Home > Knot (speed)
A knot is a unit of speed equal to one nautical mile per hour. It is 1.852 kilometres per hour precisely (approximately 1.15 miles per hour or 0.514 metres per second). Knot is usually abbreviated kt.The knot is widely used in air and sea navigation.
Because a knot is already a measure of speed, the expression "knots per hour" is a solecism. Taken literally (nautical mile/hour˛), it would be a measure of acceleration.
1 Origin
In some sailing ships, speed was measured by casting the log from the stern. The log was relatively immobile, and attached by line to a reel. Knots placed at a distance of 47 feet 3 inchAn inch is an Imperial unit of length. Sweden also briefly had a "decimal inch" based on the metric system: see below for more. According to some sources, the inch was originally defined informally as the distance between the tip of the thumb and the firses (14.4018 m) passed through a sailor's fingers, while another used a 28 second sandglass to time the operation. The knot count would be reported and used in the sailing master's dead reckoningDead reckoning (DR is a method of navigation used in ships, aircraft, and, more recently, mobile robots. Essentially it is used to estimate an object's position based on the distance it traveled in its current direction from its previous position. A navig and navigation.
This method gives a value for the knot of 20.25 in/s, or 1851.66 m/hr.
The difference from the accepted value today is a bit less than 0.02%.
2 Terms
- KTAS is "knots true airspeed", a measure of an aircraft's true airspeed through the air
- KIAS is "knots indicated airspeed", meaning the airspeed shown on the airspeed indicator
- KCAS is "knots calibrated airspeedCalibrated airspeed (CAS) is the speed theoretically shown by a simple airspeed indicator that is free from instrument error and position error. A simple airspeed indicator has only one capsule measuring impact pressure (pitot static differential). CAS mu", or indicated airspeed corrected for position errorMost aircraft have an inherent difference between (theoretical) calibrated airspeed (CAS) and the airspeed actually shown on the instrument (indicated airspeed, or IAS). This "position error" is mainly due to errors in sensing static pressure. It is usual
- KEAS is "knots equivalent airspeedEquivalent airspeed (EAS) is the airspeed which represents the same dynamic pressure at altitude that would be generated by flying at the corresponding true airspeed (TAS) at sea level. It is useful for predicting aircraft handling, aerodynamic loads, sta", which is calibrated airspeed corrected for compressibility effectsFluid dynamics A compressible flow is a situation in which the compressibility of the fluid must be taken into account. In general, this is the case where the Mach number in part or all of the flow approaches or exceeds 1. Under these circumstances, it is.
3 External link
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