Isambard's Lad

The Go-to People for ship shifting

Posted on April 11, 2012 by The Lad

Spoiler alert! A bilious fragment of truth follows. It is not the whole story but The Lad will defend it from those who will feel that it must be attacked.

The ‘slebs’ of high and low culture are celebrated in the media with acres of print and hours of video coverage. Those who harness the natural world so that it has some surplus, to support the rest of the human race go relatively unsung.

Driving along the North Wales coast at Easter 2012, The Lad caught a glimpse of a ship, the MV Carrier, grounded in a storm a few days before. The TV news announced that they would seek to re-float it after they had emptied the tanks of fuel oil. It was not a large ship but it was the size of two or three cricket pitches sat against the rocks and weighed perhaps a couple of thousand tonnes. “Shift that ship!” Who do we go to? We go to the men and women who matter. They are the engineers and mariners. They, as far as is possible in this harsh world, are the ones who apply methods beyond the ken of most others to pull irons from the fire.

There are a million possible examples those who have supported the Human Race in its battles with the harshness of the World. Here’s just two at random.

Championed by my guvnor, Isambard Kingdom Brunel, Sir Joseph Bazalgette designed and built the great sewers along the London Thames Embankment. This vanquished both the killer, cholera, which threatened the inhabitants of London and also the stench that violated the Houses of Parliament. It allowed that vast city to continue to thrive and move on to organise mercantile trade and the Empire that brought wealth to England. Building ships on a production line in the Venice Arsenale, a place in itself strangely unreported in English, that on the other hand was well reported, brought wealth to the Medici’s and supported the artists and musicians of the Renaissance.

Without those who make things the artists would be found only in the depths of a cave scratching and smearing colour on the walls. The writers reduced to muttering tales to the tribe by the light of a flickering fire whilst hunching a stinking skin closer round their shoulders. That is before they are dragged out to help the community hunt down or gather some food.

I am briefly embarrassed by being reminded that this piece was written one hundred years to the day that RMS Titanic set sail on its first, and tragically, last voyage. Is this fact a hostage to fortune and the literati? All I can say is that no product of the human mind can be perfect especially when under the control of another human being.

We know that this piece has just been a cameo irritant. Lighten up! It’s scratched that itch for the moment and we need to move on to something more considered.

Here you can see the Dutchmen, Smit. What a marvellous, blunt, simple name for engineers! They are the real marine engineers, naval architects and mariners who do amazing things. No connection , by the way, except of admiration. The Lad has seen, at a distance, some of the things that they can do in moving enormous structures across the sea and then, believe it or not, a mile or more across the land. They have done some work on the notorious ‘Costa Concordia.

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So! “Schubert Lab”?

Posted on April 2, 2012 by The Lad

Then why not “Dyson Lab”, or Lovelace, Faraday, Bamford?

The great composers of classical music are celebrated as intellectually subtle, with wide achievements that buttress our civilisation, and enrich our culture.

A series of ‘Schubert Lab’ programmes recently on Radio Three featured experts and were for the interest of the lay–person. They spoke of the keys and chords; not in general but digging deeply into named pieces of music,. The programmes must have totalled something like 3 hours over 8 days in a Schubert strand that was 200 hours overall.

One of them, for example, discussed Schubert harmonies. Laura Tonbridge, an academic, spoke to Tom Service of a song that describes a journey and then he went to the meta-level by suggesting the journey that ends six years later as another song also about a journey. Then Jonathan Cross, a pianist talked about harmonies in another song that “sets up the home key of E minor ….. and then suddenly just by changing one note he moves the bass down a semi-tone and ….the [whole song] as if flips through the other side of a mirror”.

This is no aberration: many programmes scattered throughout the 24 hours on Radio Three operate at this level. It is powerful, technical, professional stuff with no patronising. There is no pandering to an audience that is without knowledge of music theory and notation; it is aimed at those who revel in subtle, new ideas. No dumbing-down here then. And – it’s before the watershed.

The great engineers are equally subtle, with wide achievements that buttress our civilisation, and enrich our culture. Yes. Yes, alright! So too are scientists. If this is a disturbing, unacceptable idea, it is because we hear in our education and the media so little of the detail of the engineers’ work, achievements and satisfactions. There is, in this field, nothing similar to the Schubert Lab other than, possibly, ‘The Material World’ on Radio Four.

Why not have expert, practising engineers speaking of their work, the whys and wherefores?

The Dam designer could describe what the choices are in choosing the type of dam [concrete arch, earth], how to build it without it being washed away as fast as they work, and what she has to consider before the water is finally held back.

A contemporary engineer can describe fibre composite materials and their unusual, non-isotropic properties and what he applies them to.

The discovery or invention of stainless steel has tremendous resonance in the modern world. There are many others to choose from. Some stories could be told by the engineer responsible, others from longer ago could be related by an insightful, modern engineer.

There will be intensely satisfying Eureka moments. It even happens in Mathematics: how many have heard how Poincare had his? He was working on a theory in complex functions and a massive insight came to him just as he stepped up onto the platform of a bus. Its connection to non-Euclidean geometry rose from his subconscious like the filmic Jaws from the sea. It’s the Arrêt De Bus Poincaré now.

Where is the Commissioning Editor – OK. – for Radio Four or BBC Four perhaps?

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Follow the Money

Posted on February 24, 2012 by The Lad

Once upon a time, long before the title of a Chartered Engineer was even a twinkle in its Daddy’s eye, the MIMechE’s and the AMIMechE’s ruled the mechanical engineering roost, and the Institute of Mechanical Engineers required The Lad to study “The Engineer in Society”. They had in mind to make the tyro engineer look up from his drawing board and slide rule and to recognise that he needed to know that were other aspects to the world.

