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sebolino
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 1:12 pm



Quoting L-188 (Reply 11):
The metric system is a completely arbitrary system of measures and doesn't make sense.

???

Incredible to hear that.
Inches, feet, yards and gallons (different in US and UK) makes probably much more sense !!  Smile  Smile
Using the international system of units is probably the middle age of science ! Let's measure distances in inches and feet.  bigthumbsup 
 
ORDagent
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 1:41 pm



Quoting TGV (Reply 12):
The metric system is a completely arbitrary system of measures and doesn't make se

Both are completely arbitrary. However the metric system is more "rational" in the aspect that all measures are based on mutltudes of ten which makes the math involved simpler.

I remeber a public service commerical as a young kid that used the animated Star Trek series that talked about an alien species that was falling apart as they didn't convert to the universal standard of measure i.e. metric. AFAIK even though the U.K. has embraced metric measures are still given in both systems particulalry mileage measures on cars. Even though I am comfortable with metric living here in the U.S. I can't wrap my brain around "litres to a 100 Kilometers" vs. Miles per gallon.
 
Cubsrule
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 1:47 pm



Quoting ORDagent (Reply 51):
AFAIK even though the U.K. has embraced metric measures are still given in both systems particulalry mileage measures on cars. Even though I am comfortable with metric living here in the U.S. I can't wrap my brain around "litres to a 100 Kilometers" vs. Miles per gallon.

I think maybe there's a suggestion in here: use whatever measure makes more sense. For altitude, that's pretty clearly feet or hundreds of feet (because the numberes are easier). It's not as clear cut for temperature, length (on the ground), or mass.
I can't decide whether I miss the tulip or the bowling shoe more
 
Joost
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 1:53 pm



Quoting Ned Kelly (Reply 20):
Which prompts me to my question regarding Russia, do pilots in Russia for example fly at 10,000 metres instead of 30,000 feet, or do the fly at the metric equivalent of 30,000 feet which is 9144 metres? Can anyone answer this?



Quoting FXRA (Reply 32):
The former Soviet Union (at least some fo them) and China are pretty much the ony regions of the world that are all metric. And the altitudes they use are usually something like 9600m or 7200m. When flying into these regions, there is a transition area where aircraft are moved from say FL300 to 9600m.

Adding to this, I heard the story that with slightly older aircraft, including the 744, pilots can only select predefined flight level in the autopilot (290, 300, 310, etc) and that is is therefore uncomfortably flying over Russia as you need to manage your cruising altitude continuously. Can anyone confirm?
 
AF1624
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 2:45 pm

Quoting Joost (Reply 53):
Adding to this, I heard the story that with slightly older aircraft, including the 744, pilots can only select predefined flight level in the autopilot (290, 300, 310, etc) and that is is therefore uncomfortably flying over Russia as you need to manage your cruising altitude continuously. Can anyone confirm?

Not exactly. In the classics, you could select at least 100 of feet in the autopilot. So 29100, 29200,29300 and so on. But there was no conversion between feet and meters, so they had (and still have as there are still some classics flying today) to approach the correct altitude with the autopilot. For example, 10300 meters would be 33000 feet instead of 32960 feet. That's a 40 feet difference, which corresponds to a 9 meter difference, which is not that much. Well, it still is the height of a three storey building, but when you're sitting on top of a 3333 storey building, 3 more or 3 less is not a big deal.

In the new generation of boeing aircraft (737, 747, 7674 and 777) you can push a button that will bring up the indication of altitude in meters along with the one in feet on the PFD. But you still have to select an altitude in feet in the MCP. Correct me if I'm wrong but it seems to me that the FMC, though, uses only feet as altitude reference.

The latest airbuses also have that conversion possibility with the flick of a switch. When I say latest I mean 320 series, 330/340 and 380. And on airbuses you can also select an altitude in meters in the MCP. That's a plus.


As you can see on the image, there is a "METRIC ALT" switch.

[Edited 2008-04-28 08:07:33]
Cheers
 
levent
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 2:58 pm



Quoting Cubsrule (Reply 6):
How many mistakes has imperial vs. metric caused?

Surprisingly I didn't see this accident mentioned: the mid-air collision between an Il-76 and a 747 over India. Reports suggested that the accident was caused by the Ilyushin's pilots making errors converting the altitude given by ATC in feet to metres.
 
Boston92
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 3:18 pm



Quoting Levent (Reply 55):
caused by the Ilyushin's pilots making errors

Pilot error. Imperial vs metric cannot be the cause of an accident...it will always be pilot error.
 
YULWinterSkies
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 3:42 pm



Quoting Leskova (Reply 4):
doesn't really matter whether the metric system is used or not - what does matter is that it's standardized.

The HUGE advantage of metric system over imperial is the factor of 10 everywhere, not 3 (ft to yd), 16 (oz to lb), 12 (in to ft), and is there any straightforward conversion factor from ft to mile by the way? The idea that a height and a length and a distance are expressed in the SAME unit (or 10* multiple of) makes a lot more sense too. You drive x miles but fly at y ft just because by tradition horizontal distances are in mi while vertical ones are in ft. WTH??? I'd rather drive x km and fly at y km (or m)... And burning x litres of fuel to cover the y km in order to enjoy z liters of beer at my final destination...

Quoting L-188 (Reply 11):
The metric system is a completely arbitrary system of measures and doesn't make sense. in fact the meter doesn't even equal up to what it is supposed to because they made a mistake in the distance between the poles when they figure it out. They just looked at the distance to the pole and split it up by a million. No science behind that at all.

