One place that computers go to die.

AN ENGINEER’S VIEW

The Lad was getting rid of a dead little flat bed copier and a sandwich toaster. Not one device, you understand, but two items. Anyway. To the local Council Waste Recycling Centre.

There on the top of the skip for electrical equipment scrap lay a BBC computer. He was amazed that they were still around. Not that he is an expert in these things. When they, along with the Acorn [was it] and the Amstrad using Basic, were in their prime as the cutting edge of domestic computing his children were too young and he was too attached to his Sinclair hand held calculator. The Black Watch digital watch was also the latest thing then.

Are there any, outside of a museum, still operating? What did they do? Are there any emulations of them that can be downloaded and operated on the PC or the Mac? The Lad supposes that the answer to that can be found on the net. He can’t go looking for it as, if he did, nothing would ever get done.

Don’t come in from the cold.

THE ENGINEER’S VIEW

There was an item in the Sunday Times gossip column-cum-Diary on Sunday 6 February 2011 that caught the eye of The Lad. He cannot give you a hyperlink to it because the website of the newspaper seems to be subscription only. He does not subscribe and probably nor do you.

A man in the UK Lakeland was boasting that he had a refrigerator that was 55 years old and still going strong and he hoped to pass it on in his family. It crystallised a feature that, as an engineer, The Lad has often noted: the longevity, usually without any maintenance, of the domestic fridge.

In his view this is simply because most fridge’s components are lowly loaded and the loads and temperatures are almost constant. The electric motor and its pump are very quiet which indicates that they are not running highly loaded and at their limits. The rest of the components such as the radiator at the back and chilling coils inside pretty well stay warm and cool respectively throughout the day and, indeed, its life. High loads and big temperature swings are frequently the cause of failures in engineering.

Contrast this with the domestic washing machine and spin drier. The Lad makes the point that these machines tend to be less reliable than the fridge. This, he says, is due to the different duty imposed on their components. The washer drier does not operate, like the fridge, continuously. It is always being switched on and off. The drum and motors are frequently powered up and down and operate at quite high loads. The drum and the bearings are spun up and down to high speeds under high, frequently off balance, forces. The systems within the machine frequently see high temperature spikes due to the heating of the washing water which is rather corrosive due to the detergent loads. The rubbery seals are pushed to their limit during every wash cycle. On top of all this, every component of an increasingly complex machine design is packed tightly in a hot, vibrating environment.

Unless somebody out there can disagree with The Lad.

Power by the Hour

THE ENGINEER’S WAY

Pence per minute; quarters per hour; that’s the information that we all need. Not just engineers. Let me tell you that nowadays, the designers and builders of engines for aircraft do not just sell the engines to the airlines. They sell them Power. The engine builder knows how much they cost to run and the airline likes to avoid the hassle. So the builder sticks a reasonable profit on top of the running and insurance costs; lends the airline the engines and charges them for however much power the airline uses. One builder at least calls it Power by the Hour.

That’s how we all need to think, not just the engineer’s family. Save the pounds or the dollar. Make it easier to save energy. Make it easier to save power. Make it easier to save money. It’s easy to help this to happen.

The Lad has been shouting this to himself today. His power bills are sky high and painful to pay. So are yours probably. In the modern household there are a multitude of electrical appliances. Some are power gluttons: they are mainly heaters of one sort or another. Some are only sipping at the meter: IT gadgets are such. Unless you are obsessed by the problem as is The Lad or any engineer, you will have little idea about how much power it takes to heat anything. An enginer can tell you, it’s enormous. In any flavour you want, it’s gigantic; be it kilowatthours, simply pedalling a bike or, if you prefer, horsepower.

Just running the hot water tap – especially running the hot water tap – costs a fortune over the month. The Lad’s old Physics master at school said to him that the specific heat of water [that is energy required to raise water by a degree or two of temperature] is higher than almost anything else except some gases. The Lad will dig out the figures for a future post.

Big Towel rail
Can you see it? At the right above the box. (c) The Lad 2011

Anyway, there was The Lad crawling around on the floor trying to find the Rating Plate of the various heaters in the house so that he could rant at the family. “Did you know it costs gold dust to run this thing for five minutes?

Small Towel rail
Another one lurking. On the left, behind this time! (c) The Lad 2011

But the Rating Plate was round the back or underneath or, better yet, inside. He cricked his neck looking up at the plate between the base of the appliance and the floor. Then the bifocals, joys of late-middle age, were the wrong way round. The distance reading area of the bifocal, intended for seeing the football or cricket ball a hundred metres away, were failing to assist him in reading the plate one centimetre from his nose.

