Lighter-than-air technology is a lot like the game Go. It is easy to learn, but very hard to master. Many countries tried the technology, but only a few managed to master it. By far the largest number of rigid airships were built by Germany. On the other hand, the United States was the country which built the most non-rigid airships. Both countries expended large amounts of resources and effort in perfecting the technology. Other countries, in an effort to keep pace in the lighter-than-air race, created airships that were both technologically inferior and poorly operated. Many of these efforts represent some of the worst accidents in lighter-than-air history.
This technology, although considered by many to be obsolete, is actually quite useful and is coming back into use in modern technology. The following article is mostly about what we would need to do to use this technology in the post-Ring of Fire time frame.
Normally I put the definition list at the end of the article, but I have seen such a large variation in terminology, that I want to put the list up front.
Dirigible – any aircraft that is controllable as it flies through the air.
Rigid Airship – any aircraft that has a framework inside the skin which provides shape and support for the aircraft.
Non-rigid Airship – an aircraft that depends on pressurization to maintain it’s shape.
Semi-rigid Airship – an aircraft that has a keel and framework in the ends to support the load and provide shape to the airship.
Balloon – a non-powered aircraft that depends on lifting gas to make it fly.
Aerostat – any aircraft that depends on lift generated by an internal gas.
Ballonet – an internal balloon used to provide pressure and shape to a non rigid airship.
Gas cell – a container to hold lifting gas in a rigid airship.
Lift – the force that holds the aircraft in the air.
Drag – the force that impedes the aircraft as it moves through the air.
Thrust – the force that propels the aircraft through the air.
Control surface – devices that allow changes in attitude of the aircraft.
Density – the weight of a gas as measured in pounds per cubic inch.
Gross weight – the total weight of the aircraft including cargo and crew.
Certainly many of the currently used materials and techniques are not available post-ROF and so work-arounds need to be developed for those items. Further, some items are very expensive and a cheaper item needs to be developed to use it its place. Throughout the text suitable workarounds will be mentioned where possible.
How Lift Works
Lift can be generated dynamically, as in a heaver-than-air aircraft, by moving the aircraft through the air. Indeed many modern aircraft when un-powered, have the flight characteristics of a brick, and depend on a continuous application of thrust to keep the craft in the air.
Lift can also be generated statically, as in aerostats, by using a lifting gas. This gas provides lift by displacing the atmosphere, which is denser and heavy, causing the container of lighter gas to float on top of the thicker air. The lighter the gas, the more it can lift. How much a gas will lift will be described later on.
These are balloons that are attached to the ground with an anchor. Such balloons are useful as observation platforms, entertainment devices, advertising, and as a “skyhook” for use as a crane. Captive balloons used as observation points have the advantage of allowing a communication wire to be attached to the tether, making telegraph or voice communications possible.
Balloons can be used for entertainment (rides) or advertising icons. Both are effective as a result of their size, eye catching colors, position overhead, and sense of fantastic unreality.
Balloon cranes have been used in to modern times as efficient transportation devices. One of the biggest advantages is the ability to transport bulky items (like logs or large stone blocks) across distances without the need for cutting roads or obtaining access through congested urban areas. This transport is achieved via the use of a cable affixed to a mast or hill top and using a traveling block and tackle mounted on a pulley. The use of a sufficiently large balloon allows lifts of weights in the tens of tons.
This is the category of balloons that are inflated and released. Such balloons are subject to the wind and go where the wind pushes them. This does not mean that they are uncontrolled or un-guidable. They can be flown to locations by picking the wind layer going in the direction desired.
Free balloons can not “tack” like a ship because they have no counter-drag. A ship has the water it floats through to provide drag or resistance. This drag acts as a modification to the thrust of the wind allowing progress against the wind. Balloons are so large that the size of the envelope makes any secondary sail drag streamer or other passive device irrelevant. The closest a free balloon comes to tacking is when a pilot can balance the balloon on the interface between two wind layers and go in a third direction. This maneuver requires great skill and the existence suitable wind layers.