Do you think the imperial system is NOT arbitrary? Tell me where the logic behind the inch is, the mile, the pound and such... And to clarify your point the NAUTICAL MILE that you refer to is NOT imperial but a navigation unit (from which the knot is derived) (How many US a.netters get mixed up everyday here on this forum with mi vs nm? ) that indeed makes a lot of sense (or at least used to before the generalization of GPS) even though it is equal to the 60th of the 90th of the Equator-pole distance (here again if this is NOT arbitrary, tell me...).

In no way the metre has been defined as a millionth of the distance pole-to-(what?) as there is more than 1000 km between the pole and (what? Equator? Paris? the centre of the Earth?) I believe you're off by a factor of 10, as there is something very close to 10,000 km between the Equator and the poles (or an average of 10,000 km, whatever...). We all know (or should) that the Earth is not a perfect sphere neither a "perfect" sphere flattened at its pole (if this notion can mean anything perfect by itself). So because of this, the meter has been redefined as the distance traveled by light rays (photons) under perfect vacuum in 1/c second, c being the speed of light, of which we have extremely accurate estimates thanks to the relativity equations. c is a parameter much more constant than any equator-pole distance one can measure on Earth, even though I'm sure c itself's got its own uncertainty. But as my knowledge in relativity physics is limited so I'll leave that for experts. Sorry if science is annoying, but there would have been no aviation without science. Neither computers, neither internet.

The nm has an uncertaintly related to the shape of the planet but this approximation (the same than the meter initially had), however, is good enough for navigation purposes, but cannot be used to define a universal reference unit.

Quoting SCCutler (Reply 16):
then for political reasons, the process faded.

Indeed, the USSR used the metric system, so the imperial system had to be used to be different and annoying.
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mbj2000
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 3:47 pm



Quoting GrahamHill (Reply 45):
Quoting MBJ2000 (Reply 35):
Interesting thing is, that the "imperial" system is not completely dead in some parts of Europe. In Germany for example, AFAIK they still use "Zoll" (inch) in the plumbing area...

In France, we use the inch for PC monitors (not for TV screens, though...) and wheel rims.

Same in Germany, I forgot about that!
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jamesbaldwyn
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 3:55 pm



Quoting Ned Kelly (Reply 20):
I always hate it when aviation TV programs like Air Crash Investigator quote altitudes in metric when most aircraft fly at altitudes in feet! Which prompts me to my question regarding Russia, do pilots in Russia for example fly at 10,000 metres instead of 30,000 feet, or do the fly at the metric equivalent of 30,000 feet which is 9144 metres? Can anyone answer this?

Yeah - Really annoys me as well. They could at least give both values!
 
gearup
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 4:31 pm



Quoting Cubsrule (Reply 15):
I can definitely get around both systems (I have a science degree and have lived in metric countries), and I've concluded that the ONLY factor that determines which system "makes more sense" is the system you grew up with.

Not always. I grew up with Imperial in Ireland. Ireland partially metricated in the 70's, got used to that. Emigrated to Canada in 1980 which at that time was still using Imperial. I readapted to Imperial. Canada went metric in one day and I had to readjust to metric again. No problem. Also, as regards which system is better, ask yourself this question: when people do convert, do they convert to metric or from it?

Anyway which would you prefer:

Grams & Kilograms or ounces, pounds, stones, hundredweights and tons.
millimeters & kilometers or inches, feet, yards, furlongs and miles.
litres or ounces, cubic inches, quarts, Imp. gallons and US gallons.

and yes 10,000 metres sounds better to me than 30,000 feet. Just sayin'
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Pihero
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 4:44 pm

Origin of the meter :
Surprisingly enough for a lot of posters on this thread, it is equivalent to the nautical mile. The revolutioin scientists started with the grad, 100 of which would give a right angle and 400 of which the full circle. This grad was divided into 100 *minutes*... It was then decided that one minute of the earth circumference would be equivalent to a kilometer after the meter, the first handy unit was set at 1/40.000.000 of that circumference.

Now, another forgotten aspect of measuring units is that there is only one system - the International System, i.e SI -, from which all other units in used will be derived. So the foot is a fraction of the meter.....etc...

Quoting YULWinterSkies (Reply 57):
The HUGE advantage of metric system over imperial is the factor of 10 everywhere

Not only that, it has also to do with coherence and adherence to the dimensional equations of the measurements : For instance, a pressure is physically defined as the ratio of a force against surface, therefore, a unit of force would be F/S.
In this case, it comes down to a force of one Newton over a square meter (that's the definition of a Pascal). Then if the unit is not handy, change it into a more manageable sub-unit. In our example, a pascal is very low, so why not use 100 pascals as the measurement base . Et voilà, you get the hectopascal !
Another aspect is that writing down a unit is very clear : a speed is given in kilometers per hour, i.e km/h. The Yankee way of kph is another dumbing-down of a good practice (k is just a prefix meaning 1000 times of...)
What makes people laugh in Europe is when - apparently- the US still uses a measuring tape for pressures ( the in/Hg).

It is also to note that the first ICAO conference in1949 issued the so-called ICAO Tables, viewing the end of 1959 as the year of complete adherence to the final table.
In my opinion, it is very amazing to see the most advanced country in the world resisting most of the moves toward an internationally agreed common technical language. In the field of aviation, it is a bore and a chore to need a set of decoding booklets to be able to get something as *natural* as weather info.
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NAV20
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 4:50 pm

Quoting YULWinterSkies (Reply 57):
Tell me where the logic behind the inch is, the mile, the pound and such...

I can help with the measurements, anyway. It comes from the days before there were any formal methods of measuring things and people needed simple ways to judge distances, lengths, etc. An inch is the length of the first joint of your thumb - a foot is the length of your foot - a yard is the distance from your nose to your outstretched hand. The Romans used the passus, which was the length of a double pace, about five feet, as a convenient way of measuring distances; and one thousand of those make a mile.

