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Encyclopedia > Airspeed indicator
Airspeed Indicator in a light aircraft

The airspeed indicator or airspeed gauge is an instrument used in an aircraft to display the craft's airspeed, typically in knots, to the pilot. Image File history File links This is a lossless scalable vector image. ... Image File history File links Airspeed-indicator-FAA.PNG Summary Extracted from the Pilots Handbook of Aeronautical Knowledge, AC 61-23C, online at http://www. ... Image File history File links Airspeed-indicator-FAA.PNG Summary Extracted from the Pilots Handbook of Aeronautical Knowledge, AC 61-23C, online at http://www. ... Flying machine redirects here. ... This article contains information that has not been verified and thus might not be reliable. ... A knot is a unit of speed abbreviated kt or kn. ... For other uses, see Aviator (disambiguation). ...

Contents

Markings

A high sensitivity "540 degree" airspeed indicator used in a glider. The pointer swings past zero (top), but the colored arcs do not overlap. The needle shows an indicated airspeed of 60 knots.

Image File history File linksMetadata No higher resolution available. ... Image File history File linksMetadata No higher resolution available. ... For other uses, see Glider (disambiguation). ... This article contains information that has not been verified and thus might not be reliable. ... A knot is a unit of speed abbreviated kt or kn. ...

Light aircraft

Airspeed indicator markings use a set of standardized colored bands and lines on the face of the instrument. The white range is the normal range of operating speeds for the aircraft with the flaps extended as for landing or takeoff. The green range is the normal range of operating speeds for the aircraft without flaps extended. The yellow range is the range in which the aircraft may be operated in smooth air, and then only with caution to avoid abrupt control movement. Flaps are hinged surfaces on the trailing edge of an airplane wing which, when deployed, increase the lift (and drag) of a wing by changing the camber of the airfoil. ...


A redline mark indicates VNE, or velocity (never exceed). This is the maximum demonstrated safe airspeed that the aircraft must not exceed under any circumstances. The red line is preceded by a yellow band which is the caution area, which runs from VNO (maximum structural cruise speed) to VNE. A green band runs from VS1 to VNO. VS1 is the stall speed with flaps and landing gear retracted. A white band runs from VSO to VFE. VSO is the minimum steady flight speed with flaps extended, and VFE is the highest speed at which flaps can be extended. Airspeed indicators in multi-engine aircraft show a short radial red line near to the bottom of green arc for Vmc, the minimum indicated airspeed at which the aircraft can be controlled with the critical engine inoperative and a blue line for VYSE, the speed for best rate of climb with the critical engine inoperative. Tachometer showing red lines above 14,000 rpm. ... V speeds are speeds that define certain performance and limiting characteristics of an aircraft. ... Stall speed is an aerodynamic term. ... The word Flap can refer to several things. ... Main and nosewheel undercarriage of a Qatar Airways Airbus A330 The undercarriage or landing gear is equipment which supports an aircraft when it is not flying. ... Flaps are hinged surfaces on the trailing edge of an airplane wing which, when deployed, increase the lift (and drag) of a wing by changing the camber of the airfoil. ... The critical engine of a multi-engine, fixed-wing aircraft is the one whose failure would result in the most adverse effects on the aircrafts handling and performance // When one of the engines on a typical multi-engine aircraft becomes inoperative, a thrust imbalance exists between the operative and... The critical engine of a multi-engine, fixed-wing aircraft is the one whose failure would result in the most adverse effects on the aircrafts handling and performance // When one of the engines on a typical multi-engine aircraft becomes inoperative, a thrust imbalance exists between the operative and...

Airspeed indicator markings for a multiengine airplane Note airspeed indicating "blue line."
Airspeed indicator markings for a multiengine airplane Note airspeed indicating "blue line."

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Blue Line can refer to: Blue line (ice hockey) - In ice hockey, the line between center ice and each teams zone. ...

Large aircraft

The airspeed indicator is especially important for monitoring V-Speeds while operating an aircraft. However, in large aircraft, V-speeds can vary considerably depending on airfield elevation, temperature and aircraft weight. For this reason the coloured ranges found on the ASIs of light aircraft are not used - instead the instrument has a number of moveable pointers known as bugs which may be preset by the pilot to indicate appropriate V-speeds for the current conditions. VMC redirects here. ...


Jet aircraft do not have VNO and VNE like piston-engined aircraft, but instead have a maximum operating IAS, VMO and maximum Mach number, MMO. To observe both limits, the pilot of a jet airplane needs both an airspeed indicator and a Machmeter, each with appropriate red lines. In some general aviation jet airplanes, the Machmeter is combined into a single instrument that contains a pair of concentric indicators, one for the indicated airspeed and the other for indicated Mach number. Jet aircraft are aircrafts with jet engines. ... An F/A-18 Hornet at transonic speed and displaying the Prandtl-Glauert singularity just before reaching the speed of sound Mach number (Ma) (generally pronounced , sometimes or ) is the speed of an object moving through air, or any fluid substance, divided by the speed of sound through that substance... Diagram illustrating the face of a Machmeter A Machmeter shows the ratio of the speed of sound to the true airspeed an aircraft is flying. ...


