The Knowledge: How to Rebuild Our World From Scratch (22 page)

If mechanization decays away, the post-apocalyptic society will have to revive animal power. The first beasts in history to be employed as draft animals, hauling carts, wagons, plows, harrows, and seed drills, were oxen—castrated bulls—and they could be co-opted again once the mechanized tractors grind to a halt. Draft horses, such as the Shire horse, descend from animals originally bred to carry fully armored
knights across the battlefields of medieval Europe and are faster, stronger, and tire much less readily than oxen. But if you want to replace oxen with horses you’ll first have to reinvent the correct harness, a critical accessory that completely eluded the ancient and classical civilizations.

Oxen can be yoked fairly simply with a wooden beam resting across the top of their necks, with staves positioned on either side of the neck to hold it in place, or with a head yoke seated in front of the horns. The body shape of the horse, on the other hand, must be harnessed with an arrangement of straps.
The simplest system is known as a throat-and-girth harness, with one strap passing over the top of the shoulders and around the thick neck of the horse, and another underneath the belly, with the load-attachment point positioned over the middle of the back. This style of harness was widely used in antiquity, and served the chariots of the Assyrians, Egyptians, Greeks, and Romans for centuries. But it is actually totally inappropriate for the anatomical structure of the horse and simply doesn’t work for hard draft work like pulling a plow. The problem is that the front strap cuts into the horse’s jugular vein and windpipe, so that the animal practically throttles itself if it pulls too hard. The solution is to redesign the harness to shift the point through which the animal applies its force.

The collar harness is a well-padded ring of metal or wood that fits snugly around the neck, with the draft-attachment points not behind the neck but lower on either side of the body, so as to evenly distribute the load around the horse’s chest and shoulders. This anatomically sound collar—an early application of ergonomic design—was developed in China in the fifth century AD, although it wasn’t widely adopted in Europe until the 1100s. It allows the horse to exert its full strength—the animal can deliver three times more tractive force than with the older, inappropriate harness—and horse-drawn plows thus became central to the revolution in medieval agriculture.

MAKESHIFT HORSE-DRAWN TRAPS SUCH AS THIS MAY BECOME COMMON IF MECHANIZATION IS LOST.

The merging of animal traction power and remnant vehicles after the apocalypse will produce some bizarre sights. The working unit of the rear axle and wheels from a defunct car or truck can be salvaged and reappropriated to form the basis of a wooden-sided cart. Even more simple would be to slice a car in half, dump the front end with its inoperable engine, and keep the backseat and rear wheels. The addition of a pair of scaffolding tubes would serve as arms for hitching a donkey or ox for propulsion. Such makeshift traps may become common with the loss of mechanization.

However, reverting to animal power would also require the redirecting of agricultural produce to feeding livestock rather than people. During the peak of animal use for agriculture in Britain and the United States, which surprisingly occurred as late as ca. 1915 (even though mobile steam engines had existed for fifty years and gasoline-powered
tractors were already available), a full third of cultivated land was committed to the upkeep of horses.
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As well as providing traction power for drawing agricultural tools and transport overland, reclaiming the seas after the apocalypse will be a top priority for reestablishing fishing and trade, and if the capability to maintain mechanization is lost, you’ll have to rely on sailing ships.

The most basic mode of a sail makes intuitive sense to anyone who has watched bedsheets drying outside on the clothesline and billowing in the wind. Plant an upright post in the middle of your boat as a mast, and from the top sling a beam horizontally, and at right angles to the length of the hull, for a yard. Dangle a large canvas sheet from the yard, secured with ropes at the bottom, and you have a simple square-sail vessel, which has been independently invented by numerous cultures throughout history. The sail acts to trap the air blowing from behind, and even primitive ships can make good progress running with the wind. But with this rigging you’ll never be able to sail closer than about 60 degrees to the wind direction, so you’re very much at the mercy of the vagaries of the breeze.

A more sophisticated setup is the fore-and-aft sail. This is not held perpendicularly across the boat, but oriented along the line of the hull, suspended diagonally by a slanted yard or rope attached at one end to the mast. Ships rigged in such a way are far more maneuverable, and
can also tack and beat much closer to the wind—modern yachts can cut as little as 20 degrees into the wind—than a square-rigged vessel, although most large ships set a combination of both kinds of sail. Fore-and-aft rigging dates back to Roman navigation of the Mediterranean, but really came into its own during the Age of Discovery, hauling the great European exploration ships, led by the Portuguese and Spanish, across the oceans of the world to encounter distant new lands and establish long-range trade routes.

