Pitot Tube

Fact for 1/6/2021



Pitot tube also known as pitot probe, is a flow measurement device used to measure fluid flow velocity. The pitot tube was invented by the French engineer Henri Pitot in the early 18th century and was modified to its modern form in the mid-19th century by French scientist Henry Darcy. It is widely used to determine the airspeed of an aircraft, water speed of a boat, and to measure liquid, air and gas flow velocities in certain industrial applications

Structure and functioning

Pitot tubes are used on aircraft as speedometers. The actual tube on the aircraft is around 10 inches (25 centimeters) long with a 1/2 inch (1 centimeter) diameter. Several small holes are drilled around the outside of the tube and a center hole is drilled down the axis of the tube. The outside holes are connected to one side of a device called a pressure transducer. The center hole in the tube is kept separate from the outside holes and is connected to the other side of the transducer. The transducer measures the difference in pressure in the two groups of tubes by measuring the strain in a thin element using an electronic strain gauge. The pitot tube is mounted on the aircraft so that the center tube is always pointed in the direction of travel and the outside holes are perpendicular to the center tube. (On some airplanes the pitot tube is put on a longer boom sticking out of the nose of the plane or the wing.) Since the outside holes are perpendicular to the direction of travel, these tubes are pressurized by the local random component of the air velocity. The pressure in these tubes is the static pressure (ps)
Errors in pitot-static system readings can be extremely dangerous as the information obtained from the pitot static system, such as airspeed, is potentially safety-critical
There have been several commercial and military accidents due to malfunction in pitot tubes , these even include the crashes of 2 X-31s, which were used for experimenting thrust vectoring system in fighter aircrafts , in cases of malfunctions , the major reason was icing on the tube , to prevent icing in pitot tubes , anti icing systems have been installed , as there are a lot of countries where flight operations happen in cold weather eg- Ladakh , at these places , de icing instruments play a key role in the proper functioning of instruments and various flight systems