Coal
Topic Author
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### US Vs Metric Units On A/C

After looking at this pic

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I started wondering which units on the a/c's system could be different in US and Metric. Surely all a/c measure height in feet, speed in knots, and temp in celsius.

Which systems would be different?

Coal
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andrej
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### RE: US Vs Metric Units On A/C

These preferences are airline specific and differ among airlines. For example engine temps, can be also measured in fahrenheits as well as outside temps. Also fuel on board are measured in Kilos or pounds. There are many other preferences airlines choose when they are ordering new airplanes.

Cheers,
Andrej

LH648
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### RE: US Vs Metric Units On A/C

As 319 is "software" plane, is it not possible easily switch to metric system?...

Zkpilot
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### RE: US Vs Metric Units On A/C

 Quoting Coal (Thread starter):I started wondering which units on the a/c's system could be different in US and Metric. Surely all a/c measure height in feet, speed in knots, and temp in celsius. Which systems would be different?

Well Russian aircraft operate entirely in metric.

Its a pity that aviation hasn't converted over.
Imperial measurements are so antique and inefficient!
At least temps are in Celcius.
As for speed and distances, it depends what you are talking about...
because in aviation these are actually usually in Nautical Miles or Knots (nm/h). Nautical miles are neither metric nor imperial, they are degree based (ie divide the earth up into degrees,minutes etc. But things like runway lengths and altitude should have all been switched over to metric a long time ago. It is only because of the USA/UK that we still have Imperial measurements...the rest of the world uses metric for everything else.
57 types. 38 countries. 24 airlines.

FrancoBlanco
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### RE: US Vs Metric Units On A/C

Basically weight (fuel and payload) and temperature can be either displayed in Metric or U.S. units (°C/°F and kgs/lbs). Regarding weight it is rather important to know which units you are using (see the Gimli Glider), hence the sticker on the aircraft in question.

I am sure that it is not that difficult to change the software on a modern Airbus, on the other hand there is no switch or whatsoever in the cockpit. Maybe it's possible to change it on a 777 via the maintenance console behind the F/O seat, can anyone of the 777 specialists confirm that?

Air Berlin has added that specific A319 only recently, so there may have not been time yet to perform the change. If you click on the reg of that aircraft, you'll see that it still has the original Independence Air interior.

Sebastian
'Pointless!' - NY Times

Tristarsteve
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### RE: US Vs Metric Units On A/C

 Quoting FrancoBlanco (Reply 4):Maybe it's possible to change it on a 777 via the maintenance console behind the F/O seat

No its not that easy. It is controlled by pin programming. i.e. you have to physically move the pins in a multi plug so that they connect to the kgs output instead of the lbs output from the fuel quantity computor. It could be accomplished during the first maint stop, once the SB has been approved.
When I worked for GF we leased some TWA Tristars. We changed all the fuel gauges to Kgs instead of lbs to make them the same as the rest.

Stealthz
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### RE: US Vs Metric Units On A/C

If the second country to adopt the metric system had completed the change over then the last country to adopt would have been forced into changng as well!
If your camera sends text messages, that could explain why your photos are rubbish!

eddl
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### RE: US Vs Metric Units On A/C

Thank you for bringing this up (it's my photo).

Looking on the large version I see the fuel figures are measured in lbs. I am not sure about the temperature (C vs. F). Note the calculators next to both side sticks ...

 Quoting LH648 (Reply 2):As 319 is "software" plane, is it not possible easily switch to metric system?...

I have asked this myself, shouldn't be too difficult to change measuring units in maintenance checks.

Phil / EDDL

Starlionblue
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### RE: US Vs Metric Units On A/C

 Quoting Zkpilot (Reply 3):It is only because of the USA/UK that we still have Imperial measurements...the rest of the world uses metric for everything else.

The UK is officially metric, with a few exceptions. The three countries in the world officially still using Imperial are USA, Myanmar and St. Lucia. The US Military is metric (apart from aviation?).

The reason the US has been able to keep Imperial for so long is because of its enormous domestic market. The same "tactic" would not have worked for a small country that exports a large proportion of production.

Will the US ever go metric? I think so, but it will take a long time. Also, computerization actually makes dual standards easier since conversion can be pushbutton.

There are also big variations apart from the metric/imperial thing. For example, the international standard for dates is year/month/day but is not universally implemented. The international standard for decimal notation is the comma; same here. The standard for low-beam headlights is used in all countries except the USA. The list goes on.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

Coal
Topic Author
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### RE: US Vs Metric Units On A/C

 Quoting Starlionblue (Reply 8):The reason the US has been able to keep Imperial for so long is because of its enormous domestic market.

 Quoting Starlionblue (Reply 8):Will the US ever go metric? I think so, but it will take a long time.

Ummm... I don't think so. Canada did, but their population is only 1/10th of the US'. Still, it cost them a lot of money. People in the US are as confused with the metric system just as the rest of the world is confused with imperial.