When you present a fore-and-aft sail obliquely to the wind, a whole new effect comes into play. The wind filling the sail causes it to bulge outward and behave like an airfoil—the airflow rushing over the curved surface is deflected and creates a region of low pressure in front of the sail. Rather than being blown through the water with the wind drag created by a square sail, the fore-and-aft sail is sucked forward by this aerodynamic lift force. So without fully understanding the physics involved, in 1522 Ferdinand Magellan’s expedition became the first to circumnavigate the Earth using the same aerodynamics that lies behind the aircraft wing and the reaction turbine.

Using fore-and-aft rigging to catch the wind blowing across the boat, you have now created a stability problem, though, and your vessel is at risk of being rolled right over and capsizing. The solution is to load ballast low down in the ship to keep it self-righting, and to fit a keel below the hull, often shaped like an upside-down shark’s fin, to resist the tipping force of the sails. But if you are able to control these competing forces, and carefully adjust the rigging to trim the fore-and-aft sails into the optimal curve, the astounding consequence of the physics underlying their airfoil effect is that they can actually sail faster than the wind blowing them.

If you can’t salvage any serviceable hulls, you will need to build your own. Traditional shipwrighting involves fixing planks lengthwise to a frame and rendering the seams watertight by stuffing them with plant fibers caulked with pine pitch; or if you can scavenge or smelt
enough wrought iron or steel plates, you can rivet them together. Sails are essentially large sheets of fabric, an application of the same weaving technology we encountered in Chapter 4. When creating a sail, use a plain weave, and be aware that any fabric is strongest when pulled along the direction of the weft, as these threads are already straighter than the warp, and the material is readily distorted and potentially damaged if stretched along a diagonal (try this with a small section of your shirt now). Likewise, the ropes rigging everything together are produced by spinning fibers into yarn, with the yarn then twisted into strands and strands into ropes—and, if need be, ropes into cables. The pulleys and tackle blocks needed for controlling the sails are identical to those used for hoisting heavy loads on scaffolding or cranes on a building site.

Hopefully, before too long the recovering civilization will once again begin mastering metalworking and machine tools. One mode of mechanically simple transportation for personal conveyance in a post-apocalyptic world without working motors would be the bicycle. The heart of the pedal-powered bike is the crank that converts the up-down stroke of your legs into a rotary motion applicable to wheels. But there is still a major engineering problem to solve: you can’t directly couple this cycling action to the wheel, with pedals fixed to the axle like a child’s trike, because for any meaningful velocity you’d need to pump your legs like one possessed.

The simplest approach is therefore to fit a large front wheel, so that even with a modest rotation the enormous circumference confers a decent speed; this was the idea behind the ludicrous-looking penny-farthing with its four-foot wheel. A far better solution, which seems so obvious to us now but wasn’t conceived by a bicycle manufacturer until 1885, is to use gears, an ancient mechanical system, linked with a chain. Two sprockets of different sizes allow the driven wheel to rotate much faster than the pedal crank and are mechanically coupled by a roller
chain (itself very similar to a design sketched by Leonardo da Vinci in the sixteenth century). Another key working principle is that the front upright, linking the hub and handlebars, should be tilted backward slightly so that the leading wheel naturally steers into any sideways topple to bestow inherent stability on the bicycle.
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At some point, the recovering civilization will reattain the sophistication in metallurgy and engineering necessary to contemplate building engines. If the post-apocalyptic society has regressed to the stage of relying on draft animals and sails, how could it now reinvent
the internal combustion engine without reference to any surviving examples? What’s the anatomy of the heart that throbs under the hood of our vehicles?

The internal combustion engine is a great example of how any complex machinery is no more than an assemblage of basic mechanical components, all with very different heritages, and arranged in a novel configuration to solve the particular problem at hand. If you could peel back the metallic skin and dissect the family car as an organism, you’d find myriad different sub-mechanisms interacting with one another like the various organs and tissues in the human body.

So what are the key principles behind the functioning of the automobile, and how could you design one from scratch if you needed to?

We’ve already looked in Chapter 8 at the operating principle of an
external
combustion engine: the steam engine works by burning fuel to heat a boiler and force steam into a cylinder. A far more efficient use of
the chemical energy locked in the fuel is to cut out the middleman and use the pressure of hot gas produced by the burning
itself
to drive machinery. If a tiny amount of fuel is introduced into a confined space before being ignited, the explosive expansion of the resultant hot gases can be made to shunt out a piston and so perform work for you. Do this several times every second and you’ve got a regular, reliable delivery of power. To reset the cylinder for another burst, open a hole and push the piston back to squirt out the exhaust gases like the plunger of a syringe, then draw it out again to suck oxygen-laden air laced with fresh fuel through a second valve. Begin compressing this mixture to get it dense and hot before igniting it again. This four-stroke cycle is the rapidly beating heart of most internal combustion engines on the planet.

