Calculating the scale speed of OO gauge models

[Pete the Elaner]

We are stuck with metric v imperial converstions for the time being.

Like many others, my layout is built to its dimensions because that is how things will fit. I have a tunnel at 1 end of the layout & a bridge at the other, so it makes sense for these to be the timing points. This section is a scale 485' long.

For measuring speed, scale feet is more than accurate enough over this distance, but if I wanted anything more accurate:

If I wanted any more accuracy, working purely in imperial is a problem because it involves lots of fractions. For ease, we all use calculators: 485' in 4mm scale is 6.36482'. So how many inches is 0.36482'? 4.378. What use is this when working in feet, yards or even miles though? I may as well convert it to mm & just move the decimal point around as required.

 

Even within itself, Imperial uses weird conversions all over the place. I've argued with those claiming it makes more sense than metric but most can't even tell me how many yards there are in a mile.

When I tell them it is 1760 they sort of nod, but when I ask them where this figure comes from, I get a real blank look. 1760 is 8 furlongs. 1 furlong is 10 chains & 1 chain is 22 yards.

So 1 mile is 22 x 10 x 8 yards. So how many inches to a mile then? 12 x 3 x 22 x 10 x 8! Does anybody still think that makes sense?

Ok, moving on to weight (actually mass), there are 16oz in 1lb. 1 oz of water is 1 fl oz (hooray, some sense at last). There are 16oz in 1lb, so it makes sense to have 16 fl oz in a pint right? Wrong!. A US pint is 16 fl oz, but there are 20 fl oz in a UK pint.

Moving on to temperature: Celcius defines 0 & 100 as the freezing & boiling points of pure water at normal atmospheric pressure. Normal atmospheric pressure is not the easiest to achieve with absolute accuracy but let's compare it with Farenheit.

0F is the freezing point of water saturated with as much ammonuim chloride as possible. How exactly is this accurately achieved?

It gets worse though...much worse. 90F was body temperature, but this was later changed to 96F..but body temperature is actually 98.6F... so how exactly would a thermometer be calibrated? This condition is completely impossible to re-create. Why was this ridiculous scale ever adopted by anybody?

 

Is it any wonder people choose to convert to metric for speed calculations..or at least decimal yards/miles?

 

[Michael Hodgson]

1 hour ago, melmerby said:

Aircraft elevation is in feet (there is a reason)

 

Yes indeed - counting in undercarriages wouldn't be safe unless they were all the same size.

[Philou]

Close but not quite regarding water and Farenheit - 0° is the freezing point of salted water (I thought it was a saline solution - there you, I learnt something today), but the top of the scale was the boiling point of pure water at 212° (WHY?!!!) and then divided out in between. But hey, you overlooked the Réamur scale which was 0°R (freezing water) but 80°R for boiling water - go figure!

 

Just as an aside, when I worked in labs at the Polytechnic, we had to make a freezing mixture (to be used to cool another experiment at negative temperatures) using rock salt and water and I got my mix down to -45°C - proud of that or what!

 

Cheers,

 

Philip

 

 

[Michael Hodgson]

10 hours ago, The Johnster said:

It has been a long time since I've been to a model railway show here that had a bar.

 

Me too.  It's been a long time since I've been to a model railway without a bar too.

[Michael Hodgson]

2 minutes ago, Philou said:

Close but not quite regarding water and Farenheit - 0° is the freezing point of salted water (I thought it was a saline solution - there you, I learnt something today), but the top of the scale was the boiling point of pure water at 212° (WHY?!!!) and then divided out in between.

 

Actually the top of the scale was 100 degrees, being the temperature of the human body.  OK, so there's a slight discrepancy because their measuring devices weren't all that accurate back then.  And I think they believed that freezing salt water was as cold as you could go.  

[The Johnster]

It is interesting and educational (I, too, have learned something about it today, Philou), but sort of doesn't matter if you are able to use the system you are comfortable with.  Units are units and it doesn't matter what they are so long as they are consistent and a convenient size.  Someone mentioned counting how many sleepers disappear beneath the loco (or emerge from beneath the brake van) in a given period to assess speed.  The unit in this case is the sleeper spacing, and is suitable at low speed but I challenge anyone to be able to assess speed by sleeper count over given time at scale speeds more than about 20mph.

