Lighter-than-Air Craft

Simple technology returns with refinement

By Richard Mandel 799air1

The world of the twentieth century, as noted by observers of history, moved from disparate countries spread across seven continents to a globalization of ideas and manufacturing. Thanks in large part to the Internet, corporations straddle oceans as they once occupied square acres, and customers can survey and order products directly in a matter of minutes. The virtual world has placed everyone "down the hall" and "around the corner."

Once the order is placed for a product, there is still the matter of delivery. There are any number of methods for delivering items ranging from small parts up to finished automobiles, but problems begin to crop up when transporting really large devices (such as turbines for a hydroelectric dam), or making delivery to remote locations (as when a power generator is required on an oil rig in the Gulf of Anywhere).

One option would be to reduce assemblies to subassemblies and re-build everything on site. But a simple technology from earlier decades is returning, and it's back with significant improvements.

Return to the airship

The last Great Era of zeppelins was during the 1930s, ending with the Hindenburg disaster. While the hydrogen gas that gave Hindenburg its lift was not the primary cause for that ship's demise, the public's interest waned swiftly, despite the fact that airships were capable of transporting passengers and cargo between Europe and the Americas, and even to the North and South Poles. As most of the crafts were produced in Germany, the intervention of World War II quelled further development of lighter-than-air craft design. Besides which, the breaking of speed records was more attractive than the tortoise-like pace of a dirigible. There was occasional work after the war to produce airships that used helium rather than hydrogen, but there was no longer market interest in them, except for flying billboards like the Goodyear blimp.blimpsketch2

It was several years ago that another look was taken at using lighter-than-air craft for hauling large cargo, in response to a survey of members of the German Machine and Plant Manufacturers Association. The survey found that the cost to handle 300 shipments of materials that individually weighed in excess of 100 metric tons, measured over 75 feet in length or more than 12 feet in diameter, generated costs greater than $37.5 million dollars. Another critical issue was environmental impact and the consideration of how many resources such transportation required. From these needs came the company CargoLifter AG (Raleigh, NC).

Reviving a classic design

The proposed CL160 airship, expected to make its first flight in 2001, is a leviathan in the tradition of its predecessors. The vessel is to be nearly 860 feet in length and 210 feet at its maximum diameter, the equivalent of four Goodyear blimps and more than three times the length of a commercial 747 aircraft. The 14.8 million cubic feet of helium contained on-board will permit the ship to accommodate cargoes of up to 160 metric tons.blimpsketch

There are three basic methods to creating lighter-than-air craft. The non-rigid design is similar to a hot air balloon -- a bag containing the lifting agent (hot air or gas) with a gondola suspended underneath. The historical zeppelins were rigid craft, using internal structure within the gas bag to brace against unstable air currents, as well as providing strength to support a larger gondola that carried crew plus passengers and/or cargo. Part of the problem with this design is that the mass of the bracing structure subtracted from the amount of cargo that could be lifted. Contributing to the weight of structure during the zeppelin era was that the bracing material of choice was wood, which unfortunately served well as one of the contributing fuels in the Hindenburg fire. (Other contributing factors included the wood's varnish, the canvas envelope and its doping, and the powdered aluminum applied to the envelope to give it its metallic appearance.) (Powdered aluminum is presently used, among other things, as part of the propellant in solid-rocket motors.)

It was the Italians who originally developed the semi-rigid design that is the basis for the CL 160. In CargoLifter's version, a composite carbon fiber keel provides both a spine for the flexible gas bag plus load spreading for the flight deck and cargo bay. The rigid keel also will provide support for the propulsion and maneuvering drives, and the ship's tail unit. The airship's envelope will be constructed of high density multilayer foils and materials such as Mylar, Tedlar, and Aramid fibers. Calculations have indicated that a cross-sectional aspect of the airship would appear roughly heart-shaped, as the load stresses along the keel are distributed through the vessel.

Propulsion for the CL 160 will come from four marine diesel engines which, while heavier than other engines that might be used in this application, are very economical to run. It is intended that the exhaust from these engines will be circulated through an on-board recycling plant to extract the water content, which will be used to augment the airship's ballast tanks. Expected range of the CL 160, with full payload, will be more than 6,000 miles, traveling at 60 mph nonstop at a maximum cruise altitude of 6,000 feet. Additional engines will help maneuver the CL 160, and these will be standard aviation shaft power engines. Although these engines are lighter than the diesel units, they use proportionally more fuel. This is countered by the fact that these engines will be used only for short periods of time.

A working scale prototype

A 1:8 working model of CL 160, nicknamed "Joey," was created at the end of 1997 to apply the pre-calculations from the designers' computers in a real-world environment. CargoLifter's engineers also agree that a full-size airship is simply too big for classical pre-trial runs. Joey bridges the gaps where computer simulations may fall short. The prototype carries one human operator, and is serving to prove systems like optical fiber controls ("fly-by-light"). The fiber optic system, up until now not approved for civil aviation, becomes necessary because "fly-by-wire" systems are only approved for lengths up to 230 feet. The new system would offer several advantages, including weight reduction and a high level of resis tance to EMI.8507-aero

Joey also is equipped with a 1:8 model version of the load frame. Designed by a producer of crane systems, the system will apply tensing forces to the frame via ropes affixed to the ground, along with two diagonal tension cables for added stability. Based on computer simulations and tests with Joey, the load frame will be capable of being operated under weather conditions and wind loads at which mobile cranes operate today. Since the airship does not land to load or unload cargo, the total area required for a typical cargo operation would be no larger than a football field. The load frame will lower through the payload door and bring the cargo into the payload bay within the keel. Payload options will include a "multibox" container which will measure roughly 164 x 26 x 26 feet, the equivalent of 36 standard FEU shipping containers. The box contents would be accessible from four sides and the top, and could conceivably be reconfigured into completely equipped mobile hospitals and other applications.

The CargoLifter airdock, where the airships will be built and maintained, will be one of the largest man-made structures when complete, especially considering that it will hold two airships side-by-side. The first is presently being constructed at a former Soviet airbase south of Berlin in Brand, Germany, and will stand over 330 feet high and 1000 feet long. The US is being scouted for a similar facility. An arched framework will support over 107 million square feet of surface. Designers suggest that, despite heating and cooling systems to maintain constant temperatures, the hanger may still develop individual weather systems in some areas.

Payload payoffs
When the first CargoLifter enters service in the new millenium, it may be seen as a quaint throwback to days gone by. However, the company points out several time, money and environmental saving benefits for the future:

  • An airship eliminates the need to modify highways, bridges or rail lines to deliver large payloads. Likewise, there is no need for a special airfield.
  • Studies indicate that to ship a product overseas, using highway/train and ship from manufacturer to final site, average speed is 5 mph. As noted, the CL 160 will average 60 mph, with delivery of complete assemblies directly onto their mounting pad. (One proposal even suggests that bridge structures can be constructed in one location and moved to site.)
  • With the helium providing lift, the only energy expended is in thrust and maneuvering, further reducing the cost per load.

The return of the cargo airship may yet turn out like the occasional Hollywood sequel, one that is actually better than its predecessor. With modern (and safer) materials and development tools, the CargoLifter program is poised to carry transportation needs to entirely new levels.

For more information, contact:

CargoLifter, Inc., 4600 Marriott Drive, Suite 225, Raleigh, NC 27612. 919-788-0613. http://www.cargolifter.com Circle 405.