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Airspeed
In aviation, airspeed is the speed of an aircraft relative to the air it is flying through (which itself is usually moving relative to the ground due to wind). In contrast, the ground speed is the speed of an aircraft with respect to the surface of the Earth (whether over land or presumed-stationary water). It is difficult to measure the exact airspeed of the aircraft (true airspeed), but other measures of airspeed, such as indicated airspeed and Mach number give useful information about the capabilities and limitations of airplane performance. The common measures of airspeed are: * Indicated airspeed (IAS), what is read on an airspeed gauge connected to a pitot-static system. * Calibrated airspeed (CAS), indicated airspeed adjusted for pitot system position and installation error. * True airspeed (TAS) is the actual speed the airplane is moving through the air. When combined with aircraft direction, wind speed and direction, it can be used to calculate ground speed and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Indicated Airspeed
Indicated airspeed (IAS) is the airspeed of an aircraft as measured by its pitot-static system and displayed by the airspeed indicator (ASI). This is the pilots' primary airspeed reference. This value is not corrected for installation error, instrument error, or the actual encountered air density, being instead calibrated to always reflect the adiabatic compressible flow of the International Standard Atmosphere at sea level. It uses the difference between total pressure and static pressure, provided by the system, to either mechanically or electronically measure dynamic pressure. The dynamic pressure includes terms for both density and airspeed. Since the airspeed indicator cannot know the density, it is by design calibrated to assume the sea level standard atmospheric density when calculating airspeed. Since the actual density will vary considerably from this assumed value as the aircraft changes altitude, IAS varies considerably from true airspeed (TAS), the relative ve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
True Airspeed
The true airspeed (TAS; also KTAS, for ''knots true airspeed'') of an aircraft is the speed of the aircraft relative to the air mass through which it is flying. The true airspeed is important information for accurate navigation of an aircraft. Traditionally it is measured using an analogue TAS indicator, but as GPS has become available for civilian use, the importance of such air-measuring instruments has decreased. Since ''indicated'', as opposed to ''true'', airspeed is a better indicator of margin above the stall, true airspeed is not used for controlling the aircraft; for these purposes the indicated airspeed – IAS or KIAS (knots indicated airspeed) – is used. However, since indicated airspeed only shows true speed through the air at standard sea level pressure and temperature, a TAS meter is necessary for navigation purposes at cruising altitude in less dense air. The IAS meter reads very nearly the TAS at lower altitude and at lower speed. On jet airliners the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Calibrated Airspeed
In aviation, calibrated airspeed (CAS) is indicated airspeed corrected for instrument and position error. When flying at sea level under International Standard Atmosphere conditions (15 °C, 1013 hPa, 0% humidity) calibrated airspeed is the same as equivalent airspeed (EAS) and true airspeed (TAS). If there is no wind it is also the same as ground speed (GS). Under any other conditions, CAS may differ from the aircraft's TAS and GS. Calibrated airspeed in knots is usually abbreviated as ''KCAS'', while indicated airspeed is abbreviated as ''KIAS''. In some applications, notably British usage, the expression ''rectified airspeed'' is used instead of calibrated airspeed. Practical applications of CAS CAS has two primary applications in aviation: * for navigation, CAS is traditionally calculated as one of the steps between indicated airspeed and true airspeed; * for aircraft control, CAS (and EAS) are the primary reference points, since they describe the dynamic pressure ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Airspeed Indicator
The airspeed indicator (ASI) or airspeed gauge is a flight instrument indicating the airspeed of an aircraft in kilometres per hour (km/h), knots (kn or kt), miles per hour (MPH) and/or metres per second (m/s). The recommendation by ICAO is to use km/h, however knots (kt) is currently the most used unit. The ASI measures the pressure differential between static pressure from the static port, and total pressure from the pitot tube. This difference in pressure is registered with the ASI pointer on the face of the instrument. Colour-coded speeds and ranges The ASI has standard colour-coded markings to indicate safe operation within the limitations of the aircraft. At a glance, the pilot can determine a recommended speed (V speeds) or if speed adjustments are needed. Single and multi-engine aircraft have common markings. For instance, the green arc indicates the normal operating range of the aircraft, from ''V''S1 to ''V''NO. The white arc indicates the flap operating range ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Position Error
Position error is one of the errors affecting the systems in an aircraft for measuring airspeed and altitude. It is not practical or necessary for an aircraft to have an airspeed indicating system and an altitude indicating system that are exactly accurate. A small amount of error is tolerable. It is caused by the location of the static vent that supplies air pressure to the airspeed indicator and altimeter; there is no position on an aircraft where, at all angles of attack, the static pressure is always equal to atmospheric pressure. Static system All aircraft are equipped with a small hole in the surface of the aircraft called the static port. The air pressure in the vicinity of the static port is conveyed by a conduit to the altimeter and the airspeed indicator. This static port and the conduit constitute the aircraft's static system. The objective of the static system is to sense the pressure of the air at the altitude at which the aircraft is flying. In an ideal stati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Knot (unit)
