1.4 Additional thoughts
So where have we reached so far?
First we have seen that, beyond the shelf-building level of engineering, which I suppose most of us can undertake with more or less skill, there is a profession of engineering which dates back a long way. We shall examine the origins of this profession over the coming sections. Professional engineers, working either alone or in teams, can undertake much more complex tasks by virtue of their talents, training, knowledge and experience. The great diversity of engineered products has led to many specialisms within the profession.
Secondly, with each of the short case studies it has become apparent that the engineering of any period rests on prior achievements. The ballpoint pen, by virtue both of its materials and the construction methods, could not possibly have been made by the engineers of the Pont du Gard, despite their great skill and expertise. Clearly the builders of that remarkable bridge nevertheless drew on the prior knowledge of how to construct arches (the French continue the art of fine bridge building with the Millau Viaduct shown in Figure 18). This aspect of the 'progress' of engineering will occupy our attention later.
The third aspect of engineering we have seen in action is its organisational aspect. One of the engineer's roles is to ensure that resources are available to achieve the goal. Engineers control the actions of others to bring about the success of a project: they depend on the skills of their stone masons or lathe operators or welders. Badly organised engineering is just as chaotic as a badly conducted orchestra.
A fourth important realisation is that engineering is quantitative : measurement and calculation are vital to its practice. At its simplest it may only be spatial quantification, as for example to build the bridge. Further down the line though, a wide range of measurement capability is demanded. Ammonia synthesis calls for measurements of temperature, pressure, gas flow rates and chemical concentrations even within the small part of the process that we have looked at. Notice, however, that there is a big difference between being quantitative and being scientific. The builders of the Pont du Gard had no scientific knowledge of, say, the stresses in their structure; they did not design it scientifically, using theories of how arches worked. They just had the 'know how'. In contrast, the ammonia pressure vessel was constructed with full knowledge of how the material should behave, even to the extent of knowing the consequences of there being a flaw (in the welds of the vessel, for example).
Measurement implies units to measure in: metres of length, kilograms of mass and so on. Historically there have been many definitions of standards for measurement. Now we have settled more or less completely on the SI ( Système International ). But the SI is not yet universal: American engineers got astronauts to the Moon using feet and inches for length, and pounds for mass (see Different systems of units ).
Different systems of units
The SI system of units is not the only one which is available, or indeed, in common usage. The most widely used alternative is the system of pounds for mass, and feet for length. This is the 'imperial' system of units.
In the US, imperial measurements are more common than the SI metric system. This can lead to problems if there is a mix-up as to which units are being used. The NASA Mars Climate Orbiter was lost in 1999 due to a mix-up between the two systems. A computer directed the wrong thrust to be applied to bring the craft into Mars orbit because its program was in one system and its data in the other. Interestingly, Americans refer to the imperial system as 'English units'.
Not every engineering decision about a length needs to be based on an actual measurement. Most of Blanc's gauges for the parts of the M1777 musket lock were of the 'go/no go' type. A particular pin, for example, had to be small enough to enter one gauge hole but big enough not to go into another; so the pin diameter lay between the two hole diameters. The alternative approach of defining the size of the pin as, say, 5.00 mm ± 0.01 mm (that is, the diameter must fall somewhere between 4.99 mm and 5.01 mm) and providing an instrument to measure the pin to that accuracy was not available to Blanc – the micrometer (an instrument for measuring small distances) had not been invented by then and the millimetre had not been defined. For his purpose, all the pins had to be the same – give or take a bit. It probably did not matter exactly what that size was.
Activity 9 (exploratory)
When you place a ruler alongside another rule, or tape measure, do the lengths match up exactly ? If there is a difference, is it significant?
I found that there was a slight difference between the two rulers that I chose. However, since I only ever use them for coarse measuring (to within 2 mm or so) this is not a problem.
We have also seen an example of how science can inform engineers of how to proceed. Without a thorough understanding of ammonia chemistry on the part of engineers, the Haber–Bosch ammonia manufacture process could never have been developed. But, as we shall see, some remarkable achievements in materials processing have been developed without scientific understanding. We speak of the Bronze Age or of the Iron Age in archaeology because the people of those times had discovered how to get metals from minerals; and in the case of the Bronze Age, how to make various copper alloys (not just bronze) so as to enhance the properties of their metal. They did these things without any knowledge of chemistry. The role of science for engineering has been largely twofold:
- to provide new perceptions of what might be done – electric motors, transistors, radio, digital cameras, the Airbus A380, etc.
- to enable developments to be made more effectively and efficiently by underpinning experience with theory.
This brings me to the issue of design , which lies at the heart of all professional engineering. Whatever enterprise engineers are going to coordinate, it starts off as a mere feeling. A 'wouldn't it be nice if ?' sort of thing. Along the line, someone has to turn that vague aim into a practicable idea. By practicable I mean not only that whatever has been conceived of will meet the function implied by the goal, but that it can be made too. For how many ages have people watched birds and longed to fly? In mythology, Daedalus (unquestionably an engineer) made wings of feathers glued on with wax, enabling him and his son, Icarus, to fly. But Icarus flew too close to the Sun and the wax melted, resulting in the first fatal air crash. Of course, this didn't really happen, nor could it have happened. We now realise that human muscle power cannot be sufficient to get us off the ground by flapping wings. Leonardo da Vinci drew pictures of a screw-driven machine, but he had no way of powering it. The Montgolfier brothers became airborne in 1783 in the first hot-air balloon, but as the balloonist is at the mercy of the wind it isn't really 'flying'. Eventually, when the internal-combustion engine was available, we began flying – just over 100 years ago. The development from the Wright brothers' contraption to a modern aircraft demonstrates again each engineer's debt to those who have gone before (see Figure 19).
The point I want to make is that design is the creative part of engineering. It comes from inside our heads. It is a manifestation of imagination – putting experiences and ideas together in new ways to conceive of new possibilities. Note the plural: there is usually more than one way of reaching the goal.
One of the fascinating things about imagination is the surprises it springs. People had been pushing heavy things around on rollers for thousands of years without the flash of inspiration that invented the wheel. The idea of fixing an axle to the load and threading each end through rollers so they stay with the load is a subtle perception: a beautiful example of an imaginative surprise. It could have happened in any of thousands of minds at any time over thousands of years, or maybe it just happened in one mind. Whichever it was, no doubt it was accompanied by the thought 'Why didn't I think of that before?'.
But the idea had to be followed by action. Though the inventor could perceive a wheel in the mind's eye, none yet existed. How to put the idea into practice would then call for more imagination. This time it is a different kind of imagination: ideas can be tested straight away against the yardstick of practicability.