hot air dirigible design (or you could use helium if you like to spend money)

Here is my latest creation, a 16 pound airframe of a duodecahedron. It is strong enough to support itself, even with one panel missing ( this is to show interior). The total weight is less than the 2 bricks in front of it!

I am unsure whether you understand how important this structure is. If this structure was twice as big, it would float with helium balloons inside. This would then be a dirigible with the lightest weight possible.

This design is scalable. The length of the sides are approximately 30 inches, with an  approximate radius of 30 inches. The materials cost is approximately $20.

To increase the length of the sides to 20 feet would cost $80 - $100,  the fabric would be approximately another $100. The weight would be around 120 pounds, and the lift for hot alone  would be around 250 pounds. If you substitute helium for all of the hot air, you could increase the lift to 500 pounds. 

Unless I am missing something, this is exactly what you are looking for.

Michael

Anytime you put spherical objects in a non-spherical object you have wasted void space. This makes the outside shell bigger for the same amount of lift, which increases drag, which increases engine weight, which increases the structrual weight to hold those engines.

The reason for using platonic solids ( dodecahedrons, icosahedrons....) is a large shell can be assembled from fundamental shaped parts( triangles, pentagons...).

I have not in ten years been able to find aerodynamic drag data for platonic solids except for building structures attached to the ground which is not the same as what you would use on a flight vehicle.

Nice work Michael. I was just now wondering what became of your design but it looks like it has been well-developed.!

   Would love to see a drawing and a walk-around video view of it.  Or even just some details like, does it have spars between the pentagons?  Or just the shapes to give it stiffness.?

  Congrats, very novel!

Can you take a pix inside the duodecahedron?

I will do my best to get a walk around and post it for you to see. There are no spars to support the structure, so it is all open space inside.

When I make the real dirigible, I am thinking of having a center pole running from stem to stern. I will hang the gondola off of what will be called ( the pole) the keel of the ship. All the nodes will be attached by guy wires to the keel. This should make the structure extremely stable against sudden movements of the wind, etc.

Of course you understand that several of these domes can be wired together to create a cigar like shape, like the Zeppelin. The stability of the whole system increases dramatically when this is done.

How does this magic happen? It turns out that this structure is a disguised tension structure, and the strength of the dome comes from the tension that the shell fabric takes. The struts really only have to resist compressive forces.

In conjunction with the design of a personal dirigible, I want to make a hot air dirigible that could be used as a spy platform that floats at 100,000 feet, with the only fuel as sunlight. If I can get a contract for that, that will pay for the development of the personal dirigible.

Hi Swampie

Yes, you do increase the drag with a duodecahedron, compared to a sphere, for instance. There are always design trade offs. One way to minimize the drag, when you connect two or more structures together, is to stretch fabric between the outside edges of the structure, making the structure have less drag, and more cigar shaped. The extra weight from adding this fabric is more than made up by the extra lift captured by enclosing the space. Also, the insulation provided by the  fabric will become important for lowering the fuel cost to keep the structure aloft. 

Back in 2005, I made this POV-RAY model of a 3 three frequency icosas attached together at the pentagonal planes. The goofy colors give a little more structure contrast. I also have modeled 4 frequency single ellipsoids ( also shown)

As the Icosa frequency goes up, the ability to make a large ship out of standard size parts expands.

The first link is probably the better one.

I have posted the link again, just in case.

Hi Swampie

Yes, you can use smaller triangles, but then the cost of labor, materials, and then the  weight also goes up You have a stronger structure than the duodecahedron, to be sure. But I think there is another way to increase the strength, without adding so much weight. I am just waiting to see if all participants are ready for that.

Right now, I am thinking of constructing a pentagon that is 10 feet length of the side, 20 feet, or even 30 foot. I could certainly have the 10 foot pentagon ready by this weekend. Doing this will illustrate the ease of constructing the dirigible. You only have to assemble 12 of these to make an enclosed space. If you want to make a hanger, it will take 6 full sections at 30 feet and 4 half's to make a hanger with a single opening that has a diameter of 60 feet and an opening that will accommodate 20 feet diameter by 40 feet long  dirigibles.

How do you get a 20 to 30 foot span out of the standard sizes available at your local hardware store?

Is  this  geodome   the actual  envelope  that  the lift gas fills ?  Or is  there  a bladder  that  goes inside   it? 
 If  its  the  envelope itself ,  How  do  you  displace  all  the air   to  fill  all the volume with  lift gas ?

Kewell, Michael!
   I can see two of these mated together with the stern-most pentagon changed into a tapered five-sided cone to reduce the drag vacuum.
   If they were covered in marine 4 mil shrink wrap, the tightness of the covering would add firmness to the frame.
   Ideally, I think the shrink wrapping may go faster, but more comlex to figure out, if it were done over the whole assembly after it was assembled rather than pentagon by pentagon.  Any thoughts here?
Seems very lightweight and efficient to build.
    The strut connectors are they still paper plates or have you devised a firmer fitting?