Coal
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CPHGuard
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### RE: US Vs Metric Units On A/C

Am i wrong, when i say the new Boeings are metric ???

I remember an incident where a 767 made an emergency landing due to fuel starvation. As far as i remember it was due to a miscalculation, based on the airplane being metric.

But i could be wrong.

Regards
Thomas

Stealthz
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### RE: US Vs Metric Units On A/C

 Quoting Starlionblue (Reply 8):The three countries in the world officially still using Imperial are USA, Myanmar and St. Lucia. The US Military is metric (apart from aviation?).

Not quite true, The USA was the 2nd country in the world to adopt the Metric systrem, an act of congress in 1860 decreed that all govt business be conducted in the Metric system and and a further act in in 1873 (Ibelive these dates are accurate but may vary by a year ir so) adpoted the metric systema s the official units of measure in the USA, they just never really enforced it.

 Quoting Starlionblue (Reply 8):The standard for low-beam headlights is used in all countries except the USA

If your camera sends text messages, that could explain why your photos are rubbish!

TeamAmerica
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### RE: US Vs Metric Units On A/C

 Quoting Zkpilot (Reply 3):Imperial measurements are so antique and inefficient

I also prefer metric, but let's not be snobs about it. Antique is not a bad thing, and metric (S.I.) is not new. As for efficiency, imperial units such as feet or gallons are more easily halved/quartered etc. . The metric system excels for scientific pursuits, but on the level of human commerce the imperial system can be quite convenient.

 Quoting Zkpilot (Reply 3):But things like runway lengths and altitude should have all been switched over to metric a long time ago. It is only because of the USA/UK that we still have Imperial measurements...the rest of the world uses metric for everything else

Please don't assign blame. There is an obvious safety issue in converting things like runway lengths. Given that the system works as-is, why change it? Using feet may be an anacronism, but so what? It's just a number. So long as the meaning is understood the units are of no significance, and no politics should attach.

 Quoting Coal (Reply 9):Quoting Starlionblue (Reply 8): Will the US ever go metric? I think so, but it will take a long time. Ummm... I don't think so. Canada did, but their population is only 1/10th of the US'. Still, it cost them a lot of money. People in the US are as confused with the metric system just as the rest of the world is confused with imperial

I pray you are wrong. Our failure to get with the program is hampering our products in the world market. As for the US population being confused, there is no excuse for this. The metric system has been taught in our schools since the 70's! People are too stubborn and foolishly attach emotions to issues like this.
Failure is not an option; it's an outcome.

aviopic
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### RE: US Vs Metric Units On A/C

Converted loads of A/C from US to EU and I can tell it's a lot of work.
Some parts contain both standards and then it's just a matter of program pinning.
Other parts need a software change which is not bad either.
Biggest and most time consuming problem is that all overhead switch on/off notations are the other way around which requires the replacement of all lighting panels, 180 degree switch rotation and/or wiring changes.
The truth lives in one’s mind, it doesn’t really exist

David L
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### RE: US Vs Metric Units On A/C

 Quoting CPHGuard (Reply 10):Am i wrong, when i say the new Boeings are metric ???

I'm afraid so. It's an option, not a standard.

 Quoting CPHGuard (Reply 10):I remember an incident where a 767 made an emergency landing due to fuel starvation. As far as i remember it was due to a miscalculation, based on the airplane being metric.

Yes...

 Quoting FrancoBlanco (Reply 4):Regarding weight it is rather important to know which units you are using (see the Gimli Glider), hence the sticker on the aircraft in question.

... but I think the miscalculation wasn't just between metric and imperial weights, it was between fuel weight and fuel volume.

eddl
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### RE: US Vs Metric Units On A/C

 Quoting Aviopic (Reply 13):Biggest and most time consuming problem is that all overhead switch on/off notations are the other way around

Any reason for this?

3201
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### RE: US Vs Metric Units On A/C

It's almost universal to use C for temperature and NM for distance. Beyond that, most individual airplanes are either "pounds" or "kilos," and use those units consistently. Plenty of airlines have mixed fleets between lb and kg aircraft, although usually (but not always!) a single aircraft type has a single unit. Flight levels are still in "feet" (they're pressure altitudes, not geometric) for most of the world, but in China, Russia, and some other places, the flight levels are numbers of meters, but ICAO filing strips still show the feet equivalent. One of the oddest things about the units used is mixing feet for altitude with C for termperature -- you never do that in university, it's either all metric or all English, and the tables in the back of textbooks are all useless, you gotta do your own conversions.

 Quoting CPHGuard (Reply 10):Am i wrong, when i say the new Boeings are metric ???

They can be whichever -- still gotta support both as a manufacturer.

One more quick random point: NM actually make sense, vs. KM, since they have a relevant physical meaning (think degrees of latitude)
7 hours aint long-haul

aviopic
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### RE: US Vs Metric Units On A/C

 Quoting EDDL (Reply 15):Any reason for this?

