[ihunter]

A few things came out of this incident:

1) Per my first flight instructor, this is the reason students now learn how to forward slip. Up until then it was just viewed as a glider move. Thankfully the captain was an experienced glider pilot. It's required to demonstrate this maneuver for your private license (not sure about sport license).

2) This ultimately led to overhaul and standardizations for fuel / weight calculations.

3) Because the engines powered the electrical systems via the alternator, the plane lost a number of electrical systems until the ram air turbine kicked in (amazing little invention and kinda saved the day). Afterwards, many subsequent aviation systems were designed to be operated independently from requiring the alternator to be running.

Good documentary/recreation on the incident: https://www.youtube.com/watch?v=Bct1mWUp8to. Miraculous that everyone survived, the captain deserves an accolade for quick thinking.

[walrus01]

> 2) This ultimately led to overhaul and standardizations for fuel / weight calculations.

You have no idea how hard it is to get Americans to use 100% metric everything, even in the year 2016 in a highly technical field. It's incredibly frustrating. I'm amazed at the number of people under age 30 who have clearly not been taught even the basics of the metric system in middle school and high school, or intentionally disregarded/forgot it.

Working in the US domestic economy is unavoidable to do many things in US customary units when construction/physical engineering of things is involved. For example if building mission critical telecommunications towers to EIA/TIA 222G standards, everything is going to be in US customary units (the tower structure itself, the fasteners, the guy cables, the anchors, the foundation/concrete job, the dimensions of the equipment shelter, the electrical conduit, etc).

[engi_nerd]

>You have no idea how hard it is to get Americans to use 100% metric everything, even in the year 2016 in a highly technical field.

American in a highly technical field here. I have no issues with using SI units when appropriate. But there is a tremendous lock-in, at least in some areas. Aerospace is a nasty mishmash, resulting in things like aircraft that "think" about altitude in feet, fuel in pounds, gear displacement in inches, but electric field strengths in W/m^2 and geopositioning in meters. All of those choices were made long ago, I'm stuck with them. My only defenses are to keep meticulous track of units and convert where necessary (while paying attention to things like numerical error).

[walrus01]

we are pretty much resigned to the fact that buying all of the pieces to build a datacenter/colo/telecom facility, everything is going to be in US customary units, because that's what the suppliers have. It's a vicious cycle of nobody in the US choosing to stock metric items, so nobody can buy it, and all of the end users just use things that are US units. It can be the smallest things like threaded rod uses to hang overhead fiber trays in a datacenter (all of the fasteners, bolts, nuts, the rod itself, etc) are all in US units. All the way up to the largest things like $150,000 generators where all of their specifications are in US units and fuel consumption figures in gallons, etc. If it involves the construction industry it's 99% of the time going to be US customary units.

We only get down to proper metric units when dealing with the fiber itself, but even that is lashed to aerial pole-to-pole strands, where the steel strand is in US units, all of the hardware is US.

The battery backup shelves for large AGM lead acid batteries: All US units. The batteries themselves are specified in inches and pounds. Once again it can all be converted, but that's the default unit from the manufacturer. Floor loading calculations? Pounds per square foot.

[jaclaz]

A related serious incident (mistaken units) in aerospace was the NASA Mars Climate Orbiter:

https://en.wikipedia.org/wiki/Mars_Climate_Orbiter

>However, on September 23, 1999, communication with the spacecraft was lost as the spacecraft went into orbital insertion, due to ground-based computer software which produced output in non-SI units of pound (force)-seconds (lbf·s) instead of the SI units of newton-seconds (N·s) specified in the contract between NASA and Lockheed.

[engi_nerd]

Yes, this is the kind of thing we have to zealously guard against. Formal specs for data exchange are very important!

[Hondor]

I know of Chinese manufacturers making parts for US customers using out-of-spec metric materials that happen to also be in-spec for imperial. Eg a 6.5 mm steel plate that was made too thin for the 6.5 mm tolerance might be within tolerance for 1/4 inch (6.35 mm). There's a market for this "faulty but turns out to be useful" material because metric is more readily available in China.

I have a feeling that with the decline of American manufacturing, they'll feel more pressure to convert to metric because it's a bit cheaper on imported things and there's less locally made stuff that needs to convert.

[Declanomous]

The thing is that what's left of American manufacturing tends to be producing the things that you just mentioned: steel, fasteners, rebar, etc. The labor advantage that China has is more than offset by the massive weight and volume construction materials have for a given price.

