Cargo airships could be big, Eli Dourado notes, because the performance of an airship gets better as it gets bigger:
If your airship performance isn’t good enough, just double it in size. The lift will increase by a factor of 8, the drag will increase by a factor of 4, and the lift-to-drag ratio will therefore double. Still not good enough? Do it again.
To do cargo airships right, we need to make the biggest flying objects ever created. A modern cargo airship would make the Hindenburg puny by comparison.
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According to the Bureau of Transportation Statistics, average revenue per domestic ton-km is about 83¢ for air freight, 11¢ for trucks, and 2¢ for water transportation (in spite of the Jones Act).
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What we observe under these conditions is that, domestically, most of both the tonnage and value of cargo is transported via truck. Trucks are neither the fastest nor the cheapest mode of transport, but they provide a great value proposition—you get your stuff in a few days for much cheaper than air freight.
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Let’s say airships captured half of the 13 trillion ton-km currently served by container ships at a price of 10¢ per ton-km. That would equal $650 billion in annual revenue for cargo airships, notably much bigger than the $106 billion Boeing reports for the entire global air freight market. If one company owned the cargo airship market, taking only half of only the container market, it would be the biggest company in the world by revenue.
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If each airship can carry 500 tons, cruises at 90 km/h, and is utilized two-thirds of the time, that adds up to around 260 million ton-km per year per airship. To produce 6.5 trillion ton-km per year would require 25,000 such airships. This is about the number of airliners in the world today.
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When I initially started thinking about cargo airships, I thought it would make sense to take a cue from Hindenburg, which cruised at 125 km/h. As I will discuss below, maybe that is still the right choice, but even at that speed, you are on the wrong side of some unpleasant math.
The power needed to drive an airship is proportional to velocity cubed. Because the mission takes less time when the ship is moving faster, the total mission fuel required is proportional only to velocity squared. The net effect is that transport efficiency decreases quadratically with cruise speed.
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Cargo airships would probably be among the easiest vehicles to make unmanned. The sky is big and empty, but it’s especially empty over the ocean at the lowish altitudes, below airliners’ Class A airspace, where airships would fly.
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The USGS estimates the private sector price of helium to be $7.57/m³, while hydrogen is sometimes available for $0.11/m³. It would cost almost $8 million to fill our 500-ton airship with helium, and just over $100k to fill it with hydrogen. Lifting gas doesn’t get used up the same way as fuel does, but through leaks and venting, it wouldn’t be just a one-time charge. Hydrogen is cheap enough that you can design to vent it to help keep the ship trim.
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The USGS estimates that the entire planet has helium reserves of around 40 billion m³. Global helium production is only around 160 million m³ per year, enough for about 141 airships.
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Ideally, airship fuel would be neutrally buoyant, the same density as the surrounding air. This would ensure that as the fuel burned off throughout the journey, there would be no need to vent lifting gas. You could do this by using as fuel a mixture of the slightly heavier-than-air propane (C?H?) and the slightly lighter-than-air ethane (C?H?).
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With real-time wind data, it should be possible to plan a route that uses winds to minimize fuel burn and increase overall performance. It would be bringing a form of sailing back, only using tons of atmospheric data and autonomous route planning to do it in modern style.
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We’ve been assuming a cargo airship can do 260 million ton-km/year at 10¢/ton-km for annual revenue of $26 million/airship. The fuel cost of doing 260 million ton-km would be around $4 million, leaving $22 million/year for other costs including insurance, capex amortization, ground support, maintenance, and profit. This depends on a lot of assumptions, but if you can build the airship at rate production at a cost around $100 million, the math is getting close to working.
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In my experience, once you start thinking about giant cargo airships, it’s hard to stop.
Indeed, he kept thinking about airships:
You can cross the Pacific in a plane in less than a day. You can pay for parcel service that will get you your package in 2 to 3 days. But for air freight service, end-to-end delivery takes a week or more, involving multiple parties: in addition to the air carrier and freight forwarder, at both the origin and destination, there is a trucking company, a warehouse, a customs broker, and an airport. Each touchpoint adds cost, delay, and the risk of theft or breakage.
Once you account for all these delays and costs, the 4 to 5 days it takes to cross the Pacific on an airship starts to look pretty good. If you can pick up goods directly from a customer on one side and deliver them directly to a customer on the other, you can actually beat today’s air freight service on delivery time.
This changes everything. Since airships are, after all, competitive with 747s on delivery time, you can earn the full revenue associated with air freight, not just the lower trucking rates I had assumed. Cargo airship margins, therefore, can be much higher than I had realized.
Today’s 747 freighters have almost no margin. They operate in an almost perfectly competitive market and are highly sensitive to fuel costs. They simply won’t be able to compete with transpacific airships that are faster end to end, less subject to volatile fuel prices, and operating with cushy margins. A cargo airship designed to compete head to head in the air freight market could take the lion’s share of the revenue in the air cargo market while being highly profitable.