Don't know really, not even whether this is standard for the US or just limited to a few US airliners.
Anyway the rest of the world standard is "flip up = on" and "down = off" which required modification of all ex American Airlines and US Airways F100's leaving the US.
The truth lives in one’s mind, it doesn’t really exist

David L
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### RE: US Vs Metric Units On A/C

 Quoting 3201 (Reply 16):NM actually make sense, vs. KM, since they have a relevant physical meaning (think degrees of latitude)

I know it's what you meant but, more specifically, 1NM = 1 minute of lattitude.

ZRH
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### RE: US Vs Metric Units On A/C

 Quoting TeamAmerica (Reply 12):As for efficiency, imperial units such as feet or gallons are more easily halved/quartered

????? This is bullshit. You have a liter which is 100cl or 1000ml. The half of it is 50cl or 500ml. Half a gallon is what? Or a meter has 100cm or 1000mm, the half of it is 50cm or 500mm. What is a half foot or yard. At the metric system you always can add or take a zero. It is most easy to calculate. But for example with the imperial system a foot has 12 inch, etc. Much more difficult to calculate.

AsstChiefMark
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### RE: US Vs Metric Units On A/C

 Quoting EDDL (Reply 15):Quoting Aviopic (Reply 13): Biggest and most time consuming problem is that all overhead switch on/off notations are the other way around Any reason for this?

European switches have always been Up = Off and Down = On. In the USA, it's the other way around.

Mark
Red tail...Red tail...Red tail...Red tail...Red tail...Red tail...Red tail...Red tail...Damned MSP...Red tail...Red tail

eddl
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### RE: US Vs Metric Units On A/C

 Quoting Aviopic (Reply 17):Don't know really, not even whether this is standard for the US or just limited to a few US airliners. Anyway the rest of the world standard is "flip up = on" and "down = off" which required modification of all ex American Airlines and US Airways F100's leaving the US.

 Quoting AsstChiefMark (Reply 20):European switches have always been Up = Off and Down = On. In the USA, it's the other way around.

Thank you for the information!

Phil / EDDL

TeamAmerica
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### RE: US Vs Metric Units On A/C

 Quoting ZRH (Reply 19):????? This is bullshit. You have a liter which is 100cl or 1000ml. The half of it is 50cl or 500ml. Half a gallon is what? Or a meter has 100cm or 1000mm, the half of it is 50cm or 500mm. What is a half foot or yard. At the metric system you always can add or take a zero. It is most easy to calculate. But for example with the imperial system a foot has 12 inch, etc. Much more difficult to calculate

Excuse me, but its not bullshit. Most imperial measures originated from commercial usage, and "ease of use" was the only justification for the units. If you look at an english ruler, you see 12 inches. You can easily divide that into halves, thirds, or quarters...that is exactly why the foot was broken into 12 subunits; ease of division with no math required. I'm not arguing that imperial units are superior, just that they are not so bizarre as some suggest.

I'm an engineer. I do all my work in metric. I insist others do the same, which makes me very much out of step here in the US and causes me endless issues with vendors. The only difference between us, if any, is that I place no emotional stake in imperial vs. metric.
Failure is not an option; it's an outcome.

Starlionblue
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### RE: US Vs Metric Units On A/C

Absolutely. In the rest of the world, the low-beams do not leak any light above a certain defined level. So you will never get glare as you are approaching from the front of another car (unless you are crawling on hands and knees). In the US, low-beams shine some light above this level. Basically, the US system moves the one filament (out of the two) to a position where it will shine out of the casing in a downward direction. This still allows glare upwards since some light bounces off the bottom of the reflector. The traditional rest of the world system blocks light from reflecting upwards in low-beam operation, although modern lamps are a bit more advanced than that.

There are pros and cons to both. US low-beams shed more light but are worse for oncoming cars. Rest of the world low-beams are the other way around. Also, the US system renders the creation of a specific low-beam emission more difficult. Needless to say, there are passionate proponents on both sides.

I am used to the European system, so driving in the US at night is a bit disconcerting. I feel like I'm being blinded all the time. A habit thing I am sure.

 Quoting CPHGuard (Reply 10): I remember an incident where a 767 made an emergency landing due to fuel starvation. As far as i remember it was due to a miscalculation, based on the airplane being metric.

The Gimli Glider. As Mr L mentions, more of a weigh vs volume screwup than imperial vs metric.

 Quoting TeamAmerica (Reply 12):As for efficiency, imperial units such as feet or gallons are more easily halved/quartered etc.

That's just because they are used that way. In my experience, Americans use fractions more in commerce/construction/etc... Europeans use decimals. Just a habit.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

ceo@afg
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### RE: US Vs Metric Units On A/C

As I live in the UK at the moment, I've found the switches in the UK are also on when down and off when up, which is the reverse compared to what I'm used with from Norway.