 

I think it is possible to become obsessed (obsessed? railway modellers? Never!!!) with accuracy; for this purpsoe close enough is adequate and super-accuracy is porbably overkill.  Exhaust beats and wheel beats over joints are fine, though you might want to carry out super-accurate experiments to confirm that your assessments are ball park compliant.  One has to take different size driving wheels and bogie wheelbase into account.  Of my stud of GW South Wales locos, most have scale 4'7" driving wheels, and the larger wheels of a Hornby 5101 or smaller ones of the Colliery W4 give very different 'readings'.  Trevithick's Cornwall would be radically different!

[melmerby]

2 hours ago, Pete the Elaner said:

 So how many inches to a mile then? 12 x 3 x 22 x 10 x 8! Does anybody still think that makes sense?

 

63360 and I didn't need to work it out! (It's also a Robinson 8K 2-8-0 which BR gave that number to!)

It's the scale of OS 1" maps before they metricated and became 1:50000

[Steven B]

3 hours ago, The Johnster said:

Grams I can work with but prefer ounces and pounds.  I’d probably manage better if there was a centigram unit but the jump from gram to kilogram fazes me. 

 

The Centigram exists as a unit - just as the centi-litre and centimeter does (1/100th of the main unit).

There's also the decimeter, decilitre and decigram (1/10th of the main unit).

 

Much less confusing that Imperial! (three feet = 1 yard, three pints = ? - not yet a hang-over perhaps?)

 

Steven B.

[Reorte]

For all the supposed complexity of the Imperial system most people who seem to complain strongly about it appear simply to not be used to it. It's generally easy working with whatever you're used to; quite often you don't change which set of Imperial units you use (e.g. inches to miles) so it doesn't really matter how many of one go in to the other. Funny how metric's advocates never seem to get worked up about 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, 7 days in a week, differing number of days in a month...

 

So I continue to regard any push to metric as change for the sake of change, but just use whatever's convenient at the time.

 

Oh, and if you're going to get worked up about changing a definition of an inch in terms of metres it should be pointed out that the definition of metric and SI units has changed over time (most recently the kilogram - come to think of it, if we're being "logical" about it then the base unit wouldn't have the kilo- prefix).

[Michael Hodgson]

4 hours ago, The Johnster said:

I use Imperial for weights and distances, and Fahrenheit for temperature, because those units are embedded in my brain, and I think in them.  If somebody describes a thing as 15 feet long I can visualise that instantaneously, and I know straight away how an air temperature of 65 degrees Fahrenheit will feel in a 25mph breeze.  
 

I an starting to be able to do this with Celsius temperatures now after living with the Squeeze, who is Polish, for 3½ years.  Metric weights and distances are proving more resistant!  Metric is a far more logical system and easier to work with, and I do find it convenient to use millimetres and centimetres in modelling, as I understand the concept of 4mm representing a foot better than the fraction of 1/76th, but when it comes to kilometres I have to stop and do a rough mental conversion, and kilograms mean nothing to me.

 

Grams I can work with but prefer ounces and pounds.  I’d probably manage better if there was a centigram unit but the jump from gram to kilogram fazes me. 

Me too.  My gut is calibrated in pints.  There's 32 quarts to a bushel.

 

There's a lot to be said for the old measures ... used for some of the finest architecture around, and the barrel was a very practical unit of measurement.

https://stpancras.com/history/built-on-beer 

Note the delivery in shock wagons .. you don't want your pint to be all head and no beer.  

 

 

 

[Il Grifone]

I'm quite used to the imperial system - I grew up with it; the metric system wasn't even mentioned until our third year at school!

Conversely the metric system is logical and easy to convert from one unit to another - 1000 cubic centimetres of water* is one litre and weighs one kilogram.

IMHO the imperial system became obsolete the moment the metric system was invented. (Perhaps if it had not been French?) After much discussion, the conversion was set at one inch equals 25.4 millimetres. Had they chosen 25 millimetres it would have saved much trouble!

* Specified as regards temperature and atmospheric pressure, but irrelevant for normal use.

 

BOT

Scale speed is the full size speed divided by the scale (1:76.2 for 00). 100mph is approximately 2ft/60cm per second.

Philosophical considerations due to compressed distances are a matter for discussion....

 

P.S. What the **** is a bushel? I know it exists (like the rod, pole or perch) but it's a meaningless thing to me

Edited April 19, 2021 by Il Grifone

[Pete the Elaner]

7 minutes ago, Reorte said:

For all the supposed complexity of the Imperial system most people who seem to complain strongly about it appear simply to not be used to it. It's generally easy working with whatever you're used to; quite often you don't change which set of Imperial units you use (e.g. inches to miles) so it doesn't really matter how many of one go in to the other. Funny how metric's advocates never seem to get worked up about 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, 7 days in a week, differing number of days in a month...

