Ground speed is the horizontal speed of an
aircraft
An aircraft is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or by using the Lift (force), dynamic lift of an airfoil, or in ...
relative to the Earth’s surface.
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.
An aircraft diving vertically 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
In aviation, airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are:
* Indicated airspeed ("IAS"), what is read on an airspeed gauge connected to a Pitot-static system;
* Calibrated ...
.
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. 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. This might be through navigation using landmarks, radio aided position location,
inertial navigation system
An inertial navigation system (INS) is a navigation device that uses motion sensors ( accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity ...
, or
GPS. When more advanced technology is unavailable, an
E6B
The E6B flight computer is a form of circular slide rule used in aviation and one of the very few analog calculating devices in widespread use in the 21st century.
They are mostly used in flight training, because these flight computers have ...
flight computer may be used to calculate ground speed.
Ground speed radar can measure it directly.
Ground speed is quite different from
airspeed
In aviation, airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are:
* Indicated airspeed ("IAS"), what is read on an airspeed gauge connected to a Pitot-static system;
* Calibrated ...
. When an aircraft is airborne the ground speed does not determine when the aircraft will stall, and it doesn't influence the aircraft performance such as
rate of climb.
See also
*
Land speed
*
ICAO recommendations on use of the International System of Units
References
{{DEFAULTSORT:Ground Speed
Air navigation
Velocity