Under the vacuum cleaner
This time it is underneath! You try turning a vacuum cleaner upside down! (c) The Lad 2011

No, No! Do it better. Help the Mother to harangue the family to do things better. Maybe in this day and age, it will be an ecologically conscious child. “Don’t waste money!”

We need a new label that the manufacturer of the appliance is required to supply. It will be applied prominently by the on/off switch. Or it could be one that we choose to make prominent. The most visible or even the only text would be a box into which the owner can write in a number which is a running cost, cash value and, after the box, will be printed the words ‘per minute’ or ‘per hour’.

The new owner will use her utility bill [which gives a cost of power per kilowatt hour] and the Instruction Leaflet or Rating Plate either of which will give the power absorbed by the appliance to help to calculate the cash cost. The Instruction Leaflet will also have a Table with a few lines with possible cash cost per kilowatt hour charged by the utility and, next to it the corresponding cash cost per hour or minute. Like this for a 1kW appliance:
                          Electricity                       Cost
                      pence per kWhr         pence per 15min
                                  20                                5
                                  30                               7.5
                              …………. and so on……………….

Easy, says the engineer! The new owner will consult this table and she can find the number to write in the label.

The Mighty Hunter felled by the Coalition

The gripping intro to the written BBC report begins

In a distant corner of a fenced-off site in Cheshire a fleet of Nimrod MRA4 warplanes which cost taxpayers more than £4bn are being turned into scrap.

http://www.bbc.co.uk/news/uk-12297139

 

The video footage on the main News bulletin that night http://www.bbc.co.uk/news/magazine-12281640 certainly made The Lad wince. It was shot from a helicopter and showed an area surrounded by high tarpaulin and steel screens between two hangars. Within are the tattered chunks of a fuselage heaped beside another Nimrod that is clearly to be the next victim of the advancing dinosaur of a demolition machine. Both the remnants and the more-or-less complete aircraft shell have the matt, olive sheen of the treated aluminium skin of a part-finished aircraft. The RR engines have already been removed and they will at least have been saved for use in some other aircraft.

Was it wanton mindless destruction, or, as Unite’s John Fussey described it, the dismantling as ‘barbaric vandalism’?

It is fortunate that engineering design is not a function like entropy that can only be degraded by use. If it had been, then the destruction of these planes without going into service [that is some sort of use] would be more painful still. But bring the attentions of these engineers that worked on the Nimrod to another project and they will fire up other ideas into reality.

This report says that the project was 10 years in the making. The Lad has read somewhere else rather that they were 10 years late in delivery. The Wikipedia story, http://en.wikipedia.org/wiki/BAE_Systems_Nimrod_MRA4 , is very detailed and seems to confirm his memory. This and £4 billion of sunk costs and £2 billion to operate are eye watering and show that this is not a good engineering project. Whether it is the MoD or BAe that is to blame for beginning and sustaining this project is an entirely different question.

Don’t take ourselves too seriously

This is just a quick post about something that makes The Lad laugh. He is a fan of Dilbert who is greater than or on a level with ‘Peanuts’. Dilbert, with the patience of Job, daily wrestles with the low level war which is the modern technical office. The strip is about Dilbert and his co-workers and their bosses and the demons that afflict the organisation.

In this particular episode, Dilbert is confiding in his doctor who notes that he is an engineer and that this is classified as a disease these days.

See all the rest of them daily and chuckle at the incisive insights at http://www.dilbert.com  . It will improve your life.

Trussed in the ‘Scientific American’

The season of goodwill has just passed, so the Lad is on the lookout for slights.

The magazine ‘Scientific American’ is well known internationally: indeed The Lad could perhaps irritate it, that is if it deigned to notice, by referring to it as a “venerable institution”  http://www.scientificamerican.com/

The Lad read the feature “SCIENTIST IN THE FIELD” in the Jan 2011 edition. This very title of the feature has the flavour of a scientist sallying forth from the Grove of Academe to assist, and patronise, the toiling agricultural peasants.

The particular feature was on Pamela Fletcher, who holds down the job of a Global Chief Engineer, no less, for the multi-national, vehicle manufacturer General Motors. See http://www.scientificamerican.com/article.cfm?id=practically-green . She is clearly responsible for leading and managing the team of engineers who will have designed and developed the insertion of power trains into future vehicles including the like of the new US car, the Chevrolet Volt.