Another strange quirk which I simply cannot get my head round, is when debating the weight of a person here in the UK. It is not done in kilos or even pounds which I can roughly convert in my head by halving it, oh no. It's done in stones, whatever that is.

I even asked when someone said they were 10stones 4pounds, how much that is in just pounds, for me to get my head round the figure, even they couldn't convert it.

Metric is always easier, like ZRH said, it's just moving the komma.

1l
10dl
100cl
1000ml

1m
10dm
100cm
1000mm
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Coal
Topic Author
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### RE: US Vs Metric Units On A/C

 Quoting TeamAmerica (Reply 12):pray you are wrong. Our failure to get with the program is hampering our products in the world market. As for the US population being confused, there is no excuse for this

Hampering our products? Like which ones? If this is true, the world's products would be hampered in the US market.

 Quoting TeamAmerica (Reply 22):Excuse me, but its not bullshit. Most imperial measures originated from commercial usage, and "ease of use" was the only justification for the units. If you look at an english ruler, you see 12 inches. You can easily divide that into halves, thirds, or quarters...that is exactly why the foot was broken into 12 subunits; ease of division with no math required. I'm not arguing that imperial units are superior, just that they are not so bizarre as some suggest.

Yeah, but there are sooo many other ways to divide things than by thirds and quarters. What about tenths? It's easier to say that a tenth of 30cms is 3cms, which can also be expressed as 30mm, etc, than to say a tenth of 12in is 1.2in, which would be... what, an inch and a fifth? What the hell is that?

Btw, welcome to a.net!

Coal
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carduelis
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### RE: US Vs Metric Units On A/C

Not that they're used in aviation, but can anybody remind me of the difference between a US Gallon and an Imperial Gallon?

Something like a US gallon is about 5/6 of an Imperial gallon.

All through this thread posters have mentioned that the US use 'Imperial' measures!
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AsstChiefMark
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### RE: US Vs Metric Units On A/C

 Quoting Carduelis (Reply 26):Something like a US gallon is about 5/6 of an Imperial gallon

5 US quarts = 1 imperial gallon
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Starlionblue
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### RE: US Vs Metric Units On A/C

 Quoting CEO@AFG (Reply 24):Another strange quirk which I simply cannot get my head round, is when debating the weight of a person here in the UK. It is not done in kilos or even pounds which I can roughly convert in my head by halving it, oh no. It's done in stones, whatever that is.

1 stone = 14 pounds. Note that the plural of the weight unit "stone" is "stone".

 Quoting Coal (Reply 25): Yeah, but there are sooo many other ways to divide things than by thirds and quarters. What about tenths? It's easier to say that a tenth of 30cms is 3cms, which can also be expressed as 30mm, etc, than to say a tenth of 12in is 1.2in, which would be... what, an inch and a fifth? What the hell is that?

As I said, simply tradition and habit. In the US, our contactrors always used fractions. In Sweden, they decimalized (if that's a word).

 Quoting Carduelis (Reply 26):Not that they're used in aviation, but can anybody remind me of the difference between a US Gallon and an Imperial Gallon?

1 gallon [US, liquid] = 0.832 674 188 gallon [UK]
1 gallon [UK] = 1.200 949 92 gallon [US, liquid]

 Quoting Carduelis (Reply 26):All through this thread posters have mentioned that the US use 'Imperial' measures!

Indeed. US measures are variations on Imperial measures.

BTW http://www.onlineconversion.com is really really useful for this kind of thing.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

David L
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### RE: US Vs Metric Units On A/C

 Quoting AsstChiefMark (Reply 20):European switches have always been Up = Off and Down = On. In the USA, it's the other way around.

Some places in Europe cheat by having toggle buttons.

 Quoting Starlionblue (Reply 23):As Mr L mentions,

Thank you Mr. Blue, or is that Mr. Lionblue, or Mr. Hunter?

TeamAmerica
Posts: 1540
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### RE: US Vs Metric Units On A/C

 Quoting Coal (Reply 25):welcome to a.net

You mean welcome to the place where intelligent people will argue about anything, no matter how small. My point was that the imperial system evolved from practical use. A carpenter most often needs to divide by 2, 3, or 4, not 10. We are spoiled by our calculators, and limited in our thinking if we forget that mathematics is not limited to counting by 10's. Saying this does not mean I long for the return of the empire.

 Quoting David L (Reply 14):Quoting CPHGuard (Reply 10): Am i wrong, when i say the new Boeings are metric ??? I'm afraid so. It's an option, not a standard.

Attempting to veer back onto topic...I assume that you mean the flight software can display imperial or metric. Is the aircraft itself engineered in metric, with metric fasteners and the like? If so, when did Boeing convert (what year, which aircraft model)? Similarly, I assume that the major engine manufactures work in metric (right?). When exactly did GE, PW, RR go metric?
Failure is not an option; it's an outcome.