Oddly enough, the passus is still with us, in many parts of the world; because the Romans made their chariot-wheels one passus apart. That wore deep ruts in the roads that they also built, so the same measurement had to be used in Britain for centuries as the gauge of cart-wheels, to fit the ruts. When they started building railways there seemed no reason to change, which is why 'standard gauge' on the majority of railways worldwide is still four feet, eight-and-a-half inches.  

Those measurements still remain pretty intuitive - only the other day I was helping a neighbour plant some shrubs, and we spaced them in the time-honoured way by pacing the distances out.

Not just romantic - the advantage of what is now called the 'imperial system' is that most measurements could be divided by two, three, four, six, twelve, and so on; unlike the metric system, which only offers two and five, after which you start drowning in decimal points.

So would you please now tell me where the logic behind the metre is? Seems to me that it would only be really useful to someone wanting to walk (and swim) round the Earth on the Equator?  

[Edited 2008-04-28 09:54:41]
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
rfields5421
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 4:52 pm



Quoting DocLightning (Thread starter):
So why are airspeeds given in kts? Why are altitudes given in hundreds of feet?

Wouldn't it make sense for the international aviation community to switch to Metric?

Why - because in the early parts of the past century when standards were set much more of the world use knots and feet than metric. Also long distance navigation had it's origins in surface ship navigation.

Switching - would be a complete and absolute mistake filled nightmare. Tens of thousands of pilots around the world would have to learn to think differently, calculate everything differently - all their instinctive trained processes would be wrong and have to be relearned.

Now starting from scratch in a world without an imperial system - that would make sense.

But teaching old dogs new tricks is not a good idea.

Quoting FXRA (Reply 32):
The former Soviet Union (at least some fo them) and China are pretty much the ony regions of the world that are all metric. And the altitudes they use are usually something like 9600m or 7200m. When flying into these regions, there is a transition area where aircraft are moved from say FL300 to 9600m.

This is where the simplicity of the metric system breaks down for the aviation world - altitudes.

The 1,000 ft altitude differences are much easier to understand, identify and enter in control systems than a 300 meter separation.

Staying at full 1,000 meter number would work fine for altitudes - BUT there are too many aircraft in the air in much of the world for that much separation to work efficiently.
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David L
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 5:08 pm



Quoting Pihero (Reply 61):
In the field of aviation, it is a bore and a chore to need a set of decoding booklets to be able to get something as *natural* as weather info.

Ah yes, I'd forgotten about that. I've never heard "inches of mercury" used anywhere other than the USA.

Don't get me wrong - if aviation was starting again from scratch I'd favour the metric system without hesitation. It's the thought of wholesale change from one system to another that I have reservations about. The metric system is far from arbitrary.

Quoting Pihero (Reply 61):
Now, another forgotten aspect of measuring units is that there is only one system - the International System, i.e SI -, from which all other units in used will be derived. So the foot is a fraction of the meter.....etc...

Yes, it's quite amusing to read the FIFA regulations, expressed in metres but still an exact amount of yards and feet, e.g. opponents must be at least 9.15m from the ball at free-kicks.  Smile
 
xtoler
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 5:12 pm

I do remember as a little kid in the '70's there were people in the US still trying to talk us into switching to Metric. As late as the late '80's, and I think once on leave (from England of all places), I took a trip back home to Alabama and still saw road markers in both Imperical and metric, but not the major signs. If you notice on the US interstate system, there is a mile marker, well, every mile. Funny thing is, a mile and a kilometer don't add up, so some of the signs you'd see mile 230 and then under it in metric would be some number with a decimal. Oddly enough though, I went to see a buddy of mine at Dover AFB, Delaware back in '95 and all the road signs outside the base were in metirc.

After living in Europe for 8.5 years I got used to the metric system and still prefer it. The good thing though is the schools I went to always taught both in math class. It's good to know both. I just know fractions suck!

BTW when I was stationed in England it seemed like some things were measured imperically and other measurements were in metric. Another good reason to know both.

As far as aircraft, now that a lot are glass cockpit, it should be no problem to switch from one measurment to the other. Just when you are figuring fuel load and weight and balance, you better just use one or the other.
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LH423
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 5:16 pm



Quoting FriendlySkies (Reply 17):
I thought a lot of it had to do simply with the cost of converting the entire US infrastructure to metric.

No. It pretty much had to do with a lack of political will. The US congress passed the 1975 Metric Conversion Act but set voluntary target dates that weren't binding. So, once the initial novelty wore off, conversion fell by the wayside.

Quoting FXRA (Reply 32):
I doubt you'll see us Americans change in the near term (ie my lifetime), we seem to be head strong on being American and doing it our way dammit.

The 1988 Omnibus Trade and Competitive Act dictated that the metric system was to become to preferred system by the government and in business so that the US could remain competitive in an increasingly metric world. I believe it also dictated that the US would convert to the metric system by 1 September 2000, however President Clinton repealed that part of the act. So, I think it's possible that it would happen at some point, though I have a feeling it would be under a Republican president since Republicans tend to be more in favor of global trade and harmonization to that effect.

Considering how hard up the European Union is for the metric system, if even they haven't yet dictated that the metric system be standard in aviation, I doubt you'll see much change beyond the few countries that already do for the time being.

LH423
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rfields5421
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 5:34 pm



Quoting Xtoler (Reply 65):
As far as aircraft, now that a lot are glass cockpit, it should be no problem to switch from one measurment to the other.

I can do that with my Chevy mini-van today - a six year old model.

Since courtesy of Uncle Sam's Navy - is spent 12 years living and driving in countries with KM and KPH - I have no trouble using that system. But my wife......
Not all who wander are lost.
 
