The answer is to build a craft that doesn’t need ballast, or can create its own.
This was one of the goals of a now-defunct DARPA program called Walrus, which aimed to develop a test airship that would match the C-130’s 30-ton lift capacity. Phil Hunt, DARPA’s Walrus program manager, recounts that engineers explored several concepts for generating ballast on the craft. In one, exhaust from combustion engines would be captured and treated with nitrogen gleaned from the air and bottled hydrogen, a process that would produce water and ammonium—liquid ballast that would keep the craft controllable. Once the ship had landed, says Hunt, you could wheel the payload off and the ballast would be sufficient to keep the craft from wafting away.
Though Congress did not fund the Walrus program in 2006, several companies continue to work on such concepts. Hokan Colting won’t discuss 21st Century Airships’ proprietary approach. For the most part, neither will Worldwide Aeros, which is promising a vehicle called Aeroscraft, scheduled to fly in 24 to 36 months. Edward Pevzner, Aeroscraft marketing manager, will say that buoyancy would be managed in part through the compression of helium.
Officials at the SkyCat Group of Cardington, Great Britain, are more open. When viewed from the side, their SkyCat airship will look like the cross-section of an airplane wing. From the front it will look like a flattened cigar. The inside will consist of three chambers filled with helium and ballonets. The helium will provide 60 percent of the lift necessary to take off with a heavy load. For a full load, blowers will push air downward through two hover pads, keeping the craft above water, ice, or rocks. The SkyCat will use propellers to move itself forward.
After landing, the hover pads will be reversed to “suck” mode to keep the craft on the ground while its payload is wheeled off. No ballast will be necessary.
Since DARPA did not prohibit foreign proposals, the SkyCat Group had hoped to get Walrus program money to build a small SkyCat. But the agency turned that proposal down, and will not comment publicly on its decision, says spokeswoman Jan Walker. The company is presently in bankruptcy, but is hoping to claw its way out with two demo vehicles, which it calls SkyKittens. The 40-foot SkyKitten 1 earned a visit from Pentagon officials after it flew in 2000. Says Gordon Taylor, the company’s marketing director, a 50-foot SkyKitten is planned, followed within 30 months by the first operational SkyCat vehicle. That craft will carry either 20 or 50 tons of equipment; Taylor says managers haven’t decided whether to go straight to the larger version.
Competing companies have come up with designs that resemble the SkyKittens—to a suspicious degree, say the SkyCat developers.
It’s probably not going to be easy to nudge any of these concepts into the real world. A technology as simple-sounding as airships—fabric, helium, maybe a propeller or two—turns out to be surprisingly complicated. “I’ve heard—seriously—people say ‘Well, we shouldn’t have much problem doing something like that; you just take a gas bag and put a couple of engines on,’ ” Hokan Colting says, laughing. But if the design challenges can be mastered, the decidedly low-tech aircraft could become a critical part of the 21st century fleet.