Airships, also known as blimps, zeppelins, and lighter-than-air vessels, were mankind’s first true aircraft, and have been in use for well over a century now. But despite their early initial promise, the advent of much faster powered vehicles, as well as the infamous Hindenburg disaster, has consigned the technology to the backwaters of the aviation world for many decades. However, advances in technology and a vested interest in vehicles that offer superior endurance and fuel economy than modern jets and planes may see airships undergo a popular renaissance in the near future.
Airships use the same principle as balloons for lift, in that most of their volume is filled with a lighter-than-air medium. However, whereas balloons are unguided, an airship will have engines attached for maneuvering and forward motion, and will be elongated in shape to facility forward movement through the air.
Airships come in three major types: non-rigid, semi-rigid, and rigid.
Non-rigid airships have no internal framework beyond compartmentalized gas bladders, and depend on internal pressure to maintain their shape. Most modern blimps, such as the kind one would see over a sports stadium, are this type of airship.
Semi-rigid airships also require internal pressure to maintain their shape, but usually have a rigid spine or keel running along their underside in order to better distribute the suspension load.
Rigid airships have a rigid internal framework (also sometimes called a skeleton) that keeps their shape. Internal gas bladders are inflated to provide lift. The external fabric skin is there primarily to maintain the ship’s aerodynamic shape.
Lifting medium is any lighter than air gas, usually hydrogen or helium.
Hydrogen was used extensively on earlier airships, but the Hindenburg disaster caused a serious re-assessment of the gas’s use. Even though a modern hydrogen-using airships could be made much safer, so much so that the possibility of another Hindenburg would be very remote, the stigma of that disaster persists to this day. As a result, hydrogen is rarely used.
Helium is the current lifting gas of choice. Though it doesn’t provide quite the same amount of lifting power as hydrogen gas (about 92%), it is not flammable and is considered much safer to work with. However, some predict that the world’s supply of readily-available helium may run dangerously low by the end of the century, forcing a possible return to hydrogen gas or the necessity of using some other alternate lifting method.
Sometimes heated gasses are used as a lifting agent, making the airship essentially an oversized hot-air balloon.
The usual configuration of an airship is with a large, cylindrical gas envelope as its main body, with the pilot’s compartment, engines, and any cargo aligned along its lower center beam. If the craft is large enough, all of these may be arranged into a single consolidated deck underneath the keel. Zeppelins, with their rigid skeletons and internalized gas bladders, may have spare interior spaces dedicated to various purposes, such as passenger or cargo compartments.
Airships have been used for reconnaissance, exploration, advertising, research, and during their golden years in the 1920s and 30s, for long-range passenger travel and cargo transportation.
Tech Level: 10
|Lockheed-Martin's P-791 Hybrid Airship.|
A hybrid airship gets most of its lifting power (anywhere from 50% to over 80%, depending on exact design) from its gas envelope, but requires additional lift from engines to become airborne. Thus they are ‘hybrids’ of dirigibles and heavier-than-air craft like airplanes and helicopters.
A number of hybrid airship designs have been attempted over the decades, including the helistat and the cyclocrane projects by the US Navy in the 1980s and DARPA’s WALRUS program, which ran from 2005 to 2007. Lockheed-Martin is continuing to pursue the technology with its P-791 project.
Because these craft are heavier than air even when fully inflated, they can manage actual full landings instead of having to be moored. This makes maintenance as well as the loading and offloading of cargo and passengers much simpler.
The craft’s engines are usually mounted on pairs of outrigger wings or struts along the vehicle’s horizontal axis. These engines are used both for lift and for forward motion, and are usually gimballed so they can rotate to direct the airflow as needed. Because of the slow speeds at which airships usually operate, propellers are the preferred mode of propulsion as they’re the most efficient at those velocities.
Some hybrids were designed for straight vertical lift, like the helistat project from the 1980s, which had four helicopter engines attached to the gas envelop. Others are designed to take off and land similarly to airplanes, and require runways, such as the P-791. However, because of the low speeds, they require much shorter runways for both take-offs and landings than conventional airplanes. Some designers, like those behind the proposed 1000-foot long, 250-ton capacity Dynalift project, envision hybrid airships using conventional airport runways and flying the same routes, but only using 30% of the fuel of a modern jetliner.
