Serendipitously, Maggie Koerth-Baker, the brilliant science editor for Boing Boing, recently wrote about her visit to the zeppelin Eureka, just on the heels of my own posts here and at Txchnologist about airships. She offers an independent confirmation that as appealing and inspiring as these vehicles may be, they suffer from practical drawbacks that help to explain why our skies are not festooned with them.
As she writes, Maggie had been looking forward to a ride on the Eureka, which is a new technology zeppelin that carries 12 passengers and two crew, primarily for tourism but also sometimes for research jobs that need a hovering platform. The Eureka sounds like a marvelous little craft (I use “little” advisedly as an endearment, because it is longer than a 747), and Maggie’s enthusiasm for airships shines. She comes to recognize, however, that their comparatively large size, low speed, ballast and ground support requirements, and susceptibility to wind, among other considerations, do make them less practical than airplanes for most aviation jobs, as I had discussed.
It’s worth emphasizing that the Eureka is a form of zeppelin, and not one of the hybrid air vehicles on which I had focused. Those more advanced designs do have features that would give them a big edge over craft like the Eureka: they are faster, more stable on the ground, and so on. Many of the basic problems relative to airplanes still apply, however, despite the ingenuity of the hybrid makers in making the most of their vehicles’ performance.
For example, consider the susceptibility of airships to wind. Maggie quotes one of the crew as explaining, “An airship is like a big sail” about an acre in area:
That “sail” means landings, loadings, and takeoffs are tricky on windy days. On a landing, Belanger said, the wind could catch the zeppelin and push it sideways, like a beach ball skittering across the ground. The wind also moves the ship while it’s tethered down. The Eureka is 246 feet long. Not coincidentally, that’s also the radius of the mooring circle that the ship forms as wind slowly pushes it around on it’s little back wheel. All of that meant that the Eureka had to sit on the ground while planes were safely taking off and landing on the runway behind her.
The situation for hybrids is somewhat different. Because their fuselages are flatter and wider, they don’t present proportionally quite as much surface area to the wind and they aren’t lighter than air, so they can be more stable while moored. But they do still get pushed.
Of course, strong crosswinds angling onto a runway can keep airplanes grounded, too. As a representative of Hybrid Air Vehicles Ltd. explained to me, crosswinds don’t represent the same kind of problem for hybrids during takeoffs and landings: they can simply pivot and take off or land with the wind at their backs no matter which way it is blowing. That’s not a bad strength for hybrids to have.
But it seems to me that it comes at a cost. One of the claimed advantages for hybrids is that their static lift (innate buoyancy) helps them gain altitude quickly during takeoffs, so they need only very short cleared spaces as runways—perhaps just a couple of times their length. That could be a big plus in places where clearing land and building a tarmac could be difficult or expensive. But for a hybrid as long as a football field to be able to fly off in any direction, it then needs to start off in the middle of a cleared circle with a radius of at least 200 or 300 meters—conservatively, 12.5 hectares (31 acres). That may not erase the difference in cost between clearing a space for an airship and building a simple runway for planes, but it has to narrow it. Or you can confine the airships to a smaller, narrower landing space, at the cost of eliminating the crosswind advantage.
In the end, Maggie seems to draw much the same conclusion that I did about why airships are a lovely but rather marginal form of transport:
Ultimately, I came away from my visit two a zeppelin with two thoughts. First, it’s a nice reminder that the world is pretty complicated, and it got to be the way it is for many reasons. Sure, the Hindenburg contributed to busting the zeppelins’ bubble. But improved airplane engineering probably played a bigger role.
Second, impractical or not, zeppelins are still totally awesome.
Cheers to that. (And read the rest of her post.) [Update: fixed a stale URL.]
P.S. Here’s a larger view of that Eureka photo in the opening thumbnail, which I love.