Hydrogen and Helium in Rigid Airship Operations

The two primary lifting gases used by dirigible airships have been hydrogen and helium.

Hydrogen is the earth’s lightest element and can be manufactured easily and inexpensively, but hydrogen’s extreme flammability makes it unacceptable for manned airship operations.  (In addition to the obvious example of the Hindenburg disaster, dozens of hydrogen-inflated airships were destroyed by accidental fires before hydrogen was finally abandoned as a lifting gas in the 1930s.)

Helium is a relatively rare and expensive natural resource, and because helium is heavier than hydrogen it can reduce a rigid airship’s useful payload by more than half, but helium’s inert non-flammable nature makes it the only practical lifting gas for manned lighter-than-air flight.

Hydrogen and Helium:  The Basics

Hydrogen and Helium are the two lightest elements on the periodic table:

Hydrogen
Atomic symbol: H (as a gas, H2)
Atomic number: 1
Atomic weight: 1.007
Helium
Atomic symbol: He
Atomic number: 2
Atomic weight: 4.002

The atomic weight of a hydrogen atom is approximately 1/4 that of a helium atom, but since hydrogen as a gas exists only as a diatomic molecule (containing two hydrogen atoms) hydrogen gas is approximately 1/2 the weight of helium gas.

The Relative Lifting Ability of Hydrogen and Helium

Although helium weighs twice as much hydrogen, each gas is so much lighter than the air surrounding an airship that helium theoretically provides about 93% of hydrogen’s lift:

Relative lifting ability of 100% Hydrogen vs. Helium
60° F, Barometric Pressure 29.92″ Hg

Weight of Lifting Gas
(per 1,000 cu. ft.)
Weight of Air
(per 1,000 cu. ft.)
Net Lift
(per 1,000 cu. ft.)
Hydrogen 5.31 lbs 76.36 lbs 71.05 lbs
Helium 10.54 lbs 76.36 lbs 65.82 lbs

The actual lifting ability of both hydrogen and helium varies with temperature, pressure, and humidity, and in practical operation it is impossible to achieve or maintain 100% purity of either gas, giving helium about 88% of the lift of hydrogen in actual application.  To take account of varying atmospheric conditions and gas impurities, airship designers often conservatively estimated helium’s lift at 60 lbs per 1,000 cubic feet and hydrogen’s lift at 68 lbs per 1,000 cubic feet.

The Effect of Helium on Airship Range and Payload

Because so much of a dirigible’s weight is fixed (in the form of the ship’s structure and engines, called “dead weight,” and required payload, such as crew and ballast) a helium-inflated airship has a much lower useful payload and considerably less range (because it can carry less fuel) than a hydrogen-inflated airship of the same size.  For example, when the German-built LZ-126 was delivered to the United States it was inflated with hydrogen, and the ship flew from Friedrichshafen, Germany to Lakehurst, New Jersey nonstop; when the United States Navy operated the same ship with helium (as U.S.S. Los Angeles) its range was limited to 3,925 statute miles and it could not have made the same flight.

The following chart illustrates the dramatic reduction in payload from the use of helium versus hydrogen. (The information is based on Hindenburg’s Flight No. 10, from Rio de Janeiro to Friedrichshafen on April 6, 1936, as reported by U.S. Navy Lt. Cdr. Scott E. Peck.)

LZ-129 Hindenburg kg lbs
Dead weight 118,000 260,145
Crew 5,400 11,905
Provisions 3,000 6,614
Fuel 58,880 129,808
Oil 4,000 8,818
Ballast 7,950 17,527
Misc. 9,120 20,106
206,350 454,924
Gross lift/hydrogen (68lbs/1,000 cu. ft.) 215,910 476,000
Payload for passengers, mail, freight w/ hydrogen 9,560 21,076
Gross lift/helium  (60lbs/1,000 cu. ft.) 190,509 420,000
Payload for passengers, mail, freight w/ helium -15,841 -34,924

Operational Considerations

Operational considerations further decrease the useful payload of a helium-inflated airship.  As an airship rises, its lifting gas expands; an airship that begins a flight with its gas cells fully inflated must therefore release gas as it climbs to keep the cells from bursting.  Because hydrogen is easy to manufacture and inexpensive to buy, hydrogen airships often began flights fully inflated to maximize payload and released hydrogen as they climbed.  But since helium has always been a rare and expensive gas, helium airships began their flights at only 90-95% inflation, thus reducing payload, to allow their gas cells to expand without releasing helium.  In addition, hydrogen airships compensated for fuel burned during flight simply by releasing hydrogen; helium-inflated ships, on the other hand, required heavy water-recovery apparatus (to recover water ballast from engine exhaust), which further reduced the useful payload available for fuel, passengers, and freight.

(Helium blimps do not need to vent helium to maintain equilibrium; they employ internal ballonets, or air sacs, which can be inflated or deflated to maintain the blimp’s shape and buoyancy.)

While the use of helium therefore presented operational challenges, airships of sufficient size were able to operate effectively when inflated with helium.  LZ-129 Hindenburg was specifically designed to operate with helium and could easily have conducted transatlantic operations with helium as a lifting gas, and the United States Navy’s rigid airships were also able to fulfill their missions with helium; U.S.S. Akron and U.S.S. Macon were even able to serve as airborne aircraft carriers, carrying embarked fixed-wing aircraft, using the heavier gas.

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    { 60 comments… read them below or add one }

    N7Nco March 30, 2014 at 2:05 am

    Does anyone know how one would go about getting the FAA to allow a hydrogen airship for advertising or passenger use? There is almost no information provided on the regulation of its use.

    Reply

    Andy Leary March 12, 2014 at 3:57 pm

    I have stated in an earlier comment the idea of surrounding the Hydrogen-filled gas cells with another gas cell filled with Nitrogen, since it is not explosively reactive as Oxygen is with Hydrogen. Well, I would like to reshape my vision: instead of using another gas cell to surround the Hydrogen gas cell with Nitrogen, why not just fill the entire envelope with Nitrogen instead of air?

    Nitrogen, after all, is slightly lighter than air (which is a mixture of mostly Nitrogen and Oxygen), so it would function as a lifting gas, providing even more lift than the Hydrogen could on it’s own (perhaps a few extra 100 lbs worth of passengers and cargo!)

    And since Nitrogen is not very reactive with Hydrogen (although they do naturally combine together to form Ammonia, they require high heat and/or high pressure to produce significant amounts), the Hydrogen would need to pass through not only it’s gas cell but through the immense volume of the envelope filled with Nitrogen and then through the envelope itself to reach the oxygen in the air for any kind of combustive reaction to occur (essentially, you’d need a maniac wielding a chainsaw, a flamethrower, and an Oxygen mask to have any sort of chance to have a Hindenburg-sized inferno). Plus, it would keep nosy trouble-makers from easily accessing the hydrogen cells, since they would be require to wear breathing mask attached to an canister of Oxygen to enter the Oxygen-deprived environment of the Nitrogen-filled envelope (or else they would suffocate within several minutes).

    Finally, there is the inevitable problem of Oxygen diffusing back through the skin of the envelope from the Oxygen-rich air into the Oxygen-deprived envelope: how to get rid of it? Well, just turn on a simple little Nitrogen generator (i.e. an air pump attached to a Nitrogen-permeable membrane) and it will filter out at the very least 95% of any Oxygen that has managed to re-enter into the envelope.

    So, that’s what I think it would take to make hydrogen safe enough to change the public’s opinion on hydrogen-filled airships and perhaps provide the support needed for the rebirth of the industry of airships.

    Reply

    David December 20, 2013 at 5:07 pm

    One advantage of hydrogen is it is a fuel, and also can be created from fuel or water.

    So you can burn hydrogen in engine when going up to lower air pressure. Also when you need to come down you can burn it and replace with something else.

    Your diesel engine produces co2 and water… water can be turned into hydrogen again with help of electrical power, water can be separated from exhaust using heat exchangers, etc.

    If you could reduce the oxygen content in exhaust enough, you could dump the non water components into same bladder as hydrogen gas when you want airship to go down… it is possible to separate later (takes energy of course) because hydrogen gas molecules are so much smaller than everything else. Probably simpler to use other bladder.

    Obviously you would want a layer of something like helium on outside for safety reasons.

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    Stu February 18, 2014 at 8:54 pm

    Gaseous fuel was only explored with the Graf Zeppelin which was a duel-fueled aircraft. Her engines burned blau gas stored in many gas cells located in the lower third of the airship’s hull. There were also gasoline tanks that fed the engines. The gaseous fuel when burned left little if any change in the static condition of the airship.

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    david March 3, 2014 at 10:49 pm

    Back then they didn’t have hydrogen fuel cells, as much research into Hydrogen fuel enhancement of diesel engines, computers to control combustion mixtures, etc.

    So 80 years later may be much easier to plumb in hydrogen as fuel rather than just vent it.