He had to learn about what motivated a work force. That he had to have scruples and not seek to diddle others. There were some economic aspects to engineering.

Stuff like that.

Nowadays, the Institutions and the Engineering Council rely on the Universities to cover that. Which they duly do, see

http://www3.imperial.ac.uk/mechanicalengineering/study/subjects/year2/me2hmbe

The Lad did not think that they had quite got it nailed then and still does not. The twin of or undercurrent to the profession is wider than that. It is Commerce. It goes as far back as engineering if you consider the Roman Empire with its civil engineering of aqueducts and its commerce across the Empire.

Others have said that an engineer is someone who makes something for a dollar that anyone can make for five dollars. Though over-simple, it emphasises an important point. For the real engineer, economics is intimately bound up with the physical forces with which he or she wrestles. Engineering is ancient but so also is the trading that generates the wealth that funds it.

The Assassination at Bruges

Bruges in the 1120’s was already an amazingly thriving and bustling centre of trade for the whole of Northern Europe. It generated new wealth where it traded in wool, cloth, furs and jewellery. Count Charles the Good was the man who administered the rule of law in all Bruges that so facilitated the storm of trade. You can be sure that, in this financial ferment, engineers would have been busy designing ships, harbours and port machinery to keep the pot boiling.

On Wednesday 2 March, 1127, the Count was assassinated leading to great fears about its effect on trade. We know that the terrible news reached the merchants in London in only 2 days having been carried a distance as the crow flies of 150 miles. This distance, mind, was entirely over the wintry, wild North Sea covered under sail; no mean feat even today. The Lad finds this so remarkable in that it was only 60 years after the Battle of Hastings and King Henry I was on the English throne.

The Seljuk Sultans

While Bruges was in the north east of Europe, in the far south east of Europe where it butted up against Asia, there were the Seljuk Turks. Their enlightened, tolerant government and culture was at its height in the mid-1200s. The Seljuk Empire spanned the ancient trade routes of Anatolia, the famous Silk Road, the camel trails along which the riches of Persia and China were carried to the markets of Europe, and vice-versa.

With trade came wealth, so the Seljuk sultans worked to encourage, increase and protect commerce by road. They improved roads and had their civil engineers and builders build hundreds of beautiful caravanserais to encourage trade with the east.

These huge stone buildings were made to shelter the caravaneers, their camels, horses and donkeys, and their cargoes, to keep them safe from highwaymen and to provide needed travel services.

The typical Seljuk caravanserai is a huge square or rectangular building with high walls of local stone. There are fine images at http://www.turkeytravelplanner.com/architecture/SeljukCaravanserais.html .

Through the main portal, you pass the room of the caravanserai’s manager and enter a large courtyard. Around the sides of the courtyard, built into the walls, are the service rooms: refectory, treasury, Turkish bath, repair shops, etc.

At the far end of the courtyard from the main portal is the grand hall, a huge vaulted hall usually with a nave and three side aisles. The hall is usually lit by slit windows in the stone walls and a cupola above the nave. The hall sheltered goods and caravaneers during bad winter weather.

Caravans were received into the caravanserai each evening, and were welcome to stay free for three days. Food, fodder and lodging were provided free of charge, funded by endowments courtesy of the building’s wealthy Seljuk founder who had also given money for the building’s construction and for its maintenance.

Our Twenty First Century Motorway Service Stations do not benefit from the comparison!

The Merchant of Prato and the Milanese

‘The Merchant of Prato: Francesco Di Marco Datini: Daily Life in a Medieval Italian City by Iris Origo’ is one of the earlier classics of the literature in this field of economic history. It tells how the Merchant began in 1350 his path to a commercial fortune. In 1350 Edward III was on the throne of England and was a power in Western Europe.

“While kings and princes grappled and made alliances and betrayed and made other alliances, then grappled again, the merchants established their own quietly competent international estate.”

In another book ‘Hawkwood’ by Frances Stonor Saunders there is a pithy, summary of the situation only 10 years later.

“Milan was favoured by the merchants who trafficked goods between Lombardy and the great fairs of Champagne and Lyon. It was the merchants who had organised the routes through the Alps, collaborating with local authorities to police the roads, erect bridges and establish posts high in the mountains where their members could find protection from weather and brigands.

http://www.faber.co.uk/work/hawkwood/9780571219094/

All this was referring to Chaucerian times in and around the year 1360.

Note that Stonor goes on, in another accurate summary raising the shades of the contemporary engineers, to write

Milan’s trade was her lifeblood, and her bloody trade was arms, which evolved through access to locally produced iron, large quantities of charcoal from Alpine stands of timber, and the fast-flowing streams to operate tilt hammers and polishing mills.

The relationship of engineering to the Military-Industrial Complex of Eisenhower in the 20 Century foreshadowed here is an important topic that needs to be addressed in another post.

Today

Merchants and commerce are those who engineer the economics of our world into some sort of working order. Then Banking and its offshoots of derivative trading appear and are tending to de-stabilise economic activity.

Despite this, just remember the intimate involvement of engineering and commerce. Argue, if you want, whether commerce is the tool of engineering or engineering is the tool of commerce. Alternatively, symbiosis could be argued. The Lad unsurprisingly holds strongly to the primacy of engineering.

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Super Puma Down III

Posted on February 12, 2012 by The Lad

Cracks and Cleanliness

The metallurgist calculated that the markings in the crack had been advancing for between 36 and 100 flying hours before failure. He found this from the marks [behaving almost like tree rings] on the fracture surface. If he could have looked at the fracture on the other piece of the gear [never found], he may have found that more than 100 flying hours could have elapsed.