Starlionblue
Posts: 17578
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### RE: US Vs Metric Units On A/C

 Quoting TeamAmerica (Reply 30): You mean welcome to the place where intelligent people will argue about anything, no matter how small

Well, at least in the loony_bin forum. I tend to stay away from that one.

 Quoting TeamAmerica (Reply 30): My point was that the imperial system evolved from practical use. A carpenter most often needs to divide by 2, 3, or 4, not 10. We are spoiled by our calculators, and limited in our thinking if we forget that mathematics is not limited to counting by 10's. Saying this does not mean I long for the return of the empire.

This has not stopped carpenters on either side of the pond from being just as precise. It's just a question of habit.

In my mind, the big difference is that metric was developed with the goal of being a standard for all measures, while US/Imperial is a collection of measurements that were made to fit together after the fact.

The metric system was in many ways an attempt to harmonize and standardize volumetric, mass/weight, dimensional and other measurements. That's why:
- 1 liter of distilled water at standard sea level = 1 cubic decimetre = 1 kilogram.
- 1 Joule is the energy required to exert 1 newton of force for one metre.
- Since 1 watt = 1 joule/second, 1 watt-hour = 3600 joules.
- Watts are exactly equal to volts x ampères.

And so it goes on. That way all the measurements are related. I find it easy to have as a rule of thumb that one liter of water is one kg. So one liter of milk, being more dense will weight a bit more than a kilo. And one liter of petrol will weigh less. But that's just me.

Another advantage is that measurements for large distances like kilometres are exactly related with the exact same conversions (decimal) to measurements for medium distances like metres and short distances like nanometers and ångströms. In the Imperial/US system, sometimes you use yards, sometimes feet and sometimes inches. There is no continuity between them. 1 yard = 3 feet but 1 foot = 12 inches. This makes conversions between large and small more difficult. On the other hand, it gives you a unit for a specific task (e.g. inches for kitchen cabinets) which has been developed from usage instead of by edict and may be more appropriate.

The metre itself, btw, was originally defined as 1/10000000th of the distance between the North Pole and the Equator along the Paris meridian. Subsequently, it was redefined as the distance light travels in 1/299792458th of a second.

But as I said before, habit and traditioin are really important.

[Edited 2006-09-07 20:57:11]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

Coal
Topic Author
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### RE: US Vs Metric Units On A/C

 Quoting TeamAmerica (Reply 30):You mean welcome to the place where intelligent people will argue about anything, no matter how small.

Oh, like you?

You still haven't answered my questions, you ungrateful jerk.

Coal
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TeamAmerica
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### RE: US Vs Metric Units On A/C

 Quoting Starlionblue (Reply 28):Quoting Carduelis (Reply 26): All through this thread posters have mentioned that the US use 'Imperial' measures! Indeed. US measures are variations on Imperial measures.

True. Another problem with "US measures" is that there isn't a proper name for it, so we wind up using terms like "english" or "imperial" even though it is incorrect.
Failure is not an option; it's an outcome.

David L
Posts: 8553
Joined: Tue May 18, 1999 2:26 am

### RE: US Vs Metric Units On A/C

 Quoting TeamAmerica (Reply 30):Quoting David L (Reply 14): Quoting CPHGuard (Reply 10): Am i wrong, when i say the new Boeings are metric ??? I'm afraid so. It's an option, not a standard. Attempting to veer back onto topic...I assume that you mean the flight software can display imperial or metric. Is the aircraft itself engineered in metric, with metric fasteners and the like?

Yes, the flight software. That's what was being discussed. I doubt very much that the manufacturing processes are optional.

robsawatsky
Posts: 477
Joined: Thu Dec 18, 2003 7:07 am

### RE: US Vs Metric Units On A/C

 Quoting TeamAmerica (Reply 30):You mean welcome to the place where intelligent people will argue about anything, no matter how small. My point was that the imperial system evolved from practical use. A carpenter most often needs to divide by 2, 3, or 4, not 10. We are spoiled by our calculators, and limited in our thinking if we forget that mathematics is not limited to counting by 10's. Saying this does not mean I long for the return of the empire.

The origins of the imperial system including inch and foot are hotly debated with no universally agreed upon etymology. While your assertion about "practical" is probably somewhat correct, I've yet to find anything to suggest it was for ease of calculation. The more likely was due to ease of access to a measuring references, like body parts or portions thereof, including the foot, length of a thumb joint (inch), stride (yard), mile (1000 paces), etc, although these are certainly not definitive. Some cultures had foot = 10, 12 or 16 inches, so even 12 was not a universal standard.

I'd also venture that the reason that 2, 3 and 4 are such handy numbers for construction is because in the evolution of design people will tend to use dimensions that make it easy to build. Sort of like standard 16 inch or 24 inch centres on much wood frame housing; makes for easy multiples of 1.5 or 2 ft which go nicely into standard lengths of lumber. There's no magic in the numbers, it's just cooperative design and manufacturing for ease of application.

