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.)
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

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 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

 

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 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

 

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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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 »

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 »

Franny Wentzel

Would it not be possible to isolate a hydrogen gas bag inside a helium one in order to mitigate some of the payload loss and allow the ability to simply vent hydrogen for ballasting purposes?

Dean Studer
Dean Studer

I wonder about a small safe recreational use of helium to cruise around at low altitudes for short periods of time. Why couldn’t helium in a pressurized container be released to a balloon to rise up with and then a vacuum canister be used to partially deflate to come back… Read more »

FroggyZeppelin
FroggyZeppelin

Check out the Aeroscraft. I think you’ll find they’re a bit ahead of you.

BlindBat

Interesting Idea – The current thinking in these aircraft are to make them heavier than air. The Helium is just enough to zero out the vehicles gross weight. Then counter spinning GyroCopters (like a Toy Drone Helicopter) are used to lift the aircraft and provide Pitch and Roll Stability. Then… Read more »

Eric Mitch
Eric Mitch

I have been working on a design for just that. I would love to collaborate with someone who is working on the same wavelength.

Aldo Díaz
Aldo Díaz

A year ago, you wrote this, are you still interested to collaborate?

Victor Zimmer

Sadly those small pesky helium (and hydrogen) atoms have a tendency to make their way thru the material enclosing them and out into the atmosphere, and when that happens there is no stopping the United Helium Atoms Space Program

Jason Craig
Jason Craig

It would be more efficient (by orders of magnitude) to mechanically compress the bladder than use a compression technique.

Small dirigible drones will not be able to supply the power required by the compressor motors and solenoids.

bob
bob

I think your idea is a good one considering the very light tough materials available today coupled with present day solar efficient capabilities and computer controls to automatically maintain a set height and speed.

Dimitris
Dimitris

WHAT IF the balloon was made from a material that even if the hydrogen caught fire, the material would not burn and tear ? So even if the hydrogen caught fire (and assuming there would be little air inside the balloon, for example 10% air – 90% hydrogen), the air… Read more »

Trevor
Trevor

To give a quick example of how much strength is needed to contain an explosion you just need to look at auto engines. The block of the engine is very thick compared to the volume of hot gases (the fuel is turned from a liquid to a gas during combustion)… Read more »

bob
bob

The Hindenburg was very likely sabotaged by a single shot from a tracer bullet.

Phill
Phill

A single shot wouldn’t have done it. The gas needs oxygen to burn. A single shot, no matter how hot, would simply penetrate the skin and bladder, and go out the other side, moving too fast to set it off. The power of tracers in bringing down balloons during World… Read more »

Patrick Cameron
Patrick Cameron

During WWI the British spent considerable effort to develop incendiary bullets that could ignite German airships when it was found the airships were easy to perforate but very hard to ignite. Ref. Pomeroy/Buckingham bullets.

Adam Danischewski
Adam Danischewski

Excellent idea! I think it is very possible to have a flameresistant skin, hydrogen does not explode as some commenters have mentioned it needs the oxygen that is in the air. Perhaps some advance layers that release fire squelching / re-sealing material (e.g. tiny network of switchable tubes and sensors).

BlindBat
BlindBat

I wounder if anyone has tried to mix Hydrogen and Helium in a gas bag – to reduce the flammability of the Hydrogen. I realize the gasses would eventually separate as the hydrogen rose and the helium settled to the bottom – but perhaps a circulation pump could draw the… Read more »

Michael
Michael

There’s also the issue of lift. If some hydrogen burns, it combines with oxygen and forms water vapor, which is much denser than hydrogen, so even if the skin could withstand the heat and overpressure, it would still deform to envelope a smaller volume.

Hannah
Hannah

I agree with Trevor regarding the hull thickness/combustion pressure problem, but I wanted to tell you to look at the U.S. Navy’s ZMC-2. Its hull was a single, solid piece of metal–no balloonets. It was the only one of its kind and very much like a LTA soda can.

Mike
Mike

I understand why lifting gas expands as the aircraft rises, but does it really need to be vented? Can’t it just be re-compressed? I’ve worked with lightweight carbon and Kevlar tanks and high speed compressors, it strikes me that all that expensive/rare helium could just be re-compressed onboard as the… Read more »

bob
bob

I would say yes and it could be very easily computer controlled through an equation of ambient air pressure, temperature and craft weight plus load.