Hydrogen vs 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.
{ 17 comments… read them below or add one }
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!
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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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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?
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Why not use compressed hydrogen for fueling either motors or fuel cells, and storing excess hydrogen at altitude by compressing it or hydride storage ?
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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.
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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.
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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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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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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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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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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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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) Reply:
March 7th, 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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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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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 Reply:
February 6th, 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 Reply:
February 14th, 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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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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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 Reply:
December 10th, 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 Reply:
October 29th, 2011 at 9:17 pm
I agree, I only wish that Lloyd’s of London would see it your way.
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‘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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