WPIAeroGuy
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 5:48 pm

I think its not just the system you grew up on, but how everything, at least in the USA has a certain unit system with it. Any runners know how long a 5K is (not 5,000 miles for those of you who watch The Office), or how long the 800m run is. All our soda comes in 2 liter bottles, or 12 ounce cans. When I was in London it was much easier to figure out how much we drank by drinking 2 liter bottles of cider than the 16 ounce cans of the UK (440ml?). I still can't stand outside temperature in *C, 35 degrees is cold!
-WPIAeroGuy
 
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Asturias
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 8:33 pm



Quoting NAV20 (Reply 62):
Oddly enough, the passus is still with us, in many parts of the world; because the Romans made their chariot-wheels one passus apart. That wore deep ruts in the roads that they also built, so the same measurement had to be used in Britain for centuries as the gauge of cart-wheels, to fit the ruts. When they started building railways there seemed no reason to change, which is why 'standard gauge' on the majority of railways worldwide is still four feet, eight-and-a-half inches.  

Alternatively this could be a silly fictional internet rumor  Smile

http://www.truthorfiction.com/rumors/r/railwidth.htm

asturias
Tonight we fly
 
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Jetlagged
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 9:52 pm

Interesting to see even the American posters refering to US units as "Imperial". You never left the British Empire after all it seems!  Wink The US gallon is certainly different from the Imperial gallon for a start. Fluid ounces are different too. I get very confused in the US ordering a beer if I get asked how many ounces I want. Pints and liters I can cope with.....

As has been said, knots are used for navigational convenience and probably will continue to be all the time we navigate with degrees of latitude and longitude. Knots are neither Imperial or US units. They're kind of neutral.

SI units make much more sense for other measurements. Fuel weight in Kg and temperatures in deg C should be universal in aviation. If the US adopted HPa for air pressure measurement it would be a big step forward too. US industry is largely metric, it's strange that US aviation is not.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
vikkyvik
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 10:19 pm



Quoting Cubsrule (Reply 15):
I can definitely get around both systems (I have a science degree and have lived in metric countries), and I've concluded that the ONLY factor that determines which system "makes more sense" is the system you grew up with.

Eh, I'd have to disagree. I've spent my entire life in the US, and I'd MUCH rather do calculations in Metric rather than English units.

Sometimes, when a problem is given in English units, I'll convert it all to Metric, solve it, then convert the answer back to English.

Quoting Pihero (Reply 61):
In this case, it comes down to a force of one Newton over a square meter (that's the definition of a Pascal). Then if the unit is not handy, change it into a more manageable sub-unit. In our example, a pascal is very low, so why not use 100 pascals as the measurement base . Et voilà, you get the hectopascal !

I agree that it is quite convenient. The only thing that really irks me is the use of the kilogram as the base unit of mass. Why the hell isn't it the gram???!!! Ugh...the Metric system would be PERFECT were it not for that annoyance. But that's really just a personal thing  Smile

Quoting Jetlagged (Reply 70):
Interesting to see even the American posters refering to US units as "Imperial".

I actually usually refer to them as "English units".
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
Dalmd88
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RE: Use Of Metric System In Aviation

Mon Apr 28, 2008 10:55 pm

So far it seems everyone here is just talking about how the travel of aviation, ie altitude, speed, distance; or the weight aspect of the metric system. As a mechanic I am mostly effected by the parts sizes. I've never worked on an Airbus. Is the hardware metric or SAE? I have heard some older Rolls engines are the old British Standard. A real pain in the butt hauling around another set of wrenches and sockets. Even if Boeing were to say the new 737 replacement aircraft and the new 777NG are 100% metric it would take decades to get rid of the SAE aircraft.

I do admit from a sheetmetal percpective the metric system does make sence. In realitly most drawings are written in decimal inches. All the tooling is in numbered drill bits and decimal reams. I rarely used fractional while doing a sheetmetal job.
 
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Starlionblue
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 1:03 am



Quoting L-188 (Reply 11):
The answer is to go back to standard measures such as feet, inches and knots.

The metric system is a completely arbitrary system of measures and doesn't make sense. in fact the meter doesn't even equal up to what it is supposed to because they made a mistake in the distance between the poles when they figure it out. They just looked at the distance to the pole and split it up by a million. No science behind that at all.

As mentioned both systems are arbitrary. It's all in what you're used to. If you grow up with meters and liters they are completely intuitive. However as many have mentioned metric conversions between units are all very intuitive.

Quoting TGV (Reply 12):
In reality the meter was based on the earth circumference divided by 40 000 000.

No. The meter was based on the distance along the assumed sea level between the North Pole and the Equator along the Paris Meridian. Then it was based on the standard meter. Nowadays the definition is: "The metre is the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second."

Quoting SCCutler (Reply 16):
There is no useful reason why the USofA has not changed to the metric system- when I was a kid in elementary school in 1965, we were taught the metric system, and were told that we'd be fully-converted by 1970. They got as far as putting up dual-unit signs on highways, etc., then for political reasons, the process faded.

IMHO the US went too slowly. Better to make a big crash transition like the Euro. The costs and disruption will probably be lower in the end.

Quoting Ned Kelly (Reply 20):
I always hate it when aviation TV programs like Air Crash Investigator quote altitudes in metric when most aircraft fly at altitudes in feet! Which prompts me to my question regarding Russia, do pilots in Russia for example fly at 10,000 metres instead of 30,000 feet, or do the fly at the metric equivalent of 30,000 feet which is 9144 metres? Can anyone answer this?

As mentioned in Russia and China flight levels are in even meter numbers. So an aircraft has to change altitude going in and out.

Quoting FXRA (Reply 32):

I may be wrong, but 1 Ton (US) = 2,000 lbs. A metric ton (or as I alway see it written, tonne) is 1000KG, which as you points out is roughly 2,240lbs. So they're not exactly equal.

