Units of Measure


Aviation is a hodge-podge of English, metric, dimensionless, and nautical units of measurement.

  • Distance (nautical miles, nautical)
  • Altitude (feet, English, and FL which is in 100’s of feet instead of thousands, very English)
  • Airspeed (knots, nautical, and Mach, dimensionless related to the speed of sound)
  • Temperature (centigrade, metric)
  • Pressure (inches of mercury, English, and millibars, metric)
  • Visibility (statute miles, English, and RVR in feet, English)
  • Fuel quantity (pounds, English)

Our operational regime is initially 35 km above Venus to 60 km above Venus. Each kilometer would make for a good “flight level” and Aliens (the movie) made reference to “clicks” which is slang for kilometers.

However, as a former airline pilot, I like flying with knots indicated speed… and I am used to nautical miles for distance. So when I sat down to port over the altimeter, I took a pause… what units should it be in?  Feet is unwieldy at 35 kilometers (114,829 feet aka FL 1148, whatever).  Why not measure distance vertically the same that we measure it horizontally?  35 km is 18.8985 NM (60 km is 32.3974 NM) … and it gives us better resolution (the separation at tenths of NM is less than 1000 feet) so we could do a FL-type system (FL 188 to FL 324).

Doing a little research, I found that the retired space shuttle could display altitude in feet up to 400,000 depending on the phase and was also capable of showing altitude in miles from 40 to 165 (always based on static pressure).

Then again, our universe framework is metric based – it allows for faster and more accurate conversions between scales (i.e. meters to kilometers).  Similarly, Rise was metric: Rise used meters and kilometers for everything – indicated speed, vertical speed, altitude, and distance.

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