Ground speed is the speed of an aircraft relative to the ground. Information displayed to passengers through the entertainment system often gives the aircraft groundspeed 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 can only indicate the aircraft's speed relative to the air mass. The air mass as a whole 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, or GPS. When more advanced technology is unavailable, an E6B flight computer is often used to calculate groundspeed.
Ground speed is quite different from airspeed. When an aircraft is airborne the ground speed does not determine when the aircraft will stall, and it doesn't influence the actual aircraft performance such as rate of climb.
Famous quotes containing the words ground and/or speed:
“I have hardly begun to live on Staten Island yet; but, like the man who, when forbidden to tread on English ground, carried Scottish ground in his boots, I carry Concord ground in my boots and in my hat,—and am I not made of Concord dust? I cannot realize that it is the roar of the sea I hear now, and not the wind in Walden woods. I find more of Concord, after all, in the prospect of the sea, beyond Sandy Hook, than in the fields and woods.”
—Henry David Thoreau (1817–1862)
“The correct rate of speed in innovating changes in long-standing social customs has not yet been determined by even the most expert of the experts. Personally I am beginning to think there is more danger in lagging than in speeding up cultural change to keep pace with mechanical change.”
—Mary Barnett Gilson (1877–?)