Non-construction materials are already readily available in metric units. I can buy grade 8 bolts in any size, metric or US customary. I can't buy 400 x 800 plywood, and why the hell would I want to? Everything here is built on 24 or 18 inch centers. You'd have to be insane to build a house using metric dimensions.

US customary units are nowhere as difficult to use as people make them out to be, especially at the scales being used for construction. I find metric and US customary equally easy to use, and I think that metric is much easier to use when it comes to electricity, but I find US customary much easier to use for everything else.

For instance, the meter is widely held to be better than the traditional US customary units. I think this is true for science, but when it comes to everyday uses I find the US system easier to perform math with purely because it's base 2 rather than base 10, and most of the time I'm dividing things in half several times.

Need to find the center of a 1-7/8" board? It's 15/16ths, which is really easy to calculate if you understand fractions. That's basically like figuring out the center of a 50mm board -- 25mm, obviously. However if you divide each board again, you get 15/32nds, or 12.5mm. If you divide again, into eighths, you get 15/64ths, or 6.25mm.

Maybe 15/64ths seems a bit clunky, but my tools usually have markings down to 64ths, and I have bits available all the way down to 64ths. The example I picked was deliberately bad for US imperial, and it still was pretty easy to calculate.

I think US customary units are really confusing to metric types because they don't really have a reason to use fractions in daily life. Math with fractions is really easy to do in your head though, and most tradesman are doing the math in their head.

I wouldn't be surprised if we saw a bigger push towards metric as education shifts away from pencil and paper. Metric makes way more sense than US customary does when you are doing math on a computer.

[kriro]

On the flip side of this I noticed (from attending school in both countries) that in math radian was used more often than in Germany (which is a good thing imo).

[zeveb]

> You have no idea how hard it is to get Americans to use 100% metric everything, even in the year 2016 in a highly technical field. It's incredibly frustrating.

I'm equally frustrated by how hard it is to get others to use standard units instead of the French ones. There's no particular reason why 'technical fields' should mandate use of French units: one can fly an æroplane, run power to a lightbulb and get a man to the moon all in standard units — indeed, that's how those things were initially done.

[na85]

>get a man to the moon all in standard units

Not quite. At least as far as the flight guidance and navigational systems, NASA used metric internally for the moon missions and had the computer display the converted equivalent in US customary units to the crew.

http://www.doneyles.com/LM/Tales.html

[azernik]

There is a reason technical fields should mandate uniformity and compatibility, and that isn't going to happen with customary units (so called because they're not even compatible with pre-metric British units).

Sure, you can fly your plane with bolts measured in inches and fuel measured in pounds, but good link getting replacement parts or accurate refueling next time you're in a stopover in Japan or Italy or Egypt. And have a good time trying to sell machine parts into an international market, or trying to buy from that same market.

[FabHK]

Zeveb, the US customary units, "based on English measure passed by parliament under the reign of Queen Anne in 1706" [1] are inferior to the international SI units.

- prefixes based on powers of 10 are better aligned with how we calculate today, namely with base 10 numerals, and decimal fractions (unless we switch to base 12 or base 8 numerals).

- a single unit per physical quantity, together with prefixes, is better than the proliferation of units in those customary systems (often with different units of the same physical quantity in different contexts, for example length vs area vs liquid volume vs non-liquid volume, or mechanical energy vs heat energy).

- the system is coherent and somewhat minimal.

- the units are derived from the world, not from the length of some king's feet or arms or what have you. Of course, that's a somewhat subjective benefit.

At any rate: the original metre was 1/10,000,000 the distance from equator to pole (that's why 90*60=5400 nautical miles = 10,000 km, approximately). The original kilogram ("grave") was the mass of 1 dm^3 of water.

Of course, one can fly an aeroplane or get a man to the moon without SI units. One can also do it without GPS and without computers and without internet and without antibiotics and without all the other achievements of civilisation. But why would one?

[1] https://en.wikipedia.org/wiki/International_System_of_Units#...

[zeveb]

> Zeveb, the US customary units, "based on English measure passed by parliament under the reign of Queen Anne in 1706" [1] are inferior to the international SI units.

FabHK, no, French units are inferior to the standard units:

- 2 and 5 are poor factors; 2, 3, 6 & 8 are superior. We ought to switch to base 12: among other things, ⅓ is not a non-terminating duodecimal.