TeamAmerica
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Joined: Thu Sep 07, 2006 3:38 am

### RE: US Vs Metric Units On A/C

 Quoting Robsawatsky (Reply 35):The origins of the imperial system including inch and foot are hotly debated with no universally agreed upon etymology. While your assertion about "practical" is probably somewhat correct, I've yet to find anything to suggest it was for ease of calculation. The more likely was due to ease of access to a measuring references, like body parts or portions thereof, including the foot, length of a thumb joint (inch), stride (yard), mile (1000 paces), etc, although these are certainly not definitive. Some cultures had foot = 10, 12 or 16 inches, so even 12 was not a universal standard. I'd also venture that the reason that 2, 3 and 4 are such handy numbers for construction is because in the evolution of design people will tend to use dimensions that make it easy to build. Sort of like standard 16 inch or 24 inch centres on much wood frame housing; makes for easy multiples of 1.5 or 2 ft which go nicely into standard lengths of lumber. There's no magic in the numbers, it's just cooperative design and manufacturing for ease of application

Yes, I agree. I did not mean to suggest "ease of calculation" at all. Just as you say, it's that the multiples of 2, 3, and 4 tend to be handy in common use. There can be efficiencies in using multiples other than 10. Digital computers work entirely in binary, octal, or hexidecimal units, just for example.

Back to aviation: it's a given that Airbus works in metric. Does Boeing? Is the 787 entirely metric? How about the 777 and so on? When did they convert?
Failure is not an option; it's an outcome.

Starlionblue
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### RE: US Vs Metric Units On A/C

 Quoting Robsawatsky (Reply 35): I'd also venture that the reason that 2, 3 and 4 are such handy numbers for construction is because in the evolution of design people will tend to use dimensions that make it easy to build. Sort of like standard 16 inch or 24 inch centres on much wood frame housing; makes for easy multiples of 1.5 or 2 ft which go nicely into standard lengths of lumber. There's no magic in the numbers, it's just cooperative design and manufacturing for ease of application.

Agreed. And in Europe the "standard lengths" are simply different but probably just as intuitively practical.

One of my favorite measurement standards is ISO 216 paper (ok, geek warning). Well thought out and thoroughly practical.

A0 = 2x A1 = 4x A2 = 8x A3 = 16x A4 = 32x A6 = 64x A6 = 128 x A7 = 256x A8. Hey, it's binary! To get from A3 to A4, you can simply fold the A3 sheet in hafl crosswise. A0 is one square metre and has a length to width ratio equal to the square root of 2.

ISO 216 is the standard in all countries except United States, Canada, Mexico, the Philippines and Chile.

To make life simple, Cx is the standard envelope size for Ax. So a document composed of A4 sheets fits in a C4 envelope.

The practical part is that every large format is easily converted to smaller formats. So a bifold A5 greeting card is simply an A4 sheet folded down the middle. Have an A2 and need 4x A4? Slice the paper in four pieces. This means that different paper sizes can be made and processed in the same equipment. An A3 printer will take A4 paper with exactly the same paper path width.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

SlamClick
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### RE: US Vs Metric Units On A/C

I can't think of any good reason to go to Celsius for temperature. It is just as bogus as Fahrenheit. We should adopt either Kelvin or Rankine, preferably the former. At least it is based on a real constant.
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David L
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### RE: US Vs Metric Units On A/C

 Quoting Starlionblue (Reply 31):This has not stopped carpenters on either side of the pond from being just as precise. It's just a question of habit.

"Correct me if I'm wrong but..." weren't the UK components of Concorde manufactured to imperial units (or at least some of them) while the French components were made to metric units? Those seemed to fit together rather well.

 Quoting SlamClick (Reply 38):We should adopt either Kelvin or Rankine, preferably the former. At least it is based on a real constant.

That's true. How often do we hear someone say it's "twice as hot as it was a couple of weeks ago", when the temperature's gone from 10oC to 20oC?

Starlionblue
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### RE: US Vs Metric Units On A/C

 Quoting David L (Reply 39):Quoting SlamClick (Reply 38): We should adopt either Kelvin or Rankine, preferably the former. At least it is based on a real constant. That's true. How often do we hear someone say it's "twice as hot as it was a couple of weeks ago", when the temperature's gone from 10oC to 20oC?

Dear god yes. "Twice as hot" based on an arbitrary measure. Sometimes being a geek takes serious discipline.

At least Celsius used to be based on the freezing and boiling points of water. Nowadays, it's defined differently and useless even for that. Well, ok it's pretty close...

While we're on this, is there anything more apt to create confusion than the 12 hour clock?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

David L
Posts: 8553
Joined: Tue May 18, 1999 2:26 am

### RE: US Vs Metric Units On A/C

 Quoting Starlionblue (Reply 40):At least Celsius used to be based on the freezing and boiling points of water. Nowadays, it's defined differently and useless even for that. Well, ok it's pretty close...