 

So I continue to regard any push to metric as change for the sake of change, but just use whatever's convenient at the time.

 

Oh, and if you're going to get worked up about changing a definition of an inch in terms of metres it should be pointed out that the definition of metric and SI units has changed over time (most recently the kilogram - come to think of it, if we're being "logical" about it then the base unit wouldn't have the kilo- prefix).

No, the reverse is true. The move to metric is not for the sake of it.

We only cling on to imperial units because we are used to using them. They are really poor to use & my example of how many yards are in a mile highlights this. The number of people who have no idea what makes up 1760 never fails to amuse me. When asking people face to face, I have never met somebody who knows.

 

Here is another example:

Many years ago, I went to photograph a black 5 at my local main line station. I was with my father. He read the 4000 gallon tender capacity & remarked 'how much would that weigh'.

I don't know what calculations he had to make in his head, but I knew there are 4.54 litres in a gallon. Each litre weighs a kilo & there are 1000 kilos to a tonne. A ton is fairly similar to a ton.

4000 x 4.5 is 18000kg or 18 tons. That took me about a second.

Try doing the imperial maths that quickly.

 

Metric is easier to work with. a 14mm spanner is smaller than a 15mm one. Easy. A 17/32 is smaller than a 9/16. That takes a little more thinking & can allow an error to creep in.

I always use the example of getting from a yard to a mile. 22*10*8 is crazy & what do those terms mean anyway?

Metric uses standard terms & you only need to know 1 unit for any dimension, whether that is metre, gram, volt, amp, second. Kilo is 1000 times bigger, mega is 1000 times bigger than that, gig is 1000 times bigger than that.

Going the other way, milli is 1000 times smaller, micro is 1000 times smaller than that, nano is 1000 times smaller again, pico is 1000 times smaller.

 

[Pete the Elaner]

1 minute ago, Il Grifone said:

I'm quite used to the imperial system - I grew up with it; the metric system wasn't even mentioned until our third year at school!

Conversely the metric system is logical and easy to convert from one unit to another - 1000 cubic centimetres of water* is one litre and weighs one kilogram.

IMHO the imperial system became obsolete the moment the metric system was invented. (Perhaps if it had not been French?) After much discussion, the conversion was set at one inch equals 25.4 millimetres. Had they chosen 25 millimetres it would have saved much trouble!

* Specified as regards temperature and atmospheric pressure, but irrelevant for normal use.

 

BOT

Scale speed is the full size speed divided by the scale (1:76.2 for 00). 100mph is approximately 2ft/60cm per second.

Philosophical considerations due to compressed distances are a matter for discussion....

 

There is a logic to the length of a metre: 10000km is 1/4 of the circumference of the earth. I am guessing they wanted the base length (1 metre) roughly equivalent to 1 yard.

1 cubic metre of water has a mass of 1 tonne, or 1 megagramme, or 1000 kilogrammes, but since this is close to an imperial ton, why not call it a tonne?

 

A UK hundredweight is 112 pounds. What?????????????????????????

What lunatic defined that?

 

I was bought up to understand both imperial & metric. The more I learn about imperial, the more I am convinced it is crazy collection of inconsistent dimensions which should have been dumped years ago.

[Il Grifone]

I saw quoted the length of a standard Ferrovie dello Stato rail as 39 feet*. I'm sure the actual length is 39.37 feet = 12 metres.

* I'm sure nobody is interested where. Once upon a time; it's all welded now.

 

The pound is popular with traders, because it's smaller than half a kilo....

 

Edited April 19, 2021 by Il Grifone

[Pete the Elaner]

5 minutes ago, Il Grifone said:

I saw quoted the length of a standard Ferrovie dello Stato rail as 39 feet*. I'm sure the actual length is 39.37 feet = 12 metres.

* I'm sure nobody is interested where. Once upon a time; it's all welded now.

 

The pound is popular with traders, because it's smaller than half a kilo....

 

 

& pints are popular at the pub because they are larger than half litres...although most bottled beer is now sold in half litres.

[Michael Hodgson]

A country mile is officially ten furlongs (2200 yd). 

A foreign country mile may be different though - for example a Swedish mile is a bit over six statute miles, officially now 10km.

[frobisher]

46 minutes ago, Reorte said:

Funny how metric's advocates never seem to get worked up about 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, 7 days in a week, differing number of days in a month...

 

That's because the second is the only important unit with regards to time, the rest are somewhat arbitrary but are all defined in terms of the second.

