JayinKitsap wrote:

I saw in a post that the F-15 and F-16 are all in imperial sizes and dimensions. I am sure the US made aircraft from old (like the B-52 & KC-135) are Imperial sizes but the US Federal Government starting in the 80's tried to change all of its construction projects to metric, after two decades of trying they gave up and went back to Imperial there, but all of the flow meters, pressure transmitters, and industrial equipment is totally metric. Car production around then went metric, I believe Cat has been metric for 40-50 years.
So which aircraft are still Imperial dimensions and which are metric. I would venture the B-737 could be Imperial, but I expected Metric. I would be blow away if the 787 wasn't metric. Positive the F-35 is metric. Is the F-15 Imperial.

Does the instrumentation change from Imperial for WN to Metric for EK? Settable in the cockpit? Do flight computers use kg or lb for weights of fuel, etc?

bluecrew wrote:

JayinKitsap wrote:

I saw in a post that the F-15 and F-16 are all in imperial sizes and dimensions. I am sure the US made aircraft from old (like the B-52 & KC-135) are Imperial sizes but the US Federal Government starting in the 80's tried to change all of its construction projects to metric, after two decades of trying they gave up and went back to Imperial there, but all of the flow meters, pressure transmitters, and industrial equipment is totally metric. Car production around then went metric, I believe Cat has been metric for 40-50 years.
So which aircraft are still Imperial dimensions and which are metric. I would venture the B-737 could be Imperial, but I expected Metric. I would be blow away if the 787 wasn't metric. Positive the F-35 is metric. Is the F-15 Imperial.

Does the instrumentation change from Imperial for WN to Metric for EK? Settable in the cockpit? Do flight computers use kg or lb for weights of fuel, etc?

Can't speak to the design blueprint stuff. I would assume anything recent would have a multitude of measurements available, as they've all been designed with computers. That data is available in every imaginable unit.

Obviously, for InHg/HPa, it's a toggle on any newer avionics. To change between kg/lb or ft/m, it's probably just a software update, just a little update to the box. Meters are a switch in the FD, depends on the airplane though. You'd never convert the avionics to meters only though - only two countries (afaik) use them. More efficient to use a conversion table at that point, or fly the FL+1 model from China.

Also, flying in China is terrifying, if the opportunity comes, don't do it.

M564038 wrote:

Everything in aircraft are in metric. Everything.

JayinKitsap wrote:

Does the instrumentation change from Imperial for WN to Metric for EK? Settable in the cockpit? Do flight computers use kg or lb for weights of fuel, etc?

fr8mech wrote:

M564038 wrote:

Everything in aircraft are in metric. Everything.

Sure, but all the 12.7mm nuts and bolts are easily removed or installed with a 1/2inch wrench/socket.

Thrusty69 wrote:

My Snap-On 1/2” socket is clearly engraved with “1/2-12.7” right on it. Swear to god. … …

Starlionblue wrote:

I'll nitpick.

Those units are not "Imperial". They are "US Customary".

e38 wrote:

JayinKitsap wrote:

Does the instrumentation change from Imperial for WN to Metric for EK? Settable in the cockpit? Do flight computers use kg or lb for weights of fuel, etc?

The software is installed per the operating specifications of the individual airline. In most cases, the parameters are set and cannot be changed without a modification to the software. At my company, weights are in pounds (lbs), altitude in feet, speed in knots, distances in nautical miles (n.m.), etc.

The only parameter we can adjust in the flight deck (Airbus A320 series) is altimeter setting. There is a knob that can switch between in Hg and hPa.

We use charts/calculators for items that may require a conversion; for example, gallons to pounds (fuel).

e38

Thrusty69 wrote:

Jay, there’s no metric on airliners. You may have missed the jokes. No mechanic anywhere working on airliners has metric tools anywhere.

Thrusty69 wrote:

Jay, there’s no metric on airliners. You may have missed the jokes. No mechanic anywhere working on airliners has metric tools anywhere.