So, it looks like it was a problem internal to the material of the planet gear that caused it to break up. Rather, that is, than damage introduced externally to the component or outside the mechanism.

What materials does an engineer work with? With what does he design structures? Nowadays, it is most frequently with metals. On some occasions though, he may need to specify a natural material like wood [such as a building structure of internals] or a non-metallic [like fabric for the O₂ Arena roof or carbon fibre or plastics for racing car bodies]. For this post however, we will confine ourselves to considering metals.

What is it that is important about metals? Most often it is the raw strength of the material; how great the force is that is required permanently to deform it. Once permanent deformation starts to happen in a component from overload; then we do not know where it will stop. The engineer wants to avoid that. However, there are other strength aspects of metals that may, in certain tasks, trump raw strength such as fatigue strength, creep or toughness. Some metal alloys can be said to specialise in these different capabilities.

A very frequent cause of engineering failures in aircraft is fatigue. That is a failure caused by the repeated application of a stress that is smaller than the ultimate stress that will break a component with a single application. Fatigue is, by definition progressive and usually releases small pieces of metal before final failure. A failure of this type is one of which helicopter designers are extremely wary. It is compressive failure in the bearing race under the balls or rollers, called spalling. It is mainly for such chips that the magnetic chip detectors are seeking.

It helps to understand how to choose a suitable material for a design if we allow ourselves a little over-simplification. For an engineering material, just as for a recipe for something to eat, there are certain defined ingredients and a definition of how they are prepared and treated [cooked?]. For the engineer and metallurgist their chosen material is defined by two aspects. There are the ingredients which are chemical elements [mostly metals but not always]. Then there is the preparation sometimes flattening, [not unlike rolling the pastry for food] or shaping or cutting, and, usually, some form of heating and cooling.

Every material that we use can be had in different grades starting from some form of the raw and passing on up to some form of the extremely pure or refined. From the former to the latter the cost invariably increases. This is not unusual. It is true for a range of fabrics passing from coarse, denim for a pair of jeans to fine silk for a shirt. So it is for metals used in engineering from pig iron to single crystal, nickel alloy for a turbine blade. Such a turbine blade can easily be rated, in terms of the skill with which it is made and its value, as the equivalent of a Fabergé Egg.

Although most workaday components are not made from pig iron; they are at least from mild steel which is. In somewhat simplified terms, iron that had been melted together [alloyed] with around 0.2 % carbon. Most metals however include several components; frequently ten or more. Each has to be carefully controlled; present in the right amount. In the old phrase, to be not too little and not too much. Such alloying components have an important effect on the properties of materials. As we said above, usually it is strength that the engineer looks for but she may be seeking other things such as corrosion resistance or even electrical properties.

These, then, are the materials. What about their preparation?

As we have seen, metal alloys are complex assemblies of crystals. The properties of even a given alloy composition may vary depending on exactly how, on a microscopic scale, the components are arranged. Heating in an oven and cooling carefully is a frequent method for arranging the components of an alloy to provide the grade of strength that the designer decides is necessary.

Another aspect of the preparation is to ensure sufficient cleanliness. The raw materials in the form of ores or scrap often contain traces of other elements or compounds of carbon as impurities. These, after melting, may gather at the crystal boundaries. They may also gather in slightly larger quantities where they force crystals a little apart and are called inclusions. Both will be a weakness or stress concentration. For most components this is only a theoretical weakness. The weakening will either be small or extra material may be designed in.

However, this is cannot be done for some other components that are under greater stresses or where the consequences of failure are too great. For these there is no space for extra material or stress concentrations cannot be allowed to encourage fatigue failure. Aircraft components frequently fall into this category and thus do Main Gear Box planet gears. Because of this, the engineer needs materials that have vanishingly small numbers of inclusions and oxides in the material that she specifies. Clearly, good housekeeping in the production process is essential. But there is one powerful process by which material can be cleaned up. This process is actually two and together they go by the dodgy acronym of VIM/VAR, which stands for Vacuum Induction Melting and Vacuum Arc Re-melting. Good technical data can be found at http://www.cartech.com/productliterature.aspx?id=1246.

Both processes ensure that whilst ever the steel is molten, it is under vacuum to ensure that gases in the atmosphere do not help form brittle compounds that would get mixed in. The feed stock for the VIM part is melted by electrical Induction from coils wrapped around a crucible. It. The end product of this VIM part is a precisely correct alloy composition and also ingots that are of the right size and shape for the next process. The VIM furnace looks like the following.

Vacuum Induction Melting furnace timet.com

However, another important feature of high integrity materials is the small size of the crystals. Normal heat treatment can, if it is extended over too long a time, make crystals grow. If we treat the alloy in such a way as to make the crystals small or ‘refined’, the denser network of grain boundaries makes it stronger. The VAR part does just this.

Here the electrodes that come from the VIM process are again melted in the vacuum, but this time by an electric arc. A diagram of such a furnace is shown below. That is, though, not the clever bit. The secret of making small crystals comes from the way that the newly molten pool of alloy is made to re-freeze or solidify. This can be summarised as “very carefully”. The electrode insertion in the crucible; the rate at which it is withdrawn; the electric current supplied; the rate of cooling water flow; and more; will all be controlled simultaneously. This control will ensure, firstly, that the crystals are carefully formed at the right temperature and, secondly with careful cooling, they will then be frozen at a suitable size without being allowed to grow too large.

