Helium-Filled Alternate History

One of the great what-ifs of history is "What if the Hindenburg hadn't burned down on live radio- making it one of the most indelible news events of the 20th century?" And what if WWII->Cold War hadn't shifted our technological priorities toward high-altitude, high-speed jet-powered aircraft- the civilian application of which is the commercial airliner. What if airships had continued to be developed? Helium, with a molecular weight of about 4 grams / mol, is twice as heavy as diatomic hydrogen (around 2 gram/mol). However, compared to air, which is about 29 grams/mol, it's still excellent. The difference between 2 and 4 grams compared to 29- about 7%. In other words, if the Hindenburg had used helium- as it was originally designed to- it would have been able to carry 7% less payload.

The real what-if actually comes earlier. What if the U.S. (the world's only supplier) hadn't banned the export of helium to Germany in the run-up to WWII? Not counting dark matter, helium accounts for 24% of our galaxy- 12x more mass than the rest of all other elements combined. Hydrogen accounts for 73.9% of what's visible. Here on earth, the only viable source for helium is as a radioactive decay product that accompanies the natural gas from certain wells in the U.S. and a- to a lesser extent- Poland.

Helium, unlike hydrogen, isn't something you'd want to throw away. The Hindenburg was designed to use dynamic envelope control which requires a heavier airframe and a higher margin of error. That's because the helium wasn't going to be vented to make for an easy decent. Switching to hydrogen allowed the Hindenburg to carry 7% more passengers and freight according to the raw numbers. It probably would have carried several percent more because of how it was being flown.

We (now) know hydrogen is dangerous. Hydrogen is actually two gases mixed together- both consisting of diatomic hydrogen- the molecules of which are arranged differently. The exact properties of hydrogen gas depends on the combination of these two isomers, which in turn, depends on how long the gas has had a chance to reach equilibrium.

In other words, fresh hydrogen is quite different from stale hydrogen.

As for safety, when it burns, it burns rapidly, invisibly (it skips the visible spectrum but is visible in IR and UV), and- provided enough oxygen- totally. It's ignition temperature (500C) is well within reach of all manner of things, including matches and static electric sparks. One of its not-quite-saving graces is that, in its pure form, it doesn't burn at all. It needs oxygen. Also, when it burns, the flames tend to rise quickly and it produces no smoke. Most of the people who died on the Hindenburg died because they were inside the hull and had nowhere to escape to as the ship's diesel burned nearby. Out of 97 passengers and crew, 61 survived.

Helium is relatively safe. Its stable, non-reactive, and fun. The only way it can kill you is by asphyxiation- since breathing pure helium has all the health benefits of not breathing anything at all. Mix it with the right amount of oxygen, however, and you've got a superior diving gas.

Helium, if made available at the right moment, would have harnessed innovative energy that was dedicated to high speed aircraft. That shouldn't sound like a total shame. Jets are fast. And not too expensive. And safe. But they're also the only option. And they're expensive. Take a 15 hour trans-oceanic flight without enough room to unfold your knees. And then consider the following:

According to estimates, there were over 4 trillion ton-miles of intermodal domestic freight shipped in the United States during 2008. Intermodal means "by every method." The worldwide volume of freight transported by sea is over 35 trillion ton-miles. This represents 4x increase over the last four decades. And all of it, ALL OF IT, is powered by fossil fuels. In fact, around *half* of that freight volume IS fossil fuels: crude, oil products, and coal being freighted from one part of the world to another.

The most efficient mode of transport is using very large ships (boats). Boats are incredibly efficient when compared to rail, road, and runway. Boats are made of steel, which is cheap and abundant. Large ships involve a lot of surface area, and hence, a lot of friction with the water they travel through. But they also have enormous amounts of internal volume. And the bigger they are, the more favorable the ratio between area and volume. And they don't go very fast, so induced drag isn't too bad. Only problem. Boats don't work on land.

Next most efficient is rail. Low speed hence low friction. Low manpower costs. Efficient engines. Logistics are slow and, for many products, unworkable. To really do point-to-point transport, you need trucks. High manpower costs- which mitigates the highly fluid logistical challenges. Not extremely efficient, but enormously flexible. And both rail and trucking require infrastructure that needs to be maintained. And we won't discuss airfreight, which has only speed to its advantage, which solves a lot of logistical issues in one fell swoop. Remember when the idea for FedEx got a C when it was turned in as an assignment at Harvard Business School?