What we know as airships are aerostats that have the ability to be guided to a desired point regardless of the direction of the wind. The ability to guide an airship depends on the addition of thrust and control surfaces to the airship. This thrust is generally provided by propellers powered by engines attached to the airship. Also of note is the need for the airship to have a means of maintaining its shape. Moving a large object through the air faster than the air is moving causes stress on the object, and as the stress increases the object distorts in shape causing increased drag and unstable movement. Shape distortion can be severe enough to cause the venting of the lifting gasses and loss of lift.
Airships that have a system of internal stiffening are known as Rigid Airships. The internal structure provides shape to the airship and support for its equipment. Normally the frame is covered by a skin which is hardened by a “dope” that colors the skin and increases the skin’s durability. Lifting gasses are contained in gas cells which are attached to the frame. Power plants, holds, cabins, control cars, and control surfaces are also attached to the frame. This class of airship also tends to be larger as the weight of the frame increases the dead weight which in turn makes the size needed to lift the gross weight larger.
These airships are much like their rigid cousins. That is, they have a keel to support equipment. Often this includes a nose-cone frame to resist the forces created by forward movement and a tail cone to support the control surfaces. A semi-rigid design saves much of the weight attached to a rigid design but can make non inflated storage complicated. Semi-rigid designs often include elements of non-rigid designs, notably ballonets to aid in maintaining the shape of the envelope.
In a non-rigid airship, the skin is the gas-containing device. Shape of the skin is maintained by the use of a ballonet. A ballonet is a cell within the skin that is pressurized to create induced pressure on the skin and so maintain the shape of the airship. It is usually only about five percent of the total envelope capacity, and is only necessary to maintain the desired shape of the airship. It is notable that the ballonet is normally filled with air pumped in from the outside of the skin and thus can be regulated without loss of the lifting gasses. Equipment is usually mounted on the control car, which is hung from a cantenary curtain attached to the top inside of the skin.
Other Classes of Airship
In our time line, near the end of the airship age, (in the 1940s and 50s) developers were experimenting with airships called metal-clads. Metal-clads were airships that had a skin composed of aluminum and had elements of rigid and non-rigid design. The greatest advantage was that the metal skin almost completely stopped leakage of the lifting gasses. The best known of these was the US ZMC-2 called the “Tin Bubble.” The Tin Bubble was perhaps the most successful of the U.S. Navy’s airships. This airship was so reliable that it used up two sets of engines before it was retired from service.
In addition were classes where a significant portion of the lift was provided by the shape of the airship, and acted much like more standard aircraft.
Flight in LTA ( lighter than air) is a result of static lift. That is lift that exists whether the aircraft is moving or not. This lift is generated by the difference in weight of the contained gas compared to the atmospheric gas the aircraft is immersed in. By and large there are three gasses in use for lift and a few more gasses that can work but are marginal in application. In our time line, we use hydrogen, helium, and hot air as lifting gasses. Some commercial city gasses such as natural gas and ammonia are also lighter than air and have been used as lifting gasses. But they are not a lot lighter than air and require a much larger volume to be effective. Of the big three, hydrogen is the lightest and provides the most lift, approximately 66 lb per 1000 cubic feet. Helium will lift around 44 lb per 1000 cubic feet . And hot air will lift around 20 lb per 1000 cubic feet.
Each of these gasses have advantages and disadvantages. Hydrogen will burn, helium is extremely hard to find, and lift from hot air varies depends on the air pressure, temperature and humidity present during its use. On the other hand, hydrogen can lift a lot, helium is non-flammable, and hot air is easy to get and can be used with minimal crews and facilities. For example, to lift one ton hydrogen needs 30,304 cubic feet of gas, with a sphere of 39 feet in diameter. Helium needs a sphere 44 feet in diameter with a volume of 45,454.4 cubic feet. Hot air varies (18-24 lb per 1000 cubic feet) but for design purposes is centered at 20 lb per 1000 cubic feet. This results in a sphere of 57 feet in diameter with a volume of 100,000 cubic feet.