Vacuum Arc Re-melting furnace

The end product is an extremely expensive material that has a micro-structure that is so fine, clean and refined that, compared to a batch of the same alloy before treatment, it is a Premier League football pitch compared to a farm meadow.

The material of the Super Puma planet gear as designed was marketed as a material that could be VAR treated or not. If it had been then there should have been no inclusions or oxides to cause a crack. Is this a case where, despite the best efforts, some unpleasant defect still slipped through? The forensic examination of the gear said that the material composition was correct but does not explicitly say that the treatment had been checked. Could it be that this one component had been made from the correct material but which had not had, as the manufacturer’s specification allows, the VAR treatment? http://www.tatasteeleurope.com/file_source/StaticFiles/Business%20Units/Engineering%20steels/16NCD13.PDF

There might be a case for reviewing the design of the planet gear. It is currently one piece doing two jobs; the inner part is a bearing race and the outer part is the gear. As we saw a crack passed from the bearing part and into the gear part and cracked the component asunder. There could be a case, it seems at first sight, to try and squeeze a separate gear shrunk onto a bearing race into the admittedly small space available. Thus the interface between the two would act as a crack stop avoiding this type of failure.

The time that the crack took to propagate to failure whilst only one chip was detected reminds us that although in-service inspection methods must be robust, they must also be sufficiently sensitive. They must detect the deterioration of a critical component before the ability of the component to carry its design load is compromised. In this sad case, those methods did not. A major plank of a safety case is that any damaged material is released from the outside of the components. In this accident, almost certainly, the fatigue failure began and progressed until the last minutes or seconds entirely within the planet gear. Thus it was contained under its surface and away from the oil flow.

All in-service inspection methods must be such that they can always be relied upon to provide advance notice of problems. The other way lies instant catastrophe.

The engineer designers always have to be eternally vigilant about the giant forces that they harness. Those forces allow us to speed about our business. But if they escape their bounds then they revert, in an instant, to savage cruelty and destruction. So it was at six minutes to one o’clock on April 1^st 2009 when the drive exploded and the uncontrolled power flung the men on G-REDL from the heights to the depths in less than a minute.

References

Much of the interpretation and all of the engineering background in these three posts are the responsibility of Isambard’s Lad. Most of the facts and all but three of the images come from the Report on the accident to Aerospatiale (Eurocopter) AS332 L2 Super Puma published by the Air Accident Investigation Branch, Department of Transport, UK. http://www.aaib.gov.uk/sites/aaib/publications/formal_reports/2_2011_g_redl.cfm

Engineers’ responsibility

Engineering is one of the three drivers in the advancement of the human race. This blog aims to give to career seekers and also to the general public a taste of how this might be so. They are not well served by the current media. It is an engineer posting: not a ‘scientist’. It describes real professional engineering as it is in the real world usually in the present and occasionally as it was in the recent past.

For comment on this post use the ‘Leave a comment’ link below. For general comment on the blog, contact us at isambardslad@isambardkingdom.com .

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Super Puma Down – II

Posted on January 31, 2012 by The Lad

CSI Metallurgy

So! There were chip detectors fitted and working on that day, 1^st April 2009, in the gearboxes of the Super Puma G-REDL. How was it then that they had given virtually no warning that the main gearbox was a time bomb that was about to explode at any minute?

Mike M, in the business, told the Lad that a helicopter was mostly a flying collection of gearboxes. The passenger cabin is not much more than an appendage bolted to the engines and the mechanisms.

This shows the gears to the Main Rotor

For most engineering, structural failures, the earliest symptom is a crack. It, mostly, begins to open at the surface of a component. It extends, speedily or slowly, into the interior of the piece, some pieces [chips] breaking away as it does so. Final failure occurs when the crack makes the component unable to carry out its function. has not got enough sound material in its cross-section that is not cracked to cohere under tensile stresses. There is another type of failure that is particularly relevant to a helicopter. Underneath a rapidly rotating ball or roller in a bearing track [race], pieces of the track can begin to crumble away. This does not often proceed to fracture of a race as it is due to compressive stresses. These tend to keep the part pushed together rather than as tensile stresses tend to pull the component apart

The AAIB report tells us, in summary.

One chip had been found on one of the detectors some days before. The mechanics consulted the manual as to what should be done. They thought that it was just a piece of scale. They spoke to the manufacturer’s engineers by phone and email. At each end of this communication channel there misunderstandings as to what had been found, what had been done, had not been done and what should be done. The upshot was, terribly, nothing further was done because no significance was attributed to the ‘piece of scale’ In fact it was bearing steel – of dreadful import.

In the middle of the last flight, one of the eight planet gears abruptly shattered into massive fragments.

One fragment was over-run by the next planet gear. If it had been the size of a matchstick, a piece of metal would, at the speed of this gearbox, have been crushed, passed through and flung out. There would have been some damage to the gear teeth but no more. This fragment however was of an awful, irresistible size. In the subsequent examination of the wreckage it was never found but everything else was. The size of the gap of its absence tells us in itself a grim story. It would have been a hellish boulder the size of a man’s fist: quite uncrushable. It burst through the strong metal shell of the gearbox outer case, splitting it like an over-ripe tomato with a shattering explosion.

The crew saw the emergency, on-screen warning of the catastrophic fall in oil pressure to almost zero. Two seconds later the craft ceased to respond to any flight controls. The grip of the gearbox on the main rotor was broken. The helicopter rolled and yawed and pitched as though it were a paper windmill in the hand of a child. Twenty seconds later the rotor lifted – free – away from the fuselage; it tilted and then hacked and severed the helicopter tail and its control rotor. The rotor then spiralled away into the air; freed from the burden of the fuselage. What was now left, the cabin and engines together, streamlined like an egg: plunged uncontrollably towards the sea far below, carrying the desolate passengers and crew.