So here's the question we're drifting toward: could airships have had a role in transporting freight? The short answer should be obvious: no. They don't so they couldn't. There are only around 50 working airships- most of them blimps- and precious few of them are used for transporting anything resembling freight in any meaningful way. The golden age of airships ended with the burning of the Hindenburg- just as it was getting off the ground. But the reality is, airships were on their way out anyway. The Hindenburg wasn't the first airship to go down. The U.S.S. Macon, which was nearly as large- and which was filled with helium- experienced a far more dramatic trip to earth (unless dramatic = flames, in which Hindenburg wins most competitions). Hindenburg was just the most visible. Also, at the time, airships were competing, not with air travel, but with sea travel. Considering the risk of being sunk by a submarine, the definition of "safe" was a rather low mark. And the Hindenburg would have made for an extremely poor flying truck. It's crew consisted of more than forty people. It was a niche craft.

It may have been beautiful, immensely romantic, and intensely inspiring to look upon. But inspiring doesn't pay bills. And inspiration that doesn't reproduced isn't worth much.

Here's the crazy thing, though. The design for airships like the Hindenburg- that distinctive torpedo-like shape- actually pre-date the invention of the airplane by a about twenty years. Count Ferdinand von Zeppelin was making flying cigars in 1894. And there were elongated dirigibles that date back to the 1880s. By the time Orville and Wilbur started toying around with powered kites, Zeppelins were a major industry. And everyone knows that airplanes win wars while airships much prefer peace. (German Zepellins were used to bomb London during WWI but after 1915- during which they lost at least half their airships, they abandoned their use. One of them was bombed out of the air by a British pilot flying an early monoplane. Live by the bomb, die by the bomb.

So here's another big "what if?" What would have happened if airships and airplanes had been developed at the same time?

What would have happened if the following ingredients were combined in a single place?

1. Helium made available as an openly-traded commodity.
2. Aerodynamic lift theory applied to lighter-than-air craft.
3. Application of progressive materials science coupled with advanced structural engineering.
4. No intrinsic fear of airships among the general public.

I'll tell you what *might* have happened.

Airships might have matured into lifting body hybrids. Flying cruise ships. Flying trucks- able to sail on prevailing winds. Flying construction cranes. Maybe even flying towns. Flying launch platforms.

Double-Hybrid Airship

So I've been thinking about airships lately. If you've read my previous post about (actually) building flying cities, you'll know that this isn't a new idea.

I think I first thought about building a hybrid airship about six or seven years ago. It was a passing fancy: develop a set of plans or kit for building a small personal dirigible. And that's about as far as it got. Dirigible means steerable. Like a Zeppelin- which also has a rigid frame.

Airships are the quintessential romantic conveyance. They show up in alternate history, steam punk, technopunk (okay, Nebuchadnezzar was a "hovercraft"- same idea). Mummy movies. Final Fantasy games. Oh, and the Teddy Ruxpin cartoons back in the '80s. Great epicadventure, unbearable singing. And, of course, Up.

So I'm definitely not the only one who has picked up on this theme. And yet, there are no airships anymore. Sure, the DoD is fielding some radar platforms. There's the Goodyear Blimp. And don't forget hot air ballooning. That's pretty close to the spirit in question.

I was talking with a friend a couple weeks ago. I think our conversation started with a mention of Balloon Boy, and whether it was plausible to actually build such a craft. I started to think about it. The things we talked about were more to do with the spirit of the idea. I started to think about it in practical terms.

The question, as it turns out, isn't how big you build an airship, but how small. Small is cheap. Cheap is attainable. It's easy to imagine a multi-million dollar project that would be guaranteed to fly by virtue of its volume of helium. It's not so easy to imagine getting off the ground on several hundred thousand.

The airship you see in these pictures is actually more of a lifting body aircraft than it is a hybrid airship. It gets less than half of its lift from helium. To achieve the shape, it is built like a omni-directional suspension bridge. There's a open-topped box at its center that is comprised of four tent poles. These are held apart by a pair of horizontal girders that run from nose to tail. They're built like a construction crane (only much lighter).

To the left and right there are several more girders that define the lateral dimensions. Attached to these is a kind of vertical stabilizer that is in place to prevent the air moving over the lifting body from sliding sideways. Hence they are called slip limiters.

The whole aircraft weighs a little less than 16,000 lbs of dead weight. It is a little over 100' long and 80' wide- not counting the roll-control wings. The internal volume of its lifting gas is about 120,000 cubic feet. The cabin is around 1000 square feet of usable space. It uses a single diesel and a set of super capacitors to power all four ducted fans. The capacitors would power the burst of thrust needed to get airborne. After that, aerodynamic lift would take over. Ducted fans are actually more efficient a low speed- less than 100mph. This airship would max out at about 50mph.