Of the lifting gasses now used, helium is right out for the Ring of Fire. The only known source of helium in usable quantities is a set of gas wells in the western half of the North American continent. Both the location and the technology needed will make this gas impractical.
This leaves hydrogen and hot air as usable alternatives. Hydrogen will lift 30% more than helium and is much easier to get. Hot air will lift just less than half of helium, but is even more simple to get. The disadvantages are that hydrogen burns with great enthusiasm, and hot air needs the frequent application of heat to keep its lift.
Hydrogen has had a bad reputation since the 1930s, but has become much more favored in the last ten or so years. Much of the reputation was due to a number of accidents caused by an imperfect understanding of the gas and electricity. New practices and designs have significantly lowered the hazards of hydrogen. Long distance gas balloon racing has switched more and more to hydrogen due to it’s substantially lower cost and greater lifting capacity.
Most important among the new practices for hydrogen use is that the aircraft must be a single entity in relation to conducting electricity. This oneness of structure prevents arcing from one section to another section of the aircraft and denies any ambient hydrogen an ignition source. Also the envelope must be adequately vented so as to allow any leakage of gas to immediately exit the aircraft. And finally the gas cells must be frequently emptied and refilled with pure hydrogen, as oxygen has a tendency to migrate in to the gas cell, creating what is called a rotten cell. That is a cell that is easily combustible due to the availability of oxygen in the mix.
Hot air has a lower lifting capacity and requires an aircraft of roughly three times the size for an equivalent amount of lift. Also significant allowance must be made for fuel to maintain the heat in the air, this fuel is in addition to the fuel for used for motive power if any. Currently in our timeline, fuel requirements have been going down with the use of redesigned materials. A standard hot air balloon usually gets about an hour and a half of flight time from twenty gallons of fuel. New materials have allowed as much as thirty hours of flight from the same amount of fuel. Surprisingly the biggest modification has been a multiple layer approach that reduces the heat transfer out of the envelope. Hot air also has another great advantage, because the typical balloon or airship is non-rigid it stores in a much smaller space and can be handled and crewed by significantly smaller numbers of people.
Many types of aerostats need power plants. Airships need them to move through the air and hot air balloons need them to heat the air inside to provide lift. A power plant should be light. That is, they need to have a good power-to-weight ratio and should be dependable. Traditionally, diesel and gasoline have been the fuels of choice, but kerosene and propane have also been used. Due to the ability of an airship to provide static lift, lower horsepower engines are usable. Lower horsepower engines provide economy in fuel and cost of the engines. Additionally, other types of power plants have been used, with steam and hot air (Carnot cycle) engines being the most common. The lifting gas used also affects the power plant, with the power being mounted inside the envelope when using nonflammable gasses (allowing easy engine maintenance) and mounting the plants outboard when flammable gasses are used. Power plants for hot air balloons are the burners used to heat the air inside the balloon. Such burners normally provide 2 to 6 million BTUs to the air inside the envelope depending on the size of the air mass to be heated.
Modern airships are powered by a variety of means, most commonly the internal combustion engine. Such engines are in limited supply in the immediately post-ROF world, but will become more common as knowledge and tooling spread out from Grantville. Many internal combustion engines need tight tolerances and advanced lubricants, however there are large numbers of engines possible at a lower technical expertise.
In 1900 the “gnome rotary” (an engine where the cylinder block spun and the pistons were attached to the frame) was invented. This engine was a single valve (per cylinder) with the fuel fed from the center crankshaft along with the lubrication, all of which was exhausted from the cylinder each rotation of the block. This is the engine that made all early airplanes possible. Their major disadvantage was that they were a single-pass lubrication. That is, the oil is used once, and ejected from the engine. This oil was castor oil, and the engine moved in a constant cloud of oil vapor.
By the way, this accounts for the drinking tradition of fighter pilots. Since the pilot was bathed in a cloud of castor oil, they ingested large amounts of it. In an effort to absorb some kind of food value that was not “cleansed away” by the qualities of castor oil, they took in vast quantities of wine and beer as the alcohol metabolized quickly, before the colonic took everything else away. At least, that was the excuse. If this sort of engine is used in an airship, since it would be mounted below or behind the cabin, airship pilots would be “beyond” this sort of problem.
