January 2010 – Bad Engineering

I think about it a lot, but probably most people don’t. It is all around us, it permeates our existence, it frustrates us, injures us, and kills us. It is an invisible something that is almost absolutely inescapable, relentless, and uncaring. It’s in the back of every engineer’s mind and always part of his equations, but it is so ubiquitous that it is rarely noticed or given its fair due.

Myself, and a few others—a small percentage of all the engineers out there—think about it all the time.

Gravity.

Not that we delve into the cause of it—Higg’s boson, dark energy, dark matter, or what have you—but rather the everyday impact of gravity, weight, and mass on engineering projects. And what constantly amazes me is why it is always an afterthought for many engineers in many fields. Every building, car, boat, plane, satellite, rocket, kite, chair, train, bus, elevator, and etcetera must be designed for weight or mass limitations, and managing the weight or mass properties properly helps ensure a successful design while managing it poorly, or not at all, often leads to complete failure. The most common examples are with aircraft which are so sensitive to weight and centers of gravity, though there are many others in other areas:

The hovercraft that was too heavy to lift off the ground.
The plane that crashed because of too much aft weight.
The balcony that collapses from overcrowding.
The ferry that capsizes when passengers crowd to one side.
The building that collapses while under construction from insufficient temporary braces for the weight.
The airliner that can’t take the design load because it was built too heavy.
The car that can’t meet its mileage goal because it is too heavy.

The list goes on and on, with weight management, or lack of same, at the center of the problem. Yet if I introduce myself as a weights engineer I usually get a, “what’s that?”. You’re probably saying that right now. And yet, just like gravity, a weights engineer touches every part of an engineering project, from start to finish. Hers may be the ultimate systems engineering discipline, and certainly the least known. And, in many cases, it can be one of the most important. Both to life and limb, and to cost.

And we still don’t get no respect. I can live with that, but when there is no recognition at all is when I get frustrated. With most of the Western world obsessed with their personal weight, how many times do they ask about the weight of the car they are buying, or if their overloaded suitcase will affect the plane they are boarding, or if the snow load on that building is anything to be concerned with, or if that ladder can support them? Does anybody ever think that if they unloaded their trunk they would get better gas mileage? Or does the engineer ever think that optimizing their design for weight would save money and increase safety? Rarely, I think.

What’s my point? Well, I guess just this: Weight is worth thinking about. Or maybe it is better said that not thinking about weight can be dangerous and costly.

What do you think? Drop a comment below. And if you’re interested in this topic, visit www.sawe.org for more information.

Many good engineers pride themselves on their ability to do quick “back of the envelope” calculations that are accurate enough to be used as the basis for some expedient decisions. The ability to do this stems from experience, where rules of thumb and instinct about the numbers are cultivated, and from good engineering fundamentals which provide the engineer with the tools to develop the right approach and process to do the calculation, even if it is a new problem.

What can be difficult is knowing when and how to question yourself.

I recently came upon a paper (fortunately of limited distribution) where the approach, process and calculations were correct, but all the conversions from metric to English were wrong. Seems that 2.45 was used instead of 2.54 for conversion from centimeters to inches. Though it looked like a case of transposition, in fact the author said that he always thought the conversion was the former. And there lies the potential pitfall to the engineer — assuming he is correct because he always did it that way.

It’s not that I am advocating second-guessing yourself all the time, but rather that periodically we all can use a quick check on some of our fundamental constants, rules of thumb, and calculations methods to both shore up our memories and correct bad habits.

It is sort of like the driving tests that this country doesn’t periodically give to established drivers. I was in a car with a middle-aged driver who tailgated, didn’t use signals, and cut people off. When I tried to bring this to his attention (while making sure my seatbelt was on), he replied that he had been driving for thirty years. Yes, I thought, but you’ve been driving badly for all those years. His experience didn’t change the fact that he was dangerous driver.

If we have bad habits in our engineering calculations or processes, they need to be caught and corrected before they become part of our experience and thus “correct” in our minds. As engineers we need to understand the limitations of our human minds (especially, I am sorry to say, as we age) and bolster our memories with the tools of our trade such as handbooks and structured calculation processes. Though it may cost a bit in terms of pride, it shouldn’t. As far as I can see, no engineer should be faulted — by herself or anybody else — for checking their work. And while you’re at it, you might want to check those handbooks and spreadsheets too. Nothing is sacrosanct where good engineering is required, and the guys that wrote that handbook may have had some bad habits too.

What do you think? Have you ever found yourself using the wrong value, equations, or process out of habit? How often do you go back to examine your fundamentals? Drop us a comment.

Month: January 2010

All around us

Bad Habits