    Reply

    Stu April 7, 2014 at 5:03 pm

    Hydrogen would be a lovely fuel for internal combustion engines although I would reserve judgement until testing in aircraft applications was done. It burns super clean and produces a useful exhaust – water! Containing it in tanks would have to be weighed against the energy output of an equivalent amount of liquid fuel at about 8 pounds a gallon. Hydrogen storage flasks would be of heavier grade than a liquid storage tank and thus weigh more. Question is, does the potential energy of a tankful of compressed hydrogen compare favorably to the same total tank weight of a tank full of aviation gasoline? For that, hopefully someone in the know can enlighten us.

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    Francisco Carvallo October 24, 2013 at 5:20 pm
    Ahksehl June 26, 2013 at 6:20 pm

    A page on the Aeroscraft says that it takes on air to become heavier than air and expels it to become lighter than air. I think they have bladders INSIDE the helium bladders that are inflated and deflated with air by pumps. IT would not need to release helium if the bladders holding it stop expanding at a certain point and are strong enough to withstand internal pressure without rupturing. As it filled the air bladders INSIDE the helium bladder, the pressure in the helium bladder would become greater as the helium was compressed. As long as the materials can handle this then it is a good solution.

    Reply

    Ahksehl June 26, 2013 at 5:13 pm

    The aeroscraft airship design uses helium bladders that are expanded and contracted
    by mechanical means. There is speculation that they uses pumps to compress the helium and deflate the bladders. There could also be a mechanical means to do this other than pumps. If one googles expandable water bottles then perhaps some of those shapes could be used. The accordion style bottle could be a solution, also a kind of giant toothpaste tube with a roller at the bottom that would flatten it out could also be used. To deflate the tube, you simply roll it around the roller. With an accordion style device there could be hard sides attached to rings, with a silicone gasket to seal it.

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    Ahksehl June 26, 2013 at 2:25 pm

    The latest development in airships has been designing ones that are slightly heavier than air. They use vectored thrusters and a lifting shape to the body to get airborne and remain airborne. They combine the lifting capabilities of winged vehicles and lighter than air craft. Not all of the lift must come from the gases alone. Having a vehicle that is heavier than air actually benefits it in improving ground handling.

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    Ahksehl June 26, 2013 at 1:47 pm

    I have a question in regards to addressing the problem of releasing the lifting gas to prevent the gas bladders from expanding to the point of bursting. Would it not be possible to have several bladders attached to a main bladder so that when the main bladder reached a certain size the gas was allowed to inflate the “satellite” bladders?Then, as the ship descends, the gas could be pumped from those satellite bladders back into the main bladder. Perhaps the satellite bladders could be squeezed empty with a device that is similar to the “expandable toy” that we have seen on the market.

    Reply

    Paul Flaherty June 22, 2013 at 11:39 am

    I am not a scientist, but am a mechanical engineer. In thinking about the premise that combustible gases will not ignite without being in the presence of a sufficient amount of oxygen , has anyone ever thought about using hydrogen gas cells totally enclosed by a larger protective helium gas cell? This, in effect, would be a hydrogen balloon inside a larger helium balloon.

    Reply

    Dan June 24, 2013 at 12:24 pm

    That idea was actually proposed for LZ-129 and preliminary tests were conducted.

    Reply

    Stan May 28, 2013 at 2:40 pm

    This is an old idea no one has been able to pull off— yet. But still worth keeping in mind for a day when materials technology makes it feasible. Lifting gases simply require low molecular weight. Of those that are cheap and non-flammable and non-toxic, there really is only one: hydrogen oxide, also known as common WATER. Can it fly? Does every day, just go outside and look up, chances are you will see millions of tons of water floating by quietly and safely. Of course, it has no envelope and payload, those are the harder parts. Clouds do it at atmospheric temperature, but to pull any weight it would have to be kept above the boiling point at the pressure height involved. To last any useful time the envelope would have to be well insulated, and that’s where the technology needs to focus (besides getting and keeping it hot). One would assume that getting it hot would be done on the ground, as the fuel required would be rather serious (water has very high heat capacity), so insulating well would minimize energy to keep it hot. Lift regulation by temperature variation would take energy to reheat, but gaseous water doesn’t have such a high heat capacity (it’s the liquid-gas transition that takes most of it). Main problem here is injecting heat into a gas; exchange surface area must be large (heavy?) or high-speed (blowing the gas through a very hot tube). Which brings up the corrosive nature of steam (against metals mostly). So nothing is ideal. One could also explore a mix of H2O and H2 or He; at what mixture is flammability reduced to acceptable levels, or is it? Would steam with hydrogen in it be less corrosive?
    Things to thing about.

    Reply

    Justin April 15, 2013 at 2:07 am

    Been studying airships for a long time a

    I have notice Helium is a no go for airships for the simple fact that now were are at a shortage of helium. So it must be Hydrogen. Here the solution i have been thinking up. Why not a solid gas cell? It could be lighter than rubber storage and stronger (ie. less likely to puncher or be damaged). Solar is now cheaper and weights less than fuel and inter-combustion motors.

    Reply

    Greg N February 14, 2013 at 5:49 pm

    Like New tech, with insurances, H will arrive.. Like the space program a restricted travel corridors, one time passage airspace, chase plane, and a “dirigible ejection system” will bring hydrogen to the top.. No pun intended. GNiSB

    Reply

    Erkko January 30, 2013 at 3:17 pm

    One simple way of solving the ballast problem without making the system too complex is to simply cool down the exhaust fumes from the engine to the point that all the water in it condenses down. You don’t have to fiddle with complex triple layer gas bladders and fine tuning the fuel used.

    The oxygen you pick up from the air is rather heavy, so the amount of water that comes out of the tailpipe is actually heavier than the fuel that went into the engine. Especially if you use hydrogen rich fuels like methane. You toss the extra water overboard and maintain constant weight in flight.

    The bigger problem is when you drop the cargo, because you have to replace it with an equal amount of weight, at the same time, or the balloon will just shoot up from the landing pad. I don’t think you can squeeze the gas bladders enough to change the buyoancy that much, so you either have to compress the lifting gas into a tank, or load up water which may or may not be available at the site.

    Reply

    Tristan February 23, 2013 at 5:41 pm

    Balancing fuels, even between radically different fuels like natural gas and Diesel oil, is actually a lot less difficult than it might sound. Here is a link to a site marketing such engines:
    http://www.dualfuel.org/dual-fuel-engines/

    As for condensing water from the exhaust, see the main page, “Operational Considerations” section, near the bottom of the first paragraph: “helium-inflated ships … required heavy water-recovery apparatus (to recover water ballast from engine exhaust) which … reduced the useful payload.”

    A dual-fuel engine may be more complicated than straight Diesel, but it will NOT be all that much heavier than the standard engine the airship will need anyway. And methane is usually cheaper per kiloJoule than Diesel, so the combination saves money on operating costs.

    Triple-layer gas cells . . . yeah, I admit that will be tricky. But this site’s “Hindenburg Technology” page describes two-layer cells (hydrogen core, helium outer layer) that the Zeppelin designers expected to be able to build and work with even at their 1930s technology level. Surely things have advanced enough since then to make the idea feasible.

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    Robert N January 6, 2013 at 8:26 am

    ? I have asked this of several Aeronautic Engineers and they get kind of cross eyed and say I am goofy. Why cannot Airships be manufactured in a honeycomb of materials and pull a vacuum to the structure?

    If neutral buoyancy could be achieved in this manner then there would be no need for other gases to maintain lift.

    Reply

    Tristan January 19, 2013 at 11:40 am

    A commenter farther down this page by the name of Nigel has already suggested the vacuum tank concept. I explained there why it wouldn’t work, but apparently it bears repeating.

    The reason is atmospheric pressure. Atmospheric pressure varies somewhat depending on the weather, but the pressure at sea level is generally quoted as 101.3 kPa = 101,300 N/m2. Dividing this by the acceleration of gravity at Earth’s surface (which varies slightly with latitude, but is generally quoted as 9.81 m/s2) tells us that each square meter of balloon surface must withstand force equivalent to the weight of 10,326 kg. This is not a problem in a normal balloon, because the gases inside exert an equal outward pressure which cancels out the air pressure. On the other hand, a vacuum tank, by definition, does not have gas inside to counteract atmospheric pressure, and therefore must withstand this force with only rigid structural strength.

    Some math: I will assume a spherical balloon 30 m (about 100 ft) in diameter. This gives a volume near 14,137 cubic meters (m3). The standard density of air (sea level pressure, temp 20 C) is about 1.2 kg/m3, so this balloon displaces 16,964 kg of air. Helium under these same conditions has a density near 0.166 kg/m3, for a total mass of 2353 kg. This balloon has a surface area near 2827 square meters (m2). An arbitrary guess of .25 kg/m2 for the balloon skin gives 707 kg. The balloon has an overall mass of 3060 kg (1.08 kg/m2), and a useful lift of 11077 kg. To surpass this, a vacuum tank must somehow withstand atmospheric pressure (total mass-equivalent over the whole balloon surface is 29,191,602 kg) while somehow using less than 1.08 kg of material per square meter of surface area.