Let me answer the previous 3 posts here.

I am thinking of using emt (which is electrical conduit) and lashing the pipes together (a type of lamination).I will demonstrate in the next pentagon so you can see the technique.

I haver actually thought of this issue very seriously and have several thoughts that came out of those studies.

1. For a personal dirigible the cheapest and easiest solution is to have hot air that is heated inside the envelop without any interior bags. If you are using the jet motor for propulsion, put a heat exchanger around or in the exhaust plume to heat the air for the envelop.

The lift gas is the hot air from the heat source, either jet engine or a standard balloon heater. They both run on propane. So as the hot air rises, it will displace the cool air outside the structure.

The reason for the  single fabric shell is because of the weight that counts for ultralight definition. Also, the propane cost for a flight and heating the air may just be $30 for 300 miles. The helium for a weekend flight will be much more than that.

2. For a cargo lifter, a much larger ship, having helium to displace just slightly less than the weight of the craft is ideal. Then you can load the airship just like a c-17. Once loaded, you heat the airspace inside the shell to carry the load, and away you go. When you arrive at the destination, you lower and land by blowing cool air into the airspace. Then you unload. To leave, you just heat the airspace a little to have lift. Away you go. No muss. No fuss. All you need is a small crew to run the ship, none to load or unload.

Because you are using the cargo lifter every day, replenishing the helium makes sense and cents. There is a measure of safety that the cargo lifter will now have, the ability to stay aloft if something happens to heater and/or propulsion. You just open a valve from the reserve to stay aloft Load management will be better and more predictable.

Once you have your double duodecahedron hooked together, you would add a long 5 strut tail to reduce drag in the back and another one that was shorter in the front. Wrapping them with material will give the aerodynamic shape you are looking for.

As for wrapping the shrink wrap after the structure was made, I did that with little success. The wind proceeded to break the sticks before the shrink wrap would conform.

I would still do the shrink wrap on the pentagons before they were assembled together. The shrink-wrapping is a real skill, and the plastic does not want to go around corners easily.

The strut connectors are different from the paper plates and foam that I used before. They will be different again in the next iteration. Thinking about these structures that come together under tension has been a real learning  experience.

Have you done an initial SWAPc ( Size,Weight & Power,cost) estimate? If you go hot air the dodecahedrons ain't going to be small. Dude and I have offered example spreadsheets as examples on how to do this in other threads.

That's the problem with new technology. People still look at the new with old perceptions and old tools.

I have a video showing that I cam make a 10 foot square emt cube for $36. For another $100  I could cover it with plastic and reinforcements, and it would withstand a hurricane. I would just have to make sure there was enough weight to keep it from blowing away.

That's $1.36 per square foot. What other construction method can compare with that?

Similarly, if I can show you a construction method for a dirigible, that takes at most 5 working days to assemble all the pre-made parts into a working dirigible ( gondola, cigar shaped dirigible, motor attached and working, etc. - so it can take off and land), that takes a crew of 5 people to assemble, how can anything else compare to that?

Who cares if the diameter of the dirigible assembled is 80 feet across? 

I guess the best thing to do is make a video showing how a smaller half dirigible with 5 feet structural members can be assembled in a hour or less.

That would help.

The laws of physics don't change no matter how good your idea is.

I think such a system is most suitable as a hangar. I prefer non-rigid airships over rigid airships on the scale we are working at. 

And what laws of physics are those?

And why do you think a  no rigid is better?

Here is you r opportunity to explain what you mean.

I ( Swampie777) think rigid is best for safety and performance reasons. My questions stemmed from being curious about a problem I'd encountered in my design. EMT comes in 10 foot lengths. On low frequency designs, as you span larger volumes, it is easy to out run the 10 foot rib length. ( here I'm calling a rib the length from vertex to vertex.)

Additionally, if I make an ICOSA shell ( which I have primarily worked with) one of the triangle facets or a group of 5 facets will be at the top of the structure( depending on shell orientation with respect to gravity).  So my blob of hydrogen will be pushing up against a top facet or a group of 5 facets. In your case it would be a top pentagon or a group of three pentagons. As these facets get larger, the push against it transfers the load to the ribs. So from a structures standpoint, I may either rip a facet or collapse a rib. These things don't have infinite strength, so I must design them to carry realistic loads safely.

The benefits of rigidity manifest with greater size. The thickness of the envelope material increase as airship size increases. This is because pressure increases with size. At very large sizes, it is lighter to use a framed airship and minimize the envelope thickness (and weight).

But on the small scale, we can't go thinner on the envelope material. If we did, it would be damaged too easily from normal wear. So since we have to have a thick envelope anyway, we just use that (thick is relative of course). At this size, a structure would be overkill. Just my opinion, but I think my book at home says pretty much the same thing.