IIRC the US uses both. The ton is also known as the short ton (both by weight and spelling)and is 2000lb. The metric one, at 1000kg, is the tonne.

Quoting WPIAeroGuy (Reply 68):
I still can't stand outside temperature in *C, 35 degrees is cold!

Actually it's pretty hot. Big grin

Quoting NAV20 (Reply 62):
Oddly enough, the passus is still with us, in many parts of the world; because the Romans made their chariot-wheels one passus apart. That wore deep ruts in the roads that they also built, so the same measurement had to be used in Britain for centuries as the gauge of cart-wheels, to fit the ruts. When they started building railways there seemed no reason to change, which is why 'standard gauge' on the majority of railways worldwide is still four feet, eight-and-a-half inches.

As mentioned this is a myth.

Quoting Vikkyvik (Reply 71):

I agree that it is quite convenient. The only thing that really irks me is the use of the kilogram as the base unit of mass. Why the hell isn't it the gram???!!! Ugh...the Metric system would be PERFECT were it not for that annoyance. But that's really just a personal thing

Totally agree! But since kg is easily converted to g I won't complain.  Wink

Quoting DALMD88 (Reply 72):
I've never worked on an Airbus. Is the hardware metric or SAE?

AFAIK it's metric.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
vikkyvik
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 1:24 am



Quoting Starlionblue (Reply 73):
IIRC the US uses both.

Well....generally when you hear people in the US say "ton", they're referring to 2,000 lbs. I think if a person or a document of US origin was referring to a metric tonne, it would specifically say "metric tonne".

Quoting Starlionblue (Reply 73):
Totally agree! But since kg is easily converted to g I won't complain.

Glad I'm not the only one. That has bugged me for years....and I doubt I'll ever really get over it. Oh well. It's still better than pounds-mass or slugs.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
474218
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 1:33 am

Why should we all use the same measuring system when:

We don't all use the same language.
We don't all drive on the same side of the road.
We don't all eat the same foods.
We don't all drive the same cars.
We don't all pray to the same god.

I could could go on but I think you all get my point.
 
NAV20
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 1:57 am

As a matter of interest, I've only seen airborne GPS working in nautical miles. Is there a facility for putting it into 'metric' mode? And, further to that, is the Galileo system now being developed by the EU going to be in metric, or imperial, or capable of either mode?

About 'standard gauge':-

Quoting Asturias (Reply 69):
Alternatively this could be a silly fictional internet rumor



Quoting Starlionblue (Reply 73):
As mentioned this is a myth.

Most people do dismiss it as a myth - but they never advance any alternative theory. Perhaps George Stevenson did just wake up one morning and think, "I'll make the gauge four-foot-eight-and-a-half, that'll fox 'em!", but as an engineer he's surely likely to have had a more practical reason?

The practical requirement, for both chariots and wagons, was for a vehicle capable of accommodating two people sitting or standing abreast, pulled by at least one horse. And all of us will have seen the ruts that can develop in unpaved roads. It would obvously have made sense to build wheeled vehicles, particularly wagons using defined roads, to a 'standard gauge' long before the advent of railways - and the highly-organised Romans won't have been slow to realise that.

Even so I might still have dismissed it as a 'myth' myself if I hadn't visited the Roman Wall and Whitby in Northern England. In both places you can see ancient wagon tracks. And, thanks to the blessings of the internet, I was able to find a photograph that tends to confirm, for me anyway, the possibility that the 'legend' is actually based on fact. This is a (possibly Roman) road cut through rock - besides the rutways (around 4'6"apart, centre to centre), you can even see the hoofholds they cut for the horses:-

http://www.northseatrail.org/show_si...rticle.php?article_id=3249&lang=uk

[Edited 2008-04-28 19:05:43]
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
tdscanuck
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 2:07 am



Quoting Banjo76 (Reply 34):
And by the way, let's see which one makes more sense:
Imperial:
"give me that drill bit please", "which one the 17/64th or the 1/4", "the bigger please" ..... "uh"

Oh, it's worse that than. "Which one, the 17/64th, the 1/4, the A, or the 5?"

Quoting Xtoler (Reply 65):
As far as aircraft, now that a lot are glass cockpit, it should be no problem to switch from one measurment to the other.

Switching the displays is trivial. Switching the tooling, engineers', mechanics', and pilots' brains...not so much.

Tom.
 
sphealey
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 2:07 am

> As mentioned this is a myth.

Having read fairly deeply in railroad history, I find it is neither a fact nor a myth. There is some evidence for the theory posted upthread; there is some evidence that Stephenson used local tin mining carts which had a randomly selected gauge; and there is some evidence that the ratio of cart weight to the material strength of the average axle from the average foundry has remained constant from Roman times up through today's 120 (US ANSI) ton rail cars.

There is however in the US a heck of a lot of industrial equipment which has a maximum size dictated by the tunnel diameter that allows a boxcar of standard gauge to clear; I used to be involved in routing some of that stuff from one point to another.

sPh
 
vikkyvik
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 2:38 am

Hmmm, well this sort of seemed apropos to this thread...just saw this on tonight's Jeopardy:

Alex Trebek: "This distance is 9.46 trillion kilometers, give or take a few kilometers"
Contestant: "What is the diameter of the Earth?"

I suppose a fair amount of people in the US don't use the metric system much at all. When you're not used to using a certain measurement, it can be difficult to ascertain the magnitudes involved.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
NAV20
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 2:42 am

Quoting Sphealey (Reply 78):
there is some evidence that Stephenson used local tin mining carts which had a randomly selected gauge

Hi Sphealey - Stephenson hailed from North-East England which was a coalmining area. He built a lot of colliery railways before he invented the locomotive. The coal had to be delivered by wagon either to the cities or to the docks. Railways were commonplace in the region from quite early in the 19th. century, but they were for horsedrawn wagons, of course, not steam trains. Many of the wagons were also 'dual-purpose,' they ran either on rails or on the roads.