    And it gets worse: air pressure, and therefore density, decreases at higher altitude: a given volume of gas (or, in this case, vacuum tank) will provide less lift. An airship lifted by hydrogen or helium will find that the reduced pressure also causes its lifting gas to expand, so it can simply allow it to do so; the identical change in pressure means an identical ratio of expansion, so a given mass of lifting gas is still displacing the same mass of air as at lower altitude and providing the same amount of lift. A vacuum tank does not share this feature: its lift is greatest on the ground and progressively less with increasing altitude.

    Other obvious issues of vacuum lift:
    1. Since the vacuum tank must continuously withstand a tremendous amount of force from the air around it, it is likely to be prone to spectacular failure. Hydrogen, even with the fire hazard, would be much safer.
    2. With no pressure of any kind in the tank, even the slightest leak will allow air to come in, which will rapidly compromise buoyancy. Hydrogen has its own issues with leaks, but vacuum is a lot worse.

    Reply

    Terra November 26, 2012 at 1:22 pm

    I just recently became interested in airships and i happened across this site. There are a lot of really good comments and ideas floating around here. But I was just wondering if any of you have actually made one. I was thinking maybe a small design able to hold 1-5 people at the most. My brother and I were throwing this thought around and wondered if it was possible to do this with a small boat or something along the lines.

    Reply

    Brennan June 27, 2013 at 2:00 pm

    The problem with anything small is that the volume and hence lift increases with the cube of the radius, so small radii cannot lift very much.

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    Mike Dinsdale November 7, 2012 at 2:37 am

    In the design of the Trimorphic Disc Sail the issue of the expansion of the lifting gas be it helium or hydrogen is compensated for by the expansion of twelve segmented gas ballonets interconnected by hoses and small valves within a ring mesh array able to expand. This innovation was an important breakthrough factor to increase the marketability and saleability of the craft to the inexperienced masses and to encourage to widespread use of the Trimorph Craft worldwide. This is especially important where the craft will be used mainly in remote areas such as the Amazon Jungle, The Gobi Dessert, Remote Islands, High rise buildings, Himalayas, Everglades Swamps, African Savannah, Australian Outback, Swiss Alps etc. All of these places as you will have noted do not have helium on tap. Therefore in order to increase the range of use of Trimorph a means to safely allow the generation of hydrogen from water using electricity via a simple hydrogen-oxygen water catalyst was required and a design by which the pilot any passengers and the surrounding area above and below could be rendered safe from an explosion of hydrogen gas should such ever occur. With the electric water catalyst enabling hydrogen gas to be used as the lifting medium rather than helium which cannot be found in many parts of the world let alone remote areas there was a need to protect the pilot and those on the ground in the event of an explosion. Due to the design and use of 12 interconnected flame retardant segmented gas ballonets such a blow out would be very very difficult to cause in the first place. The other key safety innovation being that the upper ring mesh arrangement is supported by a larger diameter thin walled carbon fibre under-shroud disc which at it centre is connected to the motor spindle fitted into the bracket atop the flexible spar. The main advantage is the hydrogen in the ballonets can be slightly pressurised to create a firm occluded dimpling effect over the curved hemisphere of the inflated discs. This is caused via the plastic membrane of the ballonets and ripstop outer covering pushing through the carbon fibre rings connected by rubber fasteners. It should also be noted the volume of gas in the dimpled disc’s is somewhat greater in volume for the physical size of the diameter of the disc if it where smooth. As altitude is gained and the mesh expands the dimples become smaller and the surface resistance to the surrounding air lessened allowing very fast flight with little effort due to greatly reduced air resistance of the rotating discs as would be the case with normal winged craft. Be it noted the craft now at height can glide at a very fast and aerodynamically efficient rate over huge distances for a very small amount of thrust energy input from the electric motors plus gravity assist. Hydrogen can be vented to reduce the buoyancy rate of the craft to either positive or negative remembering the rate of climb or decent can be controlled by the speed of rotating of the discs. To attain lift-off the three disc are pressurised with gas before being rotated by three individual lightweight 500 watt electric motors affixed atop the flexible carbon fibre spars. The slow rotation of the disc causes air to move from the smooth carbon fiber centre apex point radially outwards over the circumference edge flowing to the underside whereupon after a short interval creates a large vortex and partial vacuum pressure differential over the upper hemisphere and a powerful vortex thrust from underneath pushing downwards pushing the underside of the discs and the craft skyward. The three vortexes generated via this process combine to create a stable triple vortex type torrent in three directions around the whole triangular area of the craft whilst the gyroscopic torque of the three rotating discs permits stability over the centre of gravity making the whole vertical lift off process very stable and inherently safe even in strong cross winds. Thus the craft can hover quietly in one spot for long periods. Ideal for fishing hunting or photography work. Great for pruning and harvesting tree tops etc. Very safe for inner city and high rise to high rise use even in strong winds. Don’t forget it one hits anything the craft will bounce off it. Very difficult to have a fatal accident on. Once the craft has attained lift-off forward thrust may then be engaged from either a single motor at the back or via the twin electric motors model with small propellers mounted either side of the pilot. The small front winglets and main stubby overhead vector wing are angled downwards to allow airflow when moving forward causing the craft to climb upwards. Where desired a steeper climb rate may be initiated by pulling on the overhead cable which pulls the three spars inwards slightly to change the tilt angle of the discs momentarily. This causes the leading disc to pitch at an angle to causing a rapid steeper climb. The reader should note the amount of lift capable of being generated at lift-off is governed by the speed of rotation of the three dimpled discs atop affixed the flexible spars and which after a short time begin to rotate in a synergistic manner of their own accord. A rather peculiar phenomena. As one may have realised the craft cannot just fall straight out of the sky like existing winged and rotary craft and thus the Trimorphic Disc Sail is an important step in the development of safe flight for mankind. It is inherently stable and therefore easy to fly and is instinctive and natural and thus safe for all round for all ages and even those who are elderly and those physically challenged. Your support is therefore warranted and welcomed. Designers both within and outside the aircraft industry are welcome to contribute their own ideas for new uses of the Trimorphic Triple Dimpled Disc System and apply for a license for its use in novel craft. And yes it can be expanded upon to very large size as a heavy lifter. Regards: Mike Dinsdale/ Freedom Skydisc International: Ph: +64-21-02217405

    Reply

    Chick August 20, 2012 at 12:31 pm

    Tristan – I will defer to you knowledge. I would appreciate your consideration of Mike’s heating gas idea with also being able to cool it. Combine that with current fiber storage and compression methods, could a more flexible system be created? Release more gas and heat it to rise…compress and cool to descend. Also I have heard that hydrogen can be used in an internal combustion engine, but modern turbines might be better. Since the design of the airship will limit speed anyway, I would not expect to get jet levels of thrust. As we have seen balloons capable of reaching very high altitudes, small jet type turbines perform better using less fuel. I would only give solar about a quarter of useful surface area. If it can offset its weight and give a plus during daylight hours it would be worth adding possibly. I think either Hydrogen or methane would do better with this concept using modern computers to control the process.

    Reply

    Tristan September 5, 2012 at 6:49 pm

    Your comment about balloons reaching high altitudes is a non-sequitur: balloons of this type must, among other things, be designed for minimum weight. The most obvious way to reduce weight is to make the thing unmanned. By definition, they will not carry passengers.

    Your description of releasing gas into the balloon to rise and compressing gas to descend appears to be an unusual phrasing of how blimps work: they use a main gas envelope with the lifting gas, and it also contains smaller ballonets filled with normal air–inflating these ballonets compresses the main lifting gas (reducing the lift it provides), and releasing air from them provides room for the lifting gas to expand into (increasing lift). This system also requires less ability to handle high pressure than taking gas out of the envelope, presumably into a rigid tank; there is much more volume for the pressure to be distributed across.

    I see little to be gained by heating and cooling the lifting gas in flight: it would require an active system to achieve and maintain those conditions, and possibly some form of insulation in the envelope. I have no way to generate numbers, but my intuition is that this would not be cost-effective. Heating gas just before takeoff might be worth it (it would cool in flight, reducing lift to offset the reduced weight from fuel consumption) but would require means to prevent the airship from taking off prematurely. This sounds fairly easy to arrange.

    One of the recurring issues of airships is that their buoyancy changes as fuel is consumed. Use of diesel or gasoline means that the buoyancy gradually increases, unless something is done to compensate.

