Pitot tube
|
|
A Pitot tube is a measuring instrument used to measure fluid flow. The Pitot tube is named after its inventor, Henri Pitot, and was modified to its modern form by Henry Darcy.
Pitot_tube_diagram.png
The basic instrument consists of two coaxial tubes: the interior tube is open to the flow (i.e. perpendicular), whilst the exterior tube is open at ninety degrees to the flow (i.e. parallel). A manometer can be used to measure the difference between these two pressures and using Bernoulli's equation the flow rate of the fluid can be calculated.
The exterior tube, with an opening parallel to the flow, will register the Static Pressure. The interior tube, with an opening perpendicular to the flow, will register the Stagnation Pressure. Stagnation pressure is made up of Static Pressure plus Dynamic Pressure (caused by the force of the fluid flowing into the tube interior). By measuring the pressure DIFFERENCE between the Static Pressure (exterior tube) and the Stagnation pressure (interior tube) allows the velocity of the fluid flow to be determined.
Pitot tubes on aircraft
Pitot tubes are used on aircraft to measure the craft's airspeed. The tube is parallel to the aircraft's longitudinal axis, and is typically mounted on the wing of small aircraft and on a pylon on the body of larger aircraft. On aircraft, static pressure is typically measured through a port on the side of the fuselage instead of on the pitot tube itself. On sailplanes Pitot tubes are used to compensate Variometers.
Most pitot tubes have a heating device to prevent freezing and ice build up.