From her own words, her curriculum vitae includes, academically, her B.Sc. and M.Sc. both in Mechanical Engineering and what appears to be the equivalent of an M.B.A. [Master of Business Administration]. Her commercial, engineering experience within GM must be considerable although not in the public domain. See http://coe.uncc.edu/newsletter/newsletter-home/91-pamela-fletcher.html .

We can, perhaps, perforce more accept with a shrug when the hacks of the common press describe engineers as scientists. Quite different however is it when the scientists try to arrogate engineers to themselves and their profession. Doesn’t it somehow aggravate the misdemeanor too that this very senior engineer is a woman?

I wonder how many other engineers have featured in this section. Perhaps if I bring this post to their attention, they will tell The Lad.

The One Hoss Shay

To add to the joys of the New Year, it seems a good time to repeat one of The Lad’s favourite texts. It’s called ‘The Deacon’s Masterpiece’. Why is a favourite of The Lad as an engineer? Firstly, although it is not one of Shakespeares’s Sonnets, the subject is quite fundamental. Optimum design is the target of most engineering design. Not many components, apart from fuses and quill shafts, are not designed with the Deacon’s principle in mind. Secondly, it’s funny.

Oliver Wendell Holmes wrote it and, even now, those subtle guys – the accountants – use the sub-title of ‘The One Hoss Shay’ as a technical term for one model of depreciation.

Anyway, enough of all that, here it is.

HAVE you heard of the wonderful one-hoss-shay,
That was built in such a logical way
It ran a hundred years to a day,
And then, of a sudden, it–ah, but stay
I’ll tell you what happened without delay,
Scaring the parson into fits,
Frightening people out of their wits,– Have you ever heard of that, I say?
Seventeen hundred and fifty-five, Georgius Secundus was then alive,— Snuffy old drone from the German hive,
That was the year when Lisbon-town Saw the earth open and gulp her down, And Braddock’s army was done so brown,
Left without a scalp to its crown.
It was on the terrible earthquake-day
That the Deacon finished the one-hoss-shay.

Now in building of chaises, I tell you what,
There is always somewhere a weakest spot,
— In hub, tire, felloe, in spring or thill,
In panel, or crossbar, or floor, or sill,
In screw, bolt, thoroughbrace,–lurking still,
Find it somewhere you must and will,
— Above or below, or within or without,
— And that’s the reason, beyond a doubt,
A chaise breaks down, but doesn’t wear out.

But the Deacon swore (as Deacons do,
With an “I dew vum,” or an “I tell yeou,”
He would build one shay to beat the taown ‘n’ the keounty ‘n’ all the kentry raoun’;
It should be so built that it couldn’ break daown!
–“Fur,” said the Deacon, “t‘s mighty plain
That the weakest place mus’ stan’ the strain;
‘n’ the way t’ fix it, uz I maintain,
Is only jest I make that place uz strong uz the rest.

So the Deacon inquired of the village folk
Where he could find the strongest oak,
That couldn’t be split nor bent nor broke,–
That was for spokes and floor and sills;
He sent for lancewood to make the thills;
The crossbars were ash, from the straightest trees,
The panels of whitewood, that cuts like cheese,
But lasts like iron for things like these;
The hubs of logs from the “Settler’s ellum,”
Last of its timber,–they couldn’t sell ‘em,
Never an axe had seen their chips,
And the wedges flew from between their lips
Their blunt ends frizzled like celery-tips;
Step and prop-iron, bolt and screw,
Spring, tire, axle, and linchpin too,
Steel of the finest, bright and blue;
Thoroughbrace bison-skin, thick and wide;
Boot, top, dasher, from tough old hide
Found in the pit when the tanner died.

That was the way he “put her through.”
“There!” said the Deacon, “naow she’ll dew.”
Do! I tell you, I rather guess
She was a wonder, and nothing less!
Colts grew horses, beards turned gray,
Deacon and deaconess dropped away,
Children and grandchildren–where were they?
But there stood the stout old one-hoss-shay
As fresh as on Lisbon-earthquake-day!

