decided to see if I could "hop up" a bilge pump. This is probably the first time anyone's ever tried to hop up a bilge pump. But I did it and it works. The first thing I thought about was to increase the size of the impeller. This was done by cutting blades from a copper pipe and gluing them to an existing impeller. This also required modifying the housing which I did using plastic pipe and a copper tube.

A bilge pump both sucks and pumps and this relation is affected by the size and shape of the housing, excurrent location and the impeller. I'm sure the bilge pump companies have this all worked out in hydrodynamic formulas. I just adjusted things until I got the most pump. The modified Johnson 500 GPH puts out more than the rule 1100 GPH. Although I don't have the numbers to support this I'm just going by a comparison of thrust that I was able to perceive in a test situation. The following photo shows the modifications to both the housing and the impeller made to the Johnson pump on the far right.

At this point I'm encouraged that the concept seems to be valid and economically feasible.
Last edited by Carcharadon; Apr 26, 2010 at 08:50 AM.
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Apr 27, 2010, 07:16 AM
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I wanted to continue experimenting with the bilge pump to see if an even larger impeller would provide additional thrust. In my first attempt the larger impeller destroyed itself as the blades just flew apart. So to correct that I placed wire around the top of the blades to keep them from spreading apart and it seems to work. However any increase is only slight although still better than the stock impeller. I'm thinking that maybe a wider impeller rather than taller might be the next dimension to explore?

I realize that the bilge pump is not designed for this. It's also intended to pass a lot of debris and so clearances might be greater than the need to develop higher pressure which is what I'm looking for. Also these modifications may shorten the life span of the pump but since it's only going to be used intermittently this isn't much of a concern at this point.

Apr 28, 2010, 07:48 AM
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This is the latest modification to a 500 GPH Johnson bilge pump.

While there may be some slight improvement it's just simpler to use a Rule 1100 GPH. Now that's not to say that a Rule couldn't be improved but at this stage I'm not ready to sacrifice a perfectly good Rule 1100.

The bigger problem is to find a compression space within the hull of the Nautilus. At the same time there needs to be enough room for all the internals. I have another hull that I can use to make a compression space. I think that the wheelhouse itself will have to be used as part of the compression area.

So at this point I'm finished experimenting with the bilge pump and I learned what I wanted to know, that it is possible to improve a pump but not without a lot of effort.

The next phase is critical because if the compression chamber is too small it won't work and if too large the other components won't fit.
Apr 28, 2010, 09:47 AM
Tom, I like way you think, and I was wondering if you may look to something more versatile in the form of a ballast container, other than that of a bottle, something that would have the flexability to expand into any open areas when filled with water and collapse when water is forced out, you may then be able to take full advantage of all the availabe space you have at hand within the hull. so long as it doesn't interfer with the pumps themselves. : ) Just a thought! Keep up the good work. Al,
Apr 28, 2010, 10:47 AM
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Hey Al, what's that they say about great minds thinking alike. A flexible bladder like a condom or bicycle inner tube could work. I would first lay down the bladder inflated within the Nautilus inverted so that the bladder would be just below the deck extending from the front to the skiff. Then I would put a layer of foam on top of that to seal it. The other alternative would be to put a layer of fiberglass about 3/4" from the deck creating a chamber.

At this point trying to weigh advantages/disadvantages?
Apr 30, 2010, 09:00 AM
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The following photos show the construction of the pressure chamber which is basically a deck below the top deck creating a space.

The chamber can hold almost 2 L as shown in the photos below and this includes the wheelhouse, it is short by about 350 ml.

The following photos show the pressure chamber. I will seal the hole in the top deck where the wheelhouse would go and see if it works. If I need to, the wheelhouse could be be added later.

The interior of the Nautilus still has room in it for the internals but unless I actually had these parts installed I can't be certain everything will fit, but this is still concept phase testing. I would not want to increase the size of the pressure chamber anymore than is seen in the picture as this is about the absolute limit.

If this doesn't work I can easily cut out the second deck used for the pressure chamber.

The next option would be to consider some type of flexible bladder which may take less space.

All that remains, is to install the plumbing into the pressure chamber and seal the top deck to see if the experiment works.

May 02, 2010, 04:27 PM
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In theory and concept it works. Practical application however is another matter. It was like the boy with his thumb in the Dyke. The pressure chamber kept springing leaks. One thing good about practical application and testing in a real environment is that important but less obvious pitfalls become apparent. Although I was able to get the experiment to work, some important shortcomings became apparent. These can be corrected. First making the pressure chamber absolutely watertight or airtight was a problem. I would patch one leak only to find another once pressure was applied. That was finally fixed. The second and more important correction is that the pressure chamber bottom deck is flat and this is more problematic than fixing leaks. If the sub were at an angle, air could be introduced to the inlet/outlet hose under pressure and exit the pressure chamber. When this happens the sub no longer regains buoyancy and would sink to the bottom. There would need to be some kind of sump which would always hold water no matter what the angle of the sub, nose up or down.
May 08, 2010, 06:24 AM
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The next phase of this experiment will involve some type of bladder. A compressible bladder with the consistency of a balloon or condom would be best.

For purposes of the experiment, the wheelhouse deck cover will be removed and a new cover made so that it can be removed for access to the pressure chamber so that a bladder can be installed. The current thinking is that a few inflated balloons or condoms will suffice, and then the cover would be secured with a few screws. The pressure chamber itself would no longer need to be perfectly airtight. However there should be no sharp edges to puncture a bladder, something I wasn't too concerned about in the first phase of this experiment.

In this way I can avoid the creation of a wet sump which would only take up more space in the Hull, and for the JetNautilus space is critical.

Again, if this works, then a more appropriate bladder can either be purchased or made. I never knew there was such a "market" for latex.

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