# Pitot tube

Pitot tube

A Pitot (pronEng|ˈpiːtoʊ) tube is a pressure measurement instrument used to measure fluid flow velocity. The Pitot tube was invented by Italian-born French engineer Henri Pitot in the early 1700s, and was modified to its modern form in the mid 1800s by French scientist Henry Darcy. It is widely used to determine the airspeed of an aircraft and to measure air and gas velocities in industrial applications.

The basic Pitot tube simply consists of a tube pointing directly into the fluid flow. As this tube contains air, a pressure can be measured as the moving air is brought to rest. This pressure is the stagnation pressure of the air, also known as the total pressure, or sometimes (particularly in aviation circles) the pitot pressure.

The measured stagnation pressure cannot of itself be used to determine the airspeed. However, since Bernoulli's equation states that

::stagnation pressure = static pressure + dynamic pressure,

then the dynamic pressure is simply the difference between the static pressure and the stagnation pressure. The static pressure is generally measured using the static ports on the side of the fuselage. The dynamic pressure is then determined using a diaphragm inside an enclosed container. If the air on one side of the diaphragm is at the static pressure, and the other at the stagnation pressure, then the deflection of the diaphragm is proportional to the dynamic pressure, which can then be used to determine the indicated airspeed of the aircraft. The diaphragm arrangement is typically contained within the airspeed indicator, which converts the dynamic pressure to an airspeed reading by means of mechanical levers.

Instead of static ports, a Pitot-static tube (also called a Prandtl tube) may be employed, which has a second tube coaxial with the Pitot tube with holes on the sides, outside the direct airflow, to measure the static pressure.

Pitot tubes on aircraft commonly have heating elements to prevent the tube from becoming clogged with ice. The failure of these systems has catastrophic consequences, like in the case of Austral Líneas Aéreas Flight 2553.

Industry Applications

In industry the velocities being measured are those flowing in ducts or tubing where measurements by an anemometer would be difficult to obtain. In these kinds of measurements, the most practical instrument to use is the Pitot tube. The Pitot tube can be inserted through a small hole in the duct with the Pitot connected to a U-tube water gauge or some other differential pressure gauge for determining the velocity inside the duct.

The quantity of air flowing through the duct each minute can then be estimated from:

:Volume Flow Rate (cubic feet per minute) = Duct Area (square feet) &times; Velocity (feet per minute) :Volume Flow Rate (cubic meters per second) = Duct Area (square meters) &times; Velocity (meters per second)

In aviation air speed is typically measured in knots.

ee also

*Airspeed indicator
*Calibrated airspeed
*Flow measurement
*Mach number
*Piezometer
*Pitot-static system
*Position error
*True airspeed
*Atmospheric icing
*Icing conditions
*PIREP
*AIRMET
*SIGMET
*Anti-icing
*Deicing

References

*cite book|last=Kermode|first=A.C.|others=Barnard, R.H. (Ed.) and Philpott, D.R. (Ed.)|title=Mechanics of Flight|edition=10th edition|origyear=1972|year=1996|publisher=Prentice Hall|id=ISBN 0-582-23740-8|pages=63-67
*cite book|last=Pratt|first=Jeremy M.|edition=3rd edition|title=The Private Pilot's Licence Course: Principles of Flight, Aircraft General Knowledge, Flight Performance and Planning|origyear=1997|year=2005|id=ISBN 1-874783-23-3|pages=gen108-gen111
*cite book|author=Tietjens, O.G.|title=Applied Hudro- and Aeromechanics, based on lectures of L. Prandtl, Ph.D| publisher=Dove Publications, Inc. | year=1934 | isbn=0-486-60375-X | pages=226-239

* [http://www.spaceagecontrol.com/pm/uploads/Main.Litroom2/naca-tn-616.pdf The Measurement of Air Speed in Airplanes]
* [http://www.spaceagecontrol.com/pm/uploads/Main.Litroom2/naca-tn-1496.pdf Investigation of the Fuselage Interference on a Pitot-Static Tube Extending Forward From the Nose of the Fuselage]

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### Look at other dictionaries:

• Pitot Tube — Tube de Pitot Tube de Pitot Le tube de Pitot et l antenne de Prandtl sont des systèmes similaires de mesure de vitesse des fluides. Ils sont notamment utilisés pour l anémométrie en aéronautique. Il doit son nom au physicien français Henri Pitot… …   Wikipédia en Français

• Pitot tube — [pē′tō, pē tō′, pē′tō, pē tō′] n. [after Henri Pitot (1695 1771), Fr physicist] 1. [also p t ] a small, L shaped tube which, when inserted vertically into a flowing fluid with its open end facing upstream, measures the total pressure of the fluid …   English World dictionary

• Pitot tube — Pito vamzdelis statusas T sritis Standartizacija ir metrologija apibrėžtis Hidrometrinis vamzdelis dujų ar skysčių greičiui matuoti. atitikmenys: angl. Pitot tube vok. Pitot Rohr, n; Pitotsches Rohr, n; Staurohr, n rus. трубка Пито, f pranc. tube …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• Pitot tube — Pito vamzdelis statusas T sritis Standartizacija ir metrologija apibrėžtis Hidropneumatinis vamzdelis visuminiam skysčio ar dujų tekėjimo slėgiui matuoti. atitikmenys: angl. Pitot tube vok. Pitot Rohr, n; Pitotsches Rohr, n; Staurohr, n rus.… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• Pitot tube — Pito vamzdelis statusas T sritis Standartizacija ir metrologija apibrėžtis Vamzdelinis įtaisas, įmerkiamas į skysčio arba dujų tėkmę ir turintis kotui statmeną cilindrinę galvutę, kurioje yra viena arba kelios slėgio atšakų skylutės. atitikmenys …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• Pitot tube — Pito vamzdis statusas T sritis fizika atitikmenys: angl. Pitot tube vok. Pitot Rohr, n; Pitotsche Röhre, f; Pitotsches Rohr, n rus. трубка Пито, f pranc. tube de Pitot, m …   Fizikos terminų žodynas

• pitot tube — pi·tot tube .pē .tō n, often cap P a device that consists of a tube having a short right angled bend which is placed vertically in a moving body of fluid with the mouth of the bent part directed upstream and that is used with a manometer to… …   Medical dictionary

• pitot tube — noun Usage: often capitalized P Etymology: French (tube de) Pitot, from Henri Pitot died 1771 French physicist Date: circa 1859 1. a device that consists of a tube having a short right angled bend which is placed vertically in a moving body of… …   New Collegiate Dictionary

• Pitot tube — /pee toh, pee toh / (often l.c.) an instrument for measuring fluid velocity, consisting of a narrow tube, one end of which is open and faces upstream, the other end being connected to a manometer. [1880 85; named after Henri Pitot (1695 1771),… …   Universalium

• pitot tube — An open end tube that points directly into the air flowing over the aircraft structure, providing pressure for the pitot and, often, the static systems. See pitot pressure …   Aviation dictionary