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Many software investors eschew hard tech startups because of their capital intensity, but it’s hard to deny that huge returns are possible in hard tech: just consider SpaceX. Bring me another SpaceX! the reluctant investors might say.
But even SpaceX looks like small potatoes next to an industry like global logistics. For a Falcon 9-sized investment, instead of revolutionizing a $2 billion/year (10 years ago) commercial launch market, you could transform a market that is at least 30 times bigger, with similar unit economics to SpaceX
The bane of all airships is the weather. High winds wreck them. Even on the ground, they must be kept in hangars.
They are a tried and failed technology, like renewables.
Airships exercise a powerful grip on the human imagination; this does not prove that they are useful, but it does mean that humans will keep TRYING to use them.
“a tried and failed technology, like renewables.”
That’s a pretty provocative throwaway line. I don’t really have a dog in the theoretical fight, but I know plenty of theorists like to line up for battles of pro-renewable versus anti-renewable. Maybe the AI trend will finally motivate the ultra-rich to pay for atomic power and finally Americans will realize fission is safer than they have been led to believe. If fission becomes widespread, most renewable projects will be abandoned.
Different aviation topic:
I would be interested to see internal combustion engines driving something like this:
https://www.cyclotech.at/
The lighter you can make a strong-enough airplane, the better. Lighter than air would be ideal. In the long run I expect lighter than air electric batteries.
I’m a total ignoramus with regard to engineering, but on an intellectual whim, could you theoretically flood closed off interior components of airplane’s with lighter than air gases to get better lift/fuel efficiency?
I imagine there are interior sections that could be made airtight relatively easily, and then just filled prior to flight. Would it be worth it?
Phileas: “Could you theoretically flood closed off interior components of airplanes with lighter than air gases to get better lift/fuel efficiency?”
There isn’t much unfilled interior space in an airplane. That’s why airships hang below gigantic balloons. And even then, how would you contain the gases?
An airplane does not have much volume for its weight, and the trick to making an airship work, as the article suggests, is to increase that ratio by going big, because doubling the size of an airship might quadruple its surface area, and thus its weight, while multiplying its volume by a factor of eight. Small containers of helium might weigh more than the lift provided.
And a bulbous aircraft with more volume would have more drag.
A cubic meter of helium can lift about a kilogram. So, a 10 m x 10 m x 10 m cube of helium could lift one ton. A 747 weighs 400 tons.
In a world with very cheap resources, we could start by building 500-meter-long dirigibles and then getting them airborne with vast quantities of helium, after which we might decide that the aerodynamics still sucked. But without huge budgets, one could not even start to make painful mistakes. Airships are so alluring in part because the high barriers to entry give impractical dreamers an excuse to never get started.
So my takeaway is that Planes simply have a different operating principle that makes any sort of hybridization between Airships and Planes, with regard to their mechanism to achieve lift, redundant at best or inhibitive at worst.
I appreciate the responses gentlemen.
A hybrid has been proposed:
THAT is interesting. So instead of, “airship-ifying,” the plane, they, “plane-ify,” the airship.
Could someone please explain to me how a heavy lift airship goes up and down without either
1. using helicopter type lift mechanisms
or
2. releasing precious lift gas
because both of those methods are horribly impractical and the first one negates any reason for an airship.
Like submarines, airships shoot for neutral buoyancy. Then thrust is generated with propellers or, conceivably, turbines, and directed opposite the desired direction of travel, whereupon the airship trundles lazily forth.
Incidentally, airliners fly so high—thirty to forty thousand feet—because the air is so much thinner, reducing parasitic drag very considerably and greatly reducing turbojet specific fuel consumption. Since airships travel so slowly by comparison, aerodynamic drag is hardly a consideration, so there is rarely any compelling reason to go more than a few thousand feet in the air.
John Smith says, “both of those methods are horribly impractical and the first one negates any reason for an airship.”
It does not. WIG plane must briefly use a liftoff engine group (much like VTOL), but when cruising is more fuel-efficient than a basic cargo plane.
Likewise, a lighter-than-air craft sometimes using one more engine is still much more economical than a helicopter. And if those are merely for maneuvering, rather than keeping the whole thing in the air, they are going to be much weaker than needed for helicopter style lift. This usually allows greater fuel efficiency or other perks.
Besides, vertical thrust can be converted or redirected to propulsion, then it’s not a waste of mass while cruising. Could be done via Osprey style turning pods or turbofans with several exhaust ports.
As to the lifting gas, it’s more fitting for slower long-term buoyancy adjustments.
What matters is the total balloon volume, usually tweaked via pressure. If you pump it into a cistern (or even into stronger inner cells) or heat/cool it, this will change pressure in the balloon without losing any gas. Though losing (and producing) gas is a viable option, sin ce cargo and other applications of “load at point A, unload at point B” sort require only modest endurance. Exotic extra-long missions would require a very specialized vehicle either way.