WesternDC6B wrote:

Something that has passed through my mind a time or two, so, here goes.

BACKGROUND: I seem to recall some Imperial/Customary-based hardware that was called "Whitworth". Sears's Craftsman Tools offered Whitworth wrench (spanner) and other such tools sets.

THE QUESTION: Did Armstrong-Whitworth, or anyone else, use Whitworth hardware?

M564038 wrote:

Well, that sounds about right.
1/2 inch is just funny phrase for 12.7mm anyway.

Tristarsteve wrote:

We used whitworth spanners on the Vickers Viscount and Vanguard when I started at BEA at LHR in 1969. I had loads of Whitworth spanners, but never used them since.

WesternDC6B wrote:

M564038 wrote:

Well, that sounds about right.
1/2 inch is just funny phrase for 12.7mm anyway.

I prefer metric for mass. In customary I am 269, but in SI I'm a slim, trim 122.

WesternDC6B wrote:

M564038 wrote:

Well, that sounds about right.
1/2 inch is just funny phrase for 12.7mm anyway.

I prefer metric for mass. In customary I am 269, but in SI I'm a slim, trim 122.

Thrusty69 wrote:

My Snap-On 1/2” socket is clearly engraved with “1/2-12.7” right on it. Swear to god. … …

Thrusty69 wrote:

Jay, there’s no metric on airliners. You may have missed the jokes. No mechanic anywhere working on airliners has metric tools anywhere.

celestar345 wrote:

Thrusty69 wrote:

My Snap-On 1/2” socket is clearly engraved with “1/2-12.7” right on it. Swear to god. … …

Never seen any metric equivelent on my snap-on set... are yours custom made?

Thrusty69 wrote:

Jay, there’s no metric on airliners. You may have missed the jokes. No mechanic anywhere working on airliners has metric tools anywhere.

The trim panel above entry doors on a 787 is fastened with 3mm hex drive - it's even mentioned in the AMM.

phugoid1982 wrote:

Oh my goodness. I just had nightmares about a Professor who studied at Caltech giving us mixed units problems in my Aero Engineering ugrad. Seriously, slugs as a unit of mass? Pound mass vs pound force. SI was just simply more elegant. Unfortunately, having grown up in the US I do think in the so called imperial units. Hard for me to think in meters and km/hr. That can be overcome with time I guess

phugoid1982 wrote:

Oh my goodness. I just had nightmares about a Professor who studied at Caltech giving us mixed units problems in my Aero Engineering ugrad. Seriously, slugs as a unit of mass? Pound mass vs pound force. SI was just simply more elegant. Unfortunately, having grown up in the US I do think in the so called imperial units. Hard for me to think in meters and km/hr. That can be overcome with time I guess

phugoid1982 wrote:

Oh my goodness. I just had nightmares about a Professor who studied at Caltech giving us mixed units problems in my Aero Engineering ugrad. Seriously, slugs as a unit of mass? Pound mass vs pound force. SI was just simply more elegant. Unfortunately, having grown up in the US I do think in the so called imperial units. Hard for me to think in meters and km/hr. That can be overcome with time I guess

gtae07 wrote:

I was an AE major, too. Our professors used both--one problem would be in metric, the other in US units. I like that approach; keeps you fluent in both. Except orbital mechanics; that's the only place in the AE school that was all-metric.

I now work at a well-known aircraft OEM. Everything is in US/imperial units. The drawings/models, the hardware, the stock thicknesses of material, and more. It works just fine. And contrary to popular belief, we still use decimals (many people seem to think that inches can only be expressed in fractions...). The kit airplane I'm building is all imperial, too. I think the only metric fasteners are the nut holding the alternator pulley on the shaft, and the battery terminal screws.

