Engineering News

Their use of helium over hydrogen is, I'm sure, a public-relations decision to mollify an otherwise potentially-skittish public. The Hindenberg is the most famous of the airship disasters of course, but just over twice as many perished (73 of 76 on-board) when the helium-filled U.S. Navy scout airship USS Akron crashed at sea off the New Jersey coast four years earlier on April 4, 1933.

Thing is, helium is a very limited resource and, if we are to believe Aeroscraft's developers' projections, these airships will require huge quantities of helium. This does not bode well for our already minute global reserves.

I suspect that, in order to be sustainable, Aeroscraft's developers will ultimately be forced to switch to hydrogen if these airships become commonplace. This is not necessarily a Bad Thing. Hydrogen was not the bad guy in the Hindenberg disaster, the airframe, materials and construction methods were.

Hindenberg's captain hurried the craft's landing in the face of an oncoming storm and, in the process, put her through several manuvers which stressed Hindenburg's interior tension wires past their breaking point. At least one wire snapped, ripping through several hydrogen cells and causing the gas to mix with oxygen. At the same time, coronal discharges (St. Elmo's fire) near one of her vents ignited the gas, and the rest is history.

The Hindenburg's skin consisted of a cotton fabric impregnated with a lacquer 'dope'. Painted canvas, essentially. There has been much speculation that it was this lacquer which greatly accelerated the exterior flame front, but the evidence indicates otherwise. Many pieces of unburnt or partially burnt exterior fabric left behind suggests that it was a combination of structural failure and the materials used.

A hydrogen-filled dirigible these days would be constructed very differently, thanks to advanced materials. The Hindenberg's hydrogen cells were, by necessity, very large. To have made them smaller would have required large quantities of treated cotton fabric - the best material available at the time - increasing the dead weight considerably and making the craft impractical.

Today mylar, kapton and many other extremely strong-but-lightweight materials are available which would allow the craft's interior to be partitioned into numerous and tiny cells. The cells, moreover, could contain oxygen-activated foams which would automatically activate to seal-off ruptures. Static discharges are mitigated by aluminising the films. From the photo I'm guessing the Aeroscraft's exterior is probably made from aluminised mylar or kapton. Future developments in lightweight materials offer even greater opportunity for sound, safe hydrogen containment. Closed-cell aerogels, for instance.

Amazingly lightweight, yet strong (think foam-filled, semi-rigid pillow), these aerogels could be engineered to flamelessly burn oxygen-contaminated hydrogen catalytically in the event of structural damage. This could be built-in as an intrinsic property of the material itself, engineered into place for just this purpose. As for the source of lifting gas? Helium is not the answer.

Hydrogen is readily available from any number of sources, including (and especially, particularly for this application) electrolysis. These craft are huge and, as such, provide ample surface area (literally acres) for thin-film, flexible, redundant photovoltaic arrays built right into the skin. The craft's power plants could be electric with nighttime operation powered by hydrogen fuel cells. So constructed, such craft could conceivably remain airborne forever. Should they need to refuel, and they will, it is a simple matter of lowering a sump into a suitable body of water. The Earth's oceans come to mind.

For my part, given a sliver of a chance you can bet I'd be the first in line to take one of these babies for a spin! HELL YEAH!

Spruce Goose? And they want to militarize this thing? How's about 'Sitting Duck?'