The knot () is a unit of speed equal to one nautical mile per hour, exactly (approximately or ). The ISO standard symbol for the knot is kn. The same symbol is preferred by the Institute of Electrical and Electronics Engineers ( IEEE), while kt is also common, especially in aviation, where it is the form recommended by the International Civil Aviation Organization ( ICAO). The knot is a non- SI unit. The knot is used in meteorology, and in maritime and air navigation. A vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour. Definitions ;1 international knot = :1 nautical mile per hour (by definition), : (exactly), : (approximately), : (approximately), : (approximately) : (approximately). The length of the internationally agreed nautical mile is . The US adopted the international definition in 1954, having previously used the US nautical mile (). The UK adopted the international nautical mile defi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Equivalent Airspeed
In aviation, equivalent airspeed (EAS) is calibrated airspeed (CAS) corrected for the compressibility of air at a non-trivial Mach number. It is also the airspeed at sea level in the International Standard Atmosphere at which the dynamic pressure is the same as the dynamic pressure at the true airspeed (TAS) and altitude at which the aircraft is flying. In low-speed flight, it is the speed which would be shown by an airspeed indicator with zero error.Houghton, E.L. and Carpenter, P.W. (1993), ''Aerodynamics for Engineering Students'', Section 2.3.3, Butterworth-Heinemann, Oxford UK. It is useful for predicting aircraft handling, aerodynamic loads, stalling etc. \mathrm = \mathrm \times \sqrt where is actual air density and is standard sea level density (1.225 kg/m3 or 0.00237 slug/ft3). is a function of dynamic pressure: \mathrm = \sqrt where is the dynamic pressure q = \tfrac12\, \rho\, v^. EAS can also be obtained from the aircraft Mach number and static pre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pitot Tube
A pitot tube ( ; also pitot probe) measures fluid flow velocity. It was invented by French engineer Henri Pitot during his work with aqueducts and published in 1732, and modified to its modern form in 1858 by Henry Darcy. It is widely used to determine the airspeed of aircraft; the water speed of boats; and the flow velocity of liquids, air, and gases in industry. Theory of operation The basic pitot tube consists of a tube pointing directly into the oncoming fluid flow. Pressure in the tube can be measured as the moving fluid cannot escape and stagnates. This pressure is the stagnation pressure of the fluid, also known as the total pressure or (particularly in aviation) the pitot pressure. The measured stagnation pressure cannot just by itself be used to determine the fluid flow velocity (airspeed in aviation) directly. However, with a measured static pressure as well it can be determined by the use of Bernoulli's equation which states: :Stagnation pressure = static pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ground Speed
Ground speed is the horizontal component of the velocity of an aircraft relative to the Earth’s surface, also referred to as "speed over the ground". 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. Theoretically, an aircraft diving vertically and unaffected by wind 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. 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 it is flying through. The air mass may be moving ov ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bernoulli's Equation
Bernoulli's principle is a key concept in fluid dynamics that relates pressure, speed and height. For example, for a fluid flowing horizontally Bernoulli's principle states that an increase in the speed occurs simultaneously with a decrease in static pressure, pressure The principle is named after the Swiss mathematician and physicist Daniel Bernoulli, who published it in his book ''Hydrodynamica'' in 1738. Although Bernoulli deduced that pressure decreases when the flow speed increases, it was Leonhard Euler in 1752 who derived Bernoulli's equation in its usual form. Bernoulli's principle can be derived from the principle of conservation of energy. This states that, in a steady flow, the sum of all forms of energy in a fluid is the same at all points that are free of viscous forces. This requires that the sum of kinetic energy, potential energy and internal energy remains constant. Thus an increase in the speed of the fluid—implying an increase in its kinetic energy—occur ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Static Pressure
In fluid mechanics the term static pressure refers to a term in Bernoulli's equation written words as ''static pressure + dynamic pressure = total pressure''. Since pressure measurements at any single point in a fluid always give the static pressure value, the 'static' is often dropped. In the design and operation of aircraft, ''static pressure'' is the air pressure in the aircraft's static pressure system. Static pressure in fluid dynamics The concept of pressure is central to the study of fluids. A pressure can be identified for every point in a body of fluid, regardless of whether the fluid is in motion. Pressure can be measured using an aneroid, Bourdon tube, mercury column, or various other methods. The concepts of ''total pressure'' and '' dynamic pressure'' arise from Bernoulli's equation and are significant in the study of all fluid flows. These two pressures are not pressures in the usual sense - they cannot be measured using a pressure sensor. To avoid potential ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
