Comment by Tankenstein 2 days ago
Just a guess, but aerospace generally works with feet for altitude and knots/mph for airspeed, internationally. I’m doing a PPL in Europe and we, like everybody, use feet and knots/mph. I believe this is because the US have been on the forefront of aerospace regulation (a set of rules called the chicago convention is the basis of all air law) and aircraft manufacturing.
Sorry, not a native speaker, I was under the impression that aerospace means air and space. I guess i meant aviation.
I didn’t imply knots are mph, I used the slash to signify “or”. They are completely different units, but both are used. Sometimes the airspeed indicator even has two scales, one for kt and one for mph.
Can confirm, all aviation worldwide deals in feet and knots. It's also because it's much easier to do calculations on the fly (literally) - in your head. Metric is precise and logical but harder to use in stressful situations.
Can you please give some real-world example of why it's easier to do calculations? Not disputing what you say, just hard for me to imagine why it would be so.
1 knot is about 100 ft/min which is very convenient for descent at a specific glide slope (i.e. for 100 knots ground speed at 5% slope you want 500 ft/min descent rate). Standard is 3° which is about 5%.
Knots are also handy for navigation as 1 nautical mile equals 1 minute of latitude. And of course a knot is 1 nautical mile per hour. So if you're doing 300 knots, that's 5 degrees of latitude per hour.
The units fit together nicely as a system.
The calculation in the metric system would not necessarily be more complicated, but it would be different because the reference points in the metric system are not directly aligned with the geography of the Earth.
"1 knot is about 100 ft/min which is very convenient for descent at a specific glide slope (i.e. for 100 knots ground speed at 5% slope you want 500 ft/min descent rate). Standard is 3° which is about 5%."
You are right. It's an easy calculation. But I would say its easy because its historically based on imperial units. Its easy to think about easy calculations like this in metric units like:
A 5% slope means descending 1 meter vertically for every 20 meters horizontally.
The gradient thing would work if ground speed and vertical speed were both in m/s, but km/h is more common in metric for a ground speed. You don't usually think in terms of hours during a climb/descent!
Glide slope of 3.6% would fit nicely though. Then, 100 km/h ground speed goes with vertical speed 1 m/s.
Metric navigation would use the fact 90 degrees of latitude is 10,000 km.
I suspect that the math is even easier using meters, meters, and meters per second than nautical miles, feet, and knots. I'll eat my hat if you can tell me the conversion from feet or inches to nautical miles without looking it up
This sums it up. Metric is nice and clean tenths, but the real world is seldomly easily expressed in clean tenths.
Another example: The feet is cleanly divisible in thirds, quarters, and twelfths, which is greatly appreciated in industry and particularly construction.
Also to be bluntly mundane, almost everyone can just look down and have a rough measure of a foot which is good enough for daily use.
Also, the "sterility" of metric doesn't do it any sentimental favours. Japan loves measuring size/volume in Tokyo Domes, for example.
Thank you, I wasn't aware of China using metres. It turns out Russia uses them as well, confusingly below the transition level.
"Metric is precise and logical but harder to use in stressful situations."
That fully depends on your cultural background. Feet, miles etc. are so foreign to me that I would be unable to calculate with them under stress.
But I am not a pilot nor a navigator, so...
No, it doesn't. I'm European, never used imperial before I became a pilot, and it's easier. Check it out, the formulas are much simpler to do in your head. Intuition doesn't matter, all that matters is that I can do the calculations quickly so I know I'm within parameter limits.
I'm curious which ones you find easier? There or a few thermodynamics equations that are much more practical in SAE. This is because the many units are often developed out of within discipline experiment, whereas metric tries to use fundamental units across disciplines.
Not for aerospace no
And knots are not mph, they're "nautical miles per hour" which are a different measure (1nm is 1.8km, not 1.6km as the regular mile")