Poll: What is the best lifting gas for a personal blimp?

What is the best lifting gas for a personal blimp? Well, I start from the asumption that a good personal blimp is motorized. And since any motorized vehicle needs energy, my first choice is methane because it provides fair lift with the best volumetric energy density and reduced danger of fire due to a narrow flamibility range. It is possible to reduce blimp volume with methane by eliminating weight in the form of fuel and fuel tanks.

Variability in lift is also highly sought after which makes steam and hot air attractive. Steam suffers from issues with condensation inside the envelope, high temperatures, the need for insulation, leakage, and high energy requirements. Hot air is comparitivly simple but has pretty poor lift.

Helium is the standard but it is expencive, invariable, leaky, and requires additional fuel to operate.

Hydrogen is great for lift but is illegal in passenger airships, kinda leaky, low energy, easily ignited, and suffers from bad publicity in airships.

One side note, hydrogen may be variable lift when used with a reversable fuel cell... that could tilt the scale a bit.

Hydrogen inner core surrounded with helium outer jacket in case of unwanted hostile ground fire?

Quick-disconnect grade 8 bolts and a very good altimeter activated parachute for the crew pod if the above listed strategy fails.

This sounds like the perfect solution to me.

I wonder what the downside might be?

Jim

Helium leakage would be at the same rate as if it were a normal helium bag. If you want to reduce the danger of fire, you could use an outter bag of nitrogen that would be cheaper and easier.

  Hydrogen Rules! Not for passenger service of course, too much negative PR to overcome, but for cargo and personal use it is groovy. You can even make it at home. An electrolyzer will even produce pressurized H2 for no extra charge.
 
   But that's fine! A little dirigible has no business in the passenger business, it's too small to carry enough pigeons for a good profit margin. If you want income, give flying lessons in it or land some cargo gigs.

   I have read Van Treuren's book, Hindenburg/Hydrogen and he says the old Zeppelins would get struck by lighting many but never ignited because, naturally, the lightning followed the aluminum frames. Being electric, lightning doesn't want to go through insulating rubber bags. That's a "duh."

            Hydrogen in the bag won't burn, not enough oxygen percentage. It has to be leaking from its bag in just the right amount to get ignited in free air.

Its true that hydrogen can't burn without air, but hydrogen's flammability range is very wide. It is something like 5-95% in air. Methane has a much narrower range something like 5-15% in air.

You might want to read this article. It's from the 1920's!

It describes a potential commercial airship using hydrogen in a clever configuration to make it fireproof.

According to the article, you could have built it for only a million and a half dollars. Your cost may vary.

NnB

Indeed you can sequester a flammable gas inside a non-flammable gas and it will be less hazardous. This is reasonable approach to carry gaseous fuel, in my opinion. 

Hydrogen is the best. If you keep some tanks and balloonets on board, you can vary the lift (pump the Hydrogen inot the tanks while inflating the balloonets). Of course, if it's rigid you don't need the balloonets...

If it escapes, it will escape upwards, so you're fine as long as your gondola is on the bottom.

I think pumping lifting gas into holding tanks is not feasible due to many factors including the weight of the tanks and the pumping machinery. These would have to be large and very light to make it worthwhile. If they could double as fuel tanks it might work. In fact, if you were to use propane as fuel, you could inflate a secondary bladder with propane and recompress it into a liquid (at something like 60 atmospheres). When the bladder fills, air will be pushed out of the balloonettes and will reduce weight. When the bladder is emptied, air will be drawn into the balloonettes and the weight will increase.

Or, you could use the same principal for boiling and condensing a phase change material. I have run numbers with water in the past and the energy requirements were too high in my opinion. 

You could also use hot air instead of a phase change material.

Or you could use aerodynamic lift, which is my choice.

     On a theoretical or fantasy story level, hydrogen is great. You can make hydrogen on the fly from rainwater with power from solar cells. From what I'm reading about hho, salt water may be a good candidate too, maybe even better than rainwater because it is more conductive. I think you need to be careful, though, chlorine just might come out too.
     A hydrogen generator is not a heavy device, and it would be good to be able to make up for loss thru leakage. In one of my blurbs I mentioned a hybrid airship, sounds very modern. Like the cars, the drive would be electric, with batteries charged by solar cells. The solar cells could also make hydrogen for lift or fuel for a hydrogen burning generator. A real sci-fi story there if ever I heard of one. I love the way a hybrid can be propelled by either the combustion or the electric drive, if I have understood the design.
     If helium could be added to the hydrogen on a regular basis, maybe the flammability could be reduced to a tolerable level. Are there any other light non-flammable gases that could help with this problem?
     While we're talking theory--- if you over charge a wet cell battery, you make hydrogen. I know lithium ion batteries are the best, but just for a story line.....you have wet cells and they store power for the motor and make hydrogen to boot!  Just add water and overcharge the batteries.
     I saw the batteries in a submersible, they were submerged in some oil so they had no air in them so they would not be affected by depth, I presume. There was a vent tube from the top of the container to collect charging gasses. Don't know where the tube went.

