Knots / Nautical Mile Per hr.
Knots:
The knot is a unit of speed equal to one nautical mile per hour, which is equal to exactly 1.852 km/h and approximately 1.151 mph.
Mariners first used the term "knot" denoting the measure of how many knots in a special line which came off a reel in a given time, using the chip log.
Definitions:
1 international knot =
1 nautical mile per hour (by definition),
1.852 kilometres per hour (exactly),
0.514 metres per second,
1.151 miles per hour (approximately).
Nautical mile:
The nautical mile (symbol M, NM, Nm or nmi) is a unit of length corresponding approximately to one minute of arc of latitude along any meridian. By international agreement it is exactly 1,852 metres (approximately 6,076 feet). The nautical mile remains in use by sea and air navigators worldwide because of its convenience when working with charts.Aeronautical terms: Prior to 1969, airworthiness standards for civil aircraft in the United States Federal Aviation Regulations specified that distances were to be in statute miles, and speeds in miles per hour. In 1969 these standards were progressively amended to specify that distances were to be in nautical miles, and speeds in knots.
The following abbreviations are used to distinguish between various measurements of airspeed.
KTAS is "knots true airspeed", the airspeed of an aircraft relative to undisturbed air.
KIAS is "knots indicated airspeed", the speed shown on an aircraft's pitot-static airspeed indicator.
KCAS is "knots calibrated airspeed", the indicated airspeed corrected for position error and instrument error.
KEAS is "knots equivalent airspeed", the calibrated airspeed corrected for adiabatic compressible flow for the particular altitude.