An alternative single instrument is the "maximum allowable airspeed indicator." It has a movable pointer that indicates the never-exceed speed, which changes with altitude to avoid the onset of transonic shock waves on the wing. The pointer is usually red-and-white striped, and thus known as a "barber pole". As the aircraft climbs to high altitude, such that MMO rather than VMO becomes the limiting speed, the barber pole moves to lower IAS values. Transonic is an aeronautics term referring to a range of velocities just below and above the speed of sound. ... Shock Waves is a horror movie from 1977 directed by Ken Wiederhorn. ...


Modern aircraft employing glass cockpit instrument systems employ two airspeed indicators: an electronic indicator on the primary flight data panel and a traditional mechanical instrument for use if the electronic panels fail. The airspeed is typically presented in the form of a "tape strip" that moves up and down, with the current airspeed in the middle. The same color scheme is used as on a mechanical airspeed indicator to represent the V speeds.In modern aircraft it even have another electronic indicator airspeed. This article does not cite any references or sources. ...


Operation

Airspeed indicator connections
Airspeed indicator connections

Along with the altimeter and vertical speed indicator, the airspeed indicator is a member of the pitot-static system of aviation instruments, so named because they operate by measuring pressure in the pitot and static circuits. Image File history File links ASI-operation-FAA.png Summary Extracted from the Pilots Handbook of Aeronautical Knowledge, AC 61-23C, online at http://www. ... Image File history File links ASI-operation-FAA.png Summary Extracted from the Pilots Handbook of Aeronautical Knowledge, AC 61-23C, online at http://www. ... Diagram showing the face of a three-pointer sensitive aircraft altimeter displaying altitude in feet. ... A variometer (also known as a rate-of-climb indicator, a vertical speed indicator (VSI), or a vertical velocity indicator (VVI)) is an instrument in an aircraft used to inform the pilot of the rate of descent or climb. ... A pitot-static system is an avionics component which directs ram air pressure and static air pressure lines into the appropriate flight instruments. ... A Pitot tube is a measuring instrument used to measure fluid flow. ...


Airspeed indicators work by measuring the difference between static pressure, captured through one or more static ports; and stagnation pressure due to "ram air", captured through a pitot tube. This difference in pressure due to ram air is called dynamic pressure. Static pressure is a term used in ventilation engineering, airspeed indication, fluid statics, hydraulics and flow measurement. ... Stagnation pressure is the pressure at a stagnation point in a fluid flow, where the kinetic energy is converted into pressure energy. ... A Pitot tube is a measuring instrument used to measure fluid flow. ... Velocity pressure is also called fluid dynamic pressure or Q given by the equation. ...

Internal mechanism of an airspeed indicator
Internal mechanism of an airspeed indicator

The static ports are located on the exterior of the aircraft, at a location chosen to detect the prevailing atmospheric pressure as accurately as possible, that is, with minimum disturbance from the presence of the aircraft. Some aircraft have static ports on both sides of the fuselage or empennage, in order to more accurately measure static pressure during slips and skids. Aerodynamic slips and skids cause either or both static ports and pitot tube(s) to present themselves to the relative wind in other than basic forward motion. Thus, alternative placement on some aircraft. Image File history File links Size of this preview: 609 × 599 pixelsFull resolution (1002 × 986 pixel, file size: 65 KB, MIME type: image/png) Figure 3-9. ... Image File history File links Size of this preview: 609 × 599 pixelsFull resolution (1002 × 986 pixel, file size: 65 KB, MIME type: image/png) Figure 3-9. ... The fuselage can be short, and seemingly unaerodynamic, as in this Christen Eagle 2 The fuselage (from the French fuselé spindle-shaped) is an aircrafts main body section that holds crew and passengers or cargo. ... Empennage is an aviation term used to describe the tail portion of an aircraft. ... A slip is an aerodynamic state where an aircraft is moving sideways as well as forward relative to the oncoming airflow. ... In flying, a skid is a specific type of slip during a turn where the sideways movement of the aircraft is outwards from the centre of the turn. ...


Icing is a problem for pitot tubes when the air temperature is below freezing and visible moisture is present in the atmosphere, as when flying through cloud or precipitation. Electrically heated pitot tubes are used to prevent ice forming over the tube. The effect of atmospheric icing on a tree. ...