    You are correct in stating that both hydrogen (H2) and methane (CH4) can be used in an internal combustion engine, but switching to either fuel will change the problem rather than actually solving it. In uncompressed gas state, both are lighter than air, and consumption as fuel will reduce the buoyancy of the airship. My earlier “Six Features of Methane” post was about the suggestion of using methane simultaneously with diesel or gasoline, so these two buoyancy effects would offset. That same post also explains in detail why I believe methane to be better than hydrogen (and why I recommend against /completely/ replacing hydrogen with methane), and I see little point in repeating it here.

    Evaluating solar–a few questions to ask:
    A. The effect of solar on range
    1. How much do the solar panels weigh?
    2. How much energy is contained in an equivalent weight of fuel?
    3. How long will the solar panels take to produce that much energy under realistic conditions?
    –If the answer to question 3 is less than the projected duration of the trip, solar panels will, on average, extend the airship’s range.
    B. The effect of solar on operating cost
    1. How much do the solar panels cost to install?
    2. How much do they cost to maintain (per megajoule)?
    3. How much does fuel cost (per megajoule)?
    –If answer 3 is less than answer 2, solar panels will eventually “pay for themselves” in reduced costs; the time required to do so involves answer 1, the difference between answers 2 and 3, and the airship’s power consumption.

    Re-stating the issue: solar panels produce energy whenever they have access to sunlight. That energy can then be used instead of consuming fuel. On the other hand, solar panels tend to be expensive to install, and make the airship more complicated, since they are an additional system that needs to be maintained and sometimes repaired.

    I agree that “jet levels of thrust,” as you put it, would be overkill. From some hasty reading on the subject, smaller turbines may be a good choice for the airship’s main engine, since they have a high power-to-weight ratio and excellent multi-fuel capability (to burn lifting gas and liquid fuel simultaneously).

    On the other hand, what I have been able to find seems to suggest that turbine engines are less fuel-efficient than diesel (compression-ignition) piston engines, especially under partial loads such as would result from supplemental solar power. They are also slow to start up/shut down, and slow to change speed in response to changing loads, although these are unlikely to be a problem on an airship.

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    Mike Strehl July 30, 2012 at 3:57 am

    Just a thought by a non-scientist. The barrier-layer concept is certainly valid, but perhaps not addressed is a hybrid type of airship. What is lighter than Helium? Why, Hydrogen, of course. Is nothing else lighter? How’s about hot Helium? By combining the lift generated by heat,(perhaps from engine exhaust, generally lost energy),one could raise the lifting power of cold Helium in much the same way that hot-air balloons work. I have no data to submit on this matter, and as stated am not a scientist. It simply occurred to me that heat energy from internal combustion engine exhaust is wasted energy. By ducting the exhaust through the bag (or most generally, bags) at least part of this wasted energy could be recovered as lift. like I say-just a thought.

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    Tristan August 8, 2012 at 2:37 pm

    I think the idea would be likely to backfire.

    If we assume that the airship is powered by some form of liquid fuel (gasoline, diesel, ethanol, whatever) then this fuel will be consumed in flight, which will reduce the weight of the airship. This leads to two problems:

    1. The weight of the airship (and thus the required lift) is greatest during takeoff, since the fuel tanks are full. My experience with cars suggests that the engine will be turned on shortly before takeoff, which means that the lifting gas would still be cold, or at least would need to be heated by other means. (Note that a car may not be the right example to use–if someone reading this has a better one, feel free to correct me).

    2. As fuel is consumed in flight, the weight of the airship would decrease. Your idea of heating the lifting gas would enhance this effect, which would make landing the airship very difficult.

    See also the “Operational Considerations” of helium above on the main page. Heating the helium would cause it to expand further, which would reduce the pressure height.

    Reply

    Ken Pedlar July 5, 2012 at 2:39 am

    I have a solution to this airship small personal easy to fly can’t fall out of the SKY stuff in the form of my very safe anti-crash anti-stall Helium or hydrogen lift Trimorphic-Disc-Sail Craft. It uses three inflatable discs able to morph to a larger size when gaining altitude with the three disc made of segmented ballonets contained within an interconnected thin carbon fiber ring mesh joined with flexible rubber type joiners where upon inflation of the ballonets they protrude through to form a dimpled hemispherical surface. The disc I might add sit atop three spars set a a specific angle in close proximity to each other to allow expansion when climbing the ring mesh attached to a center apex cap made of smooth carbon with holes for the rubber type ring joiners. The rings attaching to a larger ring able to expand also the ring mesh continuing underside where it joins to a 2/3 Chord thin walled carbon fiber undershroud disc also with holes drilled around it edge for the fasteners. The undershroud connected to an axle spindle and bearing air motor assembly which bolts into a machines holed and channeled bracket to which air hoses attached to drive the spindle rotating the disc and for injection of gas. The discs when rotating via the dimples cause the air to swirl to form a partial vacuum in the center of the upper disc while swirling the airflow radially outward over and under the edge and accelerating when moving over the smooth undershroud and down causing powerful thrust and lift upwards the vacuum above also pulling the disc upwards. The the spars connect at their base into a chassis plate with hole cut onto to insert a turntable which is attached a fully flight enabled cockpit-cabin or in peddle powered versions just a seat, frame etc. Can be made quickly via 3D Printer Tech from titanium carbon metals, ceramics and super tough lightweight plastic using powders now readily available for fusion using these new machines. Will license soon and have patent pending. Would like some help to fly machines around world doing promotions and sales and will pay good commission when underway. Great craft to start small one man women travelling business. Silent and very fast if one fit or more expensive powered version will do three hundred plus kilometers per hour. This is the way to live free as a bird and go anywhere anytime where on wants day or night in complete silence and absolute safety. Craft can handle strong winds due to gyroscopic forces generated by rotating disc and just in case you get tired one can land and convert it into a tent in ten minutes. Taking orders NOW. Don’t wait and get in fast to be first in line to receive first 100 craft with Real Gold Seal and T shirt as gift.

    Reply

    Tristan May 18, 2012 at 1:12 pm

    I have a different idea for keeping the hydrogen under control.

    Other posts have mentioned the idea of using part of the airship’s lifting gas as fuel to control buoyancy. Hydrogen is, admittedly, the obvious choice, but I feel the need to raise the question “Is it the best one?” The Graf Zeppelin, fueled by Blau gas, demonstrated that other options are available.

    Given current technology and infrastructure, I believe that the best gas to use is methane. Methane offers six distinct features that make it an excellent choice in this application. Ordered for greatest convenience of explanation (more precisely, greatest ease of referring back while explaining) these are:

    1. Methane is a convenient fuel for an internal combustion engine, with a very high octane rating of 120 and a reputation as a very clean-burning fuel. It is sold for the purpose as Compressed Natural Gas (CNG). (Note: since for purposes of the engine running on it the methane-based power gas I am describing is identical to pressurized CNG, I will at times refer to it as such for convenience.)
    A. Internal combustion engines are cheap, compact, and powerful. They are also known for the ease of producing them in flex-fuel models.
    B. Hydrogen, on the other hand, is an inconvenient fuel for an internal combustion engine, and fuel cells lack several of the above features, in particular the convenience of flex-fuel (more properly, bi-fuel or dual-fuel) operation. They are also much more expensive than internal combustion engines.

    2. Methane is buoyant: under normal ambient conditions (temp 20 C, pressure 1 bar), and to “back of the envelope” precision, 1 kg of methane takes up 1.5 cubic meters and provides buoyancy to lift 0.8 kg.
    A. The buoyancy per volume of hydrogen is around twice this (more than twice, of of sufficiently high purity), making it more suitable as the primary lifting gas; my concept calls for the use of methane to lift a more energy-dense liquid fuel (possible choices include CNG [actual Compressed Natural Gas], gasoline, ethanol, LPG [Liquefied Petroleum Gas], diesel, and DME [Dimethyl ether]), and be consumed alongside it, while hydrogen lifts everything else.
    B. Again: “Methane lifts a liquid fuel, and is consumed alongside it.” This is where the flex-fuel capability of an internal combustion engine comes into play: the airship can have one (type of) engine. This permits a weight-reducing single-engine setup, and greatly simplifies maintenance if several engines are used.
    C. If the methane and the liquid fuel are consumed in the right proportion (named above, but not very precisely, and it will vary slightly with temperature, humidity, impurities, and other factors) the airship’s static buoyancy will remain constant; I will refer to this ratio as “cruise mix.” The engine should also be able to run on a higher proportion of liquid fuel (“run heavy”) to increase buoyancy, and on a higher proportion of the methane-based power gas (“run light”) to reduce buoyancy. Since the two fuels both double as ballast, the need for directly labeled ballast (or at least the required quantity) is reduced, making that capacity available for other tasks.