As there had been only one chip found in the oil system, how did the failure start and progress without many more? Call in the metallurgists.

The metallurgists are the brothers in arms of the engineers. Tony T told The Lad that he had the best job in the world, as a failure metallurgist in an engineering organisation with an international reach. He travelled widely to study forensically a variety of failures. Luckily, none of his problems involved loss of life but even if they had, perhaps he would have helped with an understanding as a kind of memorial. If the study of metals appeals to you, go for metallurgy.

Metals are complex structures when you look at them with a microscope. Most people imagine, if asked, that even at that level metal is smooth like a bar of chocolate is smooth. Far from it. Solid metals are crystalline. In a crystal, the overwhelming numbers of atoms are lined up neatly in rows, sheets or repeating patterns. Tiny examples of crystals of this sort are sugar and salt. However a piece of metal is not one single crystal. It is almost always made up of millions of tiny crystals jammed together and each adhering to its neighbours.

Why is this? When the metal is molten, every atom is rushing madly about in all directions. As it cools, pairs of atoms begin to adhere to each other in millions of places, called nuclei. Then other atoms arrive and stick to the first two but only in a neat, repeating array. Imagine 4 footballs: three touching each other to form a triangular pattern and the fourth sitting on top and in the middle of the triangle below.. Such an arrangement could extend as far as you like if you have enough footballs. As the atomic pattern grows, forming a crystal, it continues until it hits another nearby. This is happening in all the nuclei but in a direction depending on the orientation of the first pair of atoms. Each crystal array is at a different angle to that of its neighbour. Thus as the metal cools, each of the millions of atoms in a single crystal is rushing to slip into its place in the pattern. Until, thud, – thud, – thud – and every crystal is jammed up against its neighbours and the whole mass jerks into a solid, rigid mass of thousands and millions of crystals.

In recent, two or three decades some special components such as aero-engine gas turbine blades have each been made of a single crystal. But this can be done only with enormous difficulty, technical cleverness and great expense that are not justified for any other components.

In addition to the conventional processes that are equivalent to standard police work or ‘boots on the ground’ Lots of cutting, polishing and etching with acid to show the structure under the microscope.

Then they zoomed in on the critical areas. The materials engineer has an army or techniques and instruments to study his materials??? Because of the critical importance of the investigation of this accident, she brought to bear some of the Special Forces of the army. There was conventional optical microscopy but also 3D surface optical mapping, 3D X-ray tomography, high resolution Field Emission Scanning Electron Microscopy, and (FESEM) Transmission Electron Microscopy, TEM.

The pictures below show the view, like a geologist overflying a mountain range, of the fracture surface that they had to study to tease out answers.

$Raw fracture$

This is the metallurgist's first sight through a microscope at low magnification

After a lot of close examination, the metallurgist decides that these areas of the fracture had different causes

One of the significant, engineering features of the planet gears is that the bearing track or race and the gear teeth are all in one piece. As we have said before, most of the stresses caused by the bearing rollers are mainly compressive and tending to close any cracks; but here’s the rub, with the integral gear teeth much of the stress field produced is tensile and crack opening. The result with the two fields is that in this double function component, once a crack has crept beyond the race stresses, it enters the gear, tensile stress region opening and, perhaps accelerating. It can eventually pass through the whole gear pinion and break it into pieces.

The morphology [the shape] of the fatigue crack in the second stage planet gear, 13. suggested that it had initiated from a point at or close to the surface of a highly loaded section of the bearing outer race,

The following pictures show a 3D view of their conclusions.

The metallurgist, after much work, was able to calculate the origin of the crack.

Ultimately, this suggests to The Lad that the failure and any chips began, if not entirely internally, then at least, within the compressed area of the gear pinion material body. The result? Nothing – no crack – broke the surface to provide chips until the fracture was almost complete and only minutes away from catastrophe.

What can we do about this problem, this type of behaviour? Let’s look at this in the next post.

Engineers’ responsibility

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STOP PRESS! – Free Power!

Posted on January 25, 2012 by The Lad

We interrupt this thread on the helicopter briefly to mention the latest saver of the Planet. The Searaser and some of its simpler engineering aspects.

This is another proposal for generating electricity in an environmentally friendly way. The media is again trumpeting it as encouraged by press releases. http://www.guardian.co.uk/environment/2012/jan/23/bicycle-pump-searaser-energy?INTCMP=SRCH

The fact that the media say that it works like a bicycle pump does not induce confidence. The inventor’s backers Ecotricity [http://www.ecotricity.co.uk/our-green-energy/our-green-electricity/and-the-sea/searaser] call it a double acting pump. It cannot be both. Virtually all bicycle pumps only push air into a tyre on the inward stroke; that is, it is single-acting. A double acting pump pushes its fluid both on the inward stroke and the outward stroke.

The Searaser is another oscillating device submerged in the friendly sea. The Unique Selling Point is that it generates its electricity on land to avoid electricity in the water. It is simple enough in principle. A large float at the sea surface bobs up and down with the waves. A rod attached to it passes down to a simple piston pump which is tethered to the sea floor by a cable. http://www.youtube.com/watch?v=_9jGis5V5LE

The Lad has to wonder how reliable such an arrangement can be as it flops around in the turbulence of the open sea. The pump and the float will each be subject frequently to different forces tending to flex the assembly. Even if the float and pump themselves can withstand these forces without failure; the piston rod seal at the pump will see large leverage forces. They will tend to make it leak or, at the least, make for inefficiency due to high friction. What is the L/D ratio for the bearing?