The airspeed indicator and altimeter will be rendered inoperative by blockage in the static system. To avoid this problem, most aircraft intended for use in instrument meteorological conditions are equipped with an alternate source of static pressure. In unpressurised aircraft, the alternate static source is usually achieved by opening the static pressure system to the air in the cabin. This is less accurate, but is still workable. In pressurised aircraft, the alternate static source is a second set of static ports on the skin of the aircraft, but at a different location to the primary source. Diagram showing the face of a three-pointer sensitive aircraft altimeter displaying altitude in feet. ... Instrument meteorological conditions (IMC) are weather conditions that require aircraft pilots to fly primarily by reference to instruments rather than outside visual references, as they could in Visual meteorological conditions (VMC). ...


Use

The airspeed indicator is used by the pilot during all phases of flight, from take-off, climb, cruise, descent and landing in order to maintain airspeeds specific to the aircraft type and operating conditions as specified in the Operating Manual.


During instrument flight, the airspeed indicator is used in addition to the Artificial horizon as an instrument of reference for pitch control during climbs, descents and turns. It has been suggested that Air traffic control#Instrument Flight Rules (IFR) be merged into this article or section. ... This article or section should be merged with Attitude indicator The term Artificial Horizon is used to describe devices that can indicate the position of the horizon when it is not possible to see the actual horizon. ...


The airspeed indicator is also used in dead reckoning, where time, speed, and bearing are used for navigation in the absence of aids such as NDBs, VORs or GPS. Dead reckoning (DR) is the process of estimating ones current position based upon a previously determined position, or fix, and advancing that position based upon measured velocity, time, heading, as well as the effect of currents or wind. ... A Non-directional Beacon, or NDB, is a radio broadcast station in a known location, used as a navigational aid by aircraft pilots. ... In Norse Mythology Vor is a goddess of the Aesir. ... Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...


Alternatives: Lift Reserve Indicator

Lift Reserve Indicator as installed
Lift Reserve Indicator as installed

The "Lift Reserve Indicator", or LRI, has been proposed as an alternative or backup to the Airspeed Indicator (ASI) during critical stages of flight. This is an elegant device but is rarely found in light aircraft or even transport jets. The conventional Airspeed Indicator is less sensitive and less accurate as airspeed diminishes, thus providing less reliable information to the pilot as the aircraft slows towards the stall. The actual stall speed of an aircraft also varies with flight conditions, particularly changes in gross weight and wing loading during maneuvers. The ASI does not show the pilot directly how the stall is being approached during these maneuvers, whereas the LRI does.


The LRI shows the pilot directly the Potential of Wing Lift (POWL) above the stall at all times and at any airspeed, so it is more descriptive and easier for the pilot to use. The LRI uses dynamic differential pressure and angle of attack to operate. It is very fast acting and extremely accurate at slow airspeeds, thus providing more reliable information to the pilot as airspeed diminishes and become critical.


The LRI uses a three zone, red-white-green display. During flight, the green zone is well above the stall where flight controls are firm, angle of attack is low, and the unused POWL is high. The white zone is near the stall where flight controls soften, angle of attack is high, and the unused POWL is diminished. The top of the red zone defines the beginning of the stall. The severity of stall increases as the needle travels deeper into the red. During the takeoff, the LRI uses dymanic pressure to operate and will not lift the needle above the red zone until enough airspeed energy is available to fly.


The pilot adjusts the instrument to indicate the edge of the red-white zone during minimum airspeed practice at altitude, indicating the aircraft has zero POWL beyond that point. Since the wing will stall at the same angle of attack at any airspeed, once properly adjusted the LRI will indicate the red-white edge anytime the stall is approached. This includes landing stalls, climbing stalls, and accelerated stalls. After adjustment, the black line in the center of the white indicates maximum angle of climb and maximum angle of descent with enough reserve lift for the landing flare. With practice, the pilot can use the LRI to determine the exact moment for liftoff with minimum ground roll and maximum angle of climb combined.


The LRI has been well received by STOL pilots and pilots of experimental or home-built aircraft. The LRI is very useful for short field landings, short field takeoffs, and slow speed maneuvers such as steep turns, steep climbs, and steep descents, and also allows pilots of fast or "slippery" aircraft to land with little or no float very reliably. Since the LRI is so useful at the critical lower end of the flight envelope, most pilots will use the LRI as a complement to the ASI, using the LRI for slow speed work and the ASI for cruising and navigational work.


