Why does aviation still use imperial system?

[Head in the clouds]

The metre was born of the "International Metre Commission" in 1870-1872, which then led to the creation of the BIPM (International Bureau of Weights and Measures) and in turn, SI units.It is by definition metric, .....

Actually, no. The French Academy of Sciences chose the first definition of the metre from a choice of the Paris/Pole/Meridian method and the pendulum method way before then, in 1791. The new platinum/iridium definition came from the BIPM nearly 100 years later with the '1874 Alloy' revised again five years or so later and adopted at the CGPM (General Conference Weights and Measures) and revised again about forty years later to make a small correction.

 

The Alloy definition was then replaced in the 1960s with the all-new Krypton wavelength definition and then in the 1980s it was again replaced with another completely unrelated definition, this time the distance of light travelled in a vaccuum in a specified period as I mentioned above.

 

Not that any of that really matters, except to demonstrate that the metre is not something that's ten, or a tenth, of anything else, so it, itself, is not a metric quantity.

 

As far as the inch being more appropriate for machine engineering, I'd be interested if you could get support for that contention from the engineering powerhouses of Germany. Or Russia. Or anywhere else except countries which have clung to imperial measurements! Maybe the Germans were never so crash hot at machine engineering after all?

The Germans are exceptional engineers, both structural and machine. To paraphrase a well known engineer's creed - 'if you are ever unsure about your design, just ask yourself "would the Germans do it that way"'.

 

However their excellence may rather be a case of 'despite the metric measuring system, rather than because of it'. While in Africa, and also in Australia I got to know a lot of ex-patriot German engineers, toolmakers and machine, and without exception they work using the imperial measures rather than their native metric - YMMV of course.

 

The Russians may well also have been at something of a disadvantage using metric for machining measurement. Other than in very specialised areas like their early space program it took their general industry longer than most developed nations to establish reasonable universal precision. For the most part they built bigger, heavier and stronger but much less precisely.

 

 

[facthunter]

The Imperial one grew like topsy from merchants I believe. It's not really a logical system more random than organised. Even the Brits have shown millimetres in auto sizes. for a long time The yanks will pay eventually for dragging their feet. At the changeover point it's a nightmare.

 

With parts Coded parts (selective fitting) are usually in half thou increments and you run four, so that ranges over a total of 2 thou. This is on things like Pistons, but done lees than it used to be

 

Fractions of a thou are common. Usually done in tenths (except for half) This is to define running clearances, usually in ball or roller bearing applications.

 

Some rollers are supplied in increments of 2 tenths of a thou from .0004 under to .0006 over the nominal size, giving a total range of a thousanth of an inch, overall. I think what you get used to is what determines you preference. 3937 is the conversion figure. Most round it out to 40 making 25mm same as one inch but it isn't. Nev

 

 

[Old Koreelah]

You have a totally different measurement for 1nm than what I use old K:what the:

Whoops. 60nm=1 degree.

 

 

[Soleair]

When I was studying Engineering at college, we used units like slugs and poundals. Just so much more interesting than boring old kilograms and joules.

 

 

[Gnarly Gnu]

 

(Just posted for a chuckle, I only follow Celsius temps).

 

 

[dutchroll]

When I was studying Engineering at college, we used units like slugs and poundals. Just so much more interesting than boring old kilograms and joules.

Yeah when I did aerodynamics at Uni we used slugs as well. We had an old lecturer who clung vehemently to imperial measurements (I'm almost certain that a portrait of the Queen must've adorned his dining room at home) on the basis that "a foot is divisible by lots of whole numbers" which struck me as a grossly illogical argument because there are plenty of imperial units which are not, and there's no consistency whatsoever between the number of "sub-units" per "unit" anywhere across the imperial measurement system.

 

 

[fly_tornado]

so can anyone explain the wire guage thing?

 

 

 

[kasper]

so can anyone explain the wire guage thing?

Yes - its a quaint and charming hangover of a bygone age where ragamuffins ran along the rails and collected fallen coal sell to feed their dear sick mothers.

It just like Whitworth threads - something to give you that warm inner glow if you are the nostalgic type and something to give you an increased risk on a burst blood vessel if you have to bloody well deal with ANOTHER set of incompatible systems on an airframe - and yes, one of the airframes I have has tubes that are specified in SWG so this is one of my blood pressure builders.

 

And for fun OTHER wire gauges are available AWG not the same as SWG

 

 

[fly_tornado]

one of the problems I have come across with my Tornados is the small imperial nuts and bolts they look like m3 and m2 but they aren't.

