Why is aircraft speed measured in knots

A Mach number below 1 means that the plane moves subsonic. A Mach number above 1 indicates supersonic flight. The Mach number is critical because a number of phenomena take place just around Mach 1 transonic speed , for example a sudden increase in drag induced by shock-wave generation sonic-boom.

Aircraft that are not designed to fly supersonic will break up at Mach 1. The shape of the aircraft can cause parts of the aircraft being at or above Mach 1 while the fuselage is subsonic.

Flying near Mach 1 can be quite dangerous, for most fast but subsonic aircraft Mach 0. High flying aircraft, like passenger aircraft, can reach that limit easy while descending. The speed of sound changes with the compressibility and hence temperature of air, the Mach number is dependent on altitude as the air temperature drops at higher altitudes. The precise relation between TAS, Mach number and altitude is a complicated formulae and depends in essence on the local weather pattern determining the pressure and temperature gradients in the atmosphere.

For the complete V speed "definitions" list please visit Wikipedia. Here a small abstract. Note that V speed definitions can depend of local Flight rules. Most V speeds depend on the aircraft configuration how much it weights etc. V speeds are used to compare aircraft performance and will be mentioned in the aircraft flight manual AFM.

During take-off the speed at which the aircraft safely can take-off even when one of more engine fails "eats a bird". The co-pilot FO will call out V 1 during take-off, the pilot will check if all engines are running and decides to continue or abort take-off. The speed at which the nose-wheel leaves should leave the ground. As the speed increases the yokes will be pulled at V r.

It is also the speed at which the aircraft still can be stopped if there is a critical failure. Mach 1 means that you are traveling at the speed of sound or Since the speed of sound varies with the density of air or whatever material it is transmitted through , one needs to determine the density of the air the aircraft is flying through.

Notice as the altitude increased, the density of air decreases as does the speed of sound in knots. This log was thrown into the sea by sailors while letting the knotted rope slide through their hands for 30 seconds.

The standards and recommendations given by ICAO are based on their acceptability across the globe and followed internationally by everyone connected to air navigation, including pilots and air traffic controllers.

In aviation, the air routes are defined in terms of waypoints latitude, longitude and their distance is expressed in terms of nautical miles, hence, the utilization of knots provides a quick estimation of time and speed requirements for aviators. Airspeed represented in terms of knots also indicates that it is fundamentally different from the Ground Speed. As the airspeed of an aircraft is calculated directly from the pressure of the airflow hitting the aircraft, it may be significantly different from the speed it actually moves over the ground.

So, whenever a comparison in the speed of aircraft versus ground vehicles is needed, we are presented with a challenge. But it is important to note that there are three distinct types of airspeeds:.

In aviation, clear communication is essential to ensure the safe progress of flights, and efficient use of radio frequencies. Therefore, a ship traveling at 15 knots could go 15 nautical miles per hour.

In , the international nautical mile was standardized at 6, feet; it was adopted by the United States in A nautical mile is different from a mile on land, which is based on walking distance. The Romans first defined a land mile as 1, paces or pairs of steps; it was set at its current measurement of 5, feet by Queen Elizabeth I in