Types of airspeed measurements

Memory aid: ICETEA (beverage) but drop the ending EA to get Indicated->Calibrated->Equivalent->True


At increased Density Altitude, for the same given indicated airspeed the aircraft's true airspeed (TAS) will be higher, but the same indicated airspeed limits (IAS) apply. Likewise, most efficient cruise speed, total drag, available lift, stall speed, and other aerodynamic information depend on calibrated, not true airspeed. Most aircraft exhibit a small difference between the airspeed actually shown on the instrument (indicated airspeed, or IAS) and the speed the instrument should theoretically show (calibrated airspeed or CAS). This difference, called position error, is mainly due to inaccurate sensing of static pressure. It is usually not possible to find a position for the static ports which, at all angles of attack, accurately senses the atmospheric pressure at the altitude at which the aircraft is flying. Density altitude is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation. ... Indicated airspeed (IAS) is the airspeed read directly from the airspeed indicator on an aircraft, driven by the pitot-static system. ... True airspeed (TAS) is the speed of an aircraft relative to the airmass in which it flies, i. ... Calibrated airspeed (CAS) is indicated airspeed, corrected for instrument error and position error. ... This article belongs in one or more categories. ... In this diagram, the black arrow represents the direction of the wind. ...


Bernoulli's principle states that total pressure is constant along a streamline. Pitot pressure is equal to total pressure so pitot pressure is constant all around the aircraft and does not suffer position error. (However, pitot pressure can suffer alignment error if the pitot tube is not aligned directly into the oncoming airflow.) Bernoullis Principle states that for an ideal fluid (low speed air is a good approximation), with no work being performed on the fluid, an increase in velocity occurs simultaneously with decrease in pressure or a change in the fluids gravitational potential energy. ...


The position of static ports must be selected carefully by an aircraft designer because position error must be small at all speeds within the operating range of the aircraft. A calibration chart specific to the type of aircraft is usually provided.


At high speeds and altitudes, calibrated airspeed must be further corrected for compressibility error to give equivalent airspeed (EAS). Compressibility error arises because the impact pressure will cause the air to compress in the pitot tube. The calibration equation (see calibrated airspeed) accounts for compressibility, but only at standard sea level pressure. At other altitudes compressibility error correction may be obtained from a chart. In practice compressibility error is negligible below about 3,000 m / 10,000 feet and 100 m/s / 200 knots CAS. Equivalent airspeed (EAS) is the airspeed which represents the same dynamic pressure at altitude that would be generated by flying at the corresponding true airspeed (TAS) at sea level. ... Calibrated airspeed (CAS) is indicated airspeed, corrected for instrument error and position error. ...


The true airspeed can be calculated as a function of equivalent airspeed and local air density, (or temperature and pressure altitude which determine density). Some airspeed indicators incorporate a slide rule mechanism to perform this calculation. Otherwise, it can be performed with a calculator such as the E6B handheld circular slide rule. For a quick approximation of TAS add 2% per 300m / 1000 feet of altitude to IAS (or CAS). e.g. IAS = 52 m/s /100 Knots. At 3000 m / 10,000' Above Sea Level, TAS is 62 m/s / 120 Knots. A typical 10 inch student slide rule (Pickett N902-T simplex trig). ... The front of a metal E6B. An E6B flight computer commonly used by student pilots. ... A typical 10 inch student slide rule (Pickett N902-T simplex trig). ...


See also

This article contains information that has not been verified and thus might not be reliable. ... Six basic instruments in a light twin-engine airplane arranged in the basic-T. From top left: airspeed indicator, attitude indicator, altimeter, turn coordinator, heading indicator, and vertical speed indicator Most aircraft are equipped with a standard set of flight instruments which give the pilot information about the aircrafts... Diagram illustrating the face of a Machmeter A Machmeter shows the ratio of the speed of sound to the true airspeed an aircraft is flying. ... This article belongs in one or more categories. ... V speeds are speeds that define certain performance and limiting characteristics of an aircraft. ...

Sources

  • (2004) Airplane Flying Handbook. U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration. FAA-8083-3A. 
  • (2005-11-25) Instrument Flying Handbook. U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration. FAA-H-8083-15. 
  • (2003) Pilot's Handbook of Aeronautical Knowledge. U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration. FAA AC 61-23C. 

Installing and flying the Lift Reserve Indicator, article and photos by Sam Buchanan http://home.hiwaay.net/~sbuc/journal/liftreserve.htm Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 329th day of the year (330th in leap years) in the Gregorian calendar. ...


This article incorporates text from Airplane Flying Handbook, a public domain work of the United States Government.
This article incorporates text from Instrument Flying Handbook, a public domain work of the United States Government.
This article incorporates text from Pilot's Handbook of Aeronautical Knowledge, a public domain work of the United States Government.
The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ... A work of the United States government, as defined by United States copyright law, is a work prepared by an officer or employee of the U.S. government as part of that persons official duties. ... The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ... A work of the United States government, as defined by United States copyright law, is a work prepared by an officer or employee of the U.S. government as part of that persons official duties. ... The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ... A work of the United States government, as defined by United States copyright law, is a work prepared by an officer or employee of the U.S. government as part of that persons official duties. ...


 
 

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