However, hybrids are derided in some aircraft circles as being the worst of both worlds, at least for the designs so far proposed. They tend to have poor aerodynamic characteristics, can be difficult to control, and are vulnerable to extreme weather and winds.
Many of the airships seen in steampunk and alternate-world science fiction seem to be advanced hybrid designs. Examples include the airships seen in the anime film Castle in the Sky and the webcomic Girl Genius.
Tech Level: 12
|The proposed Strato Cruiser airship, designed by Tino Schaedler and Michael J Brown.|
These are full airships, which get 100% of their lifting power from their gas envelope.
A number of societal trends and emerging technologies seem to be converging toward the eventual revival of true airships as a widely available means of transport. The future of hybrids still seems dubious, and further development of true airships to take advantage of their characteristic strengths may follow instead. New materials, technologies, and approaches may create a number of radically new designs.
The potential fuel economy and endurance of airships make them an increasingly attractive mode of transportation. Though slower than many modern heavier-than-air craft, they could ultimately move cargo and passengers cheaper, especially over very long distances.
Some important innovations being actively researched for advanced airships are listed below.
-- Optimized Aerodynamic Shape: The traditional cigar shape of older airships worked very well for the slow speeds they were designed to fly at. Newer airships, however, will be designed for higher speeds, and to use some of their forward motion to help generate lift. Their cross section may more closely resemble an airplane’s wing, with a flattened bottom and a rounded, tapering top. Seen from above or below, they will also have a more pronounced teardrop shape.
-- Vectored Thrust: Aside from the usual stabilizing rear rudders, future airships may also have one or more pairs of outrigger wings. These would help not only with stability, but may be used to mount gimbaled propeller engines for far greater maneuverability and lift capacity. The motors would be able to rotate with a large amount of freedom, perhaps even being able to fully spin at 360 degree or angle themselves outward, depending on the sophistication of the exact design.
-- Advanced Materials: Considerably stronger, more lightweight materials will be used in the construction of future zeppelins, such as advanced composite laminates, carbon nanotubes, and graphene. These will allow the airships to be able to handle greater aerodynamic forces and loads, while at the same time allowing much lighter vehicle weights.
-- Solar Cells: Many dirigibles have a lot of upper surface area exposed to the sun. The topside of the airship may be covered with lightweight, high-efficiency solar cells, with the power generated being fed into batteries. This extra power will not only provide for the electrical systems aboard, but will also help to run the craft’s engines, lending the craft a great deal more fuel efficiency. Some airships may also use the solar cells to heat the lifting gas, affording them greater buoyancy.
-- Vertical Configurations: Though the traditional vision for airships is to have them laid out horizontally like most other aircraft, some designs have been proposed for a more vertical-oriented configuration. These tend to be slower than their longitudinal cousins, but are more stable and able to handle inclement weather better. Some proposed vertical-configuration designs envision them as heavy lifters, basically airborne cranes for military and construction use. Other see them as used for luxury travel, such as the proponents of the Aircruise design, who see them as mobile, floating hotels and penthouses.
The Aircruise proposed design, created by Seymourpowell to be a
'luxury hotel in the sky,' is an example of a vertical configuration airship.
-- Dynamic Buoyancy System: Of all the possible future innovations, it is this one which may allow airships to eventually become the useful workhorses of the air many of its boosters envision. These systems will allow airships the same type of versatility heavier-than-air vessels enjoy, while giving up none of an airship’s advantages.
Dynamic buoyancy systems have been tried before, as maintaining the same buoyancy throughout a voyage was essential for the craft to operate nominally. However, different weather effects and the consumption of fuel would alter the buoyancy throughout the journey. These older systems often came in the form of heating or cooling the lifting gas, expelling the gas as fuels was consumed, or using water condensation for additional ballast. Gas expulsion was the only one that worked well, but added to expense as the gas had to replaced at the end of every voyage or leg thereof.
The futuristic Dynamic Buoyancy System uses a much different principle. The exact design envisioned varies, but the basic idea is that the internal gas bladders have two way pumps, one to inflate the bladder with gas and the other to evacuate it and compress it back into holding tanks. Air from outside the craft may be pumped into the outer layer of the bladder cell, using its pressure to help compress the bladder and gas within. To re-inflate the bladder, gas is pumped back in, and its expending pressure is used to push the air in the outer cell back outside the craft again through one or more specialized pumps.