EIGHTEEN HUNIDRED came and found
The Deacon’s Masterpiece strong and sound.
Eighteen hundred increased by ten;
— “Hahnsum kerridge” they called it then.
Eighteen hundred and twenty came:
— Running as usual; much the same.
Thirty and forty at last arrive,
And then come fifty, and FIFTY-FIVE.
Little of all we value here
Wakes on the morn of its hundredth year
Without both feeling and looking queer.
In fact, there’s nothing that keeps its youth
So far as I know, but a tree and truth.
(This is a moral that runs at large;
Take it.–You ‘re welcome.–No extra charge.)
FIRST OF NOVEMBER,–the Earthquake-day.
— There are traces of age in the one-hoss-shay
— A general flavor of mild decay,

But nothing local, as one may say.
There couldn’t be,–for the Deacon’s art
Had made it so like in every part
That there wasn’t a chance for one to start.
 For the wheels were just as strong as the thills,
And the floor was just as strong as the sills,
And the panels just as strong as the floor,
And the whippletree neither less nor more,
And the back—crossbar as strong as the fore,
And spring and axle and hub encore,
And yet, as a whole, it is past a doubt
In another hour it will be worn out!

First of November, ‘Fifty-five!
This morning the parson takes a drive.
Now, small boys, get out of the way!
Here comes the wonderful one-hoss-shay,
 Drawn by a rat-tailed, ewe-necked bay.
“Huddup!” said the parson. —Off went they.
The parson was working his Sunday’s text,
— Had got to fifthly, and stopped perplexed
At what the– Moses–was coming next.
All at once the horse stood still,
Close by the meet’n’-house on the hill
–First a shiver, and then a thrill,
Then something decidedly like a spill,
— And the parson was sitting upon a rock,
At half-past nine by the meet’n’-house clock,
— Just the hour of the Earthquake shock!
—-What do you think the parson found,
When he got up and stared around?
The poor old chaise in a heap or mound,
As if it had been to the mill and ground!
You see, of course, if you‘re not a dunce,
How it went to pieces all at once,
— All at once, and nothing first,
— Just as bubbles do when they burst.
End of the wonderful one-hoss-shay.

Logic is logic. That’s all I say. 

First of November, ‘Fifty-five!
This morning the parson takes a drive.
Now, small boys, get out of the way!
Here comes the wonderful one-hoss-shay,
 Drawn by a rat-tailed, ewe-necked bay.
“Huddup!” said the parson. —Off went they.
The parson was working his Sunday’s text,
— Had got to fifthly, and stopped perplexed
At what the– Moses–was coming next.
All at once the horse stood still,
Close by the meet’n’-house on the hill
–First a shiver, and then a thrill,
Then something decidedly like a spill,
— And the parson was sitting upon a rock,
At half-past nine by the meet’n’-house clock,
— Just the hour of the Earthquake shock!
—-What do you think the parson found,
When he got up and stared around?
The poor old chaise in a heap or mound,
As if it had been to the mill and ground!
You see, of course, if you‘re not a dunce,
How it went to pieces all at once,
— All at once, and nothing first,
— Just as bubbles do when they burst.
End of the wonderful one-hoss-shay.

 

Logic is logic. That’s all I say.

 

Just roll those carriage builders’ technical terms around your tongue.

A great old engineer, HL Cox, who guided The Lad at one time introduced him to it. He was a specialist in the design of optimum structures.

Happy New year

Start the car; slow the wear

DO as The Lad does, on the coldest days. He starts the car and runs it at about twice the tick over speed or so for about a minute [whilst sitting in the driver’s seat of course]. Meanwhile put the blower on the windscreen and recirculating at full chat. This way heating and reheating the same air will get it hot sooner than heating fresh charges of outside air. Put the rear window heater on. Then switch off, lock the car and return indoors and have breakfast for ten minutes or so. After that the engine will have got itself and the oil warmer by conduction mainly. Now come back and drive off to work or wherever at a reasonable speed.

DO NOT start the engine and leave it on tick over for the ten minute breakfast, then get in and drive madly away or even quietly away. One reason is that a lot of people have had their car stolen by a thief walking up, getting in and driving away. The more certain reason is that the tick over method induces vast amounts of wear in the engine.

ball bearing and shaft
Some of these are whirling all the time.

Even at slow tick over speeds, engine pistons are still being flung to and fro in the cylinders; many shafts are whirling at high speeds and gears are rapidly meshing. These must all be stopped from wearing amazing quantities of metal away and the engine then becoming at best inefficiently petrol gulping. Eventually it will stop because the leaks through the worn parts mean that it will not have enough power even to turn itself over. The oil has a vital function in the engineering of the engines by keeping metal sufaces apart. But, when the engine is cold, there won’t be any oil there.

Why is this? Even the most modern oil will be much thicker [engineers call it more viscous] when it gets as cold as it has recently been in the UK, that’s why.

