Pitot Tube

Pitot tube, which is widely used in aircraft, is used to convert dynamic pressure to IAS (Indicated Air Speed) with static systems. It takes its name from the French Aeronautical Engineer Henri Pitot. The first reason it appears is that it is requested to measure the flow of the Seine River. The French Scientist Henri Pitot, who took on the task, designed the device in 1732 and became the first person to use it. Later, in the 20th century, when technological developments followed, it was used as a speed measurement device in aircraft designed and is still used. It is a device that enables measuring the total pressure of the fluid (air) and the fluid velocity accordingly. It is placed on the aircraft where the air flow is regular or not affected by external factors (nose tip, wing leading edge, etc.). The tube is placed in the direction parallel or opposite to the direction of fluid (air) movement. While the fluid (air) passes through the pitot tube, it measures the resultant (Static + Dynamic) pressure, the dynamic pressure created by the relative motion of the plane and air and the static pressure created by the air on all surfaces (including the pitot tube).

The pitot tube is part of the pito-static system in aircraft. The total pressure from the tube allows the diaphragm in the system to expand. Static pressure from static holes causes the diaphragm to contract at the rate of static pressure. The resultant dynamic pressure of these two movements arises and this information is transferred to the scale on the speed clock.

Total pressure (pt) = Static pressure (ps) + Dynamic pressure (1/2 rho V2)

Pitot tubes are vital parts as they transfer important data such as the speed of the aircraft to the pilots. There are 2 pitot tubes in the nose for both pilots on the plane, and information is transmitted to each of them from two different pitot tubes and is always confirmed. Since the air temperature around 35000 feet is around -50 -55 C degrees due to the altitude in the flight, pitot heating systems are generally used in aircraft to prevent icing. When there is no flight, for example maintenance, handar, they keep the inlets closed with protective covers to protect the pitot tube from dirt. If the cover is left on or if the pitot tube is completely blocked for any other reason, the speedometer will show 0 (zero). However, if both the pitot hole and the drain line under the tube are clogged, it acts like an altimeter, that is, it shows a constant speed. Many aircraft accidents have occurred due to the pitot tube malfunction. In 1996, one of the pitot tubes of a Boeing 757 belonging to Birgen Airlines was clogged because it was not closed during maintenance, and it transferred data that would mislead pilots, which caused the pilots to be mistaken and the plane crashed in 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.


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