    3. Methane is widely available and cheap to produce, either as natural gas (fossil fuel) or biogas/biomethane.
    A. Methane has the advantage over hydrogen that it can be harvested from natural (or cultivated) sources while hydrogen must be synthesized industrially. It is possible for natural gas to contain more energy than was spent in the industrial processes of producing and refining it, a feature hydrogen lacks.
    B. In terms of the parameter “easy to produce as a biofuel,” methane is far ahead of all other contenders. Cows are notorious for their methane production. Landfills are also known to produce methane, and even human sewage will work. It is also easier to refine to fuel grade than the more famous ethanol: the primary contaminants in raw biogas are water vapor (H2O), carbon dioxide (CO2), and hydrogen sulfide (H2S); the last two are much more soluble in water than methane, and can be washed out, with the resulting “sweetened” gas being subsequently dehumidified. Ethanol requires some form of sugar to ferment (which competes much more with food production), and then energy-intensive distillation to get the water out.
    C. Most industrial hydrogen is produced by “steam methane reforming,” a chemical reaction which can be summarized as CH4 + 2 H2O –> 4 H2 + CO2. In terms of fuel, it seems cheaper and more efficient to simply use the methane directly rather than bothering with hydrogen. There is also the issue of removing the CO2 completely enough for a fuel cell: last I heard they were extremely easy to damage with fuel of this type, requiring even more expensive electrolysis hydrogen.

    4. Methane, while flammable, is much less so than hydrogen: it requires a narrower range of mix ratios to burn in air (5-15%, compared to 4-75% for hydrogen) and requires a more powerful spark to ignite.
    A. Methane is not assumed to completely eliminate the need for an inert safety gas barrier, but it should reduce the required thickness or quantity.

    5. CNG fuel (or, more precisely, an internal combustion engine running on it) is highly tolerant of contamination by hydrogen.
    A. The United States Department of Energy website (“Alternative Fuels Data Center”) cites an experiment (http://www.afdc.energy.gov/afdc/fuels/hydrogen_blends.html) where CNG was blended with 20% by volume of hydrogen to reduce emissions.
    B. It worked, but the dual-fuel nature of the engine complicates the situation, and the greater buoyancy of hydrogen will require more liquid fuel to compensate, which will probably defeat the purpose.

    6. Hydrogen is notorious for its tendency to leak, and can escape even through barriers that are tight against air (nitrogen and oxygen). Helium shares this tendency, while methane does not.
    A. Combined with points 4 and 5 above, this makes methane power gas an excellent tool for keeping the airship’s hydrogen under control. My concept calls for three-layered gas cells: a core cell of hydrogen (primary lifting gas) a surrounding layer of natural gas (fuel, secondary lifting gas, buoyancy compensator) and an outer layer of inert safety gas (helium doubles as lifting gas, nitrogen is much cheaper and less prone to leaks).
    B. The leaks hydrogen is so well-known for will be into the methane power gas, which (as above) tolerates significant levels of hydrogen quite well. It also features a high turnover rate (i.e. it is consumed very rapidly relative to the amount carried on board) and a deep cycle (i.e. the power gas layer is nearly emptied before it is refilled). This combination nicely prevents hydrogen from accumulating there.
    C. Since the level of hydrogen in the power gas is kept low by normal operations, the amount that can leak past the power gas layer into the safety gas and gondola is severely reduced. The hydrogen is kept largely safe as an inherent effect of operations; the only requirement is that the airship remain in active use and good repair.

    Reply

    Andy Leary May 10, 2012 at 9:57 pm

    I have recently become interested in airships and have come up with an idea to solve the problem of a leaking Hydrogen gas cell.
    The second line of defense would still involve the usage of a surrounding gas cell of a safer, nonflamable gas. I was thinking Helium, but after looking over some of the comments here, I think Nitrogen would be the better way to go. Not only is it not as reactive as Hydrogen or Oxygen, it is very plentiful (hence very cheap), easy to obtain, and still provides a slight amount of lift, since it is slightly lighter than the oxygen in the mixture of gases in the air.
    But the first line of defense would be the type of material used to contain the hydrogen. Sure, there are plenty of polymers to choose from that would provide a very tight seal around the hydrogen cell. But what happens when, for example, the sharp end of a screw driver or a jagged-edged piece of metal falling from a support beam punctures the cells and the gases (both the safety and Hydrogen gas) start to escape? If nobody notices or can repair the cells within a short span of time, the Hydrogen to Oxygen ratio inside the airship would rise to dangerous levels. So, I have found a solution: Fix the problem, right then and there.
    How? Well, with a self-healing material, of course! If the puncture hole could be sealed up by the material itself within a matter of seconds, the dangers of elvated hydrogen levels in the air would be solved. And I have an example of such a product that could be inspired from, if not used at all. Last year, on the PBS scientific television program NOVA, a type of self-healing material called BattleJacket was presented. This material was designed to envolope the containers of trucks transporting fuel in the middle east and would seal up the holes caused by bullets that would be shot into it’s side, thus preventing fuel leakage. It is made up of two sheets of very elastic plastic that would stretch as the projectile went through and would then snap back into position with only a pinprick-sized hole. And sandwiched inbetweem the two sheets was a layer of fine particles that would soak up the leaking fuel, causing them swell them up, and seal the hole. This material (with a few minor changes, of course) could be the answer to Hydrogen leakage problem and would promote a more realible and confident practice of storing Hydrogen gas, making Hydrogen airship travel a safe and practical endevor!

    Reply

    Tristan May 20, 2012 at 9:04 pm

    Self-healing gas cells sound very expensive to me. They also sound heavy.

    One of the reasons I suggest methane involves a different mindset and thought process than you are showing.
    We both saw “Hydrogen tends to leak.”
    You thought “How can I keep the hydrogen from leaking?” (You answered “Self-sealing gas bag, between the hydrogen and a safety gas layer.”)
    I thought “How can I arrange the situation so that I don’t need to care?” (I answered “Triple-layer gas cell: core cell of hydrogen, second layer of methane for fuel, then an outer layer of safety gas.”)
    Put another way, I worked around the problem, you worked against it.

    I accepted hydrogen leaks as inevitable, and worked around the problem by ensuring that they would be into a layer of methane, which is both tolerant of such a situation and (since the methane layer doubles as a fuel tank) continuously cycled to quickly dilute whatever hydrogen leaks in to an insignificantly low level. Inert safety/barrier gas (He or N2) lacks both of these features.

    With the methane layer in place, hydrogen leaks are only a problem if spectacularly large, or if they go on for a long time without being repaired (and the leaked hydrogen replaced). The solution is low-cost and low-tech, and well within the capabilities of currently available technology.

    Working against the issue with a self-sealing gas cell, I see several issues:
    1. Tech: You yourself seem to admit in your post that you do not know how to build such a thing, and it will almost certainly require a lot of Research and Development (R&D) work to be possible.
    2. Cost: The large amount of R&D to make it feasible (maybe even to make it possible) means that they would be at the “cutting edge” of technological development–in other words, a prototype. Prototypes are not cheap.
    3. Weight: I am aware of self-sealing fuel tanks being used on World War 2 fighter planes; one of their notorious problems was the significantly increased weight relative to a plain (non-self-sealing) fuel tank. An airship gas bag has much more surface area, which implies that making it self-sealing would come with a huge, and likely prohibitive, increase in weight.

    Your self-healing gas bag idea does not sound practical to me. More than that, I believe that you approached the problem the wrong way, asking the wrong questions.

    Reply

    DK February 8, 2013 at 4:02 pm

    Tristan,
    your arguments against Andy’s suggestion also apply for your suggestion of a three-layered gas cell approach.

    In general you (two) are thinking too complex. The safety issue is not small leakage volumes by diffusion losses but damages to a hydrogen cell. The hydrogen volumes set free by a damage cannot be controlled by a inert gas layer. No way.

    In Germany hydrogen is still used as a lifting gas for aerostats. There is currently no airship utilizing it but some baloons. Recently the CargoLifter CL-MK250, which is a super-pressure hydrogen cargo baloon (more on this please see here: http://cargolifter.com), got authorized.
    The electro-static issues and with that the problem of unwanted ignition of a baloon are similar to that of an airship and nevertheless they are safe because their design strictly avoids build-up of oxyhydrogen internally.

    The Hindenburg was mainly destoyed because it’s gas managment was designed to (actively) build up oxyhydrogen inside the ship so it burned rapidly during the accident whith all the fatal consequences. And this applies more or less to all fire accidents of hydrogen airships in the past. They all had the issue of oxyhydrogen being present internally.

    Reply

    Andy Leary July 11, 2013 at 6:20 pm

    ===NITROGEN vs. METHANE===
    I decided to use nitrogen rather than methane as my primary barrier gas for several reasons:
    1) It can easily and cheaply collected (all you really need is an air compressor and a semipermeable membrane to separate out the oxygen)
    2) It naturally bonds with hydrogen to for ammonia gas (which is not only lighter than methane, but is also much less combustible), there-by storing the leaking hydrogen—rather than merely diffusing it—safely and securely.
    3) It is significantly lighter than methane, providing a boost in total lifting power.