The engineers who designed your car engine set the number of cylinders and their size, the way it grabs hold of your car, the way the electronic systems will control it, the exhaust system and answered a myriad of other questions. At around this time the engineers had to design a pump and oil system to push the oil around the engine and galleries to get them to all the sliding surfaces and rolling parts. This oil system will be optimised to work best with hot oil and a hot engine because this is how it spends the great proportion of its life. Except for those few minutes on the cold days at start up. With cold, cold oil being very much thicker it is pushed towards the surfaces much more slowly and little arrives. Wear is rampant.

You can find here an excellent discussion of the how and why of lubrication. It has some American wording and technology and is a little technical. http://www.zddplus.com/TechBrief11%20-%20Internal%20Combustion%20Engine%20Lubrication.pdf

The Lad will agree with any souls who want to argue that the time of running and the engine speed that it runs at could do with being optimised to acieve the best result of minimum wear. It is so that also the optimum figures are likely to be different for every car and engine. All the same, the method of The Lad will be far, far better than leaving the car at tickover for ten minutes on its own. besides which the theft is a terrible blow to the pride. The insurance won’t pay up either.

Peterson and the danger at every corner.

“Where’s Peterson?”

It was a query from someone at the Stress Office door to no one in particular. There were ten or so Stress Engineers at their desks; some were poring over their stress pads covering them with calculations using their Otis King cylindrical calculator; others were staring thoughtfully out of the windows and ignoring their Fowler’s circular calculator [both calculators are more accurate than a slide rule]. A copy of Chambers’s [a thick book of seven figure logarithms much more accurate than a slide rule] stood ignored on a shelf: not used since someone’s Detail Office days. The Stress Office product is calculation. “Try the Design Office”.

The search was not for a person but for a book.

A small number of books are so influential within a group, that the author’s name is enough to identify it exactly. So it was for several books among The Lad’s group of ’60s and 70’s design engineers.  ‘Peterson’, ‘Kempe’s’, ‘Rollason’ were some. It is probably the same for any close-knit, professional group; not just the engineers. This piece is about the first-named; the others will come later.

Peterson front cover
The front cover of Peterson © 2010.

A slim volume, it is a maroon, hard-back with its title in gold, embossed lettering on the front cover. Called “Stress Concentration Factors”, by R E Peterson [Manager of Mechanics Department, Westinghouse Research laboratories], it was published in 1953 by John Wiley and Sons, Inc and Chapman Hall. There was no title on the spine due to its unique binding. Almost every page of the book was a full-page graph that had to be scalable: each page therefore had to lie completely flat leading to the spiral wire binding protruding through the back.

Peterson spiral bound spine
Peterson spiral bound spine © 2010

One of the most important measures in the engineer’s design tools is ‘Stress’. It is true that his task is to wrestle with forces but most forces can be withstood if the component is robust enough. The usual design measure therefore is not ‘force’ but ‘force per unit of component area’. Just as the ‘price’ of an item is not always the most important number to the canny shopper; he will often compare goods or large or small packs with the ‘price per kilogram’. So it is with ‘stress’: we define the tensile strength of metals shown by experiments on plain test specimens as the stress [pounds per square inch in Peterson’s day – newtons per square metre nowadays] that they can reach in a single loading before they begin to fail.

However, and this is where Peterson came in, real components are often not of a ‘plain’ shape and the vicious menace of metal fatigue is always waiting around every corner. In the 40’s and 50’s many propellors fell off ships and in 1954 two Comet jet passenger aircraft, the pride of the UK, exploded and crashed into the sea killing all aboard.  http://web.archive.org/web/20091026195856/http://geocities.com/CapeCanaveral/Lab/8803/fcogalyp.htm

One of the features of the Mark One Comet had been its large rectangular windows. Unfortunately no allowance, or at least not enough allowance, had been made for the increased stress at these corners. The result of repeated pressurisation led to apparently low stresses in the fuselage greatly increased by unrecognised stress concentrations leading in turn to metal fatigue. The result was the aircraft at over 30 000ft split open explosively and plunged it and its passengers into the sea.

It had been known before these and other accidents that the tensile strength measured from single loading was not the only measure of strength for metals. A component could fail at a much lower load if there were many cycles off and on. This lower stress is called the fatigue strength and is smaller, down to a lower limit, the more loading cycles that the component sees. The problem was that stresses in real components with holes or with more or less sharp corners or, worse – sharp scratches, were much higher close to the holes, corners or scratches than in the ‘plain’ sections.