I don't think there can be much doubt that wagons were built with the wheels pretty much a standard width apart; and that the early railways adopted the same gauge. To my mind, the only thing that is open to question is whether the Romans set the original standard or the British dreamt it up for themselves later on.

http://www.dmm-gallery.org.uk/gallery/0004-000.htm

[Edited 2008-04-28 20:06:01]
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
Pihero
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 8:35 am



Quoting 474218 (Reply 75):
Why should we all use the same measuring system

Because we communicate with each other and we trade with each other. as for US products, they conform to the EU directives on packing and consumer information, especially on weights and volumes. They are metric.

Another point worth mentioning is the use of big numbers : a US billion is a millard and a non-US billion is a US trillion so, if I am not mistaken, a billion billion is in fact a trillion or a millionth of a quadrillion, but in reality worth a quintillion, right ?...  Confused  Confused

Quoting L-188 (Reply 11):
The knot however is based on the circle and that makes sense since we live on a big sphere.

The knot is a measure of speed. And the Earth is not a sphere but a potatoid Big grin

Quoting L-188 (Reply 11):
The Nautical Mile(Sea mile) is a measure of distance, equalling 6080.27. This value was chosen because it is practically the length of one minute of arc of a meridian, or of one minute of arc of the equator.
The key word is "practically".

That definition made sense in 1942 when my copy was published and still does today.

Nope. Not anymore. See this from a document of the University of North Carolina (I chose a US source to show my complete neutrality in this } :
"The SI currently accepts the use of certain other metric and non-metric units traditional in various fields. These units are supposed to be "defined in relation to the SI in every document in which they are used," and "their use is not encouraged." These barely-tolerated units might well be prohibited by future meetings of the CGPM. They include:

the nautical mile and knot, units traditionally used at sea and in meteorology;
"

Quoting L-188 (Reply 11):
There are 360 lines of latitude on the earth, which is oddly enough shaped as a 360 degree arc or circle if you prefer. Each of those lines is split up into 60 minutes of longitude which are 6080.27 feet long....on knot...how about that?

Sorry, but you are wrong. There are only 90 degrees,North or South of the equator and the lengths of these latitude circles - therefore the length of a given arc - vary with the latitude. One minute could approximate one Nm on the Equator, but half of that at latitude 60°.
 Confused
Contrail designer
 
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Starlionblue
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 9:32 am



Quoting Pihero (Reply 81):
The knot is a measure of speed. And the Earth is not a sphere but a potatoid

Potatoid, is it? While cute, I'm pretty sure the Earth is a spheroid.

As in (and respect to anyone who gets the reference): "Hurl that spheroid down the field...
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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GrahamHill
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 10:14 am



Quoting David L (Reply 64):
Yes, it's quite amusing to read the FIFA regulations, expressed in metres but still an exact amount of yards and feet, e.g. opponents must be at least 9.15m from the ball at free-kicks.

True! I never paid attention to that. I guess it's an old heritage of the English rules, isn't it? Anyway, 9 meters or 9.15 meters, it does not make much difference  Wink Big grin

Quoting Vikkyvik (Reply 79):
Alex Trebek: "This distance is 9.46 trillion kilometers, give or take a few kilometers"
Contestant: "What is the diameter of the Earth?"

Ouch... Big grin

Quoting Starlionblue (Reply 82):
I'm pretty sure the Earth is a spheroid.

It is indeed.
"A learned fool is more foolish than an ignorant one" - Moliere
 
David L
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 11:26 am



Quoting NAV20 (Reply 76):
As a matter of interest, I've only seen airborne GPS working in nautical miles. Is there a facility for putting it into 'metric' mode?

All the receivers I've used allow the selection of all of the commonly used units.

Quoting NAV20 (Reply 76):
And, further to that, is the Galileo system now being developed by the EU going to be in metric, or imperial, or capable of either mode?

That will depend on the receivers, not the "system".
 
Pihero
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 11:33 am



Quoting Starlionblue (Reply 82):
I'm pretty sure the Earth is a spheroid.

Hey ! Can't I have my ellipsoid-shaped potatoes, please ?

..."True geodetic datums were employed only after the late 1700s when measurements showed that the earth was ellipsoidal in shape. "...
and
..."Ellipsoidal earth models are required for accurate range and bearing calculations over long distances.
Loran-C, and GPS navigation receivers use ellipsoidal earth models to compute position and waypoint information.
Ellipsoidal models define an ellipsoid with an equatorial radius and a polar radius.
The best of these models can represent the shape of the earth over the smoothed, averaged sea-surface to within about one-hundred meters.
"...

More of it here

The latest world geodesic survey in 1984 is the basis for GPS-based positioning for air navigation purposes.
We cannot shoot a GPS approach if the airport is not "WGS 84".
Contrail designer
 
CosmicCruiser
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 12:32 pm



Quoting Ned Kelly (Reply 20):
Which prompts me to my question regarding Russia, do pilots in Russia for example fly at 10,000 metres instead of 30,000 feet, or do the fly at the metric equivalent of 30,000 feet which is 9144 metres? Can anyone

All areas that use meters eg. Russia, China, use rounded meter levels,
eg. 11,900m = 39,100'
10,700m = 35,100'
6,900m = 22,600'
China now uses RVSM between 8,900m (29,100') and 12,500m (41,100')

Our altimeters show both altitude levels and it is a little uncomfortable seeing 22,637' indicated at 6,900m.
 
bond007
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 1:11 pm



Quoting JayDub (Reply 21):
They are both acceptable...and the same arguments for which system is "better" can be made on either side of the fence.