You’ve got two options for triggering the combustion of the fuel once it’s in the cylinder, and this marks the difference between modern gasoline and diesel engines. Volatile fluids like ethanol (or gasoline) can be vaporized by mixing them with air in the carburetor before being introduced into the cylinder and ignited with an electrical spark plug. Mixtures of heavier hydrocarbon molecules like diesel can be sprayed into the cylinder as a fine mist at the end of the compression stroke, to vaporize and ignite spontaneously as a consequence of the temperature surge from extreme pressurization of the air. (Anyone feeling the nozzle of an air pump after filling their tires will have noticed how warm it can get from the air compression.) Or you could, as we saw at the beginning of the chapter, fuel your engine with gas piped directly into the cylinders.

For powering a vehicle, though, the challenge now is to convert the reciprocating back-and-forth movement of the pistons into a smooth rotation that can be used to spin wheels or a propeller. The device that performs this crucial translation of motion is the crank, as we saw with the bicycle. The crank is often used in machinery, with a pivoted
connecting rod linking the reciprocating component and rotating shaft (on a bicycle, it is your leg that comprises the connecting rod coupled to the pedal crank). The earliest known appearance of such a crucial mechanism was installed on a third-century-AD Roman waterwheel, where it converted river-powered rotation into the drawing back and forth of long wood saws.

Modern engines, which team up the power of multiple firing pistons, employ a slight modification known as a crankshaft, which has a series of handle-like kinks spaced along its length to allow a whole row of pistons to drive rotation of the same spindle. Even with several cylinders firing in a staggered sequence, the explosive impulses turning the shaft are still jerky, and a way to even out the rotation is needed. This time the solution is provided by ancient pottery technology. A flywheel is stuck on the end of the crankshaft and functions in exactly the same way as the heavy stone disk on a potter’s wheel, storing rotational momentum and smoothing the spin.

Another ancient mechanical component is needed to coordinate the opening and closing of the valves that admit fuel and expel exhaust gases from the cylinder during the power cycle. The cam has an elongated, off-center shape, so that as it turns on a shaft it can be used to rhythmically lift up a lever or push away a “follower” rod. In our history cams were employed in trip-hammers, where the power of a waterwheel was used to repeatedly raise a heavy hammer and then drop it for a blow as the cam catch passed and released it. Cams were known to the ancient Greeks and reappeared in medieval machinery in the fourteenth century. In the modern combustion engine a set of cams, driven from the main crankshaft, allow the operation of the inlet and outlet valves to be perfectly timed with the piston cycle.

If you’re intending to use your engine to power land vehicles, rather than to simply spin the propeller on a boat, there are a few more technical challenges you need to solve. With the core design of the engine
settled, the next mechanical problem is delivering that driving force to the wheels. One of the most intuitively comprehensible parts in an automobile power plant is the transmission: in essence it is no more than a box that allows you to change which pairs of gears are meshed together, operating on the same basic principle as gear chains dating back to the third century BC. The internal combustion engine turns (or revs) at a very high rate, and so low gear ratios, whereby the drive shaft gear is larger than the gear it is engaged with on the engine shaft, are used to trade spin speed for turning force. This greater torque is needed particularly for accelerating or climbing hills.

THE FOUR-STROKE INTERNAL COMBUSTION ENGINE, MADE UP OF CYLINDERS AND PISTONS, A CRANKSHAFT TO DELIVER THE POWER TO THE FLYWHEEL, AND A CAMSHAFT TO COORDINATE THE OPENING AND CLOSING OF VALVES.

A related piece of equipment facilitating gear changes is the clutch. In many automobiles this assembly bears the engine power through a roughened disk in firm contact with the flywheel—ironically, it is friction that allows the smooth operation of the motor. The disk and
flywheel can then be pulled apart to disconnect the engine from the drive shaft. Similar systems were used in early woodworking tools such as the lathe to allow the mechanism to be disengaged from its power source.

The first cars cut and pasted bicycle technology, and drove the rear axle with a chain and sprocket. A more efficient method to transfer the engine power is a spinning drive shaft, but it must be afforded a degree of flexibility to avoid it snapping with the jolts of driving. How, then, do you allow a rigid rod to bend or flex in any direction while still conferring power? The solution lies in positioning two universal joints along its length. Each of these is composed of a pair of connected hinges, a design that was first depicted in 1545.

