The blimp, the airship, the dirigible. Whatever you call them, you probably don’t find yourself thinking about them too often. They were an easy way to get airborne, predating the invention of the airplane by decades. And yet, they suffered—they were too slow, too cumbersome, and often too dangerous to compete once conventional planes hit the scene.

And yet! Here you are reading about airships once more, because some people aren’t giving up on this most hilarious manner of air travel. Yes, it’s 2024, and airship projects continue apace even in the face of the overwhelming superiority of the airplane.

Why Float?

As the world reckons with decarbonizing the economy, air travel has fallen under the crosshairs. As you might imagine, lofting gigantic metal tubes full of people into the air takes a great deal of energy. Aviation makes up a significant 2.4% of global carbon dioxide emissions. Work is underway to cut aircraft emissions through new efficiency measures and the use of biofuels, but demand for services continues to increase. Fiddling at the margins here isn’t going to solve the problem to any great degree.

Airships seem to offer some tantalizing bonuses to energy efficiency, however. With buoyancy provided by helium, airships don’t need forward propulsion to generate lift. Airplanes have to burn fuel to generate thrust to get enough speed up for the wings to work. All the while, the process of generating lift also generates drag, which costs fuel to overcome. In contrast, airships simply float upwards, essentially for free. The work of fighting gravity is done by the lifting gas in the airship’s bladders. Usually, it’s helium, because the Hindenburg disaster put most of us off ever riding in a hydrogen-filled airship.

Airships must still use fuel of some sort for propulsion to actually get to their destination. However, their minimum power requirements aren’t set by a need to maintain lift via wings. The airship will still float no matter how low the speed. Thus, where an airliner needs powerful engines just to get airborne, an airship can make do with less. This opens the prospect for electric airships, which could be a clean method of air travel if powered by renewable energy. Much research is ongoing in this area to determine whether such a method of transport could be feasible.

Slow Solar Airships

A paper published in the International Journal of Sustainable Energy recently explored the concept of an airship that uses onboard solar panels to harvest energy. Normally, we discount the idea of using solar panels on a vehicle for propulsion, as the surface area is too small to capture a meaningful amount of power. However, airships are huge, changing the calculations somewhat. The paper explored optimizing travel routes to enable the airship to fly between destinations using battery power and energy from the sun. It builds heavily on prior work, as many such papers do, but it’s rare to see one that references a publication from Zeppelin in 1908.

A solar-powered airship must optimize its travel path to get the most out of the energy available from the sun. Credit: Pflaum, Riffelmacher, Jochner, 2022

The paper based its theoretical airship design around using thin-film solar cells, which are light, flexible, and efficient all that the same time. The idea is that an airship’s skin would form an excellent surface with which to capture energy from the sun.  Proposing a large airship design, it would see an area of over 13,000 square meters covered in cells, weighing in total around 6.6 tons. Such a craft would have to be carefully piloted to make the most of any available sunlight, both with regards to the timing of its journey and its angle to the sun. Done properly, though, the paper concluded that such a craft could achieve emissions just 1-5% of those of a conventional aircraft.

But what of practicality? The paper worked with a theoretical design capable of hauling 100 to 200 passengers on routes between Madrid and Las Palmas, and London and New York City. The journeys planned were roughly 1,760 km and 5,566 km respectively in their shortest, most direct routes. In the latter case, the journey would take 48 hours from New York to London, far longer than the usual 8 hour plane flight. Going back, the numbers are even worse, taking 76 hours on average thanks to typical prevailing winds and available sunlight.

Potential flight routes from New York to London (blue), and London to New York (green). Prevailing winds play a huge role in flight time. Credit: Pflaum, Riffelmacher, Jochner, 2022

Right away, it’s easy to see why we’re not blimping from city to city today. Or should we say airshipping, because blimps typically refer to smaller craft without rigid frames. No matter how cheap or efficient, few of us could afford the time to spend two or three days travelling by airship. Beyond the strain of such a journey, which would almost certainly necessitate sleeper cabins, you’d also need to take multiple entire seasons of TV to watch to get you through. You won’t get through Friends (around 88 hours) but you’d get through Seinfeld (around 69 hours) just fine, assuming you didn’t sleep between London and New York.

That’s not to say the technology is useless. The International Conference on Electric Airships took place to examine a number of potential uses for these cleaner forms of travel. Cargo doesn’t always have to move quickly, and could be a viable use for such airships. There are potential uses on some smaller passenger transport links, as well as uses for travelling to remote areas where conventional aircraft may be difficult to service. The conference also saw researchers sharing ideas on hybrid powertrain designs for clean airships, ultra-light solar solutions, and analyzing the economics of various use cases.

New blimp projects continue to pop up, like the Pathfinder 1 from LTA Research. Modern composite materials can help improve a design, but airships still have some difficult fundamental drawbacks that aren’t so easy to overcome. Credit: LTA Research

In any case, the well-documented flaws with airship travel aren’t stopping development in this space. Catching the headlines of late is the Pathfinder 1, a 400-foot airship built by LTA Research. That makes it almost twice as long as a Boeing 747-8, or roughly half as long as the largest Hindenberg-class Zeppelins. The company has been granted a special airworthiness certificate for the large aircraft, with testing to take place throughout 2024. It has a skeleton made of titanium and carbon fiber, supporting 13 bladders filled with helium to provide lift. Unlike some other modern airships, it’s not a hybrid lifting body design, and actually looks not that far removed from the airships of the 1930s, dangling gondola and all. The aim is for the airship to support disaster relief efforts in areas where conventional aircraft infrastructure may be damaged. It will also explore the use of hydrogen fuel-cells for cleaner power, though it is currently built to rely on diesel generators to run its electric motors.

Ultimately, airships aren’t going to replace planes any time soon. They’re simply too slow to get the job done. At the same time, they seem to keep popping up in niche uses here and there. And true, it could be that one day, air cargo is supported by large helium airships running on solar power for cleaner haulage. But for now, it seems like the basic fundamentals of airships will keep them as a neat obscurity, rather than a key technology underpinning global trade.