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Another English/Metric "Spacecraft" Problem
SuperDry writes "There's been another spacecraft failure that's been attributed to an English/Metric units problem, this time at Tokyo Disneyland's Space Mountain. An axle broke on a "spacecraft" (a.k.a. roller coaster train) mid-ride, causing it to derail (nobody was hurt). The final investigation report has been released, and the root cause has been determined to be a part being the wrong size due to a conversion of the master plans in 1995 from English units to Metric units. In 2002, new axles were mistakenly ordered using the pre-1995 English specifications instead of the current Metric specifications. Apparently size does matter, even if it's only a 0.86mm difference."
From the Article:
In September 1995, the design specifications for the size of the axle bearing for Space Mountain vehicles was changed from inches to the metric scale. Accordingly, the axle diameter was also changed, in this case from 44.14 mm to 45.00 mm. However, appropriate action to revise and maintain the design drawings was neglected. Consequently, two different drawings existed within our company after the changes were made and the old drawing showing the 44.14 mm diameter was used to order (in August 2002) the axles that were delivered in October 2002.
They actually changed the specs. The conversions were all done correctly but they failed to update everyone.
In the automotive industry being off by that 'gigantic' mile of a discrepancy can be the difference between an entirely safe system or a potentially dangerous event just waiting to happen.
Anything from rubbing away the lining of important wires or hoses, different stress locations resulting in tear apart pieces that shouldn't be tear apart can happen by being off by that much...
0.86mm might at well be 3 feet off. A part that comes out that far off is nothing but scrap material. (Well at least in our area of automotive work.)
If you ignore the other uses of a tool, does that make the tool less useful, or you less useful?
Well, if you RTFA, you'd see that the parts were ordered using older specifications, and the parts delivered were consistent with the designs that were ordered. The problem was they put it in an order for the wrong size.
Consequently, two different drawings existed within our company after the changes were made and the old drawing showing the 44.14 mm diameter was used to order (in August 2002) the axles that were delivered in October 2002.
WWJD.... for a Klondike bar?
Please don't say English/Metric units. The UK is effectively metric now, all schoolchildren are only taught metric units and everything has to be priced in metric units. I don't even have intutitions about how long feet are or how heavy a stone is. Pretty much everyone under the age of 25 only deals with litres, metres and kilograms. The only exception is vehicle speed, which is still measured in mph (and hence all our road signs are in mph). You won't, however, catch any British Engineers or scientists using Imperial units.
Better ways to describe them would be "Imperial" (what we call them), "American" or "Archiac". I think it's about time the US caught up with the rest of the world and ditched these stupid and difficult-to-remember units once and for all.
If you had read the article, you would know that the problem was, while converting to metric, they also changed the specification of the axle size, but didn't record the new axle size correctly. So, the problem really had nothing to do with any mathematical error, just an error in incorrect documentation.
A modern day witchhunt.
http://www.laughingplace.com/News-ID108300.asp
Great set of columns, by the way. I've always been a fan of how some of the disney technology was invented and implemented.
Isn't the American version slightly different, in respect to fluid units, etc?
Only with respect to fluid units. And the base unit, the ounce, is the same. Measurements based on the pint are different: a US pint is 16oz an Imperial pint (the only legal Imperial measure left in the UK!!!!) is 20oz. A gallon is 8 pints, a cup is a half-pint, but a US gallon or cup is 4/5 of the British counterpart.
I thought the Brits moved glacially since the UK has been metric since 1971... officially (except for beers. I don't know how long road measure will remain Imperial). Then I found out that the US has been co-metric since Ben Franklin (http://www.nist.gov).
No system of measure is inherently better or worse than another. But, when everybody you trade with uses a different system, it might be time to reconsider (not that the UK should adopt the Euro....)
The .86 error was because someone decided that they wanted round numbers, so when they changed the spec, they decided to round up. Well, in the process they forgot to throw out the old documentation. So, they ordered the correctly sized part for the old spec and got it wrong.
Probably a good example for software engineering class. "See, changing the specification, once released, may result in bodily harm!"
(And the right term for "metric" is "SI").
SI units are legal in the United States and have been for a very long time. The inch was set at precisely 25.4 mm _by definition_ in July 1959.
The additional units, such as inches, miles, quarts, pounds, etc. which I believe are all legally defined by reference to SI units, are officially and properly referred to as "U. S. Customary" units. They have, of course, a strong historical connection to English units.
Unofficially, "Metric" and "English" are the U. S. customary designations for "SI" and "U. S. Customary."
"How to Do Nothing," kids activities, back in print!
Bzzzzt. Thanks for playing!
From boson.physics.sc.edu :
At the beginning of the eighteenth century, the Danish astronomer Ole Roemer (famous for making the first measurements that showed that the velocity of light is finite) devised a temperature scale of his own for use with the alcohol-in-glass thermometers that he constructed. His thermometers attracted the attention of Gabriel Fahrenheit (1686-1736), a manufacturer of meteorological instruments in the Netherlands. In 1708 Fahrenheit traveled to Copenhagen to meet Roemer and see his thermometers, which were based on two reference points. For one reference Roemer used a mixture of ice, water, and salt to reach the lowest temperatures then attainable in the laboratory, which he called zero. His other reference was the boiling point of water, which he arbitrarily designated as 60 degrees.
Fahrenheit returned home to make thermometers like Roemer's. In 1714 he overcame technical difficulties with alcohol thermometers by substituting mercury as the expanding liquid. The use of mercury extended the range of temperature measurements from well below Roemer's zero to well above the boiling point of water. Furthermore, mercury expanded and contracted more uniformly than the other liquids then in use. As a result, Fahrenheit could mark his mercury thermometers more accurately and with finer divisions.
By 1724 Fahrenheit had adopted a new scale, similar to Roemer's but with much finer divisions. For the zero point he chose the same reference as Roemer. However, since his thermometer was intended for meteorological observations, he wanted a second reference point that would be nearer the maximum observed temperature for weather. He chose the normal temperature of the human body as the upper reference point, which he called 96. Fahrenheit gave no reason for his choice of 96, but it may have been due to his desire for a finer scale and because 96 is evenly divisible by 2, 3, 4, 8, and 12.
Why didn't Fahrenheit choose the freezing point of water for his zero reference, as Newton had done before him and as Celsius did later on? Perhaps Fahrenheit was influenced by Roemer, or he may have wanted to avoid the inconvenience of repeatedly using negative temperatures during winter. Also, in the early 1700s it was widely believed that water did not always freeze at the same temperature. Soon, using his newly calibrated thermometers, Fahrenheit learned that water always froze at 32 on his scale. He immediately added this third reference point to his instruments.
Any sufficiently well-organized Government is indistinguishable from bullshit.