    ===YOUR CRAFT===
    I would also like to point out some rather disturbing flaws in your system:
    1) Your barrier gasses are expensive (I’m assuming your secondary barrier gas is helium, since it is the lightest inert gas there is) and cannot be cheaply replaced. Nitrogen—on the other the hand—can easily be extracted from the air with a decent nitrogen generator. Compare that with following gas prices:
    Helium (Bottled) = $160 per 1,000 cubic feet
    Methane (Bottled) = $8 per 1,000 cubic feet
    Nitrogen (Bottled) = $150 per 1,000 cubic feet
    Nitrogen (Generator) = $1,000 (Single Purchase Cost)
    So, as you can see, nitrogen (actually, a nitrogen generator, to be precise) is an essential part of any economically feasible and reliably airship design of the 21st century.
    2) While methane is a tried and true way to power your engines and generators, it is expensive, wasteful, and down-right dirty when you compare it with my own system. Instead of using a polluting, inefficient internal combustion engine, I would instead use clean, efficient electric motors to power my airship.
    So, where do I get my power from? Why, from solar panels covering the top of the airship, soaking up good ol’ sunshine! It’s clean, free, and abundant. But what if it’s a cloudy day or even nighttime? Well, here’s the genius of the whole system: during the day, excess power collected from the sun is channeled to an onboard container of water, where it zaps it into hydrogen and oxygen, the former of which can be stored away tanks—or more likely, pumped in with the rest of the lifting gases to replace any hydrogen that has manage to leak out. Then at night, using a fuel cell, the hydrogen is recombined with oxygen from the air, which releases electricity, and is turned back into water (which can be used all over again—YEAH!!).
    Not only is this a very environmentally friendly way to power my vessel, its dirty cheap! After the initial cost of the solar panels (by-the-way, they can be light and flexible enough to roll into a ball and kick around your drive nowadays), the generators, the motors, and the wires, you might not have to pay a single cent for fuel. As long as the sun keep shining, you can reuse that same water over and over again—plus, if you are ever running low, you can always drop down and suck up some water from any fresh water lake you happen to be hovering over.
    3) And even with you three layers of protection, if something manages to penetrate all three of them, hydrogen will manage to escape until someone comes along to notice the hole and patch it up…if they don’t decided to have quick (and unfortunately, final) smoke first.
    My design incorporates a material that is able to heal all but the largest of holes. So, contradictory to your statement, YOU are the one who must take care and worry about patching leaks.
    “Work smart, not hard.”

    ===REBUTTAL===
    Now, as for your three concerns you listed about my self-sealing material, let me get a few things straighten out:
    1) Tech: Even though I don’t know how to make it, there is a company already making a product (called BattleJacket) that with a few tweaks would be perfect for the job. Here’s their website, which not only has the description of BattleJacket but also a video demonstrating the product’s self-healing abilities under extreme circumstances: http://www.rhinoliningsindustrial.com/applications/military/battle_jacket/76/95
    2) Cost: The technology, research, and development are already here. Only a few tweaks are needed to apply it to the gas cells—think of it as buying some buckets of paint to paint your house; it’s not that much.
    3) Weight: Pretty much all the stuff you need to make BattleJacket is two thin sheets of lightweight plastic and a thin layer of tiny spongy beads sandwiched in-between. If I only put on just one layer of the stuff, it probably wouldn’t weigh much more than your design’s two outermost layers combined. Plus, your comparing your WWII airplane fuel tank example with my modern day tanker-truck example; by your logic, cars should still be solid-steel death-traps, radios should still run on tubes, and cigarettes should be healthy for you. Technology and knowledge evolves as time passes by, friend.

    ===Conclusion===
    So, when you compared our two ideas, you see a clear difference: mine solves the problem of leaks, while yours ignores it. “Quality beats quantity, pal.”

    Reply

    hhaddow February 22, 2012 at 6:41 am

    With modern alloys, polymers and carbon fiber could we not make a far lighter airship to counteract the reduced lift of helium.
    Have a photovoltaic surface on the topside to reduce fuel use (or to even replace it if we can store the energy without adding to much weight) with the correct materials we could control the temperature of the gas so that its rest temp causes the lift needed for flight and we can cool it to descend. one thing i do know is it would be much cheaper that a jet the Hindenburg used 130 kg/h diesel at 125 km/h a 737 uses 1925 kg/h kerosene at 809 km/h (so to accurately read fuel efficacy you have to factor it against speed (and thus distance) so we will divide one hours fuel by one hours distance and have have 1.04 kg/km/h for the Hindenburg and 2.37 kg/km/h for the boeing, so for fuel per hour and for fuel per distance per hour the Hindenburg (which used ‘weighty’ metals and ‘inefficient’ engines) beats the modern jumbo jet

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    Dreamer, not Engineer January 8, 2012 at 1:28 am

    Has anyone considered the potential of using a Hydrogen as both the lifting gas and as a fuel source?

    I have been dreaming of a simple concept:

    1: Take a solar airship, use cells of Hydrogen with a gas barrier for safety if necessary
    2: Make sure that the solar power produced is excessive vs the electric motors in best conditions (full noon sunlight) such that full power at other times is easily achievable, while excess power at peak times is expected
    3: Incorporate a small collector for atmospheric water vapour plus a simple and low weight electrolysis unit
    4: Incorporate a couple of Hydrogen Fuel Cells and a backup H tank or 2
    5: Make whole thing a Hybrid Air Vehicle

    Indefinite flight? A battery of Hydrogen for when the sun sets? The Ability to burn altitude for thrust? The ability to recharge Hydrogen from the Atmosphere using Solar Power? A greater lifting capacity than He Airships? Oxygen as a WASTE product?

    Assuming that the dangers of Hydrogen Airships are soluble, Is this feasible?

    Reply

    Tristan May 16, 2012 at 9:17 pm

    Your concept, while impressive on paper, appears to be well beyond the capabilities of current technology.

    1. Hydrogen is a powerful lifting gas with very low energy density. In other words, both production (electrolysis) and use (fuel cell) of hydrogen will mean large changes in the airship’s buoyancy, unless you have some scheme to counteract this. From what I can tell, you will be much better off with a battery, which will have negligible effect on buoyancy as it charges and discharges.

    2. Hydrogen has an unimpressive well-to-wheels efficiency. Electrolysis in particular involves a great deal of wasted energy. Again, you would be better off with a rechargeable battery.

    3. Last I heard, fuel cells were expensive and very finicky (easily damaged by things like CO2 in the fuel). Not that the batteries I am recommending aren’t also expensive, but they do at least have the reputation of being fairly idiot-proof.

    4. You say this airship wants solar panels on the roof to produce peak power greater than engine cruise demand. Have you done the math to make sure this is feasible? Not that I have either, but I am much less optimistic than you are.

    I agree with the idea of using part of the lifting gas as fuel, but I am convinced that hydrogen is not the gas to use. More precisely, I am convinced that current technology is not capable of using it effectively in this way.

    Reply

    Tristan May 16, 2012 at 10:29 pm

    EDIT: I just did an attempt at the math of a solar-powered airship. I based most of my numbers on those this site quotes for the Hindenburg.

    Length: round to 245 meters
    Diameter: round to 41 meters
    Top surface area: 10045 square meters
    Assume 80% of this area can be illuminated for power generation.
    Assume the solar panels are 40% efficient.
    Noon sunlight intensity: Appears to be near 750 Watts per square meter
    This gives around 2.4 megawatts of solar power

    Comparison: The Hindenburg is specified to have had 4 engines, which in cruise setting produced 850 hp (about 630 kW) each.
    Total power: 2.52 megawatts

    Summary: Solar power can offset a significant portion of fuel use, and is almost certainly a worthwhile investment, but is not capable of powering the airship on its own; supplemental power from some other source will be needed.

    Reply

    Dreamer, not Engineer May 21, 2012 at 9:49 am

    Thanks so much Tristan for doing the math and your well considered response. I avidly read your response on using Methane as a fuel source and lifting agent – its a great idea. I naturally have a greenie distaste for internal combustion engines, but the arguments re waste methane are naturally well worth considering.

    I was actually quite surprised at the result of your maths re. how much power the solar cells could generate vs the power of the Hindenburg – I thought the math would be far far worse re solar collection – and to be honest, you were relatively optimistic re. solar cell output power wise.

    Nonetheless, the fact that the solar airship came so close to parity with its (albeit early 20C) internal combustion comparison gives great hope for me that you *could* build a serious solar powered HAV which could almost match a beast like the Hindenburg for speed, but with zero emissions.