Parts of the lower surface would consist of transparent Tefzel, allowing passengers to look straight down, through a Tefzel window- and transparent helium- at the ground below. And the ground would never be very far away. The cabin would be unpressurized. It would solar heated (like a greenhouse) and actively cooled using air conditioners. Parts of the airship's top surface would be covered with lightweight, thin-film photovoltaics. It's conceivable that the aircraft could cruise on solar power alone- albeit at minimal speed. Because of its low speed and enormous area, it might actually be able to achieve meaningful lift from thermal activity. A soaring airship. In such a mode, the ducted fans would be used for extremely tight maneuvering, not for forward thrust.

The amount of usable cabin space would be on par with that of a 50' sailing yacht. It would be capable of landing and taking off from water. Because it would be heavier than air, it would need to be anchored, but not hangered when not in flight.

It would take off at about 20mph.

The airship could be flown using aerodynamic controls. Yaw would be managed with the twin rudders attached to the aft ends of the slip limiters. Angle of attack would be managed with the substantial elevator at the aft end of the main body. Roll would be managed via the side wings.

The internal gas volume would be separated into a number of chambers by a super thin layer of Mylar. Once airborne, the craft would be able to maintain flight even if all of its lifting gas were lost (assuming that the wing surface is mostly intact.)

Here's my Facebook page on the subject. Same thing, presented differently.

A New Method of Acheiving Lift

Yesterday's post about how to actually build a Cloud Nine.

Ways of achieving lift. Plus one that's never been used.

Rocket lift. One of the oldest forms of lift. Stay on one side of a long-lasting explosion and you will find yourself flying.

Airfoil lift. Again, very old. Kites use this. Essentially, a combination (to a relative degree depending on airspeed, wing chord, wing loading, etc) of downward deflection and an upward-pulling low-pressure area above the wing. Used in gliders, powered aircraft, ekips, rotorcraft, frisbees.

Hotter than air lift. Relatively recent invention. A form of lighter-than-air lift. Heating normal air lowers it's pressure relative to the surrounding air, making it lighter. Requires a heat source. Is highly dependent on the relative temperature of the surrounding air. Doesn't work well in warm weather.

Light gas lift. More recent still. Helium or hydrogen has a lower molecular weight than the air thas surrounds it. Doesn't need extra heating, works regardless of relative temperature. Economical for use or large airships. Low cost way of staying aloft for a long time.

Accelerated air lift. It's debatable whether this deserves to be a category of its own. Like rocket lift but works by moving the air, not by controlling an explosion. Insects use a version of this. Insects (with the exception of butterflies and their ilk) don't use airfoil lift.

Eh, okay. Electrostatic lift. Electrically inducing an ionic flow. Check youtube.

And then their's one more that has never been exploited before.

Low-pressure lift. It's a form of lighter-than air lift. Instead of heating the air to lower its weight by lowering its pressure, or simply using a lower weight gas to begin with, it is possible, though very difficult, to achieve lift by lowering the pressure.

Essentially, by removing air from the lift volume, you make the lift volume lighter. But you can't do that with a balloon. A balloon would just get smaller, equalizing the pressure difference as it did. You need a rigid wall. The more air you remove, the more rigid it needs to be.

With Cloud (see previous post), which requires a rigid wall to begin with, it would be possible to to pump a few percent of the air out of the inside of the volume. This would put positive pressure, pushing inward, on all parts of the structure simultaneously (though not equally- an approximately 17% difference from top to bottom due to differences in atmospheric pressure).

Each percentage point of air removed from the interior would translate into more than a hundred tons of additional lift.

This method can also be used in concert with light-gas lift and hot-air lift.

But it's a risky approach because, if you breach the envelope, you lose the extra lift. Instead of relying on low-pressure lift at all times, it could be used as an emergency back-up plan. Powerful pumps could quickly remove some of the air to boost altitude. It would be used as a first resort- particularly in areas where dropping a hundred tons of water might not be particularly neighborly. It could also be used after water ballast had already been dropped, as a last-resort emergency maneuver.

Actually, low pressure lift is an old idea. Otherwise known as vacuum lift, it dates to 1670 when a brilliant Jesuit priest named Francis Lana conceived of an airship held aloft by airtight copper spheres from which the air had been pumped out. To make a copper sphere strong enough, however, would require making it too heavy to fly. In fact, no such metal is strong enough on the scale Lana had in mind (about seven meters in diameter).

By building extremely large, and by lowering one's expectations of acheiving near-total vaccuum, it's actually conceivable.