In 1903 the Wright brothers made their engine in a bicycle shop. This was a standard internal combustion engine of four cylinders using the Otto cycle. Such engines are not high compression, efficient, or even very powerful. But they work, dependably and every time (mostly). Further, such engines can be made with low tolerances and primitive machine tools.
Steam power is also an option. A steam generator (a flash boiler), a light weight engine, and a condensing coil can be made well within the weight limits available.
Last, a Carnot cycle engine removes even the need for water as a working fluid, but does so at a need for much higher tolerances. So much so that the internal combustion engine, with it’s low tolerances claimed the position of first choice among engines, and so received almost all the research and development in our culture.
Envelopes are constructed from materials that are impervious or resistant to passage of the lifting gas. Of note is that the rigid frame airship has gas-containing cells inside the frame with a cloth covering over the frame that provides a smooth surface to the outside environment.
Traditionally the great airships of the 1930s used a material called goldbeaters skin to form the gas-containing area. Goldbeaters skin is made from the lining of an ox stomach and had the dual properties of being impervious to hydrogen gas and of making gas-tight seals when the edges are properly treated and placed together. The problem with this material is that the total amount of “skin” per oxen is very small (not much larger than a sheet of paper), and thus needs a lot of dead oxen, with over 200,000 used for a ship like the Hindenburg.
Currently most airships use a layered fabric made from cloth treated with latex or Mylar. Mylar is also used solo as a gas-containing material in some airships. Gas balloons are made from treated nylon, because the lifting gas is vented in flight as part of the control process. Hot air balloons are normally made from treated rip stop nylon. It is important to note that the use of the nylon imposes a maximum usable temperature, as too much heat will melt the envelope.
Physically the envelopes are normally made from a set of segments called gores. The gores are sewn together using “French seams” which are double sewn and leave no loose ends. Additionally some seams may have a load-bearing tape or wire enclosed to provide strength to the envelope and give places where the load can be attached.
The best envelope ever constructed was that of the ZMC-2, a semi-rigid airship called by its crew the “Tin Bubble.” This envelope was a three layer sandwich of aluminum that allowed gas leakage only at the valves and outlasted two sets of engines. Alas, large quantities of aluminum are probably out of reach for the near- and mid-future in the 1630s.
By far, the largest number of envelopes were made from latex-impregnated fabric. Over 150 such aircraft envelopes were made for the US Navy alone. Nylon, polyester, and rayon are also popular materials for envelopes. Of all of these, the cotton and latex fabric is the most feasible for the ROF. Cotton cloth is available in large quantities from India, and latex is found in usable quantities in a number of common plants notably dandelions, ragweed, and milkweed. And so the manufacture of this fabric is possible in the post ROF time line.
The material of choice for airships is aluminum. As previously mentioned, aluminum will not be available in large quantities for some time. Rigid airships will need something else. A substitute, actually used by the German navy in World War I, was wood. Split and laminated spruce is light, strong, and provides many of the properties of aluminum. The downfall of wood is its slightly greater weight by volume for the same strength, and its tendency to absorb moisture. Moisture makes the wood heavy and can cause degradation of the lamination in the frame. One of the cures is to coat the frame in varnish. This excludes the moisture but adds to the overall weight.
Aerostats have both civil and military uses. Almost any conceivable activity can be customized for either use. At first glance the military would seem to be a higher priority, but commercial uses may greatly outstrip military uses in value.
The most immediate use would be transportation. Properly constructed, an airship can move large cargos to remote areas with little or no infrastructure on the receiving end. An airship of 1.5 million cubic feet (440′ X 70′) would carry 50 tons gross weight. Assuming fifteen tons of vehicle and crew, that gives thirty-five tons of cargo delivered anywhere.
