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Aircraft speed: Difference between revisions
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External links + Copying some V speeds from V Speeds before deleting that page + Some tidying up
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(External links + Copying some V speeds from V Speeds before deleting that page + Some tidying up) |
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For (near-)supersonic planes the speed can be expressed in Mach. | For (near-)supersonic planes the speed can be expressed in Mach. | ||
==Expressing speed== | == Expressing speed == | ||
=== Ground speed === | === 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. | ||
One needs to know the GS in order to see how long a flight from A to B actually takes. Nowadays GS can be directly measured using a GPS system, and some aircraft equipped with such a system have a GS indicator. The GS can be calculated from TAS by correcting it for the prevailing wind at altitude or by measuring the time between passing two points on the ground [[radio beacons]] with a known distance, but in Flightgear you can always cheat and get it from the property browser under <tt>velocities/groundspeed-kt</tt>. | One needs to know the GS in order to see how long a flight from A to B actually takes. Nowadays GS can be directly measured using a GPS system, and some aircraft equipped with such a system have a GS indicator. The GS can be calculated from TAS by correcting it for the prevailing wind at altitude or by measuring the time between passing two points on the ground [[radio beacons]] with a known distance, but in Flightgear you can always cheat and get it from the property browser under <tt>velocities/groundspeed-kt</tt>. | ||
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=== True airspeed === | === 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. | ||
The difference between TAS and GS is that the air itself may move with respect to the ground (that's wind), and dependent on course relative to the wind direction a discrepancy between TAS and GS is induced. TAS can't really be measured directly but needs to be calculated, unless standing still on the ground where the TAS can be "seen" with the windbag. | The difference between TAS and GS is that the air itself may move with respect to the ground (that's wind), and dependent on course relative to the wind direction a discrepancy between TAS and GS is induced. TAS can't really be measured directly but needs to be calculated, unless standing still on the ground where the TAS can be "seen" with the windbag. | ||
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=== Indicated airspeed === | === 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]. | |||
Airspeed is usually measured with a [[#Pitot tube]] at the front of the aircraft. The IAS can be the CAS. The IAS is not the TAS since the pressure differs greatly with [[altitude]] (more specific the density of the air). The higher the [[altitude]] the lower the IAS while flying the same TAS. | Airspeed is usually measured with a [[#Pitot tube]] at the front of the aircraft. The IAS can be the CAS. The IAS is not the TAS since the pressure differs greatly with [[altitude]] (more specific the density of the air). The higher the [[altitude]] the lower the IAS while flying the same TAS. | ||
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=== Calibrated airspeed === | === 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. | |||
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 airspeed === | === 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. | |||
At high altitude, the compressibility of air changes, so even CAS becomes more and more unreliable. For the [[SR-71]] Blackbird with a ceiling of 85.000 feet, the CAS becomes very unreliable and the plane has to be flown based on a EAS. For more conventional aircraft, EAS is not used. Thus, EAS is what a perfect dynamic pressure sensor would show when properly calibrated for the air compressibility at the current altitude. The EAS is the calculated result from the ram pressure (measured by the [[#Pitot tube]]) and the static pressure (measured by the [[altimeter]]). | At high altitude, the compressibility of air changes, so even CAS becomes more and more unreliable. For the [[SR-71]] Blackbird with a ceiling of 85.000 feet, the CAS becomes very unreliable and the plane has to be flown based on a EAS. For more conventional aircraft, EAS is not used. Thus, EAS is what a perfect dynamic pressure sensor would show when properly calibrated for the air compressibility at the current altitude. The EAS is the calculated result from the ram pressure (measured by the [[#Pitot tube]]) and the static pressure (measured by the [[altimeter]]). | ||
