Airships may finally prove useful for transporting cargo. The problem of variable buoyancy is being overcome.
author: Benjamin Sutherland
October 30, 2024 | The Economist
In 1783 the Montgolfier brothers lofted a trio of farm animals over Versailles in a hot-air balloon, in what remains the most iconic demonstration of the power of lighter-than-air craft. Since then such vehicles have adapted to carry ever more—and ever more distinguished—passengers. But they have rarely been used to transport cargo.
This is a wasted opportunity. Floating objects, whether boats, bubbles or blimps, can be moved and parked with relative ease. Because airships boast such exceptional “lift-to-drag ratios”, as engineers put it, they also consume relatively little fuel. This makes them—at least in theory—ideal freight vehicles.
The big stumbling block so far has been the need for variable buoyancy: the ability to compensate for weight changes when loads are picked up and dropped off. Simply releasing the lighter-than-air “lifting gas” from the sacs in which it is held is a non-starter. Maintaining stockpiles wherever deliveries are made is logistically difficult and expensive (helium, the most commonly used lifting gas, now costs about $35 per cubic metre, the amount needed to lift a single kilogram).
Now, however, a handful of firms say that they have devised feasible alternative systems for adjusting buoyancy. If their plans hold up, airships designed to move everything from felled trees to prefab buildings could soon take to the skies.
One straightforward way to control buoyancy is to take on and release ballast. Though large amounts of sand or dirt cannot be extracted or dumped at will, water is easier to handle. For that reason, Flying Whales, a company based near Paris, has designed a 200-metre-long “flying crane” helium airship called lca60t (mock-up pictured above) to hold up to 60 tonnes of water ballast. Sébastien Bougon, the firm’s boss, reckons it would be practical for moving rocket sections and powerline towers; transporting logs from forests to sawmills; and carrying heavy equipment like turbine blades and prefab hospitals to remote areas. With help from aerospace partners including Boeing, Pratt & Whitney and Thales, he hopes to have the first airship built and certified by early 2028.
Up, down and away
One alternative way to reversibly change an airship’s buoyancy is to compress its helium. The newly available space can then be filled by drawing in (and pressurising) heavier air from outside. Flying Whales, for its part, eventually hopes to shift from water ballast to compression kit with help from Air Liquide, a French gases producer that is one of its financial backers.
Aeros, a Los Angeles-based maker of advertising and surveillance airships, has already developed such a compression system. Its plan is to operate floating warehouses that will serve as hubs for fleets of drones shuttling e-commerce packages to nearby homes and businesses. The firm’s chief executive, Igor Pasternak, says a modified version of its 40E Sky Dragon airship, which carries a payload of one tonne, is to begin a “commercial demonstration” above Los Angeles County by early 2025.
Operating a floating hub of this kind has proved too ambitious for some. Amazon patented such a concept in 2016 and Walmart applied for a similar patent the following year, though neither American retail giant appears to have pursued the idea. Aeros is undeterred. ShipBots, a firm that currently uses lorries to deliver parcels in Los Angeles, has agreed to pay Aeros $5m for 1m such deliveries. ShipBots’s boss, Payam Ahdoot, says the goal is to have a drone in a customer’s backyard within 90 minutes of being summoned.
Though Aeros is tightlipped on the specifics of its compression system, some consider the approach to be impractical. The naysayers include Bob Boyd of at2 Aerospace, a firm in Santa Clarita, California, that is designing an 87-metre-long airship for industrial deliveries of up to 23.5 tonnes. He believes that equipment for compressing gases is too heavy and generates too much heat for an airship.
Instead, at2 is seeking variable buoyancy with a “hybrid” airframe. This means the airframe is shaped so that forward motion creates a differential in air pressure capable of providing lift, just like an aeroplane’s wings. at2’s z1 Hybrid Airship was designed for a top speed of 111kph and, if needed, a runway takeoff. The faster it moves, the more weight it can manage.
Additional ways to handle weight changes are also being pursued. Atlas lta, an Israeli airship maker near Tel Aviv, is combining a hybrid airframe with gas compression in a cargo airship able to carry 165 tonnes, just over five shipping containers at maximum weight.
Some are even venturing beyond helium to hydrogen, a lighter and less expensive lifting gas. h2 Clipper, a company based in Santa Barbara, California, believes these upsides outweigh risks posed by hydrogen’s flammability. h2 Clipper has produced a design for a mammoth 305-metre-long airship to be filled with enough hydrogen to carry a payload of 200 tonnes. Such systems are not cheap: the cost of building the first full airship could reach $400m, says Rinaldo Brutoco, h2 Clipper’s founder. Even so, he believes future operators of his airships will profitably provide two services in particular. One is the floating warehouse others are pursuing; the other is resupplying fuel depots with liquid hydrogen, no pipeline required.
The world of lighter-than-air flight has long attracted dreamers, so a note of caution may be in order. That said, if airship deliveries do become commercially viable, the industry will get a much-needed lift. ■
