seems slightly odd to use an angular unit for airspeed; the linear equivalent would technically depend on altitude. I guess airplanes don't actually fly high enough for that to matter.
It was only ever approximately accurate anyway, a NM is no longer an arc minute because that is inconsistent even along lines of latitude, so it had to be pinned to 1.852km.
Aviation, broadly speaking, inherited all of its navigation techniques from the maritime world. In particular, prior to radio methods and to some extent today aviation navigation is based primarily on dead reckoning periodically corrected by observations, which is a technique that was pioneered in marine navigation. Since early pilots learned to navigate from seafarers, their units and conventions became strongly embedded in the field. It is, after all, still not unusual to refer to an aircraft as a ship, especially informally.
Ironically the metric system suffers the same theoretical "error" as the not-an-arc-minute-anymore NM because the meter was originally defined by taking the distance from pole to equator (to the best of their knowledge at the time) and then shifting the decimal point to get something human scale.
Initially, yes. The story itself is quite fascinating, and the Wikipedia page on the metre is a good starting point.
This was a hot topic during the 19th century as different improvements in the techniques and devices used to measure the Earth showed that the first measurements were imperfect, however good they had been at the time, and that the whole idea is not workable because the Earth is not a sphere. This lead to the formal definition of the metre as the length of a prototype in 1889.
I imagine that the mental adjustment from sphere to almost but not quite a sphere must have been harder than a switch from flat earth to spherical. You just expect reality, if it matches a certain mathematical principle, to match perfectly.
This has not been the case since 1889, when the metre was formally defined as the length of a prototype metre bar. So the metric system has not suffered the same error for more than a century.
Of course, the metric system has not been in use since 1960, but this is also true for the SI.
Oh, I think I didn't even read that correctly since it seems like it's just a mistake. A knot is, for historic reasons, a term for NM per hour. An NM is defined by latitude.
I believe that the term knots originates from a method of measuring speed at sea by use of a twisted rope and a sea anchor, but perhaps that's apocryphal. Presumably though the definition in terms of NM was a later improvement.
While I don't have any real evidence for this, I would speculate that part of the reason for the enduring use of knots in aviation is that, much like the old twisted rope, it links the unit to the instrument. The speeds usually quoted for aircraft are in KIAS, Knots Indicated Airspeed, a measurement which is basically defined by what the instrument shows. It is intentionally uncorrected for various errors in the instrument design. This happens to be convenient because many of the same factors that affect the instrument calibration also affect the aircraft handling, so handling at 100 KIAS tends to feel similar even though the actual speed varies by altitude etc. KCAS and KTAS, Calibrated and True Airspeed, are both KIAs after correction for various errors and are useful for certain calculations but not nearly as often as KIAS. My point is that it might be helpful to use Kts rather than MPH or KPH because it helps keep these factors in mind and helps to reduce ambiguity about whether a number is indicated or true, although people very frequently just write knots when meaning KIAS.
Of course for ground speed none of this matters but ground speed isn't really a "flight" concern per se, more just used for navigation calculations.