Speaking of friction, how much power at the pump is wasted through friction losses pushing the water through pipes from the pumps miles out at sea all the way to the land and its power generating turbines?

Each pump cannot be scaled up beyond the scale set by the sea wave length. If it is built much bigger than, say, one or two wavelengths like a ship, it will become stable – like a ship – and not move up and down at all or very little.

Full engineering design and development details cannot be expected to be given in the press. It seems clear to The Lad though that there is a very long way to go before the engineering production model is workable. Even then the economics will still be an unconquered enemy.

Note also that a reservoir is needed on land at a suitable height. This is to provide enough potential energy to generate a useful amount of power whilst not needing too much pressure head. Too high a working pressure for the system will lead to even more design problems. The storage of water in the reservoir is also needed to smooth out the variations in pressure inherent with an oscillating pump and also to provide some back up for these days, and they undoubtedly exist even in the UK, when the waves are small or in a flat calm.

But again, how big will the reservoirs need to be for every pump farm to provide continuous power and not have its beneficiaries sitting in the dark. After all the UK weather is known to everyone to vary from day to day. There tends to be a comparable number of weather states that are “too much” or “too little” as there are that are “Goldilocks”.

The video shows the first model giving some squirts of water that are, not to put too fine a point on it, not very big. Perhaps that is the origin of the Bicycle Pump name. Later models seem to give a better flow rate, it has to be admitted. Nonetheless, still the supporters of such proposed systems still cannot show, even if they understand it, the gigantic amounts of unremitting, 24/7 power generated by the Base Load Power Stations for a modern society.

The Lad is aware of an existing water power generating scheme on a nearby, quietly flowing river. To see the amount and velocity of the outflow which generates only 150kW is a reality check on the water flow and plant required. This is how it can, more realistically, be done. Visit here to see something of it; http://www.derwent-hydro.co.uk/our_sites/index.html . The Lad has no connection at all with this small organisation.

So, assuming that much can be done to develop the system, how many fully-engineered assemblies would be needed to generate, say, a megawatt hour of electricity? What is the cost per unit of electricity from such assemblies at the Grid?

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Super Puma Down – I

Posted on January 8, 2012 by The Lad

Without Warning?

It was April 1^st 2009 and the Eurocopter Super Puma L2 helicopter was expecting to land at Aberdeen at 1314 hrs. This was still 20 minutes away but, at the 2000 feet cruising altitude, the coast landfall 10 miles away was just in sight.

The crashed helicopter was one like this

It was about half way through its busy schedule to and from the rigs that day, flying at nearly full speed with a full complement of 2 pilots and 14 passengers. The co-pilot radioed base that all was normal. Only twelve seconds later came two MAYDAY calls

Below, was a modern, powerful, rig supply ship, the ‘Normand Aurora’, on a so-far uneventful trip. Someone on watch on the bridge changed all that. It was good visibility and there was a shocked shout of alarm. Two miles away, the helicopter was hurtling into the sea with separated rotor following it. Then came the bangs, the black smoke and the explosion. The ship swung towards the smoke.

Normand Aurora was the nearest ship to the crash site and rushed to the rescue.

Launching their fast,-rescue inflatable. It hit the water with a loud slap and accelerated away. Leaving the mother ship quickly far behind as its helmsman gripped the steering wheel with white knuckles and stiff-armed the throttle fully forward. He and his crew were desperate with hope that there would be something that they would be able to do: that there would be someone that they could help among the unfortunates in the helicopter cabin that had plummeted into the sea at high speed. But fearful at the same time. After the headlong two miles, its crew found a large circle of churning water. Within there were life rafts and debris. They also saw eight people; none were alive.

Epicyclic Gears

Recovered from the sea bottom. Note the missing pinion at four o'clock.

Above are planet gears from the downed helicopter showing corrosion from their immersion in the sea. They are without an outer casing destroyed in the accident. There should be eight gears but it can be seen that one is missing. The destruction of the one, missing planet gear was the cause of the tragedy. Above shows only a part of the gear boxes and trains in the Super Puma [and other similar helicopters].

Had there been no advance warning of the impending catastrophe at all?

The drive shaft from each of the two engines in the helicopter runs at 23 000rpm [that is, the internals of each engine is rotating 380 times in one second or around 5 times as fast as a family car engine!]. The main rotor blades rotate at 265rpm. This means that the helicopter design engineer had to design a gear box to give a reduction of nearly a factor of 100. It has to fit in as small space and have as low a weight as possible.

When the designer needs to slow down the rate of rotation of a shaft by a large amount like this, she usually goes for an epicyclic gear design. These are commonly known as a sun and planet gear sets. This is what is found in a Super Puma between the fast spinning engines the relatively slowly rotating main rotor.

This epicyclic design was shown in the textbooks of The Lad like this, and similar diagrams are still shown today.

The textbook version is rather lightweight compared to the real thing.

In real life where very large power has to be transmitted in as small a space as possible, there are more planet gears than in the textbook diagram. They fill the circumference and each is wide and massive. Such planets of half of the Super Puma epicyclic gear train are shown in the salvage photograph above.