I can work in metric--math is math--but I find it a lot harder to *think* in metric. But that's probably because I've spent most of my life designing, fixing, building, and operating things in imperial units.

flipdewaf wrote:

I once heard it said that if you invent/commercialise a technology then you get to choose the technical language around it, including the units…

Fred

M564038 wrote:

It’s like, everything else equal, counting 0.9, 2.5, PI, 5.5, 7.7, 9.3, 11.5 instead of 1-10 and insisting it is a completely equal, practical alternative to regular counting of how many eggs you have left in the fridge.

gtae07 wrote:

M564038 wrote:

It’s like, everything else equal, counting 0.9, 2.5, PI, 5.5, 7.7, 9.3, 11.5 instead of 1-10 and insisting it is a completely equal, practical alternative to regular counting of how many eggs you have left in the fridge.

That's a poor analogy, not least of which because eggs are countable items, not dimensions of arbitrary length. If I'm working in inches and such, it's all still practical. Especially on the aero engineering side, we do all the designing in decimal inches and don't insist on trying to divide feet by 10. We also don't dig up absurd units (the tired old "furlongs per fortnight as one example :roll: ), nor do we insist on using fractions everywhere. Or do you think we design to standard metric sizes and use inches out of spite?

Yes, metric is computationally convenient if you wish to convert between different units of the same dimension (length, mass, etc). Beyond that there is no inherent advantage or superiority--a centimeter is not inherently "better" than an inch, a gram is not inherently "better" than a slug, Kelvins are not inherently "better" than Rankine, any more than two is inherently "better" than five. Both are arbitarily-defined units of measure, and one is not inherently superior (morally or otherwise) because one happens to be originally based off some poriton of the earth's circumference, or off the boiling and freezing points of water at standard earth atmosphere, rather than some other equally-arbitrarily-chosen thing. Go anywhere else in the universe and those reference points are meaningless. Even the sacrosanct base 10 numbering system we use day-to-day is just an artifact of the standard number of digits on our hands--an alien culture with 12 digits on their primary manipulating limbs would probably find inches and feet an entirely sensible system and would think we're crazy for trying to use base 10 everywhere.

If you stick to one unit system it really is transparent to the user. You can work just as effectively in one as you can in the other.

As for why the US hasn't switched... two factors, I think:
1. Primacy of educaton - people are typically going to be resistant to changing away from that which they learned and used first. And even when you learn a different system, unless you are constantly using the new one in a variety of situations, you wind up continually doing mental conversions to get that intuitive grasp of "what does that physically look like?".
2. Existing industrial standards - trying to switch to new standards is a massive undertaking. The capital investment in machinery and equipment (sawmills for wood, all manner of fastener production, standard sheetmetal sizes, tubing forms, etc) is enormous and most of that can't simply be reprogrammed at will. Construction in the US is heavily built around "dimensional lumber" ("2-by") and 4ft by X products (drywall, plywood/OSB, etc). Cinderblocks are a standard 8x16 size. Plumbing is in inch sizing. Building codes are standardized around these materials, and the prescriptive building codes are all based on those materials.

In the aerospace industry the fasteners, sheet sizes, material allowables, and more are all based on US/customary/imperial units. The entire supply chain for decades' worth of aircraft production is based on that, to avoid having to requalify all of your materials and go through ridiculous import troubles and supplier difficulties, everyone keeps using this hardware.

As for why these things stuck around in the US in particular... I suspect a lot of it has to do with the post-WWII era. The US industrial machine (and the US mainland itself) did come under direct attack during the war. Unlike almost all the other combatants, the US came out of the war with a massive and undamaged industrical base, a strong economy, and little to no basic rebuilding of social infrastructure required. We got a huge head start in the aerospace field because of that, and by the time other nations were able to catch up the units we were using at the time were entrenched.

gtae07 wrote:

I was an AE major, too. Our professors used both--one problem would be in metric, the other in US units. I like that approach; keeps you fluent in both. Except orbital mechanics; that's the only place in the AE school that was all-metric.

