The two primary lifting gases used by airships have been hydrogen and helium.
Hydrogen is the earth’s lightest element, and it can be obtained easily and inexpensively, but its flammability makes it unacceptable for manned airship operations.
In addition to the famous Hindenburg disaster, dozens of hydrogen airships were destroyed by fire, and no American airship has been inflated with hydrogen since the crash of the U.S. Army airship Roma in 1922. The use of hydrogen as a lifting gas for passenger airships was completely abandoned by the late 1930s.
Helium’s non-flammable nature makes it the only practical lifting gas for manned lighter-than-air flight, but it is scarce and expensive, and the use of helium can reduce a rigid airship’s payload by more than half.
While the use of helium presented obvious operational challenges, airships of sufficient size were able to operate effectively when inflated with helium. LZ-129 Hindenburg was designed to operate with helium and could have conducted transatlantic operations to North America, although with a much smaller payload, with helium as a lifting gas, and the U.S. Navy’s rigid airships were also able to fulfill their missions inflated with helium; U.S.S. Akron and U.S.S. Macon served as airborne aircraft carriers, carrying embarked fixed-wing aircraft, using the heavier gas.
Hydrogen and Helium: The Basics
Hydrogen and Helium are the two lightest elements on the periodic table:
Atomic symbol: H (as a gas, H2)
Atomic number: 1
Atomic weight: 1.007
Atomic symbol: He
Atomic number: 2
Atomic weight: 4.002
The atomic weight of a helium atom (4.002) is approximately four times that of an individual hydrogen atom (1.007), but since gaseous hydrogen is a diatomic molecule containing two hydrogen atoms (H2), helium gas is only twice as heavy as hydrogen gas.
The Relative Lifting Ability of Hydrogen and Helium
Although helium weighs twice as much hydrogen, because each gas is so much lighter than air helium provides about 93% of hydrogen’s lift at full purity. In practical operation it is impossible to achieve or maintain 100% purity of either gas, reducing helium’s lifting ability to about 88% of the lift of hydrogen.
The actual lifting ability of each gas varies with temperature, pressure, and humidity, and 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.
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.)
(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 Effect of Helium on Airship Range and Payload
In actual use, because of physical realities and operational considerations, the use of helium can reduce an airship’s payload lift by almost half.
Fixed Weight vs. Lifting Gas
Much of an airship’s weight is fixed (the dead weight of the ship’s structure and engines, and required weight such as crew and ballast) so the entire effect of the reduced lift of helium is absorbed by the ship’s payload; a helium-inflated airship therefore has a much lower payload for passengers and freight, and a much shorter range (because it can carry less fuel), than a hydrogen-inflated airship of the same size.
Operational factors further decrease the payload of a helium-inflated airship.
Lower initial inflation:
As an airship rises its lifting gas expands, so an airship that begins a flight with its gas cells fully inflated must release gas as it climbs to keep the cells from bursting. Because hydrogen is inexpensive and easy to manufacture, hydrogen airships usually 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 only 90-95% inflated — thus reducing payload — to allow the gas cells to expand without the need to release valuable helium.
Exhaust recovery apparatus:
Hydrogen and helium airships also had different means of compensating for the lost weight of fuel burned in flight. Hydrogen ships simply released inexpensive and easy-to-replace hydrogen, but helium-inflated ships required equipment to recover water from engine exhaust to compensate for the weight of burned fuel and avoid releasing valuable helium; the weight of this heavy equipment further reduced the payload available for fuel, passengers, and freight.
Payload Effect of Helium versus Hydrogen
LZ-126/U.S.S. Los Angeles gives a real world example of the difference between operating the same ship with helium versus hydrogen.
When the German-built LZ-126 flew from Germany to the United States for delivery to the U.S. Navy in 1924 it was inflated with hydrogen, and the ship made the flight from Friedrichshafen, Germany to Lakehurst, New Jersey — 5,006 miles — 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 transatlantic flight. And never again did the ship fly as long as it did on its delivery flight with hydrogen, which lasted 81 hours, 32 minutes; ZR-3’s longest flight with helium was a little over 48 hours.
|LZ-126 / ZR-3 Los Angeles||LZ-126 (hydrogen)||ZR-3 (helium)|
|Gross lift||179,266 lbs||153,000 lbs|
|Empty weight||77,836 lbs||90,400 lbs|
|Useful lift||101,430 lbs||63,100 lbs|
The following chart illustrates the dramatic reduction in payload between helium and hydrogen by comparing the actual payload from a Hindenburg flight across the South Atlantic using hydrogen with the same flight if the ship had used helium.
|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|
Inflated with hydrogen, Hindenburg was able to carry 21,076 lbs of payload; if the ship had been inflated with helium it could not have made the flight at all.
(Information is based on Hindenburg Flight No. 10, from Rio de Janeiro to Friedrichshafen on April 6, 1936, as reported by U.S. Navy Lt. Cdr. Scott E. Peck.)
Doesn’t the comparitive % of lift provided change significantly with altitude and pressure? One way or the other.
I wonder how vacuum (for theoretical vacuum airship) compares to hydrogen and helium?
Not a practical or serious concept.
