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Aircraft speed: Difference between revisions
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==Expressing speed== | ==Expressing speed== | ||
=== Ground | === Ground speed === | ||
*[http://en.wikipedia.org/wiki/Ground_speed '''Ground''' speed (GS)] is the horizontal speed in which the aircraft moves relative to a fixed point on the ground. | *[http://en.wikipedia.org/wiki/Ground_speed '''Ground''' speed (GS)] is the horizontal speed in which the aircraft moves relative to a fixed point on the ground. | ||
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GS is the velocity in the horizontal direction of the aircraft. I.e. in a steep dive, the aircraft can move very fast, but because the motion is chiefly vertical, the ground-speed can be very small at the same time. This is where the GS differs from the ground-speed of a car. | GS is the velocity in the horizontal direction of the aircraft. I.e. in a steep dive, the aircraft can move very fast, but because the motion is chiefly vertical, the ground-speed can be very small at the same time. This is where the GS differs from the ground-speed of a car. | ||
=== True | === True airspeed === | ||
*[http://en.wikipedia.org/wiki/True_airspeed '''True''' airspeed (TAS)] is the speed in which the aircraft moves relative to the surrounding air. | *[http://en.wikipedia.org/wiki/True_airspeed '''True''' airspeed (TAS)] is the speed in which the aircraft moves relative to the surrounding air. | ||
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Often TAS and GS are assumed (confused) to be the same, they are not. | Often TAS and GS are assumed (confused) to be the same, they are not. | ||
=== Indicated | === Indicated airspeed === | ||
*[http://en.wikipedia.org/wiki/Indicated_airspeed '''Indicated''' airspeed (IAS)] is the number displayed on the [http://en.wikipedia.org/wiki/Airspeed_indicator airspeed indicator]. | *[http://en.wikipedia.org/wiki/Indicated_airspeed '''Indicated''' airspeed (IAS)] is the number displayed on the [http://en.wikipedia.org/wiki/Airspeed_indicator airspeed indicator]. | ||
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At sea level, a IAS of 400 knot roughly corresponds to 400 knot TAS. At 80.000 feet (the cruising altitude of a [[SR-71]]), the IAS of 400 knot corresponds to a TAS in excess of 1600 knot (..that corresponds with about Mach 3 at that altitude). | At sea level, a IAS of 400 knot roughly corresponds to 400 knot TAS. At 80.000 feet (the cruising altitude of a [[SR-71]]), the IAS of 400 knot corresponds to a TAS in excess of 1600 knot (..that corresponds with about Mach 3 at that altitude). | ||
=== Calibrated | === Calibrated airspeed === | ||
*[http://en.wikipedia.org/wiki/Calibrated_airspeed '''Calibrated''' airspeed (CAS)] is calculated from the [[#Pitot tube]] measurement and correcting it for standard errors. | *[http://en.wikipedia.org/wiki/Calibrated_airspeed '''Calibrated''' airspeed (CAS)] is calculated from the [[#Pitot tube]] measurement and correcting it for standard errors. | ||
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Modern equipment can most often can indicate the CAS. For navigation the CAS is the first step to calculate the GS. | Modern equipment can most often can indicate the CAS. For navigation the CAS is the first step to calculate the GS. | ||
=== Equivalent | === Equivalent airspeed === | ||
*[http://en.wikipedia.org/wiki/Equivalent_airspeed '''Equivalent''' airspeed (EAS)] takes into account another correction (above [[#Calibrated airspeed]], this time having to do with air properties rather than sensor errors. | *[http://en.wikipedia.org/wiki/Equivalent_airspeed '''Equivalent''' airspeed (EAS)] takes into account another correction (above [[#Calibrated airspeed]], this time having to do with air properties rather than sensor errors. | ||