To see how designers calculate the variables in a real design of epicyclic gears see – http://www.roymech.co.uk/Useful_Tables/Drive/Epi_cyclic_gears.html

Magnetic Chip Detectors

Even though the designers seek to make engines and gearboxes as reliable and free from the risk of components failing as possible there is still a need to keep a check on machinery health. For a Power Station generator or a car engine there is no great, inherent problem to be anticipated if it rapidly comes to a halt after 30 sec of noisy running. It is quite a different problem if the engine is powering an aircraft flying several miles high over the ocean. Here a significant risk of such a sudden stop is not acceptable. They must head off such failures before they happen. They must search for signs of any problems well in advance.

The magnetic chip detector is one of the neat ideas that help maintenance teams do this. It is a simple concept. Many of the most highly stressed components are made of steel which is magnetic. One of the commonest symptoms of failure, when such a component wears or suffers fatigue cracking, is that chips of metal are generated and released from the parent component. The oil, as it is circulated throughout the engine, washes such chips away and usually takes it to the lowest part of the engine. En route, if it washes over a single small magnet, it will be captured by the magnet. The maintenance team simply unscrew the magnets at regular intervals and an early alarm can be raised if any chips are found sticking to the magnet.

Such detectors are positioned at various places within the engine oil flow where any chips may be washed over them. An alternative design is to provide twin magnets close together. Coupled to this type of device is a power supply and electronic detector to signal to the helicopter pilots, even in flight, when a chip bridges the two magnets. Such a design is shown below.

This is the operating principle of the more capable design that can provide a signal in flight

There are many such detectors designed into the Super Puma. Several are in the vicinity of the main gear box. The design of such detectors is another one of the many examples of the nexus where the design principle of “simple and reliable” approaches close to the principle of “too crude for the risk burden”. The designer has to consider which is the truth in every such case. Did the detectors work this time or not? If not, why not? See the next post.

Memento Mori

Engineering turns the forces to the benefit of mankind and the results have immense consequences. These consequences are, on the whole, beneficial but sadly, as with any efforts of the human race, for some individuals can be malign.

Bloody skirmishes to understand each way that a structure can fail and to avoid them all are a repetitive feature in engineering history. For ordinary structures most of the skirmishes have been avoided and, nowadays, fewer new ones appear. But fresh demons occasionally burst forth to confound us in new campaigns to complete new tasks or use new materials. When they do, they extract their price in blood or treasure.

Professional engineers have to be continually alert. The engineer knows that the nature of her or his work usually brings great benefit. But it can, also on occasion, bring tragedy.

So it was with G-REDL on 1^st April 2009.

Engineers’ responsibility

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Madeleine trumped by Ruby Loftus

Posted on December 17, 2011 by The Lad

Trefolex and Tufnol ride again in Mechanical Engineering 101.

Famously, the hero of Marcel Proust’s multi-volume novel, “A la Recherche du Temps Perdu”, found that memories of a period many years before were triggered by a smell and taste of tea and a dipped madeleine.

Immediately the old gray house on the street ….. rose up … and the entire town, with its people and houses, gardens, church, and surroundings, taking shape and solidity, sprang into being”
http://www.gutenberg.org/catalog/world/readfile?pageno=29&fk_files=1466063

Risking the bathetic after such a graceful idea and prose, The Lad found the opposite the other day: smells from his youth were triggered by this striking picture. It had been featured in a recent exhibition, Women War Artists (now closed), at the Imperial War Museum, London – website www.iwm.org.uk .

IWM2850 Dame Laura Knight - 'Ruby Loftus screwing a Breech-ring'. 1943, Oil on canvas

Instantly, the workshop with its high roof appeared; it’s the Fifties. Machine tools are ranked in bays each controlled now by an apprentice in a white boiler suit. Each bay patrolled by its white coated Instructor. There was the low rumbling of the milling machines, the hum of the lathes just like the one in the picture, the hiss of the grinding machines. Equally pervasive was the smell of cutting oil and often the raw, burning smell of machined Tufnol – a composite material of linen and resin – still going It seems, [http://www.tufnol.com/tufnol/default.asp ].

But if it is a really vile smell you are after then it is in the fitting bay in the corner of the machine shop. Here are the benches and vices where there was hammering and a continuous swish of filing. There, on the bench were the pots of Trefolex, a thread-tapping paste, green coloured and with a vile stench. You can still get it today [http://www.warrenbestobell.co.uk/trefolex-cutting-compound.asp ] though they may have got rid of the smell by now.

The Training School entertained both Trade Apprentices and Technical Apprentices. The Trade Apprentices were being aimed at careers as skilled machinists; whereas the Technical Apprentices were intended for the draughtsman’s career. Notice the suffix ‘man’. No women or girls then in the Fifties: they were all long gone after the Second World War. Not even an office girl. “Disturb the youths, you know”.

But, contrary to the popular vision, the Training School does not represent the milieu of the professional engineer. It is Mechanical Engineering 101 where, then, he or nowadays often she discovers the basics before moving on. The mechanicals move on to design or work on new products for the machines to make, the production guys to introduce better machine tools or ways of dealing with difficult materials.

It was here, in the Training School, that The Lad first tried cutting an external screw thread on a lathe with a single point tool. He found it difficult while the Trade Apprentices seemed always only to thrive on the challenge. Then they moved on to using the same technique to cut an internal thread. This is what Ruby Loftus in the picture is doing: under intense pressure in War time using the high skill of cutting what would be a buttress thread for a breech block of an artillery piece.

This magnificent picture though is much more interesting than just for the memories of The Lad. The picture is, most importantly, but also so powerful, painted in 1943 the middle of the War, shows only a one male, a single small figure in the distant background. The thunder on the Home Front had changed everything. The painting of this picture shows that the changes were so radical that they had to be recorded. It was a peak in women’s employment never reached again even today. However, almost 70 years later, girls and women do take their proper place as apprentices and professional engineers.