To expand, the weight required to maintain the vacuum outweighs any benefits. The concept has been explored with certain designs at small scales, and they often blow up. The idea…doesn’t fly
If hydrogen was used, would it be possible to use a fuel cell for ballast? Create hydrogen through electrolysis for lift, fuel cell creates electricity for weight? For a fully sustainable energy future, hydrogen will likely be a part of that future. Transportation is a major issue for hydrogen. Has… Read more »
I’ve been contemplating this concept too, for years. With modern tech, the Hindenburg design would have 10x more payload I think. But it still wouldn’t beat transatlantic ships as those are extremely fuel efficient; it would win on speed, number of trips per year and could find a niche with… Read more »
why so many crew ? why oil and hydraulic system when you can use fly by wire ? why too much fuel when we have nore powerful and efficient piston engines ? why don’t use carbon fiber instead of alumminium ? and what is Misc by the way ? Damn… Read more »
Very interesting! What would be the practicality of either mixing a small amount of hydrogen with helium (I gather less than 3.9 mol% of hydrogen in helium is classified as not inflammable)? Or perhaps isolating an interior envelope of hydrogen in an exterior envelope of helium? An internet search seems… Read more »
WOW, great minds think alike!! I was wondering that too. Considering Helium’s scarcity and hydrogen’s lifting power (and my fascination with airship travel) I had wondered about a design of the same thing – a hydrogen interior surrounded by say a graphene based skin (or something similar since I believe… Read more »
Hi John Greener, Not sure why I neglected your reply so long! Clearly there’s some enthusiasm for the idea, and Antony has demonstrated there’s a precedent. Surely a hydrogen envelope tapped only for buoyancy reasons, and otherwise isolated from the air by a static reservoir of helium, would be no… Read more »
The Germans investigated this idea for use in the Hindenburg, with a small hydrogen cell suspended within helium gas bags, the idea being that as the ship rose, the inexpensive hydrogen would be released. Tests were undertaken and the final design and location of the gas valves on the ship… Read more »
Thank you kindly, Antony, I should have an opportunity to read up on that this Summer. Alas, it sounds like one more historical missed opportunity.
There is a reference to this system on page 93 of The Golden Age of the Great Passenger Airships Graf Zeppelin and Hindenburg by Harold Dick and Douglas Robinson (1985) and page 37 of Zeppelin Hindenburg by Dan Grossman, Cheryl Ganz and Patrick Russell (2019).
Today scientists are developing hydrogen powered cars. Their great challenge is said to be the small amount of hydrogen produced for the cost of extracting it with complex and expensive machinery. If early in the 20th century we were able to produce the extreme amounts of the gas for dirigibles… Read more »
Hydrogen is cheap to produce. The problem with cars is that they need a network of gas stations, and thats not cheap
Helium is so light that when it escapes, it floats to the top of the atmosphere, where solar heating accelerates individual molecules to escape velocity, and the helium gradually “evaporates” from the earth never to return. New helium is a biproduct of radioactive decay, a very slow process, but the… Read more »
You’re missing a salient point, helium is obtained from rock which were found only in the USA. They wouldn’t sell it to the Germans in the first place, so they went with the only other gas they could use. The most fascinating thing about helium is that as it doesn’t… Read more »
It puzzles me that Hydrogen is dismissed by so many. Commercial rigid airships had an excellent safety record over all (in times of peace) and that at a time when we knew far less about materials, risks of sparking due to stress on metals or static sources and other charge… Read more »
I agree with you. I would not hesitate to fly with a H2 filled machine. The materials we have now are much less permeable and would loose much less of the H2 which the paranoid of fire would appreciate as a safety item. However fire would be very unlikely due… Read more »
Exactly. I’m thinking of doing this(just retired). Aluminized mylar should conduct away any static. Fifty internal pancake cells should make trimming safer. Also, old vacuum tubes had “getters” that would absorb and oxygen that migrated into the tube, each cell would have getters with indicators that would let you know… Read more »
I suggest carbon fiber, lighter,stronger and is not conductive for electricity
My thoughts exactly. Its not even that easy to get a significant hydrogen explosion or fire – you need to mix hydrogen with air in an enclosed volume and provide a spark. Just spark is not enough, even inside of the gas bag, as there’s not enough oxygen in the… Read more »
I agree 100% with Mr keil . OK some people died in the H B crash. This was the first time a crash was caught on film so lots of people saw it world wide. These days planes go down , many catch fire, 200 or more die but people… Read more »
It would be wonderful to see a working model. At least practical specs and a material list. The ability of solar powered craft would further enhance the craft’s safety and would just flat out be cool,
Agree as well. There is a recent documentary highlighting how difficult it was for the RAF to bring down hydrogen filled Zeppelins in WWI. They invented exploding rounds, flaming tracers and nothing could seem to set them alight. Only by mixing the two rounds and concentrating all fire to one… Read more »
Investigate the use of graphene bladders to contain the lifting gas as well as other structural components of an airship. Graphene could reduce dead weight considerably.
Not to mention the added strength, and very nearly bullet proofing. I’m vagly aware of the properties of Graphene so wonder about the conductive properties too. If I have heard right Graphene is a very good conductor so that would make it much safer from static electricity such as lightening.… Read more »
I think even using just regular carbon fiber would be able to reduce the weight of the hull significantly and maybe it would even make sense to make gas bags out of kevlar or some modern material which would probably be much lighter than whatever they made gas bags out… Read more »