    More exotic dreamy notions such as utilising atmospheric water vapour to recharge Hydrogen leaks are just concepts of course – fit for science fiction. Which I dabble in. :)

    Reply

    Tristan May 21, 2012 at 8:02 pm

    The point of my initial reply was “your so-called ‘simple concept’ is a lot less simple than you seem to think it is.” We will not be able to build something like that without another breakthrough or two. And yes, the figures for the solar panel were very optimistic. Even “top surface area” was optimistic, since it assumed a rectangular shape and airships have aerodynamic peaked ends. The math assumptions were optimistic, maybe even foolishly optimistic, and it still wasn’t enough power; realistic power estimates would probably be two-thirds to half of the number I gave, and that’s before we start getting into cloudy days and night-time operations.

    When evaluating a nifty new idea, my first thought is “Can we pull this off?” If that answer is “no,” then I consider that the end of the discussion. For this reason, I place heavy emphasis on “current technology and infrastructure” as I put it in my “six features of methane” post. I acknowledge that technology does change and advance, but I place the emphasis on current capabilities rather than trying to predict future developments.

    Given current technology and infrastructure, fuel cells are an emerging prototype technology. As such, they are buggy and expensive. I favor internal combustion engines (and, to a lesser extent, batteries) because they are well-developed mature technologies, and I do not understand the “greenie distaste for internal combustion engines” you mention. Could you try to explain that?

    Practicality/feasibility is always my first consideration, and cost is a very big, very crucial, part of that. Since fuel cells are a buggy prototype technology, a commercial vehicle using them for power will not be profitable (i.e. won’t happen, or at least won’t last long) without a lot of advertising cleverness to convince the customers to pay a premium and subsidize your research project for you.

    I am not impressed with hydrogen. As above, current technology places it as an energy storage medium, not an energy source; rechargeable batteries have easily-comparable input and output types, and are much more self-contained and user-friendly. As above, current technology and infrastructure is not capable of producing hydrogen in a way that allows it to contain more energy than was spent in the industrial processes of producing it. Until that changes (incidentally, there are genetic engineering experiments being done in this direction) I will dismiss hydrogen fuel cells as over-hyped. If you’re serious about solar power (and zero emissions), I would recommend optimizing it with a rechargeable battery and a “plug-in hybrid” attachment to charge off the electrical grid as well as from the solar panels.

    I like methane because it solves so many problems at once.
    1. It is both a very convenient fuel and an acceptable lifting gas, allowing very convenient control of buoyancy.
    A. Simple liquid fuel increases the airship’s buoyancy as it is consumed, which needs to be accounted for to keep the airship under control. A battery removes this effect, which is definitely a convenience improvement.
    B. The methane and liquid fuel combination produces a simultaneous decrease and increase (respectively) in buoyancy; the default cruise mix arranges to cancel these out, but the real point is that these two pulls can be changed to taste on the fly — the engine is the ballast valve to decrease and increase buoyancy. Dumping labeled ballast (probably water) and valving off hydrogen will be reactions to emergencies, rather than aspects of routine operations.

    2. As a barrier layer to contain leaks, methane vastly improves the safety of hydrogen, and is superior in this role to nitrogen and helium.
    A. Nitrogen and helium are an improvement over direct leaks into the gondola and nearby airspace, but they still provide a place for hydrogen to accumulate and eventually reach problem status.
    B. Methane is flammable in its own right, so it (probably) does not eliminate the need for a safety gas layer, but methane is much less prone to leaks than hydrogen; this reduces the need, or at least the required thickness, of an inert barrier gas layer. Since it serves as fuel, it requires a much higher hydrogen concentration to reach problem status and simultaneously provides less opportunity for hydrogen to accumulate to such a high concentration.
    C. I mentioned the Blau gas of Graf Zeppelin at the time, and methane is also an improvement over this: methane is, like hydrogen, a lifting gas, so leaks will tend to drift up and away from the airship; Blau gas had components which were denser than air and would thus pool in inconvenient places like the keel and gondola. There is also the practicality detail that natural gas has probably replaced Blau gas in any other applications it may have had.

    3. Current technology and infrastructure is designed for fossil fuels, and we can’t just switch to a new way of doing things overnight; I tend to consider biofuels (which are produced to be compatible with this fossil fuel infrastructure) to be the best way to go right now, while we figure out the best way to do things and build the new infrastructure to do things that way.
    A. As I said in the “six features of methane” post (feature #3) methane is, to the best of my knowledge, the biofuel that can be produced, refined, distributed, and used most conveniently/easily/cheaply. Increased use of biogas/biomethane is therefore an improvement not only over fossil fuels, but over other biofuels as well.

    Reply

    Alfons Hughes December 20, 2011 at 4:03 am

    Why not use compressed hydrogen for fueling either motors or fuel cells, and storing excess hydrogen at altitude by compressing it or hydride storage ?

    Reply

    dorn hetzel December 17, 2011 at 3:06 pm

    The flammability of hydrogen is only an issue in the presence of an oxidizer. Perhaps a double envelope could be used with an inner (and much larger by cubic volume) envelope of hydrogen surrounded by an outer envelope a few meters in thickness containing helium (or even nitrogen). The primary purpose of the outer envelope would be to suppress the interaction of the internal hydrogen with the environment. Any leak of the inner hydrogen envelope could be detected by sensing hydrogen in the barrier envelope, and likewise, and leak from the outside could be detected by atmospheric gasses mixing in the helium or nitrogen.

    Even though it wouldn’t provide much net lift, nitrogen could be nice for the outer envelope because it easily obtained by separation from the atmosphere, and so could be vented and refilled with ease to maintain a proper pressure in the outer envelope. It would also act as a natural fire suppressant for the hydrogen.

    With a carbon fiber structure, I suspect that very large and light airships could be constructed today. At least partial solar power should be feasible, especially since lithium batteries are even proving sufficient for some heavier than air craft.

    Reply

    sls4ak October 29, 2011 at 9:14 pm

    As an inert gas to safe out hydrogen, nitrogen is the simple fix. It should be remembered that the Hindenburg fire also involved having a skin that was sealed with nitrocellulose lacquer which is far more flammable than anything that we would suggest today.

    That said I seriously doubt that it would be possible to find an insurance underwriter for a hydrogen lofted airship… fool me once?

    The use of electric electrolysis liberated hydrogen is far overstated, otherwise there would be more electric power plants that made hydrogen in the off peak hours and stored the hydrogen for burning during the peak hours. Most hydrogen is generated now and in most future plans use petroleum namely natural gas.

    Hydrogen powered stationary plants would have far fewer complications than hydrogen powered vehicles, logically it seems that until we see hydrogen powered power plants that all other hydrogen power is a fallacy.

    Reply

    sls4ak October 29, 2011 at 9:11 pm

    As an inert gas to safe out hydrogen, nitrogen is the simple fix. It should be remembered that the Hindenburg fire also involved having a skin that was sealed with nitrocellulose lacquer which is far more flammable than anything that we would suggest today.

    That said I seriously doubt that it would be possible to find an insurance underwriter for a hydrogen lofted airship… fool me once?

    The use of electric electrolysis liberated hydrogen is far overstated, otherwise there would be more electric power plants that made hydrogen in the off peak hours and stored the hydrogen for burning during the peak hours. Most hydrogen is generated now and in most future plans use petroleum namely natural gas.

    Hydrogen powered stationary plants would have far fewer complications than hydrogen powered vehicles, logically it seems that until we see hydrogen powered power plants that all lther hydrogen power is a fallacy.

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    Stefan Gieselmann October 26, 2011 at 3:26 pm

    I’ve wondered the same as Hunter Stanley above — a dirigible with solar-cell exterior driving electric motors would remove two problems: the weight of fuel; and the weight of fuel changing as it was burned.
    Not sure how much extra the envelope would weigh, and then add in the weight of batteries for continued nighttime operations…
    But such a set-up should work out in terms of lift/payload, no? Using the Hindenburg data above saving 58000 kg of fuel leaves a lot of room for the additional weight of the envelope and batteries. Assuming 58000kg of fuel equals 58000 litres of Diesel, at we’ll say $1/litre, one is also saving $58000 in fuel per trip! And suddenly, the operating costs go way down, weighed against the higher initial investment of a solar-powered design.

    At some point, the economics will make sense, regardless of the lifting gas.

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    Bob August 13, 2011 at 12:52 am

    I am doing a little history on “Carnival Balloon Vendors” from about the turn-of-the-century to about the 1920s. I have been looking everywhere for a picture of the hydrogen and/or helium “Tanks/Cylinders” these oldtime venvors used to use. But as yet I have been unable to find a single one. I was hoping someone here might direct me to a website where these tanks are pictured and discussed. Any assistance in this regard will be deeply appreciated.

    Thanks.

    Bob

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    C. Cossins August 1, 2011 at 12:07 pm

    I have found this page very useful, as I plan on constructing an airship of a reasonable size. I believe the flammability of hydrogen may be reduced if it were possible build some fire retardent into the envelope. As well as this, perhaps if a lightweight polymer that is totally airtight were to be fitted as the envelope, this will prevent oxygen mixing with the hydrogen and supplying an oxidizer. Its a pity the public confidence in airships has diminished to the point that their use has been discontinued.