The purpose of Peterson was to provide the engineers with factors to multiply the simple stresses to give the higher stresses at changes in sections in components of every sort under every type of loading such as tension, bending and twist. The book is made up almost entirely of full-page charts: there are 125 of them culled from 174 references from the world’s literature at that time. A mammoth task. They were drawn by the hand of that (long gone) craft of the tracer using a template for the lettering. The few other pages show a digest of the relevant theory.

Slotted bar chart
Chart of the possible stress concentration in a slotted bar

The sample chart shown deals with the simplest of problems. A bar in tension with a notch in it. The vertical axis on the left gives the stress multiplication factor for use with fatigue calculations. You can see that it can easily reach two and a half times the simple stress and more. The amount depends upon the radius of the slot, the bottom axis, and the parameters of the widths of the bar and the ‘throat’ under the slot.

Tragically for the Comet passengers, the fuselage had been designed before the advent of Peterson. But we can be assured that the book did prevent many more fatigue failures and probably many deaths.

The Lad has a small collection of textbooks and professional reference books in editions contemporary with those that he used including Peterson. He had never seen another hard back binding like it. The Lad’s copy of Peterson came to him damaged with masses of ancient, cellophane tape like toffee over the wire binding. Ian Pell, the bookbinder of Derby, very skillfully recovered it for him by re-backing it to bring it nearer to its original condition. Thank you, Ian.

There was, The Lad remembers, a wry comment then by the Stress Engineers about the trials of their job. Typically each engineer is wrestling to analyse the stresses in some elaborate structure as complex as a large bridge. She would say,

” I spent three months calculating the areas. Then I spent four months calculating the loads. When I had done that, they had changed the area.”

The same complaint would probably be still expressed today were it not for the fact that, as a civil engineer friend of mine said, nowadays the cost of computation is effectively free. Along with that, the modern Finite Element Methods of computation allow today’s engineer to calculate stresses on a component using its actual shape. In those days instead, they used an idealised shape and then a factor to account for the real shape.

Today, Peterson sleeps.

The eternal question: Can you answer for it?

[This post was triggered by a particular picture that I planned to include in this post. I found though that the license to show it was too expensive. It can be viewed at the link below or via any search engine under the terms ‘image Concorde accident’. See note at the end of the post]

The Lad knows of few photographs (of Concorde aflame at takeoff) that show so clearly the threat that hangs over engineers as they seek to do their job. There is a harsh graininess in the image that is common to the records of tragedies. 

http://www.guardian.co.uk/world/2010/dec/06/air-france-concorde-crash-timeline?intcmp=239  

At their maximum take-off thrust, several times greater than at any other time in the flight, there is a shouting roaring from the engines . From this surge stems the great lift forces from the wings that impell one hundred tons or more thousands of feet vertically into the air in seconds. The nose is pointing up: concentrating on its race into the blue. That leap has happened a thousand times before. This time it is different: there is a plume of flames larger than the craft itself streaming back from the fuel tank. These flames melt the control surfaces that are part of the wing and the aircraft, within two minutes, turns horrifyingly onto its back and flies into the ground as fast as it rose from it. Those servant forces that make the aircraft fly are now the masters. They reduce the elegant Concorde into fiery wreckage. More than a hundred passengers  and several people on the ground had their lives taken. 

Who would have predicted a loose part from the previous take-off on the runway; the tire hitting it and exploding; the flying tyre fragments puncturing the fuel tank and the fire destroying the machine and its passengers? Think of the hapless mechanic and his boss who were deemed responsible for the loose part not being fitted correctly. That could be any of us. 

The engineer’s job is, as The Lad has said before, is to harness natural forces for the benefit of other human beings. He mostly has success in the task that he sets himself and persuades vast forces to do his bidding: at any time those forces can bite back and do evil commensurate with the good. Like the tiger, a pet for many years, becoming an angered animal suddenly exploding back to its animal nature and destroying its ‘owner’. 

As an engineer, she has to ask herself at all times, “Can I stand up in a Court and justify all my technical choices?”

Running the risk of demeaning a serious topic The Lad has to note a couple of points. The first is about, once more, the bad ways of a reporter. The reference in one report to a titanium part that burst the Concorde tyre was apparently too mundane so it was given an entirely imaginary,  journalistic boost as ‘ the stray strip of super-hard titanium’. Titanium is used in aero-engineering for its high strength and light weight and not for hardness.

The second point is that the Press Association found itself unable to offer to The Lad a one off use of the image without a ‘reasonable intro offer’ fee of nearly £60 [for a year]. As I said above it can be found, and apparently legally viewed, using any search engine.