Quoting Starlionblue (Reply 73):
As mentioned both systems are arbitrary. It's all in what you're used to.

I completely disagree. I think if you really take an unbiased look at both systems, it's tough to say that metric doesn't make much more sense, purely because of the units of 10/100s etc.

Quoting BrianDromey (Reply 41):
o be fair I think the metric system is slightly easier to understand because of its realtionship with multiples of 10. Each unit is a multipliplication of the meter by a factor of 10, with the appropriate naming (eg nano, pico, mili, kilo, etc). This nomenclature can be used with any metric unit eg, volume, sound, etc.

Correct. If you take this as perhaps the only difference between imperial and metric, then it is makes metric superior over imperial.

The yard and the meter may well be somewhat arbitrary in definition, but a kilometer or a millimeter is certainly not an abitrary conversion but extrememly intuitive, whereas a foot, yard, inch, mile is anything but that.

Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
NAV20
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 1:28 pm



Quoting GrahamHill (Reply 83):
Anyway, 9 meters or 9.15 meters, it does not make much difference

It would probably mean that the poor referee has to push them back three yards instead of two before you can take the kick......  Smile

Quoting CosmicCruiser (Reply 86):
All areas that use meters eg. Russia, China, use rounded meter levels,
eg. 11,900m = 39,100'
10,700m = 35,100'

That's rather worrying - any sort of rounding is bound to reduce separation, one way or the other. It would surely be safer to stick to one system or the other?

If I'm allowed a joke, I remember buying some battens for a cupboard I was building during the first week after Australia went metric. I asked for them cut to about six feet and the counter guy at the timber yard said, "Metric, mate, all metric now." So of course I said, "OK, 'about' 1.8288 metres then."

Luckily he realised that I was joking, he was a big bloke. We shared a laugh and he headed for the shelves. Halfway there he turned round, came back, and said (a bit sheepishly, I'm glad to say), "Sorry mate, forgot to ask - do you want them in four-by-two or three-by-one-and-a-half?"
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
CosmicCruiser
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 1:57 pm



Quoting NAV20 (Reply 88):
any sort of rounding is bound to reduce separation, one way or the other.

Well they're still separated by 300m or approx 970'. That's also why most of us SLOP in China RVSM.
 
NAV20
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 2:17 pm



Quoting CosmicCruiser (Reply 89):
Well they're still separated by 300m or approx 970'.

Sure, CosmicCruiser - but the trouble with the metric system in general is that the primary dimensions are just too big. A metre is too long for most building or woodwork, a litre is far too big if you're buying a beer or even a bottle of wine, temperatures in Centigrade are far too crude. Whatever you're trying to measure or plan or do, you usually start drowning in decimals within seconds.
"Once you have flown, you will walk the earth with your eyes turned skywards.." - Leonardo da Vinci
 
Dalmd88
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 2:29 pm



Quoting Tdscanuck (Reply 77):
Oh, it's worse that than. "Which one, the 17/64th, the 1/4, the A, or the 5?"

That's easy, which size does the paperwork call for? BTW the order from largest to smallest is 17/64th, A, 1/4, 5. 17/64 is the first over -8 hi-lok. The actual interferance fit ream size isn't in memory anymore, maybe a .263? A, I can't think of much use for. 1/4 is a common -8 rivet. A 5 is a first over -6 cherry-max.
 
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Starlionblue
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 3:05 pm



Quoting Bond007 (Reply 87):
Quoting Starlionblue (Reply 73):
As mentioned both systems are arbitrary. It's all in what you're used to.

I completely disagree. I think if you really take an unbiased look at both systems, it's tough to say that metric doesn't make much more sense, purely because of the units of 10/100s etc.

Fair enough. I meant "the basis of both systems is arbitrary". I agree completely that the actual mechanics of metric are much simpler to understand and use.

Quoting NAV20 (Reply 76):

Most people do dismiss it as a myth - but they never advance any alternative theory.

You make a good argument.

Quoting Starlionblue (Reply 82):
As in (and respect to anyone who gets the reference): "Hurl that spheroid down the field...

Still no takers?  Wink
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
bond007
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 6:02 pm



Quoting NAV20 (Reply 90):
Sure, CosmicCruiser - but the trouble with the metric system in general is that the primary dimensions are just too big. A metre is too long for most building or woodwork, a litre is far too big if you're buying a beer or even a bottle of wine, temperatures in Centigrade are far too crude. Whatever you're trying to measure or plan or do, you usually start drowning in decimals within seconds.

Well, the same argument can be made for imperial measurements, of course!

If a metre is too long, then so is a yard!

A litre too big for a bottle of wine?? AFAIK most, if not all bottles sold here are 750ml ... not imperial measures.

Too big for a beer .... so what I get in the USA ... an 8oz bottle of beer, a 12oz, 16oz glass .... gimme a break... makes no difference. Pints of beer in Europe aren't pints anyway, right? They're half-litres??

One thing I haven't heard mentioned is the ease of entering metric/decimal values into computer systems, as opposed to imperial.

Jimbo
I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
 
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Asturias
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 6:11 pm



Quoting NAV20 (Reply 76):
Most people do dismiss it as a myth - but they never advance any alternative theory.



Quote:
Where did the four-foot, eight-and-a-half-inch standard originate? Gabriel says it was from a Englishman named George Stephenson. Carts on rails had been used in mines in England for years, but the width of the rails varied from mine to mine since they didn't share tracks. Stephenson was the one who started experimenting with putting a steam engine on the carts so there would be propulsion to pull them along. He had worked with several mines with differing gauges and simply chose to make the rails for his project 4-foot, eight inches wide. He later decided that adding another six inches made things easier. He was later consulted for constructing some rails along a roadway and by the time broader plans for railroads in Great Britain were proposed, there were already 1200 miles of his rails so the "Stephenson gauge" became the standard.