The dignity of Ruby and her concentration on the complex machine and work piece stands four-square with the haughty gaze of Henry VIII in Holbein’s painting. http://darkpassenger.tumblr.com/post/727152626/hans-holbein-portrait-of-henry-viii-1537 The painter was Dame Laura Knight who had, pre-war, specialised in painting dancers and circus performers. http://www.damelauraknight.com/biography.html . Though less important, The Lad believes this powerful painting is also the most accurate, realistic canvas of a rare subject – a snippet of Production Engineering. Unless, that is, someone else knows better.

There is the contained poise and tension of the lean of Ruby. It is that of a dancer yet with stillness. Countering the figure of Ruby and closely observed, are the dark, gleaming masses of the lathe: the tool post, the carriage and the tail stock. The tools are there too: a scraper to remove burrs, an internal calliper for measurement, parting–off tools and tool holders and a ring spanner for the bolts on the carriage.

Ruby is gazing intently at the spot lit tool. It is cutting the thread inside the breech ring during the very brief period as the tool passes from the side of the work piece nearest her out of the side within the rotating chuck. Her hands are not just supporting her but a part of her vital control of the machine. She rests the fingers of her left hand on the tool post to check and confirm the faint, continuous, humming vibration showing that all is well with the single point cutting tool. Her right hand performs the same check on the gearbox driving the feed screw and confirms that the carriage is moving. That same right hand was also well placed to switch off the drive to carriage and work piece in an instant when it left the inside surface of the work piece before reversing it back out in the same helical groove of the buttress thread but with a slightly deeper cut.

Now, in the Twenty First Century, a CNC Turning centre does it all more quickly, just as accurately but with less involvement of a human operator – male or female.

Posted in Engineers in the World, Production Engineering, Vintage | Leave a comment

Some machines swim

Posted on December 1, 2011 by The Lad

One, unseen, already-submerged diver was filming near to a hole in the thick ice sheet above: as the elegant cylinder dropped vertically at high speed through the still, -1°C, water below. Immediately, as though alive, the vehicle swung gracefully into level flight towing a tail of yellow cable behind it. Ministering to and checking on the machine on this, one of its early test swims, was a black-clad, scuba diver.

The Lad was transfixed by the magic sight in the vast under seascape of a thousand shades of blue and green. The voyager looked as though it had been born there instead of being designed by human beings. Tell-tale features, though, were the lights: a white searchlight beam for a camera and a pair of scarlet, laser beams lancing through the gin-clear water from each side of the nose of the vehicle. Another was the complex internal structure clearly visible with, not the fluent curves of a living body, but the lineaments of straight lines and exact circles of a densely packed machine. It was about 2m long and 20 cm in diameter.

It was the 30 November 2011 and “The Frozen Planet” Part 6, ‘The Last Frontier’ on BBC Television that was the unexpected carrier of the strikingly beautiful images of this example of the art of the engineer.

Then the vehicle darted straight ahead at least twice its previous speed into a corridor among the irregular blocks of the ice pack above. It gave an impression of a shark but without any sweep of a muscular tail but with a rapidly accelerated spin of a propeller.

The Lad was captivated and vowed to find out more of this masterpiece. A search only just begun and the results will be reported here. This machine seemed to The Lad to encapsulate what engineers do.

Posted in Design in the World, Engineers in the World, Views | Leave a comment

Not in the Media

Posted on November 21, 2011 by The Lad

The movers and shakers of the media live by the word and the image: therefore they attend only to those with a rich word stock or some excited footage. Discuss.

The Lad is in one of his periodic bouts of surly introspection about how the world owes engineering, if not the continuous, close attention that his ego suggests, at least more frequently a proper look.

Today – a random day – triggered this when he noticed some randomly spaced topics in the press.

Eight hundred or so smartly written words are given over to a theatre director and an actor performing a version of Macbeth single handed in Gdansk, Poland. It spoke of how they both got there, the problems of the rehearsals, the highly strung performances and, finally the relief when it was all over. Deeply realistic, technical, and actorly detail there was on the struggles of the actor. The worries of the director radiated from every word.

One thousand words and five full colour images [two being full page] tell us about a music radio station broadcasting a wide variety of pop and jazz globally from the UK. The pivot of the article is their disc jockey. Oh yes, by the way, the DJ is young ,female with long blonde hair of course.

A review noted that a book had been published of a lost novel by Jack Kerouac, “The Sea is my Brother”. He, at the age of 20, had sailed with the American merchant navy for all of three months. Hallo? The insubstantiality of this miniscule scrap of experience bearing the weight of the title and plot of a first novel claiming realism was accepted without comment.

Trying to avoid being too patronising or obnoxious, these are solemn delineations of the fine detail of transitory matters. The Lad wants to know how we get frequency of media attention devoted to the less transitory engineering.

An easy answer is that the topic is not ‘interesting’ or that such a question “tells us more about the questioner than about the world”. Too slick: we need a more thoughtful answer. It’s not “Culture” you say? But it is or at least should be when the machines and their makers shape our world or fill our field of view in some places or modify our behaviour. Another easy answer is ‘It’s boring.’ Or ‘It’s not interesting.’ This may well be true but why is it not interesting or boring? It needs to be more than an answer of better writing: provide constructive detail.

Real engineers have struggles and triumphs. They are of every technical, personal and gender stripe: there are chemical, civil, mechanical, electrical, stress and production engineers There is an end-product or sometimes a dramatic failure: a true, rich textured creation to end on.

Hell! Is it back to the rich verbosity and the exciting or excited footage?

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