 

 

[Reorte]

The more I hear of people saying "imperial should've been abandoned years ago" the less convinced I am

 

As for the "why not make the inch 25 mm?" question, that would deviate quite quickly from everything done in inches beforehand, whereas the difference in 25.4 mm are insignificant in most cases. Sometimes definitions change for whatever reason, but the goal is to usually avoid deviating too much from the previous size, e.g. why the metre is defined in terms of the speed of light and a rather arbitrary-seeming fraction of a second. The most recent redefinition was the kilogram in 2019, to move it away from being defined by the mass of an arbitrary lump of metal to being defined by fundamental physical constants. In virtually all practical considerations the difference in definition made no noticeable change; the definition was chosen to fit the previous size (presumably to within a certain degree of error - when the old measure is a particular physical object there will always be limits to which the accuracy of anything else can be compared with it).

 

Edited April 19, 2021 by Reorte

[Reorte]

7 minutes ago, frobisher said:

 

That's because the second is the only important unit with regards to time, the rest are somewhat arbitrary but are all defined in terms of the second.

How's that different from the imperial length measures?

 

Come to think of it, the grad never caught on either, leaving us with 360 degrees in a circle, or 2 pi radians (mathematically very convenient but hard for mental arithmetic and visualisation, and certainly not a metric-type approach).

Edited April 19, 2021 by Reorte

[Il Grifone]

The German inch (Zoll) was different depending in which part of Germany one lived (also in how many made a foot). Understandably they standardised on the metre!

 

The first town one comes to entering Italy from France on the Riviera is Ventimiglia (20 miles). I've never been able to find out from where it's supposed to be 20 miles.

 

EDIT

According to Wikipedia, it's a corruption of the original name and nothing to do with distance , but is about twenty nautical miles from Nice. (Another imperial inconsistency!)

 

There's a video on Youtube about why we don't have metric time, but I could never be bothered to watch it.

 

Incidentally the metric multiples are Greek greater than one and Latin smaller than one. Useless information....

Edited April 19, 2021 by Il Grifone

[frobisher]

1 hour ago, Steven B said:

The Centigram exists as a unit - just as the centi-litre and centimeter does (1/100th of the main unit).

There's also the decimeter, decilitre and decigram (1/10th of the main unit).

 

More correctly, the decimetre if you're saying decilitre...

[frobisher]

2 minutes ago, Reorte said:

How's that different from the imperial length measures?

 

One's a measure of time, and the other's are measures of distance. 

 

Anyway, as it stands, they do not form a fundamental part of either the Metric or Imperial systems.

 

[melmerby]

50 minutes ago, Pete the Elaner said:

 

Here is another example:

Many years ago, I went to photograph a black 5 at my local main line station. I was with my father. He read the 4000 gallon tender capacity & remarked 'how much would that weigh'.

I don't know what calculations he had to make in his head, but I knew there are 4.54 litres in a gallon. Each litre weighs a kilo & there are 1000 kilos to a tonne. A ton is fairly similar to a ton.

4000 x 4.5 is 18000kg or 18 tons. That took me about a second.

Try doing the imperial maths that quickly.

 

 

 

A gallon (imperial not US!) of water weighs 10lbs

Therefore 4000 galls weighs 40000lbs. To convert to tons 40000/2240 which is about 18 tons, just as easy.

Mind you that is one of the few imperial measurements that are easy!

Edited April 19, 2021 by melmerby

[melmerby]

22 minutes ago, Il Grifone said:

According to Wikipedia, it's a corruption of the original name and nothing to do with distance , but is about twenty nautical miles from Nice. (Another imperial inconsistency!)

 

 

The Nautical mile has nothing to do with the imperial mile (apart from the name), being a subdivision of the circumference of the earth being 1 minute (sic) of latitude along a line of longitude.

It is now defined as exactly 1852 metres

[The Johnster]

This seems to be one of those polarising subjects where entrenched opinions are wont to clash.  I have a suspicion that much support for Imperial units is rooted in a longing for the Imperial past, storms in channel Continent isolated, British is best sort of thing.  I use Imperial because I’m used to it, it’s my comfort zone, but accept that metric is the superior system. 
 

This sort of prejudice probably goes back to the horrors of the French Revolution and the subsequent Napoleonic wars; there was still a residual element of Boney as a boogie man when I was at school in the 60s.  He was no saint, but no Hitler either, though my history teachers seemed to consider them as on a par.  Still an element of thinking that anything as European as the Metric system was fundamentally capital B Bad, and an assault on some sort of mythical British dammit Carruthers way of life.  One sees the same thing with identity cards, a very sensible and rational idea that would be political suicide here.