In everyday life it's a convenient scale relative to what we experience but it's clumsy when comparing the temperature of liquid helium to the temperature of an oven.

 Quoting Starlionblue (Reply 40):While we're on this, is there anything more apt to create confusion than the 12 hour clock?

I don't mind if people stick to one or the other, e.g. "11:35 PM", "23:35", "18 hundred hours". It's the in-betweenies that get me, e.g. "23:35 PM", "11:35 hundred hours".

 Quoting Starlionblue (Reply 40):Sometimes being a geek takes serious discipline.

Yes but I keep forgetting.

TeamAmerica
Posts: 1540
Joined: Thu Sep 07, 2006 3:38 am

### RE: US Vs Metric Units On A/C

Searching the forum archives I found a posting that said that Airbus uses "standard" fasteners, listing the sizes in metric (e.g. 6.35mm rather than 1/4 inch). True or not? Does a mechanic have to change tool sets between Airbus & Boeing?

 Quoting Starlionblue (Reply 40):While we're on this, is there anything more apt to create confusion than the 12 hour clock?

Agreed. No logical reason for maintaining the antiquated time measurements currently in use.

A decimal clock was suggested in the same period that the metric system originated: http://en.wikipedia.org/wiki/Decimal_time but it never caught on. My high school physics teacher had a decimal time clock in the classroom, and it was a topic of hot debate. Most interesting that measuring time is such a prominent exception to the building blocks of the metric system, yet is pretty much universally agreed upon.
Failure is not an option; it's an outcome.

Starlionblue
Posts: 17578
Joined: Fri Feb 27, 2004 9:54 pm

### RE: US Vs Metric Units On A/C

 Quoting TeamAmerica (Reply 42):A decimal clock was suggested in the same period that the metric system originated: http://en.wikipedia.org/wiki/Decimal_time but it never caught on. My high school physics teacher had a decimal time clock in the classroom, and it was a topic of hot debate. Most interesting that measuring time is such a prominent exception to the building blocks of the metric system, yet is pretty much universally agreed upon.

Ah yes. The decimal clock. Well, some things just refuse to change I guess. Ironically, the current method timekeeping is almost, but not quite, in synch with the Earth's movement in the Solar System, leading to leap seconds and leap years. So it's not even correct!

 Quoting TeamAmerica (Reply 42):Quoting Starlionblue (Reply 40): While we're on this, is there anything more apt to create confusion than the 12 hour clock? Agreed. No logical reason for maintaining the antiquated time measurements currently in use.

If nothing else, AM/PM is one extra significant figure. 24 hour timekeeping is more efficient datawise. 4 significant figures instead of 5.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

Zkpilot
Posts: 3903
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### RE: US Vs Metric Units On A/C

 Quoting Starlionblue (Reply 8):There are also big variations apart from the metric/imperial thing. For example, the international standard for dates is year/month/day but is not universally implemented. The international standard for decimal notation is the comma; same here. The standard for low-beam headlights is used in all countries except the USA. The list goes on.

Most countries around the world would say that today is the 08/09/06 ie the 8th of Sept 2006. Take a look at your passport next time...
comma?? I've only seen the comma used for decimals in some countries in Europe. The fullstop/period is used internationally to represent decimal places. Commas are used to represent thousands eg 1,020.23m (which for our American friends is 1.02023 km or 102023cm or 40 166.535 433 071inches or 3 347.211 286 089 feet. Imperial/US just isn't that simple really. Which leads to this:

 Quoting TeamAmerica (Reply 12):I also prefer metric, but let's not be snobs about it. Antique is not a bad thing, and metric (S.I.) is not new. As for efficiency, imperial units such as feet or gallons are more easily halved/quartered etc. . The metric system excels for scientific pursuits, but on the level of human commerce the imperial system can be quite convenient.

I'll reply but ZRH has done it well here:

 Quoting ZRH" class=quote target=_blank>ZRH (Reply 19):????? This is bullshit. You have a liter which is 100cl or 1000ml. The half of it is 50cl or 500ml. Half a gallon is what? Or a meter has 100cm or 1000mm, the half of it is 50cm or 500mm. What is a half foot or yard. At the metric system you always can add or take a zero. It is most easy to calculate. But for example with the imperial system a foot has 12 inch, etc. Much more difficult to calculate.

I'd like to add that a 1/4 of a metre is 25cm (0.25m) 1/5 is 20cm. The only measurement which is slightly harder to get is 1/3 because it is divisible to infinity.. 33.33333333333333333333333333333333333333cm
So usually it is just 33.3cm.

 Quoting TeamAmerica (Reply 22):Excuse me, but its not bullshit. Most imperial measures originated from commercial usage, and "ease of use" was the only justification for the units. If you look at an english ruler, you see 12 inches. You can easily divide that into halves, thirds, or quarters...that is exactly why the foot was broken into 12 subunits; ease of division with no math required. I'm not arguing that imperial units are superior, just that they are not so bizarre as some suggest.