 

 

[Oscar]

Yeah when I did aerodynamics at Uni we used slugs as well. We had an old lecturer who clung vehemently to imperial measurements (I'm almost certain that a portrait of the Queen must've adorned his dining room at home) on the basis that "a foot is divisible by lots of whole numbers" which struck me as a grossly illogical argument because there are plenty of imperial units which are not, and there's no consistency whatsoever between the number of "sub-units" per "unit" anywhere across the imperial measurement system.

Curiously, the Japanese - a metric country, mostly - paid homage to the mighty slug. The Toyota Tiara was one such expression.

 

It always amused me, that the quintessential English Gentleman's land possession was often measured in roods. Perches for the pheasants I could understand, but presumably Roods was used as a quantification of the surly peasants.

 

 

[facthunter]

Wheel spokes are done in Gauge sizes. Try BA threads for logic. Nev

 

 

[Oscar]

Wheel spokes are done in Gauge sizes. Try BA threads for logic. Nev

BLOODY BA.... I was 'bequeathed' a vast quantity of BA taps from an old mate who used to be an instrument maker at CSIRO - probably more than 100 of the buggers - ranging in size from 4BA ( I think, never really audited them) down to things that could do intensely personal things to female mosquitos without permanent harm. I tried to sort them out into sizes and gave up when I couldn't bloody read the size markings with a jeweler's magnifying glasses headband.

 

Mind you, I have certain intellectual difficulties in automatically selecting number drills as well. Please, somebody help me: from where would the idea to have started at #1 as 0 .2280" have sprung? Yes, I know it was derived from the Stubs Wire Gauge, but Who TF was Stubbs?, and why was his decision on sizes adopted by anybody? NO bloody number drill has anything but a slap-and-tickle relationship with inches OR mms, other than maybe at the end of a desperate drinking session in the last bar open in town. At least Letter drills start of with A and work their way up....

 

 

[dutchroll]

Wheel spokes are done in Gauge sizes. Try BA threads for logic. Nev

There you go again.

Using "British" and "logic" in the same sentence.

 

 

[DrZoos]

It is / was hard enough to get yanks to read and write once, without asking half educated adults to convert what they know to a logical and better system. Until then the world will remain semi metric... Despite the obvious advantages of a metric system..

 

 

[facthunter]

The AN aircraft system is good. It's about the only dependable system available to us here. Nev

 

 

[Old Koreelah]

Wrong thread, probably been on here before, but can't resist:

 

*Army Pipe Specification*

 

1. All pipe is to be made of a long hole surrounded by metal or plastic centred around the hole.

 

2. All pipe is to be hollow throughout the entire length - do not use holes of different length than the pipe.

 

3. The ID (inside diameter) of all pipe must not exceed the OD (outside diameter) - otherwise the hole will be on the outside.

 

4. All pipe is to be supplied with nothing in the hole, so that water, steam or other stuff can be put inside at a later date.

 

5. All pipe should be supplied without rust; this can be more readily applied at the job site

 

Note: Some vendors are now able to supply pre-rusted pipes. If available in your area, this product is a recommended thing, as it will save a great deal of time at the job site.

 

6. All pipe over 500 ft in length should have the words "LONG PIPE" clearly painted on each side and end, so the contractor will know it's a long pipe.

 

7. Pipe over 2 miles in length must also have the words "LONG PIPE" painted in the middle so the contractor will not have to walk the entire length of the pipe to determine whether or not it is a long pipe or a short pipe.

 

8. All pipe over 2 metres in diameter must have the words "LARGE PIPE" painted on it, so the contractor will not mistake it for a small pipe.

 

9. Flanges must be used on all pipe - flanges must have holes for bolts, quite separate from the big hole in the middle.

 

10. When ordering 90 degree or 30 degree elbows, be sure to specify left-hand or right-hand, otherwise you will end up going the wrong way.

 

11. Be sure to specify to your vendor whether you want level, uphill or downhill pipe - if you use downhill pipes for going uphill, the water will flow the wrong way.

 

12. All couplings should have either right-hand or left-hand threads, but do not mix the threads, otherwise, as the coupling is being screwed on one pipe, it is being unscrewed from the other.

 

13. All pipes shorter than 25 millimetres are very uneconomical in use, requiring many joints - they are generally known as washers.

 

14. Joints in pipes for piping water must be water-tight - those in pipes for compressed air, however, need only be air-tight.

 

15. Lengths of pipes may be welded or soldered together - this method is not recommended for concrete or earthenware pipes.