- It is better to have multiple units for multiple purposes: anyone measuring interstellar distances in inches or metres rather than in parsecs or lightyears is, simply, wrong. One always has the freedom (and indeed, the professional obligation) to use only one unit where it matters (e.g. anyone measuring bread pans in fractions of a mile or metre is, again, simply wrong.

- The system is scaled to human beings, and eschews superficial minimality (BTW: steres and hectares). There are many useful units at human scale, with a few units where needed outside that scale (there's not really much need for a lot outside of human scale).

The units are derived from the world: the nautical mile is equal to one minute of latitude (that's 1/60th of 1/360th); a pint is a pound of water.

- The units are useful for manipulating concrete quantities. Half a volume of liquid is itself a useful measure, as is double (it goes mouthful → jigger → jack → gill → cup → pint → quart → pottle → gallon and so on, doubling all the way up until a tun). As a computer guy, it's pretty awesome to see 64, 128 & 1,024 in my unit quantities.

As I note elsewhere, I'm in support of rationalisation of the system: history has not been kind (c.f. rulers who kept the tax per unit the same, but decreased the size of the unit). I think that there's definitely improvement to be made.

But throwing it all out and adopting a decimal system goes in exactly the wrong direction.

[FabHK]

I enjoy the discussion, and agree that base 10 is suboptimal. Base 8, 12, or 16 would be preferable (8, 16 due to affinity to the binary system; 12 due to the factors). However, we are stuck with 10 for now. (Surely there's an argument against God here.)

If we lived in a base 8 or base 12 world, a radically rationalised version of the customary royal measures based on doubling or factors 8 or 12 might be preferable. But we are not.

> It is better to have multiple units for multiple purposes.

Why?

Differences in scale are easily accounted for with the prefixes:

mili, micro, nano, pico, femto, atto takes you down to 10^-18; with zepto and yocto you get to 10^-24.

kilo, mega, giga, tera, peta, exa takes you up to 10^18; with zetta and yotta you get to get to 10^24.

[GrumpyBen]

Why do you call them French units while it has been an internationally agreed system for decades?

[walrus01]

"french" units?

countries which have officially adopted the metric system vs those which have not: https://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Me...

[run4yourlives2]

You'd have a stronger point if you had France vs. US and no other standards.

In reality, you have the accepted world standard and the US one, with a small smattering of UK units thrown in. To argue the entire world should switch back to the US standard instead of the other way around is ridiculously obtuse.

[zeveb]

> To argue the entire world should switch back to the US standard instead of the other way around is ridiculously obtuse.

The entire world switched to one country's system once. All of Europe used substantially the same system, and switched from it to one country's radically different system.

There's no reason it couldn't be done again. If it made so much sense to do one thing (of course, I don't actually think it did make that much sense: it was in the main driven through by governments seeking to radically break with the past) then surely if it makes sense to do something else, we all ought to?

[crikli]

Pretty sure #1 isn't accurate. I wasn't required to forward slip (or side slip, for that matter) on my FAA checkride nor have I been required to do so during any biennial flight review.

Edit: I'm dead wrong. :)

[dbenjamin]

#1 is not accurate but for different reasons.

A forward slip is absolutely required for a PPL checkride and has been for decades (if you'd like a source, see page 45 of the definitive FAA ACS: https://www.faa.gov/training_testing/testing/acs/media/priva...).

However, transport category aircraft (among other issues) have swept wings, which are far less stable in a slip - so slips are neither taught nor recommended for jets.

[phumbe]

Looks like forward slip to landing has been in the Private Pilot Practical Test Standards [1] since at least Nov 2011

[1][PDF] https://www.faa.gov/training_testing/testing/test_standards/...

[dbenjamin]

Here's it as a required maneuver in 1995 :)

https://www.faa.gov/documentLibrary/media/Advisory_Circular/...

[crikli]

Huh. I'm wrong then obviously. Wonder if it's never come up as I tend to forward slip on crosswind landings. Don't recall a DPE ever even mentioning slips.

[oceanplexian]

It's interesting that slips are now more prevalent in training, because they were absolutely crucial when I learned to fly (In a J3 Cub w/ no flaps). It's absolutely a blast and can get you on the ground a LOT faster than 30 degrees of flaps will.