Editing Ground speed

{{Short description|Horizontal speed of an aircraft relative to the ground}}
{{Refimprove|date=June 2019}}
'''Ground speed''' is the horizontal component of the velocity of an [[aircraft]] relative to the Earth’s surface, also referred to as "speed over the ground".<ref>{{Cite web|url=https://www.grc.nasa.gov/www/k-12/airplane/move.html|title=Relative Velocity - Ground Reference|website=www.grc.nasa.gov|access-date=2019-06-08}}</ref> It is vital for accurate navigation that the pilot has an estimate of the ground speed that will be achieved during each leg of a flight.

Theoretically, an aircraft diving vertically and unaffected by wind would have a ground speed of zero. Information displayed to passengers through the entertainment system of airline aircraft usually gives the aircraft ground speed rather than [[airspeed]].

Ground speed can be determined by the [[vector sum]] of the aircraft's [[true airspeed]] and the current wind speed and direction; a [[headwind]] subtracts from the ground speed, while a [[tailwind]] adds to it. Winds at other angles to the heading will have components of either headwind or tailwind as well as a [[crosswind]] component.

An [[airspeed indicator]] indicates the aircraft's speed relative to the air mass it is flying through. The air mass may be moving over the ground due to wind, and therefore some additional means to provide position over the ground is required to determine ground speed. This might be through navigation using landmarks, radio aided position location, [[inertial navigation system]], or [[GPS]]. When more advanced technology is unavailable, an [[E6B]] flight computer may be used to calculate ground speed.  [[Ground speed radar]] can measure it directly.

Ground speed is quite different from [[airspeed]].  When an aircraft is airborne, its ground speed is not related to the likelihood of a stall, and it doesn't influence the aircraft's performance, such as [[rate of climb]].

== See also ==
* [[International Civil Aviation Organization#Use of the International System of Units|ICAO recommendations on use of the International System of Units]]

==References==
{{Reflist}}

{{DEFAULTSORT:Ground Speed}}
[[Category:Air navigation]]
[[Category:Velocity]]