 

16. Other commodities are often confused with pipes - these include: conduit, tube, tunnel and drain. Use only genuine pipes

 

17. Pipes with rifling in them to temporarily store projectiles while they are enroute the target must be marked “FOR MILITARY USE”

 

 

[DrZoos]

OK , i haven't seen that one, its GOLD

 

 

[Oscar]

OK, you just HAD to bring pipe into this conversation, didn't you?

 

Because that opens up the whole issue of pipe thread specifications: BSP. BSPT. NPT. NPTF. NPTM. JIS. AN. And no doubt, there is at least one, adopted by the UK Guild of Greengrocers and the Latvian Plumbers Collective, that involves hand-carved taps and dies to a specification that is a trade secret.

 

The whole problem, is engineers. Let an engineer loose to develop a standard and the bugger will INVARIABLY decide on something different from what everybody else has used. It's in their DNA.

 

I have three aero-engineers in my family, and I have to carry around a length of (thin-walled, as a gesture towards humanitarianism) lead pipe when I visit them, in order to beat them into submission over the details of any designed thing that I actually build for them.

 

Nowadays, when they want things made for them ( e.g. engine test facilities), I require them to state what the thing they want built has to DO, and them tell them to bugger off so I can get on with it. It was either that, or having to stake them to individual anthills and suffer the noise of debate over the type of stakes used, the wire specification, the chemical composition of the ant attractant medium - it goes on...

 

 

[Head in the clouds]

A bit earlier FT asked about wire gauges and people have spoken about the merits, or lack of, of the various thread-forms (which are widely misunderstood). On other forum threads the reasons for the use of different materials, fatigue, metallurgy, drills, drilling, cutting edges, all sorts of matters that have direct relevance to our sport are something of a mystery to many of those of us who participate.

 

For those who seek to learn about all this and much, much more, there is the Machinery's Handbook. It is the 'Bible' for Mechanical Engineers, Draftsmen, Toolmakers and Machinists. It has been published continuously for over 100 years since 1914 and gets bigger each year. It's now on its 30th edition. Interestingly it's getting cheaper, when I got my first one about 35 years ago it cost $140, now it's about $70 and you can get used ones for under $60 from Amazon. Occasionally you can pick up a good used one from a second-hand book shop for $10-20 if you're lucky.

 

My first two got souvenired by people who must have needed them more than I did, so currently I'm using one passed on to me by my old toolmaker mate Bazza who passed away last year. It is the nineteenth edition and was printed in 1973 and has 2500 pages. Newer ones do have a little more information in them (the current edition has 3000 pages) but the older ones have almost anything we'd ever dream of needing or wanting to know about, so don't pass it up if you spot one on a dusty bookshelf.

 

I've posted a few pictures below which show the Contents Headings, if you can read them in the images.

 

 

 

 

 

 

 

 

[SDQDI]

If you all think pipe threads are confusing you should have a look at some of the threads on recreational flying.com:teacher:

 

 

[DrZoos]

What about the nuts on RecFForum, now there's quiet a few of them...and some nutless nuts as well..

 

 

[coljones]

How do you go adding fractions of an inch. I used to have a calculator just for that. One of those card things with a rotating wheel. In the end I found it easier to convert to mm and do the addition.

you could always convert to decimal.

If the frogs were real mathematicians they would have declared the metre to be 1/2000 of a nautical mile rather than a very poor approximation of the distance from Paris to the north pole (or was it the length of the kings hip).

 

Base 12 is actually very good because it is much easier to package a dozen (4x3, 6x2) than decimal (only 5x2) and 1/8ths are easy to estimate - just keep folding in half - very hard to do for 10ths

 

 

[DrZoos]

If they made a mm 1.60934 mm in length they could have saved us a lot of headaches

 

 

[spacesailor]

And Still NO "Metric Time" comments.

 

ARE you all too scared to look it up?.

 

The French refused to use it.

 

spacesailor

 

 

[Himat]

you could always convert to decimal.If the frogs were real mathematicians they would have declared the metre to be 1/2000 of a nautical mile rather than a very poor approximation of the distance from Paris to the north pole (or was it the length of the kings hip).

 

Base 12 is actually very good because it is much easier to package a dozen (4x3, 6x2) than decimal (only 5x2) and 1/8ths are easy to estimate - just keep folding in half - very hard to do for 10ths

No, base 12 is difficult when counting on the fingers, base 8 is quite easy even with 10 fingers.

 

If the meter was a fraction of the nautical mile would have been a good idea.