The shape of the internal bladders in this scheme will be much less like inflatable balloons, and more like cylindrical or box-like cells for greater efficiency. On old style zeppelins, such internal structures would have been too heavy to make the airship much use. However, the much lighter, much stronger materials on the technological horizon means such a system could be adopted without adding too significantly to the airship’s weight or performance.
This system would allow the craft to control its relative buoyancy throughout its voyage easily, by reducing or expanding the volume of lifting gas as needed. Its use goes far beyond this, however. It could also increase its buoyancy to maximum for heavy cargo lifting, and it could decrease it in the face of high winds, allowing it much greater control and stability during inclement weather. More, since the buoyancy can be reduced to zero, the ship could actually fully land instead of having to be moored. The latter would greatly expedite the loading and offloading of passengers and cargo, and allow the craft to use already-existing commercial airports (albeit with their own special landing zones).
The dynamic buoyancy system would by necessity have to be computer controlled, allowing the pilot to alter the buoyancy as needed as the vessel moved along. However, expanding or deflating the inner bladders would be a slow process no matter how sophisticated the system, and though the airship would be able to handle a much greater variety of situations than its static-buoyancy cousins, response time would still be sluggish at best.
The disadvantage of dynamic buoyancy systems is that even with the newer uber-materials, they will still add significant weight and cost to a vehicle, and may be eschewed where price or lifting performance is preferred over precision maneuvering.
In the future, airships may go one better than gasses like hydrogen and helium, by literally using nothing: a vacuum. Using cavities ‘filled’ with vacuum, a vessel could obtain the maximum possible static lift airship technology would be capable of.
Using the same materials and configuration, a vacuum airship would only get about 18% more lift than an identical vehicle using helium. However, with helium relatively expensive and worldwide supplies of it thought to be limited, vacuum airships would offer a more efficient alternative.
A number of technical hurdles remain before vacuum airships could be made practical, such as coming up with materials and a design with a strong enough weight to mass ratio to keep the lifting chamber from collapsing from external pressure. With the near-future development of stronger advanced composites and carbon nanotube materials, however, a practical vacuum airship design should be possible.
Vacuum airships would probably look and handle very similarly to modern and near-future advanced airships already discussed; an outer fabric skin would still be necessary for a practical aerodynamic shape, solar cells over the top would still prove useful for power generation, and so on.
The inner lifting chambers would have a different character, either reinforced cylinders or tetrahedral or geodesic spheres for optimized strength. These may be anchored at multiple points to the craft’s main skeleton, for extra structural reinforcement. Whereas gas bladders on earlier types of airships were designed to keep the gas pressure in, here the emphasis would be on keeping the atmospheric pressure out.
Mobile airtight partitions on their interiors may allow outside air to be filled in or be pushed back out as needed, altering the lifting volume and allowing a dynamic buoyancy system very similar to that discussed for other airships. Since there’s no lifting gas to compress or re-inflate, the operations of a vacuum-based buoyancy system may be considerably faster.
It should also be noted that if a major mishap were to occur to one of the lifting chambers, instead of bursting into flames like the Hindenburg, a vacuum airship would instead implode violently. Also, where minor piercings in the gas envelope on an earlier airship might result in a slow but easily repairable leak, a minor hole in a vacuum chamber could implode the entire thing. Even if it survives without collapsing, the violent influx of air into the chamber could skew the airship’s maneuvering with the unexpected thrust, and would of course negate a significant portion of the vessel’s buoyancy very quickly.
Vacuum airships would likely be significantly more expensive than gas-using airships to construct, but since the vacuum in their lifting chambers would never have to be replenished, their operating costs over a long period may be considerably less.
Vacuum airships were mentioned in the novel The Diamond Age by Neal Stephenson.
http://www.military-heat.com/91/p791-hybrid-airship-project/http://www.popularmechanics.com/technology/aviation/airships/4242974 http://www.ecofriend.org/entry/20-sustainable-airships-promising-a-clean-future-of-transportation-and-surveillance/ http://airshipworld.wetpaint.com/page/Vacuum+Buoyancy http://www.rusring.net/~levin/levin3d/dz.htm (in Russian) http://www.orionsarm.com/eg-article/48586cc9eb91a