Power requirements for an airship are significantly lower than aircraft of the same capacity due to static lift of the gas. Handling and storage can be greatly simplified with proper terminal design and vectored thrust engines (Mount them on pivots to allow maneuvering against the wind.)
Militarily this would allow the delivery of high priority cargos to the battlefield. Commercially, an airship could pick up a cargo from the factory and deliver it directly to the customer, even position the cargo in the case of a large item like a generator rotor for a large hydraulic plant. A company, “Cargolifter” had built a prototype and had obtained terminal facilities to begin operations in 2002. It lost funding in the stock market crash of that year, and so never built beyond the prototype.
The ability of an airship to hang in one spot makes it an unsurpassed observation platform. Combined with a radio, and a telescope, airships can provide search and rescue, survey, and battlefield reconnaissance. Tether balloons also have great utility as an observation platform and gave significant advantages to the forces using them in the American Civil War. Convoys escorted by blimps used by the US Navy suffered no losses to submarines in WWII due primarily to the airship’s ability to maintain station on the convoy and look directly down into the water for the submarines. Also the Navy had a number of rigid airships that were used as scouting elements for the fleet allowing a very large area to be surveyed in combat conditions. These airships were also aircraft carriers and could launch and recover aircraft while in flight to further expand their coverage.
Another use is to lift really large loads with a minimal infrastructure. “Sky Cranes” were used in the logging industry to reduce the need for cutting roads and make transportation fast and easy. Tethered balloons can lift and position large loads in crowded urban environments. Militarily, a cargo lifting balloon can speed cargo load-on in forward areas without the need for heavy cranes or large scale ground stabilization for lifts and loaders.
The last area that I will mention is recreation, including passenger transport. The Graf Zeppelin (LZ127) logged more than a million miles of passenger transport. All these miles were without accident and using hydrogen as a lifting medium. The Graf also made the first non-stop flight across the Pacific in 1929. In the 20’s and 30’s numerous point-to-point air routes were in use as fast luxury travel in Germany. While the Queen Elizabeth could make twenty knots, the Graf averaged eighty. So an Atlantic crossing would take the ship an average of twelve days. The airship could make the trip in three. The most common run for Graf Zeppelin was Berlin to Buenos Aires nonstop. It was not until after World War II that any commercial airplane could attempt the same trip.
Another item that needs to be specifically covered is the handling of the airship in rough weather conditions. Like fixed-wing aircraft, airships have conditions where they cannot fly. High wind conditions, and thunderheads are the two biggest killers of airships. In a high wind, that is 60 miles an hour or more, airships have great difficulty in flying against the wind. One early proto-type aerostat was scheduled for a trip into Germany, but was delayed several days, because no progress can be made against the wind. While this was not fatal for the airship, it did cause the airship to have a delay in its service.
The other big weather problem are extreme thunderstorms. The Shenandoah, an airship flown by the U.S. Army, was lost when its captain decided to fly through a line squall of thunderheads. This resulted in the airship being broken into three pieces and the death of over half of the crew. However, these weather conditions also affect fixed-wing aircraft in very much the same manner. Even at our level of technology, the weather still is king. Therefore an airship needs special facilities to keep it safe from the weather when not in use.
This is usually a hangar large enough to contain the whole airship and strong enough to resist any wind that hits it. An alternative to a hangar, is to have a tower with a pivot connector that hooks to the bow of the airship, and a track that circles the tower, so that the back of the airship can be connected to a cart that runs on the track. This allows the airship to change its orientation much like a weathervane so that wind resistance is minimized. Certainly the most important means of safe flight in bad weather is knowing when not to fly.
In describing sample aerostats the following criteria will be used:
Purpose, gross lift, weight, useful lift, cubic capacity, shape, dimensions, speed, power plant, lifting gas used, and rough cost.
First a small thermal airship.
This is a recreation and sport aircraft designed for local use buy a hobbyist.
The cubic capacity is 150,000 feet.
The gross lift is 3000 lb @ 20 lb per 1000 cubic feet.
The weight of the airship is roughly 1500 lb (600 lb envelope, 400 lb basket, 500 lb fuel and power plant).