Actually, pressure tanks and equipment do not have to be heavy!
I have seen the pressure tanks on the Varialift proof of concept vehicle and they are large and lightweight due to their thinwall construction.
That means they can hold a lot of low pressure gas but cannot contain high pressure gas and that is OK for the purpose of buoyancy control.
The second advantage of low pressure storage is that the compressors only have to slightly compress the gas and don't have to be heavy duty models, only high volume models, similar to a turbine fan.

<< If helium could be added to the hydrogen on a regular basis, maybe the flammability could be reduced to a tolerable level.>>
  Good question. Any chemistry majors out there with the answer?
   The concentration of helium would have to be less than 20% to not defeat the purpose of having an inexpensive lift gas.
   Nitrogen is inert and might also be used to dilute hydrogen lift gas. Nitrogen has neutral weight in air which is 85% nitrogen already. Maybe its filler/buffer action on burning hydrogen molecules would moderate the flame to a low and slow burn which wouldn't be as dangerous as a rapid conflagration.

<<<Hydrogen inner core surrounded with helium outer jacket>>>
    This would help H2 safety fears a lot. It would work well if someone could figure out how to do it cheaply. Any ideas?

    We are talking about personal skyboats on this website and that means cheap skyboats. Just imagine a hot air balloon encased in another balloon. You automatically double the weight and the price and the necessary volume of lift gas. Not good. It would never catch on for personal recreational use.
  The answer is to ignore the people with hydro-phobia and build something that flies. Go to another country which isn't paralyzed with hydro-phobia, if need be. Personal skyboats will not happen without the employment of safe clean renewable HYDROGEN.
high cheers from the Nav

Another question is what combination of lifting gas, fuel, and engine is best. I think this is important to discuss because the choice of lifting gas closes some fuel/engine options and opens others.

Examples: 

hydrogen, hydrogen, fuel cell

helium, gasoline, IC engine

methane, methane, IC engine

helium, battery/solar, electric

hot air, etc
    

I'm very flexible on this subject, will go with the flow. I think most people will not want flammable lifting gas. It will be interesting to see how many are interested in it, though. Don't forget hybrid drive. It's very modern an politically correct. To attract interest, practicality and cost of construction will be as important as anything.

     Is that a picture of the Varialift unit? Don't think I've heard about it, will google. I did send an email to somebody wanting to build a ship to supply the Alaska oil projects. Four motors, like Paisecki, gyro hell.
     As far as the hydrogen cell idea, great. Cheap weather balloons full of hydrogen inside a sealed rigid ship with helium or some other safe gas taking up the space between them. Makes for some interesting options.

I think hydrogen and helium are too expensive and leak easily.
Hot air and steam require power.
I think methane is the best option for very small airships. It is cheap enough and does require high quality envelope to prevent leakage like hydrogen and helium.
I know methane is flammable but what could ignite it?

I pretty much agree with you. I'm not sure how the price of hydrogen compares to methane but both are cheaper than helium. Methane is a large molecule so it doesn't move through the envelope as easily.

Another issue with methane is the range of mixtures under which it can ignite. While hydrogen can ignite with almost any air to fuel ratio, methane's range is much narrower and therefore much more difficult to ignite. That is a positive mark for safety. 

Mikek, I had considered a series hybrid drive system for my design (as you know). But, there isn't as much benefit in a hybrid system for an aircraft because there is no need for regenerative braking. But there are possibly other benefits like centralizing the generator's weight, ect.

How does methane compare to the others for lift?
The hybrid idea is for the cruiser model, not the prototype. I would want solar power for the cruiser, costs plenty, but you'll have power all day. Light batteries don't hardly exist, seeing some progress in new age capacitors, you never know. The whole ship could be a large capacitor, wouldn't that be wild. The combustion motor would just be a backup in case something went wrong, handy as a gas compressor, etc.
As far as regeneration, imagine the ship tacking down the ocean on a cloudy day, dragging the 'chein-de-mer'(Rousson's device for sailing an airship) and having the props driven by the passing air. Maybe it wouldn't be enough air to use for generating power, don't know.