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    Nigel March 28, 2011 at 5:16 pm

    If lift increases with height, then either modern aerodynamics might handle it better or initial lift could include collapsible supplementary hydrogen above the main tanks. Then again, increasing lift might no longer be a problem given the ability to pressurise occupied areas like aircraft. The same may be true of ‘gas bags’ in general. Lift is a matter of displacement so ideally a rigid tank would hold a vacuum. Minimal helium pressure to prevent collapse is all that becomes necessary. All accomodation could be within the hull and a flatter aerodynamic shape with ‘wings’ holding the buoyancy tanks could allow the craft to be only slightly lighter than air, using air compresssor trim tanks for ballast: not so much an airship as an aerostat.

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    Tristan May 28, 2012 at 6:37 pm

    Lift does not increase with height. If it did, balloons and such would simply float most of the way into space, rather than running into an altitude service ceiling.

    As height increases, pressure decreases. The lifting gas expands in the reduced pressure; each kg of lifting gas is still displacing just as many kg of air as at lower altitude (lift per kg of lifting gas is unchanged) but must occupy a larger volume to do this (lift per cubic meter of lifting gas decreases).

    I also have doubts about your comment “a rigid tank would hold a vacuum. Minimal helium pressure to prevent collapse is all that becomes necessary.” My understanding is that the “minimal helium pressure” that results in the lightest overall structure is equal to ambient pressure; the additional rigidity and reinforcing to withstand atmospheric pressure without the aid of internal gas pressure would weigh more than supplying that pressure with helium or hydrogen.

    Specifically, atmospheric pressure at sea level is a little over 100 kPa. In other words, each square meter of surface area the vacuum tank has must withstand force equivalent to the weight (in Earth gravity) of slightly more than 10,000 kg.

    If we assume a spherical balloon 10 meters in diameter, it will have a volume around 525 cubic meters. The density of air at sea level pressure is about 1.2 kg per cubic meter, so the tank displaces 630 kg of air. An equivalent volume of (nearly pure) helium would be 87 kg (about 190 lb, if that’s more convenient for you), for a lift of 543 kg, minus the weight of the balloon skin itself.

    A vacuum tank with the same dimensions would have a surface area of 314 square meters. Atmospheric pressure on that surface would be equivalent to the weight of nearly 3,250 metric tons (3,250,000 kg). It is not feasible, with current technology, to construct such a tank to weigh less than 87 kg: 87 kg divided across 314 square meters is about 277 grams (about 17 oz) per square meter.

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    Tristan May 28, 2012 at 6:50 pm

    Oops, typo. 277 grams is actually more like 10 oz, not 17.

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    T.G.Hinsley March 5, 2011 at 11:20 pm

    I have looked to find out the source of the hydrogen used in airships, and not yet found the answer. Can anyone tell me?

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    Dan (Airships.net) March 7, 2011 at 6:57 am

    Hydrogen was produced many ways, including a chemical process involving caustic soda and ferro-silicon, but generally it was produced in airship quantities by the electrolysis of water.

    Hydrogen is also a by-product of certain crude oil refining processes; for example, during 1936, when Hindenburg needed to take on additional hydrogen at Lakehurst, it was purchased from an oil refinery in New Jersey.

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    Hunter Stanley January 30, 2011 at 7:38 am

    In a purely hypothetical setup, it seems that a hydrogen airship easily be handled safely simply by replacing the petroleum based engines with solar cell powered electric motors. Heat and spark near the main gas chamber could be virtually eliminated. An additional aspect is that the extra energy from the cells could be used to generate more hydrogen through eletrolisys in water. It would simplify payload calculation as it would remove fuel as a factor and turn the “fuel” equivalent for the solar setup into fixed dead weight. And you’d have a “green” aircraft for what its worth

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    Steve De Marino January 13, 2011 at 11:52 am

    One of the things we began to study in a totally non-technical way was the feasibility of a return of hydrogen airships using more modern materials, i.e. carbon fiber, using solar cells on the outside of the rigid frame, things like that. Has anyone ever looked into mixing the two gasses and how reactive that is? Perhaps a proper blend of the two materials would provide a good lift while reducing the flammability of the situation? Dont know enough chemistry to see whether or not that would work.

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    Michael Hopp February 6, 2011 at 6:43 pm

    Well Steve, I’m not sure if this will help or not, but I found this: http://www.halfbakery.com/idea/Float_20airship_20with_20hydrogen_2fhelium_20blend

    It seems there are some manner of technical issues with gas mixture…

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    Martin February 14, 2011 at 11:56 am

    In short, yes – this can easily be done today. There are a whole range of inert polymers that will not react with hydrogen and are capable of containing it safely. This wouldn’t of itself protect from puncture type problems but there are potential means of dealing with that using say carbon fibre reinforced outer shells. The H2/He mix doesn’t help greatly as H2 becomes flammable at about 7-10% H2 in air and explosive with a little more H2. Once it reached that sort of level due to a leak it would be flammable/explosive irrespective of the presence of He. Mix would just slow down a little the time it takes to reach problem status. The addition of flame smothering gases would be too heavy to add in sufficient quantities to do anything useful.

    Incidentally the material on Al/Fe2O3 thermite reaction on another page is correct but partly misses the point. The ratios only matter if you want to liberate a specific amount of heat to melt the so-produced iron for the purposes of in-situ rail welding say. Significant quantities of powdered aluminium remain dangerous irrespective of what they are mixed with – you don’t have to initiate the formal thermite reaction to have problems. That said the thermite reaction per se clearly has nothing to do with the Hindenberg as it’s rather difficult to initiate and does not happen spontaneously.

    Martin. [BSc (eng), BSc (chem) PhD (chem/phys)].

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    steve December 18, 2010 at 8:53 am

    I completely agree. With today’s technological advances I seriously doubt if hydrogen is not the best option. Should not be too difficult to do it safely. Yesterday is gone, live for the future.

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    Francisco Carvallo December 9, 2010 at 11:45 am

    It would be interesting if new technologies could further the developement of “combination” gas cells, like those planned for the Hindenburg & Graff Zeppelin II were incorporated in the discussion. Have 2 gas cells with hydrogen cells surrounded by helium to keep it protected. The problem with keeping hydrogen “safe” is that it would need to be stored in heavy sealed, pressurized containment units, which would defeat the greater lifting capacity (much like the water recovery sytems used in the American ships in the 1920′s-1930′s). Helium is very viable nowadays due to the reduction in weigh of airships due to modern materials: cas in point the Zeppelin NT weigs 2,200 lbs and is 12 feet longer than a jumbo jet. The only problem is that it can carry only 14 people and 3,000 lbs of cargo. Making a truly “rigid frame” modern airship would increase the size and weight carrying ability by a huge margin!! Unfortunately I’m not holding my breath witing for that to happen.
    Cheers!

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    Tony Holroyd December 10, 2010 at 10:02 am

    The biggest problem as I see it is that helium is a rare gas, produced by radioactive decay. There are only limited supplies available and other uses already account for a substantial demand. Price has risen substantially over the past several years, indicating that demand is begining to outstrip supply.

    A large Airship the size of the Hindenburg would require about 10million cubic feet of helium. More would be needed every year to replace losses. If Airships were rolled out on a large scale as an alternative to trains and aeroplanes, it is unlikely that helium would be avialable in the quantities needed to make the Airship a large scale alternative.

    Hence, it may be better to look at engineering solutions that allow us to use hydrogen safely. With modern materials such as kevlar and carbon fibres, gas cells could be much stronger and far less porous than the cotton gas bags of yesteryear. Hydrogen detectors could be placed within the ships frame and the whole outer cover could be purged with nitrogen as an additional safety measure. Any hydrogen that leaks out could be removed by fan from the crown of the outer cover and purged through a vent in the ship’s upper fin.

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    sls4ak October 29, 2011 at 9:17 pm

    I agree, I only wish that Lloyd’s of London would see it your way.

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    Tony Holroyd December 8, 2010 at 7:31 am

    ‘but helium’s inert, non-flammable nature makes it the only practical lifting gas for manned lighter-than-air flight.’

    I think that this is highly questionable. It is rather like looking at a WW1 petrol engine and concluding that the dangers presented by flamable petrol vapours make the use of petrol impractical as a fuel. That may have been the case in WW1 (where petrol vapours resulted in many casualties), but is it really the case today?

    I would be interested in investigating just how far modern technology and a safety engineering approach could reduce the risks associated with rigid Airship operations. Ultimately we would need to analyse the residual risk created by hydrogen, compare it to the increased operational costs of using helium and make a decision. The point is that you need to do the analysis before you can say what is pracrtical and what is not.

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