The airship is an ellipsoid (cigar shaped).
The airship is roughly 160 feet long by 40 feet in diameter.
In still air the airship can attain 30 mph.
The airship is powered by two 40 hp air-cooled engines with ducted fan propellers.
Lift is provided by hot air created by burners internal to the envelope.
The rough cost is 80,000 to 95,000 $USE primarily due to the cost of the fabric.
This airship is a recreational vehicle for a hobbyist. The design is based around the thermal airships in current use in our time line for competition and light advertising. It is a pressurized envelope with internal burners. Pressure in the envelope is maintained by a fan forcing air in to the envelope and controlled by a pressure relief valve in the nose. Landing and emergency venting of the envelope is by means of “parachute” valve in the top front of the envelope. This allows the venting of hot air for rapid descent or emergency deflation on landing if needed.
The construction is basically non-rigid, with the load of the “car” carried on cantenary wires from the crown of the envelope. Control surfaces are mounted on the car, and consist of an inverted “V” tail placed in the slipstream of the engines.
Operation of the control surfaces is by means of cables between a yoke in the pilot’s position and the tail planes. The engines are mounted on the rear sides of the car and can be pivoted 270 degrees for climb and dive. Control of the engines is also by cables and include speed and pivot position. Instrumentation includes an altimeter, a vertical sink indicator, fuel gauge, an internal temperature readout for the envelope, and a sight ring for estimating speed.
A flight would proceed as follows. With the car and envelope unloaded from storage, the car would be oriented with the long dimension of the envelope parallel to the wind (bow upwind). The envelope would be spread out in preparation for the cold inflate. The bow line is attached to an anchor strong enough to hold the airship against any wind present.
The envelope pressure valve is tested, the burners are mounted to the car outside of the envelope (which is displaced to the side for the test) and hooked up to the propane supply tanks. The burners are then test fired for a preflight check. After the burners cool they are mounted inside the envelope and the envelope is sealed.
Cold inflation is by the fan used to maintain pressure in the envelope. Unlike a hot air balloon, the cold inflation causes the envelope to fill and stand above the car even without the hot air. During cold inflation the control surfaces and engine tilt are operated to insure that they are functioning. Once cold inflation is complete, the burner pilot-lights are lit and the burners are operated to put hot air in the envelope. The crown vent is checked to insure that the control rope is free and functioning.
As the lift increases, crew and passengers are boarded. The engines are started and run through their power range then set to idle. The burners are run until positive lift is achieved. The engines are run up until the bow rope is slack, then the anchor is cast off and some tilt is given to the engines to lift off.
During flight attention is focused on maintaining level flight via the VSI and burner control. The pilot also maintains the desired course. Maximum recommended altitude is 18,000 feet. There are serious oxygen issues over 15,000 feet. Typical endurances for this type of airship is two and a half to three hours. Recommended flight times should not exceed two hours, allowing a reserve of air time for emergencies.
Landing is begun by approaching the desired landing site from downwind, and flying against the wind up to the landing site. The airship loses altitude by allowing the air in the envelope to cool, venting air, and engine tilt as needed. The ground crew captures the bow rope and attaches it to the anchor. The air is allowed to cool (or is vented) until negative buoyancy is achieved. Any ground operations are carried out such as ground crew holding lines, or maneuvering the basket. Also, more fuel and passengers or cargo could be loaded, and so start another flight.
Shut down of the airship requires that the burners are extinguished, and allowed to cool. Then the pressure fan is stopped, and the crown vent is opened. The tanks are removed and the envelope is rolled up and placed in the car, and the airship is placed in storage.
Next, a rigid cargo airship
This is a medium-sized ridge airship primarily used to transport cargo.
Gross lift is 50 tons (100,000 lb)
The airship weighs about 15 tons (with fuel and crew)
Useful lift is around 35 tons.
The envelope holds 1,500,000 cubic feet.
The airship is an ellipsoid (cigar shaped) with external control car, control surfaces, and engines.
