Pitot Tube – Working Principle

Pitot tube is an instrument used to measure the total pressure in fluids and consequently the velocity of the fluid. It was designed in 1732 by the French scientist Henri Pitot. In fact, the reason for its occurrence is that it is desired to measure the flow of the Seine River. In the 20th century, it began to be used to measure the speed of aircraft in passenger and fighter planes. The Pitot Tube is placed in areas where the air flow is regular, such as the tip of the nose and the wing leading edge in aircraft.

The maintenance of the pitot tube is very important, as it transfers data about speed to the pilot. It should not be clogged and frosted. There are pitot heating systems in the tube and this prevents icing. In order not to clog and protect from dirt, protective covers are used when there is no flight and the tube inlets are kept closed.

Pitot Tube – Working Principle

Unfortunately, there have been accidents in aviation history due to pitot tube malfunction.

In 1996, the needed data of pitot tubes of a Boeing 757 belonging to Birgen Airlines could not be transferred to the pilot because the pitot tubes were clogged and the plane crashed into the Atlantic Ocean. After this accident, the differences in data transfer of pitot tubes were discussed. And it was realized that there was no pitot tube data difference warning in aircraft until that day, and a radical change was made and a warning system was developed.

Working Principle of Pitot Tube

 The tube is placed parallel to or opposite the direction of fluid movement. As the fluid passes through the tube, it measures the combination of dynamic pressure (pressure created by the relative movement of the vehicle and fluid) and static pressure (the pressure created by the fluid on all surfaces), that is, the total pressure. The incoming total pressure causes the expansion of sensitive diaphragm in the system. The static pressure from the static holes causes the diaphragm to narrow at the rate of static pressure. The combination of these two movements gives dynamic pressure and this information is reflected in the scale on the speedometer.

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