Hydrogen and Helium in Rigid Airship Operations

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.

Hindenburg disaster at Lakehurst

Hydrogen fire destroys Hindenburg, May 6, 1937

 

Burning wreckage of the U.S. Army's hydrogen airship Roma; Norfolk, Virginia - February 21, 1922.

Burning wreckage of U.S. Army hydrogen airship Roma. Norfolk, VA, February 21, 1922.

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:

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 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.)
Net Lift
(per 1,000 cu. ft.)
Hydrogen5.31 lbs76.36 lbs71.05 lbs
Helium10.54 lbs76.36 lbs65.82 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

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/ZR-3:

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 AngelesLZ-126 (hydrogen)ZR-3 (helium)
Gross lift179,266 lbs153,000 lbs
Empty weight77,836 lbs90,400 lbs
Useful lift101,430 lbs63,100 lbs

 

LZ-129 Hindenburg

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.

LZ-129 Hindenburgkglbs
Dead weight118,000260,145
Crew5,40011,905
Provisions3,0006,614
Fuel58,880129,808
Oil4,0008,818
Ballast7,95017,527
Misc.9,12020,106
206,350454,924
Gross lift/hydrogen (68lbs/1,000 cu. ft.)215,910476,000
Payload for passengers, mail, freight w/ hydrogen9,56021,076
Gross lift/helium  (60lbs/1,000 cu. ft.)190,509420,000
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.)

 

 

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Steven Lehar
Steven Lehar

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 »

Martin Davenport
Martin Davenport

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 »

Peter Keil
Peter Keil

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 »

D Frank Robinson
D Frank Robinson

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.

Tsayper
Tsayper

Could they pump ocean water for ballast instead of getting it from exhaust?

Tom
Tom

Hi Been reading the blog with interest. One thing to add. About 2 years ago in California that had massive find of H3 Helium. http://www.livescience.com/51402-helium-leaking-from-earth.html H3 Helium is direct from the earth’s core. This gas was found in a oil well So could be capped and pumped for the rare… Read more »

Martin Davenport
Martin Davenport

Hi Tom, once helium gas been released into the atmosphere it rises and escapes our gravitational pull (as it’s such a small and unreactive element), so maybe we should ditch all helium balloons.

Siber
Siber

I believe, if you look at things logically, that hydrogen is the only option we will have going forward. Helium is costly to produce and escapes the atmosphere when released while being inordinately rare. Hydrogen is more powerful as a lifting gas. The issue of safety in regards to hydrogen… Read more »

Jason
Jason

Has anyone explored the idea of a rotating gaseous cylinder (horizontal rotation) as a means of preventing loss of Hydrogen or Helium? What about using specific molecular frequencies to prevent the loss of gas? What about a combination? Would it be cost effective? That would be an interesting myth-buster episode.

Jason
Jason

I saw the Airlander on TV recently. Even with Ballonet(s) there is plenty of room inside for two large Hydrogen balloons. Perhaps this could reduce the size of Airlander. With less overall mass perhaps the airlander could move more efficiently. My question is, “At what temperature can helium’s lift match… Read more »

Jason
Jason

If we heat the helium up to 550 degrees kelvin it should have a density similar to hydrogen. That is if the hydrogen stays at standard temperature and pressure. I wonder how close to 550k could be achieved with microwaves and passive solar heating. – The kevlar would probably melt.

Bananabender
Bananabender

An internal report by the Zeppelin Company showed that the fire that destroyed the Hindenburg was actually due to the extremely flammable aluminium/iron oxide (aka Thermite) based dope applied to the outer skin of the craft. This was struck by lightning and caught fire well before the hydrogen ignited. A… Read more »

Christopher E Jones
Christopher E Jones

Is it possible to utilize hydrogen and helium in a single craft in a two sectioned bladder? Would it give any advantage if it were possible? Also what if the craft was gas lifted by towed over ground like a trolly ( ftom its belly) and it utilized existing electrical… Read more »