The envelope is about 440 feet long and 70 feet in diameter, cargo is slung below the keel.
As equipped the airship can travel 65-70 mph at full power.
Power is provided by six nine-cylinder steam engines, with 300 hp generated when running at full speed. (2200 rpm, 400 psi). Engines are rotary, with bash valve steam admission, composed of nine single-acting pistons each. Exhausted steam is recovered and condensed. Steam is made by mono-tube “flash” boilers, with a boiler, condenser, and engine all housed in each “pod.”
Lifting gas is hydrogen, with an average lift of 66 lb per 1000 cubic feet. This is a SWAG but cost should be in the neighborhood of 1.5 to 3 million $USE.
This airship is a cargo hauler. The airship has a frame with a skin on the outside and gas cells inside for lift. Control car engines and cargo are mounted outside the envelope. The cargo is carried in a container slung below the keel of the airship below the center of gravity. Further the container should be standardized to also fit truck and railcars, making it a true intermodal system. (Note that anything that can be balanced and slung could also be carried.) All the engine pods are powering ducted fans, and are mounted so as to be rotated for vectored thrust, allowing the airship to be “parked” while loading and unloading the container or cargo.
Such airships could pick up and deliver cargo almost anywhere. When not in use more elaborate basing systems are needed. Best is enclosed hanger space, allowing the airship to be stored in “flight,” or filled with lifting gasses. Next best is a central tower with a ring of track around it, this allows the airship to be docked to the tower by the nose and rotate around the tower in accordance with the wind. The ring track allows the rear of the airship to be tethered to a rail car, allowing control of the whole airship on the ground.
Air crew would include enough bridge crew to stand twenty four hour watches, (Helm and watch officer x 3) and a chief engineer, and enough engine crew to stand watch on each engine pod, (1+(6*3)), and a cargo officer. This gives a crew of at least 15.
Off duty crew are accommodated inside the envelope at the keel of the airship. Since the gas cells of this ship are smaller than the skin of the ship, there is sufficient room for crew quarters a small living space. It would be not much more than a space to sling hammocks when not on duty. Food preparation would be without flame, so would probably be cold prepared foods in flight. While this ship is capable of longer flights, it would be most used for one or two day trips.
Such an airship should also have enough fuel for ten days cruise, giving a sustained cruise of 12,000 miles at fifty mph. Such a speed would allow easy one day trips to any part of Europe. A typical day would be, at the main base, fuel and preflight, load ballast, launch, fly to intermodal yard and pick up outbound container, (20,000 lb of cane crushing widgets, and 40,000lb of mixed cargo), drop ballast, fly to Amsterdam intermodal yard, drop container, pick up 60,000 lb container of new world Rum, return to Magdeburg intermodal yard, drop cargo, pick up ballast, return to base, moor to handling equipment, move to hanger, rinse and repeat. Bulk cargos could make lots of money. In 1657, England averaged 400 ships a year, with 150 tons of cargo each, just of sugar.
Last, a sky crane.
The aerostat is a tethered balloon, used as a construction crane.
Balloon gross lift is four tons. (8,000 lb)
The weight of the flying tackle (balloon, lift harness, ropes and pulleys, etc) is 3,000.
Max free lift is 5,000 lb , working lift is 4,000 lb.
Cubic capacity of the aerostat is just under 121,300 cubic feet. (hydrogen at 66 lb per 1000 cubic feet)
The aerostat is a sphere, roughly 28.7 feet in diameter. 2588 square feet surface area.
Aerostat is tethered, no power plant or on board crew.
This aerostat is a stationary lifting device. It’s purpose is to pick up heavy things and put them, precisely, in an exact spot. The envelope is constructed of sealed cloth inside a net. The net supports the “flying tackle” that is, ropes, pulleys, and control systems. The balloon is tethered to the ground by three adjustable anchor ropes.