=== Mach number === | === Mach number === | ||
* The [http://en.wikipedia.org/wiki/Mach_number '''Mach number''' (M)] is the speed of the aircraft divided by the speed of sound (at that altitude). It is a calculated number without a unit. | |||
*The [http://en.wikipedia.org/wiki/Mach_number '''Mach number''' (M)] is the speed of the aircraft divided by the speed of sound (at that altitude). It is a calculated number without a unit. | |||
The aircraft's behaviour at Mach 1 at sea level is about the same as the behaviour of the aircraft at an altitude of 60000 feet. | The aircraft's behaviour at Mach 1 at sea level is about the same as the behaviour of the aircraft at an altitude of 60000 feet. | ||
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The Mach number is measured/calculated from the same information as the EAS ([[#Pitot tube]] and [[altimeter]]) | The Mach number is measured/calculated from the same information as the EAS ([[#Pitot tube]] and [[altimeter]]) | ||
==V speeds== | == V speeds == | ||
For the complete V speed "definitions" list please visit [http://en.wikipedia.org/wiki/V_speeds Wikipedia]. Here a small abstract. Note that V speed definitions can depend of local [[Flight rules]]. Most V speeds depend on the aircraft configuration (how much it weights etc.) so must be calculated forehand and must be included in the flight-plan. V speeds are used to compare aircraft performance and will be mentioned in the aircraft flight manual (AFM). | For the complete V speed "definitions" list please visit [http://en.wikipedia.org/wiki/V_speeds Wikipedia]. Here a small abstract. Note that V speed definitions can depend of local [[Flight rules]]. Most V speeds depend on the aircraft configuration (how much it weights etc.) so must be calculated forehand and must be included in the flight-plan. V speeds are used to compare aircraft performance and will be mentioned in the aircraft flight manual (AFM). | ||
*M speeds are expressed in Mach. | |||
* M speeds are expressed in Mach. | |||
<!-- please add to this list when needed --> | <!-- please add to this list when needed --> | ||
{| | {| | ||
|- valign="top" | |- valign="top" | ||
|V<sub>1</sub> || Take-off decision speed & Critical engine failure recognition speed. | | V<sub>1</sub> || Take-off decision speed & Critical engine failure recognition speed. | ||
During take-off the speed at which the aircraft safely can take-off even when one (of more) engine fails ("eats a bird"). The co-pilot (FO) will call out V<sub>1</sub> during take-off, the pilot will check if all engines are running and decides to continue or abort take-off. | During take-off the speed at which the aircraft safely can take-off even when one (of more) engine fails ("eats a bird"). The co-pilot (FO) will call out V<sub>1</sub> during take-off, the pilot will check if all engines are running and decides to continue or abort take-off. | ||
|- | |- | ||
|V<sub>2</sub> || Take-off safety speed. | | V<sub>2</sub> || Take-off safety speed. | ||
|- | |||
| V<sub>3</sub> || Flap retraction speed. | |||
|- | |||
| V<sub>A</sub>|| Design manoeuvring speed. Above this speed it is a bad idea to make sudden manoeuvres. | |||
|- | |||
| V<sub>C</sub> || Design cruising speed, also known as the optimum cruise speed, is the most efficient speed in terms of distance, speed and fuel usage. | |||
|- | |||
| V<sub>D</sub> || Max dive speed (for certification only) | |||
|- | |||
| V<sub>FE</sub> || Maximum flap extended speed. | |||
|- | |- | ||
|V<sub> | | V<sub>LE</sub> || Maximum landing gear extended speed. | ||
|- | |- | ||
|V<sub> | | V<sub>LO</sub> || Maximum landing gear operating speed. | ||
|- | |- | ||
|V<sub> | | V<sub>MO</sub> || Maximum operating limit speed. | ||
|- | |- | ||
|V<sub> | | V<sub>NE</sub> || Never exceed speed. | ||
|- | |- | ||
|V<sub> | | V<sub>NO</sub> || Maximum structural cruising speed or maximum speed for normal operations. | ||
|- valign="top" | |||
| V<sub>R</sub> || Nose-wheel take off speed. | |||
The speed at which the nose-wheel leaves (should leave) the ground. As the speed increases the yokes will be pulled at V<sub>r</sub>. It is also the speed at which the aircraft still can be stopped if there is a critical failure. The co-pilot (FO) will call out "rotate" during take off. V<sub>R</sub> is very similar to V<sub>ROT</sub> and V<sub>REF</sub>. | |||