Interestingly, the 4-foot, eight-and-a-half inch width has not always been the standard in the U.S. According to the Encyclopedia of American Business History and Biography, at the beginning of the Civil War, there were more than 20 different gauges ranging from 3 to 6 feet, although the 4-foot, eight-and-a-half inch was the most widely used. During the war, any supplies transported by rail had to be transferred by hand whenever a car on one gauge encountered track of another gauge and more than 4,000 miles of new track was laid during the war to standardize the process. Later, Congress decreed that the 4-foot, eight-and-a-half inch standard would be used for transcontinental railway.

Here is the alternative theory. Your story is really cute, but I find this explaination to be far more satisfactory. The anecdote you told was an internet rumor from back when people thought email was kinda cool.

It is, as so many of those rumors, unfounded but entertaining.

asturias
Tonight we fly
 
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Jetlagged
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 6:28 pm



Quoting Vikkyvik (Reply 71):
I agree that it is quite convenient. The only thing that really irks me is the use of the kilogram as the base unit of mass. Why the hell isn't it the gram???!!! Ugh...the Metric system would be PERFECT were it not for that annoyance. But that's really just a personal thing

The cgs system does use the gram as it's unit of mass, but then you would have to accept the centimeter as the unit of distance. The SI unit of mass is the Kg. To use the gram would not be logical, or practical. Meters are similarly more convenient than centimeters for distance.

Quoting Vikkyvik (Reply 71):
I actually usually refer to them as "English units

At my (English) University they were always referred to as US units.

Quoting Vikkyvik (Reply 74):
Well....generally when you hear people in the US say "ton", they're referring to 2,000 lbs. I think if a person or a document of US origin was referring to a metric tonne, it would specifically say "metric tonne".

Really? Now that is confusing. The imperial ton is 2240 lbs, which is quite close to the metric tonne (2204.6 lbs).

Quoting Starlionblue (Reply 82):
Potatoid, is it? While cute, I'm pretty sure the Earth is a spheroid.

IIRC it's an oblate spheroid, rather like me these days!

Quoting L-188 (Reply 11):
The Nautical Mile(Sea mile) is a measure of distance, equalling 6080.27. Ths value was chosen because it is practically the length of one minute of arc of a meridian, or of one minute of arc of the equator

The international standard nautical mile is 1852 meters, 6076.1155 feet. That is very close to the average minute of arc. Even the US adopted that in 1954, so the US definition you quote is long out of date. The old British definition of 6080 feet was a rather arbitrary 800 feet more than a statute mile and only approximated to the minute of arc definition.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
NoWorries
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 6:36 pm

With gasoline selling for $4/gallon, now would be a great time to switch to litres ...  duck 
 
vikkyvik
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 6:51 pm



Quoting Jetlagged (Reply 95):
The cgs system does use the gram as it's unit of mass, but then you would have to accept the centimeter as the unit of distance. The SI unit of mass is the Kg. To use the gram would not be logical, or practical. Meters are similarly more convenient than centimeters for distance.

My basic point was that it seems to me that the kilogram should have been called the gram - to bring it in line with the other SI units, where the basic unit doesn't have any prefix (meter, second, liter, etc.). That's always bugged me, and will continue to do so  Smile

Quoting Jetlagged (Reply 95):
At my (English) University they were always referred to as US units.

Hah. That is amusing.

Quoting Jetlagged (Reply 95):
Really? Now that is confusing. The imperial ton is 2240 lbs, which is quite close to the metric tonne (2204.6 lbs).

I had never heard of an Imperial ton until I had a class with a professor who hailed from England. We were probably discussing something very similar to this thread in class - i.e. the difference between units, and he mentioned that he'd always learned a ton as being 2240 lbs. He had some rhyme that he was taught in order to remember 2240 lbs, which I cannot remember.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
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Jetlagged
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 7:31 pm



Quoting Vikkyvik (Reply 97):
My basic point was that it seems to me that the kilogram should have been called the gram - to bring it in line with the other SI units, where the basic unit doesn't have any prefix (meter, second, liter, etc.). That's always bugged me, and will continue to do so

I understand, but that would be even more confusing, and you'd have to rewrite history. If you reclassified the kilogram as a gram, everything written up to now would have to be edited. It seems that when the metric system was drawn up (pre-revolution) the base mass unit was named the grave, and so had no prefix. It was defined as 1000 grams. A gram is the mass of a cc of water, but is too small to be of practical use. Post revolution "grave" was deemed politically incorrect (a nobleman's title) so the name kilogram was adopted.

http://en.wikipedia.org/wiki/Grave_%28mass%29

http://www.bipm.org/en/si/history-si/name_kg.html
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
vikkyvik
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RE: Use Of Metric System In Aviation

Tue Apr 29, 2008 7:43 pm



Quoting Jetlagged (Reply 98):
I understand, but that would be even more confusing, and you'd have to rewrite history. If you reclassified the kilogram as a gram, everything written up to now would have to be edited. It seems that when the metric system was drawn up (pre-revolution) the base mass unit was named the grave, and so had no prefix. It was defined as 1000 grams. A gram is the mass of a cc of water, but is too small to be of practical use. Post revolution "grave" was deemed politically incorrect (a nobleman's title) so the name kilogram was adopted.

Oh trust me, I'm not saying we should change it.

I just wish it was done that way in the first place  Smile

Since basic SI units are all inter-related, a gram would have been the mass of a liter of water. Instead, a gram is the mass of a milliliter of water. Oh well.

Now I suppose I could get REALLY picky and say that a liter should be a meter^3 of water, and a gram should be the mass of a meter^3 of water  duck 

But I'd settle for just having the base units be non-prefixed.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

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