3 ms·

Mostly convention, but some minor adva tages I can the of: - 'knots' is faster to say on the radio than 'kilometers per hour' - the way the world is divided

by kabes 3y ago

Mostly convention, but some minor adva tages I can the of: - 'knots' is faster to say on the radio than 'kilometers per hour' - the way the world is divided in wgs84, maked it so that 1 degree of latitude equals exactly 60 miles. So that makes quick measurements a bit easier.

spookie 3y ago
Didn't know about your second point, makes sense
defrost 3y ago
Don't degrees of latitude have varying arc lengths as latitude changes from the equator with a major axis to the poles with a minor axis? What with the Earth being an ellipsoid and not a sphere and all that?
- snovv_crash 3y ago
  It depends what geoid model you use, and once you go down that rabbit hole it depends on the local gravitational field which is affected by things like mountains, not only the centrifugal effect. For a sailor in the 16th century, assuming a sphere was perfectly adequate when combined with 1 degree = 60 nautical miles.
  - defrost 3y ago
    The actual shape of the Earth is independent of which ellipsoid model is chosen to locally or globally "best match" the actual shape. The geoid model is the surface of gravitational equipotential and is a "shape of the gravitational field" not a "shape of the physical earth". If we were discussing 16th century sailors rather than 21st century aviation you might have had a point.
    - snovv_crash 3y ago
      ...isn't that pretty much what I said? The origin of nautical miles is from 16th century sailors. And 21st century aviation doesn't need anything more accurate than WGS84. The people who need custom geoid models and local coordinate systems are surveyors.
- kabes 3y ago
  It's the longitude that changes. Note that lat parralels are horizontal, but you measure on which parralel you are, so you measure north-south position.
  - defrost 3y ago
    It's the curvature of the earth that changes local radius - greater at the equator, less at the poles. Hence the arc distance of a fixed angle changes also. I believe you're thinking of distance between lines of longitude which converge at the poles and are at maximal seperation at the equator. I was referring to the arc distance (surface distance) between lines of latitude which don't converge to zero but do get a little smaller closer to the poles (due to the lesser minor radius of the ellipsoid shape to the earth - oblate sphereoid, squashed sphere, not a perfect ball, etc.)
- xvinci 3y ago
  In my PPL training you either use the latitude-axis (X) on the equator only, which you will not have in your maps when flying in US or Europe. The alternative is to use the longitude axis (Y) which will always be 1° = 1 NM which can then be readily used in a "what is my groundspeed in knots per hour and what is my ETA" - so to the best of my knowledge you are correct. Then again I am no native speaker. But it really helps you as in you are able to pick any distance you want to fly on the map and by moving your fingers to the Y axis roughly guess the distance within a few seconds. Even in a very small cockpit and with turbulence. So i absolutely see the need for this with relation to navigation.

by kabes 3y ago

spookie 3y ago

Didn't know about your second point, makes sense

defrost 3y ago

Don't degrees of latitude have varying arc lengths as latitude changes from the equator with a major axis to the poles with a minor axis? What with the Earth being an ellipsoid and not a sphere and all that?

snovv_crash 3y ago
It depends what geoid model you use, and once you go down that rabbit hole it depends on the local gravitational field which is affected by things like mountains, not only the centrifugal effect. For a sailor in the 16th century, assuming a sphere was perfectly adequate when combined with 1 degree = 60 nautical miles.
- defrost 3y ago
  The actual shape of the Earth is independent of which ellipsoid model is chosen to locally or globally "best match" the actual shape. The geoid model is the surface of gravitational equipotential and is a "shape of the gravitational field" not a "shape of the physical earth". If we were discussing 16th century sailors rather than 21st century aviation you might have had a point.
  - snovv_crash 3y ago
    ...isn't that pretty much what I said? The origin of nautical miles is from 16th century sailors. And 21st century aviation doesn't need anything more accurate than WGS84. The people who need custom geoid models and local coordinate systems are surveyors.
kabes 3y ago
It's the longitude that changes. Note that lat parralels are horizontal, but you measure on which parralel you are, so you measure north-south position.
- defrost 3y ago
  It's the curvature of the earth that changes local radius - greater at the equator, less at the poles. Hence the arc distance of a fixed angle changes also. I believe you're thinking of distance between lines of longitude which converge at the poles and are at maximal seperation at the equator. I was referring to the arc distance (surface distance) between lines of latitude which don't converge to zero but do get a little smaller closer to the poles (due to the lesser minor radius of the ellipsoid shape to the earth - oblate sphereoid, squashed sphere, not a perfect ball, etc.)
xvinci 3y ago
In my PPL training you either use the latitude-axis (X) on the equator only, which you will not have in your maps when flying in US or Europe. The alternative is to use the longitude axis (Y) which will always be 1° = 1 NM which can then be readily used in a "what is my groundspeed in knots per hour and what is my ETA" - so to the best of my knowledge you are correct. Then again I am no native speaker. But it really helps you as in you are able to pick any distance you want to fly on the map and by moving your fingers to the Y axis roughly guess the distance within a few seconds. Even in a very small cockpit and with turbulence. So i absolutely see the need for this with relation to navigation.