|- | |- | ||
|V<sub> | | V<sub>Ref</sub>|| Landing reference speed or threshold crossing speed. | ||
|- valign="top" | |- valign="top" | ||
|V<sub>S</sub> ||Stall speed or minimum steady flight speed for which the aircraft is still controllable. | | V<sub>S</sub> || Stall speed or minimum steady flight speed for which the aircraft is still controllable. | ||
|- valign="top" | |- valign="top" | ||
|V<sub>S<sub>0</sub></sub> || Stall speed or minimum flight speed in landing configuration. | | V<sub>S<sub>0</sub></sub> || Stall speed or minimum flight speed in landing configuration. | ||
|- | |||
| V<sub>S<sub>1</sub></sub> || Stalling speed in a specified configuration | |||
|- | |- | ||
|V<sub> | | V<sub>X</sub> || Best angle of climb speed | ||
|- | |- | ||
|V<sub> | | V<sub>X<sub>SE</sub></sub> || Best angle of climb speed, one engine out | ||
|- | |- | ||
|V<sub> | | V<sub>Y</sub> || Best rate of climb speed | ||
|- | |- | ||
|V<sub> | | V<sub>Y<sub>SE</sub></sub> || Best rate of climb speed, one engine out | ||
|} | |} | ||
==Pitot tube== | * Not knowing the (complete list of) V speeds has caused dramatic accidents. It has occurred that the pilot and co-pilot were not aware of the minimal speed of an aircraft during landing with one engine damaged causing loss of control just before touch-down (the pilot gave full throttle hoping to gain speed expecting to get back control causing the left-over engine push the aircraft to one side). | ||
== Pitot tube == | |||
The [http://en.wikipedia.org/wiki/Pitot_tube pitot tube] is the tool to measure the airspeed. It is a tube directed forwards, exposed to the airstream. The air is being pushed inwards (rammed) by the motion of the aircraft and the (ram) pressure is measured. The measured pressure is corrected indicating the airspeed. The ram pressure is also called the dynamic pressure opposite the static pressure that us used to indicate [[altitude]]. Bigger aircraft have two pitot tubes and the indicator displays the average of the two. However, most often only one pitot tube is used to control the autopilot, even when the indicator is connected with two. | The [http://en.wikipedia.org/wiki/Pitot_tube pitot tube] is the tool to measure the airspeed. It is a tube directed forwards, exposed to the airstream. The air is being pushed inwards (rammed) by the motion of the aircraft and the (ram) pressure is measured. The measured pressure is corrected indicating the airspeed. The ram pressure is also called the dynamic pressure opposite the static pressure that us used to indicate [[altitude]]. Bigger aircraft have two pitot tubes and the indicator displays the average of the two. However, most often only one pitot tube is used to control the autopilot, even when the indicator is connected with two. | ||
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Ice is a known cause of blockage of the pitot tube hence there are pitot heaters that should prevent forming of ice. Another known cause of blockage are insects. Blockage of pitot tubes is a known cause of some very dramatic accidents and every pilot should learn how to deal with strange behaving speed indicators and autopilots. | Ice is a known cause of blockage of the pitot tube hence there are pitot heaters that should prevent forming of ice. Another known cause of blockage are insects. Blockage of pitot tubes is a known cause of some very dramatic accidents and every pilot should learn how to deal with strange behaving speed indicators and autopilots. | ||
==Additional information== | == Additional information == | ||
<!-- repository (I so love that word) for anything speed related --> | <!-- repository (I so love that word) for anything speed related --> | ||
*Velocity: A vector combining speed and (angle of) direction. Often used as synonym of speed. | * Velocity: A vector combining speed and (angle of) direction. Often used as synonym of speed. | ||
*[[Understanding Supersonic Flight]] | * [[Understanding Supersonic Flight]] | ||
== External links == | |||
* [http://en.wikipedia.org/wiki/V_speeds V speeds] on English Wikipedia | |||
* [http://www.ecfr.gov/cgi-bin/text-idx?SID=08466be6bfab4f37b995be61ff13ec21&node=14:1.0.1.3.11.3.164.8&rgn=div8 US. CFR 14 §25.335 – Design airspeeds] Do note that these are EAS (equivalent airspeed), not IAS (indicated airspeed). | |||
* [http://code7700.com/v-speeds.html V-Speeds] at Code 7700 | |||
[[Category:Aviation]] | [[Category:Aviation]] | ||