Once you’ve got your vehicle tearing along, the next pressing issue is to devise a means by which to conveniently steer the wheels from the driving seat. The earliest cars used a tiller, borrowed directly from marine technology for controlling a boat’s rudder. But with a little more thought a far better solution was found, this time co-opting technology originating in ancient water clocks dating back to around 270 BC. The rack and pinion is a mechanism formed by combining a pinion gear and a long bar cut with corresponding teeth. The steering wheel in the cab is linked by a shaft to turn the pinion, which displaces the rack sideways left or right to angle the front wheels.

One final engineering issue arises when you have two wheels fixed on the same axle. As the car rounds a corner, the outer wheel needs to turn slightly faster than the inner, and if they are rotationally locked together both can end up slipping or dragging, making it difficult to steer and damaging the tires. A system known as the differential, an assemblage of no more than four gears, allows both wheels to be driven by the engine while turning at different rates. This ingenious device was applied in European mechanisms from 1720, and possibly dates as far back as 1000 BC in China.

So if you peel back the skin of a brand-new sports car, something you might consider to represent the peak of modern technology, you’ll find a mishmash of components co-opted from mechanisms stretching far back through time: potter’s wheels, Roman sawmills, trip-hammers, wood lathes, and water clocks.

The internal combustion engine is a miraculous contraption, able to transform the chemical energy latent in fuel into smooth motion, and it underlies much of transport today (alongside the jet engine for fast aircraft and the steam turbine of large ships). We’ve looked at ways to produce your own gas or liquid fuels to feed these engines, and a full fuel tank offers such a fabulously dense reservoir of energy for traveling great distances before needing resupply that combustion will surely once again play a role in long-range overland and marine transport within a post-apocalyptic society well matured in its recovery. The problem, though, is that without easily accessible crude oil the civilization after ours may well be limited in its fuel sources: the proliferation of motor vehicles from the 1920s on was enabled by the cheap availability of gasoline from oil refineries. So, what might be an alternative developmental pathway for establishing transport infrastructure in a society rebuilding from scratch?

Rather than cultivating crops and picking out only a portion of the plant to be pressed to biodiesel or fermented to ethanol, it may be better to simply burn the whole harvest. Heating boilers to drive steam turbines and generate electricity makes a far more efficient use of the total sunlight energy captured by fast-growing biomass crops like switchgrass or miscanthus, or coppiced woodland. The electricity supply generated sustainably from biofuels as well as wind power and hydropower can be shunted down overhead wires to power trains and trams along fixed routes, or to recharge batteries for smaller vehicles. An electric car can travel farther on an acre of crop than an internal combustion engine filled with biofuel from the same harvest, and, what’s more, a boiler driving a steam turbine can be fired with far
lower-grade plant matter than is required for biofuel synthesis. And if you generate that electricity in a combined heat and power (CHP) plant, you can use the waste heat to warm buildings in the vicinity. An energy-restricted post-apocalyptic society will need to use coordinated thinking to maximize the efficiency of its fuel consumption, and it seems likely that the urban transportation of a post-apocalyptic civilization will be predominantly electric.

In fact, electric vehicles have been common once before. In the early years of the twentieth century, there were three fundamentally different automobile technologies battling for supremacy, and electric cars held their own against competition from steam- and gasoline-powered alternatives, as they are mechanically much simpler and more reliable, as well as quiet and smokeless. In Chicago they even dominated the automobile market. At the peak of production of electric vehicles in 1912, 30,000 glided silently along the streets of the USA, and another 4,000 throughout Europe; in 1918 a fifth of Berlin’s motor taxis were electric.

The drawback of electric cars with their own onboard batteries (rather than trains or trolleys taking a continuous feed from a power line over the track) is that even a large, heavy set cannot store a great deal of energy, and once depleted the battery takes a long time to recharge. The maximum range of these early electric vehicles was around a hundred miles,
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but this is farther than a horse and in an urban setting is more than adequate. The solution is, rather than waiting for the battery to be recharged, you can simply pull into a station for a quick battery pack exchange: Manhattan successfully operated a fleet of electric cabs in 1900, with a central station that rapidly swapped depleted batteries for a fresh tray.

So with a combination of biofuel-fed internal combustion engines and electric vehicles, an advancing post-apocalyptic society will be able to provide for its transportation requirements even without the abundant oil that we benefited from in our development. Now it’s time to turn from the transport of people and materials to the conveyance of ideas: in the next chapter we’ll explore communication technologies.