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:
“All I’m telling you is that that little creature in there has as much right to live as you do. Don’t forget, you invaded his world. You sank a pipe six miles into the ground and when he climbed up you set dogs on him, shot him.”
—Richard Fielding, and Lee Sholem. Superman (George Reeves)
“Spig Wead: I’ve been thinking what a heel I’ve been about you and about my own kids. I don’t know, when I do something, I go all the way. Living. Gambling. Flying. I tap myself out. I guess that’s the way I want it to be. Maybe even the way I am.
Minne Wead: Star-spangled Spig. Damn the martinis, full speed ahead and don’t give up the ship.”
—Frank Fenton, William Wister Haines, co-scenarist, and John Ford. Spig Wead (John Wayne)