I now work at a well-known aircraft OEM. Everything is in US/imperial units. The drawings/models, the hardware, the stock thicknesses of material, and more. It works just fine. And contrary to popular belief, we still use decimals (many people seem to think that inches can only be expressed in fractions...). The kit airplane I'm building is all imperial, too. I think the only metric fasteners are the nut holding the alternator pulley on the shaft, and the battery terminal screws. I can work in metric--math is math--but I find it a lot harder to *think* in metric. But that's probably because I've spent most of my life designing, fixing, building, and operating things in imperial units.

gtae07 wrote:

2. Existing industrial standards - trying to switch to new standards is a massive undertaking. The capital investment in machinery and equipment (sawmills for wood, all manner of fastener production, standard sheetmetal sizes, tubing forms, etc) is enormous and most of that can't simply be reprogrammed at will. Construction in the US is heavily built around "dimensional lumber" ("2-by") and 4ft by X products (drywall, plywood/OSB, etc). Cinderblocks are a standard 8x16 size. Plumbing is in inch sizing. Building codes are standardized around these materials, and the prescriptive building codes are all based on those materials.

Aquila3 wrote:

Well i have this problem.
I work now for an EU company that produces machines with some parts made in US.
So i have to carry always both toolsets when i have to fix something.
Inches and feet are not a problem, but one thing throws me out, and that is gauge of the screws.
A 6-32 x 3/8 would be gauge 6 screw with 32 threads per inch, 3/8 long.
But why gauge 6?
How I find out a gauge 6 from a gauge 4? I mean metric screws i can measure them (if i really need to) with a caliper and be sure this is M3 or a M4 . But even with caliper in inches (they have almost always both scales) I cannot get gauges.
Is there a practical way? Do you look at the socket size or hex head size?
Is a gauge 12 always double diameter of a gauge 6 or is it completely arbitrary?
Why don't you use simply 1/8 and 5/32 screws like we do for M3 and M4 ?

kalvado wrote:

Small inch threads like 1/8 are taken by pipe threads, and you don't want to add them to the mess. Having NPT 1/4 and 1/4-20 as totally different things is good enough to make things messy.

gtae07 wrote:

kalvado wrote:

Small inch threads like 1/8 are taken by pipe threads, and you don't want to add them to the mess. Having NPT 1/4 and 1/4-20 as totally different things is good enough to make things messy.

Pipe thread (NPT) has nothing to do with standard UN (Unified National) threads like 1/4-20. UN thread is based off of the nominal OD of the fastener, so the major diameter of the external thread is going to be a tiny bit less.

Pipe threads (NPT) are tapered and made for sealing fluid connections. One should remember that pipe is specified by nominal inner diameter, not outer (like tubing). That's why a 1/8 NPT male fitting has a much larger thread than 1/4".

Also remember that the #6, #10, etc. thread as well as NPT were carried over from outside the aerospace industry. You also don't see a lot of NPT on newer transport-category equipment, though it's still common on light aircraft.

ZaphodHarkonnen wrote:

M564038 touches on it but doesn’t make part of their point clear. For decades the US Customary Measures as defined by NIST are defined in reference to Metric/SI. So 1 inch is so many millimetres. A pound is so many grams. Basically making the conversions multiplication by various constants.

This is tangential to the rest of the discussion. But still an interesting point. Also UK (Imperial) measures are defined differently for some measures. So the US and UK measure could appear to be the same but be slightly different in reality.

StTim wrote:

The customary units vs imperial units that is commonly misunderstood is the use volume one.

A US Gallon = 3.78541 Litres
An Imperial Gallon = 4.54609 Litres

Also I heard recently that there are three separate miles in the US.

1 Nautical miles = 1,852 Metres
1 Mile = 1,609.34 Metres
1 U.S. survey Mile = 1,609.347 Metres. This is what is commonly called the statute mile. Not much difference but it is there.