In use, the balloon would first be topped with off with gas for the day’s work. The control tackle (the three tether ropes) are let out until the balloon is above the first load of the day. The flying tackle is attached to the load, and the control tackle is let out until the balloon is above the desired unloading position. The maneuvering of the balloon is by means of the three control tackles. The flying tackle is then let out until the load is in position. The load is removed from the flying tackle, and the balloon is repositioned for the next load.
System cost is the envelope and the tackles. The envelope is 2588 square feet of fabric, and the netting. The four tackles are a set of blocks and rope each strong enough to hold the max load (16,000 lb allowing safety factor). Total cost should be close to 150,000 $USE.
The Grantville Connection
In Grantville, purpose-built lifting and recreational aerostats will come in to existence as soon as the need is perceived. Some members of the community have prior experience with sport ballooning, and others may have a historic interest. Lifting balloons may be especially attractive when high-capacity cranes are found to be difficult to build, with movement of the crane systems being another large concern. Information sources to be found in Grantville are encyclopedias and personal libraries of the sport ballooning enthusiasts in town. Most notably, the Encyclopedia Americana, and the Encyclopedia Britannica. While the articles are not highly detailed, they do give enough information to get lighter-than-air technology started. The biggest factor in lighter-than-air development will be that the people know it is possible and will try stuff until they make it work.
The biggest concern however will be overcoming the “it’s not modern enough” bias built in to the up-timer mentality. In our time line, airship travel was abandoned just as really efficient airships entered the market. This abandonment has been attributed to the dangers of flammable lifting gasses, but is probably more due to the outbreak of World War II.
Post war, the facilities and technologies created during the war lead the aviation industry in a different direction. Airplanes were available from army surplus, air bases were located around the world, and we had gotten used to the idea of large airplanes with internal combustion engines. With such momentum, research and development of airships did not recommence until the 1980s.
The Rest of the World
Airships will be very attractive to down-time political units. Static lift provides flight with much lower horsepower demands. Also, airships give a limited technology plant a lot of “bang for its buck” when large numbers of complex engines are difficult or impossible to make. Large lifters will allow comparable cargo amounts to be shifted, and will allow the “We fly too” for the polity. As with many other concepts, just the knowledge that it is possible will spur development.
In regard to those hostile to Grantville or the USE, having something that flies will allow them to gain some equality on the field of conflict. The benefits from scouting alone make any kind of aerial vehicle well worth the effort. This is not exclusively limited to powered airships. Tethered balloons with some type of signaling apparatus, either a wired teletype, or even signal flags, can be invaluable on the battlefield. Having timely pertinent information as to what is really going on and can be an enormous force multiplier. Said information can be the difference between winning or losing the battle especially in this time period.
Another use that may be of interest to the world is to have a small airship as part of the equipment of a naval warship. The small airship is not intended to do any combat, but it is to be used as a scout to increase the amount of area that the warship can see and therefore control. Having such a scout will allow fewer numbers of ships to control larger amounts of space, thus making each ship much more flexible in allowing the use of fewer ships for the same amount of work.
Lighter-than-air vehicles will have a window of utility where they can be the best alternative for a developing aeronautical program, especially outside the Ring of Fire. As has been stated, lighter than air vehicles will allow nations who are developing new technology, to maximize the amount of aerial capacity for the material they expend in their flight programs. Well-developed airships will be able to carry more weight sooner than comparable aircraft, especially as ground facilities will have to be developed for those aircraft. Nevertheless, heavier-than-air aircraft will dominate where air speed is more important than capacity. To say it another way, if you want to go in comfort take an airship but, if you want to get there right now take the plane.
Gone with the Wind-Manual for Gas Ballooning by Walter Muller, Astrid Gerhardt, and Gerhard Hurk, (Sept. 2002)
Free and Captive Balloons by Ralph H. Upson. (1926)
Theory of Ballooning No. 1-305 by the US War Department (Oct. 1940).
A Short Course on the Theory and Operation of the Free Balloon by C.H. Roth, Instructor (1917)
Manual for Balloon Cutters by the US War Department (1918) Document 881
Military Observation Balloons (Captive and Free) by Emil J. Widmer (1918)
Flammable Gases by Don Overs. (1981)