Read my comment above. Metric is much easier to break up. Whats 1/10th of a foot? 1.2 inches? The beauty of metric is that it is both decimal and easily converted to percentages... ie 2/10 of 1 metre is 20cm or 0.2m which is 20%. 0.23m is 23% of a metre.

 Quoting SlamClick (Reply 38):I can't think of any good reason to go to Celsius for temperature. It is just as bogus as Fahrenheit. We should adopt either Kelvin or Rankine, preferably the former. At least it is based on a real constant.

How about that 0degC is frozen water and 100degC is boiling water?
It's quite easy to know with metric that a swim in water that is 25deg is quite pleasant whereas 15deg is quite cold. 35 deg is nice and warm like a hotpool.
When someone says its -10degC outside you know that it is pretty damn cold, that 30deg is a nice warm summers day and that 40deg is scorching hot day (which is 104degF).
As for the other good thing about Celcius... it is the same unit of measure as Kelvin just that it has a different reference point. If the temperature goes up 10degC then it also goes up 10degK.
Kelvins reference of course being absolute zero -273(.something)degC meaning that 0degC is 273degK... good for science etc but Kelvin is not much use for practical everyday things... "oh yes what a lovely day it is outside it must be 298degK..."
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TeamAmerica
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### RE: US Vs Metric Units On A/C

 Quoting Zkpilot (Reply 44):Read my comment above. Metric is much easier to break up. Whats 1/10th of a foot? 1.2 inches? The beauty of metric is that it is both decimal and easily converted to percentages... ie 2/10 of 1 metre is 20cm or 0.2m which is 20%. 0.23m is 23% of a metre.

Agreed that metric is clearly superior for nearly all purposes. Not conceded that dividing by 10 is relevant to all things, which is entirely my point and not worthy of "bullshit".

Why do we have 60 minutes in an hour, 24 hours in a day? Why do we use 360 degrees of longitude? This sub-discussion started with a comment about efficiency, and my response was only intended to say that 10 is not sacred - other number systems can be efficient (I used the word "convenient") and we lose something if we forget that. I offer no defense of the imperial, english, US standard or whatever the heck you wanna call it.

Not gonna debate this any further, as my desire is to talk about aviation and we just can't seem to get back to the topic.
Failure is not an option; it's an outcome.

MarkC
Posts: 238
Joined: Tue Apr 25, 2006 8:10 am

### RE: US Vs Metric Units On A/C

First, let me apologize for getting back on topic.

Some of the engine components are designed by companies that use metric. These are converted to US units for the manufacturer's use.

All the engine maintenance manuals are primarily in US, but also show metric conversions. I would expect that aircraft maintenance manuals are the same.

Starlionblue
Posts: 17578
Joined: Fri Feb 27, 2004 9:54 pm

### RE: US Vs Metric Units On A/C

 Quoting Zkpilot (Reply 44):Most countries around the world would say that today is the 08/09/06 ie the 8th of Sept 2006. Take a look at your passport next time...

Well, I was talking about the international standard, not what is actually used in a lot of countries.

My passport is Swedish so it uses the the ISO 8601 standard, which is yyyy-mm-dd. To avoid misunderstandings, it also says 5 NOV 1971.

 Quoting Zkpilot (Reply 44):comma?? I've only seen the comma used for decimals in some countries in Europe. The fullstop/period is used internationally to represent decimal places.

De facto standard in many places. However, the ISO standard allows both comma and period and recommends the comma.

To quote wikipedia: Another method of writing numbers is the international system writing style [1]. They write the number fifteen million as "15 000 000". The only punctuation mark is the decimal mark; a period in English text, a comma in all other languages (however ISO standards recommends the use of comma instead of points also in English speaking countries).

 Quoting Zkpilot (Reply 44):How about that 0degC is frozen water and 100degC is boiling water?

Almost but not quite accurate. But good enough if you're outside the lab

 Quoting TeamAmerica (Reply 45):10 is not sacred - other number systems can be efficient (I used the word "convenient") and we lose something if we forget that.

Agree completely. It will also be interesting to see how things change in the next 100 years.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

Posts: 3697
Joined: Thu Nov 08, 2001 1:04 am

### RE: US Vs Metric Units On A/C

 Quoting MarkC (Reply 46):All the engine maintenance manuals are primarily in US, but also show metric conversions. I would expect that aircraft maintenance manuals are the same.

The airbus manuals show metric values...

Its not just items in the Cockpit. All of my tools are UNF Imperial. 3/8ths, 7/16ths etc etc... If they changed to metric, they'd have to change all the aircraft tooling & equipment. The metric/imperial battle wont ever be changed...
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Starlionblue
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Joined: Fri Feb 27, 2004 9:54 pm

### RE: US Vs Metric Units On A/C

Not so sure. It might never end, or maybe it will. But it won't be settled in the next 20 years
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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