While cursing my bad luck, I noticed that the passenger one row up and across the aisle had an equally deformed tray table. The flight attendant saw immediately upon setting down his drink that it would not stay in place on the slope. She returned to the galley and came back with the aluminum tab she had broken off a pop-top can, and she used it to shim up the cantilevered tray at its main hinge. When she came with my drink I asked for the same mechanical assistance, and she obliged. The fix was just right, and the table was perfectly flat and horizontal even when fully opened across the seat. Thank goodness for shims, and for mechanically inclined flight attendants.
The folding tray table was obviously designed to satisfy a considerable number of constraints, which it does. Thus, it is relatively lightweight, as well as compactable and deployable. These latter two qualities mean it has moving parts that are capable of getting out of kilter. Armrest tray tables clearly have not been designed to take the forces imposed by infrequent fliers wrestling with the puzzle of how the thing deploys and stows, or by frequent fliers who use the table as a crutch for rising out of their seat. Such overloads naturally can and do throw the mechanism out of alignment. All designs have limitations, but not every user respects them.
The case of the airline tray table points out one of the asymmetries of the designer/user interrelationship. The failure of an armrest tray table to deploy into a flat and level surface, perhaps leading to a drink spilling into a passenger's lap, might result in a product-liability lawsuit, with possible career-altering implications for the table's designer. But a passenger who engages in heavy-handed misuse of the table, causing it to be permanently off level when in its deployed position and thus setting the stage for a drink spilling into some future passenger's lap, can simply walk off the plane when it reaches its destination. Neither life nor design is always fair.
Entertaining musing on the give and take of good design. What's the greater takeaway for engineers, though? Don't factor use case into your efforts for fear of legal repercussions? That seems like a cop-out to me. After all, not every flight enjoys the benefit of having mechanically-inclined flight attendents on board.
Professor Petroski's final point in this article alludes to the fact that product liability law requires a product to be safe not only in its reasonably expected use, but also any reasonably expected misuse. Engineers are often horrified to learn that the law requires us to take potential misuse of a product into account. Ironically, although we bristle at the idea of other people misusing our products, we also excel at coming up with creative new ways to "use" products others have designed. Some of the new uses which particularly creative engineers find for things may not fall into the "reasonably expected" category.
It's been years, but I remember a flight with, I swear, that same tray table "design," which made it completely unusable when deployed. And that was so obviously the case that I could not understand how the design ever got accepted and the tray table installed, in thousands of planes. I was not so fortunate as Professor Petroski, however, in my flight attendants. This all makes me think less of the legal issues than of the designers/users and use case issues.
The nice thing about the tray tables that Professor Petroski describes is that they are not attached to the seat back. Anything is better than that. If I put my laptop on one of those, the person in front of me glances back over his/her shoulder to let me know I'm bothering them. Worse, when the person in front leans back, the tray table is suddenly so close that there's no room to work.
Ann, Beth, Dave & Prof. P., I write this as you Professor wrote your article on arm chair design....with toung in cheek. The story starts with me being the only person, other than crew, left on a plane durind a short layover. A AL Mechanic arrived and went to work on one of the tables you all described. He almost instantly recived a loud message over his 2way "you have 5 minutes". He started to work very delicatly and expertly for the next 10 minutes when he received a VERY loud call "you need to pack it in we have to load."
Being a company man (I determined by his appearence) he reached down to his tool belt, holstered his Phillips Head screw driver swept his hand dirrectly to the hammer loop, grabbed it , pounded the table into the midseat container, flipped the cover closed and annouced towards the Captain "All fixed sir she's ready to go have a good flight" while exiting the aircraft.
THIS ALL HAPPENED FASTER THAN THE TIME IT TOOK ME TO WRITE THIS. It sticks in my mind to this day because I am also a Pilot.
I've had another rude awakening this week: no matter how hard I try, how intelligent I may be; there is always one idiot "smarter" than me who will discover the way to damage the machine. This week, the idiots won.
Arlo Guthrie has a thing or two to teach engineers about "reasonably expected misuse", from his song Alice's Restaurant:
"Kid, I'm going to put you in the cell, I want your
wallet and your belt." And I said, "Obie, I can understand you wanting my
wallet so I don't have any money to spend in the cell, but what do you
want my belt for?" And he said, "Kid, we don't want any hangings." I
said, "Obie, did you think I was going to hang myself for littering?"
Obie said he was making sure, and friends Obie was, cause he took out the
toilet seat so I couldn't hit myself over the head and drown, and he took
out the toilet paper so I couldn't bend the bars roll out the - roll the
toilet paper out the window, slide down the roll and have an escape.
One thing I don't think the airlines or designers really considered is the lifetime of the product in this case. Is it reasonable to expect something that gets as much use as a tray table to last the lifetime of the plane. Those are typically flown for many years. They should have designed them to easily replaced (say during a layover) and refurbished in the shop.
Airplane tables are useful... as mouse pads. I had access to a bunch of old trays being thrown out. For black or featureless tables they make very nice mouse pads! No bending or warping. Conversation piece too.
As for use on aircraft, they do leave a lot to be desired. However, there is little choice. Make a great table and someone will lean on it and bend it. Make it stronger? Not only heavier but more tempting to lean on. Live with it - and carry a pop can tab.
I have come across those tables that pop up from between the seats and have never had any problems with them. Probably being an experienced engineer helps a bit there. I have been on lots of flights where I had to hold my drink so that the bumps would not launch it into my lap, or somebody else's lap. I agree that the ones that fold out of the back of a seat are much nicer, although I have never been able to use a computer on a plane.
If you want a real challenge though, try to utilize the footrest on one of the Amtrack trains. There is a button on the armrest to release it, but in the trains that I have ridden there is nothing to make it move once it is released. The only way we figured out to use the footrest is to grab it with a hand and pull it into position. My guess is that the springs were removed to prevent terrorists from somehow utilizing the footrests for something, or possibly to prevent idiots from doing something really stupid with them.
I really would preferr that our legal system stop rewarding idiots and fools for injuring themselves, and instead, fine them for being so stupid. OF course, then we would have the lawyers seeking customers under some other premise, and that might be worse.
Iterative design — the cycle of prototyping, testing, analyzing, and refining a product — existed long before additive manufacturing, but it has never been as efficient and approachable as it is today with 3D printing.
People usually think of a time constant as the time it takes a first order system to change 63% of the way to the steady state value in response to a step change in the input -- it’s basically a measure of the responsiveness of the system. This is true, but in reality, time constants are often not constant. They can change just like system gains change as the environment or the geometry of the system changes.
At its core, sound is a relatively simple natural phenomenon caused by pressure pulsations or vibrations propagating through various mediums in the world around us. Studies have shown that the complete absence of sound can drive a person insane, causing them to experience hallucinations. Likewise, loud and overwhelming sound can have the same effect. This especially holds true in manufacturing and plant environments where loud noises are the norm.
The tech industry is no stranger to crowdsourcing funding for new projects, and the team at element14 are no strangers to crowdsourcing ideas for new projects through its design competitions. But what about crowdsourcing new components?
It has been common wisdom of late that anything you needed to manufacture could be made more cost-effectively on foreign shores. Following World War II, the label “Made in Japan” was as ubiquitous as is the “Made in China” version today and often had very similar -- not always positive -- connotations. Along the way, Korea, Indonesia, Malaysia, and other Pacific-rim nations have each had their turn at being the preferred low-cost alternative to manufacturing here in the US.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.