A pitot tube is a thin metal tube that sticks out and was invented by French engineer Henri Pitot to measure the speed of a fluid, usually air.
On aircraft the device acts as a speedometer: it has a small opening at the front that allows ram pressure to enter the pressure chamber while it simultaneously captures the static pressure that is always present; together these pressures feed data to the airspeed indicator, which measures the difference between ram pressure from the pitot tube and static pressure from the static port, thereby displaying the aircraft's airspeed.
The pitot and static ports are connected to their respective instruments using lines, and their placement, often near the nose, must avoid disturbance from the boundary layer to keep readings accurate.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is the definition of a pitot tube on an aircraft?
A pitot tube is a device used to measure the speed of a fluid, usually air, and it is widely used to determine the airspeed of aircraft. Pitot tubes feed data to the airspeed indicator.
A pitot tube on an aircraft is a small opening that faces forward, usually taking the form of a thin tube about 10 inches (25 centimetres) long and roughly inch (1 centimetre) in diameter. Pointed in the direction of travel and mounted on the outside of the aircraft, it is part of the pitot-static system that supplies pressure data to the flight instruments.
The forward-facing orifice admits the oncoming airflow. This main opening allows ram (total) pressure to enter the internal pressure chamber. The device is also called a pitot probe, and when its static ports are incorporated in the same appendage it is known as a pitot-static tube or Prandtl tube.
What is the purpose of a pitot tube on an airplane?
The pitot tube's basic job is to measure impact air pressure.
It measures the flow velocity of air. It determines ram pressure, also called dynamic air pressure.
By comparing that total pressure with the static pressure at the airplane's static ports, the airspeed indicator calculates and displays how fast the airplane is going.
Thus, the pitot tube's continuous measurement of impact pressure lets pilots know their exact airspeed at every moment of flight.
The pitot tube's main function is to measure airspeed by converting the active force of approaching atmospheric air into a signal that registers on the aircraft's airspeed indicator. This measurement is the foundation of the pitot-static module, which also supplies data for additional aviation computations such as altitude and vertical speed. The information is crucial for keeping the aircraft above its stall speed during departure and touchdown, and it feeds the aircraft's inclination of attack subsystems and Mach index for high-speed flying. Without accurate pitot data, secure and restricted flying becomes unfeasible, and airspeed indicator errors can lead to dangerous flight conditions.
How does a pitot tube work on a plane?
A pitot tube works by comparing the pressure of moving air with the pressure of surrounding still air. A center tube always points in the direction of flow, and a small opening in that tube allows total pressure to enter a pressure chamber inside the Airspeed Indicator. A second tube has holes on the sides to measure static pressure, and this static pressure fills the ASI case. Because air exerts pressure against motion, also called ram pressure, the difference between the two pressures creates dynamic pressure.
More air coming in means faster airspeed, so the diaphragm arrangement within the Airspeed Indicator flexes, and the ASI needle shows airspeed. The transducer refines the measurement by recording the strain in a thin element with an electronic strain gauge, while vents are electrically heated to prevent blockage by ice.
Where is the pitot head on a plane?
On most aircraft the pitot tube is most often located on the wing, mounted clear of the boundary layer so it samples free-stream air. On faster or smaller designs the pitot tube is on a longer boom sticking out of the nose of the plane, again placed ahead of any disturbed flow. In some home-built models such as Thorp T-18s and Pazmany PL-2 the pitot head is moved higher: the pitot is at the top of the vertical fin, above the propeller stream where it is clear of slipstream turbulence. Commercial aircraft follow the same logic, so the pitot tube is located on the vertical fin or on a short mast on the lower forward fuselage, always positioned so the pitot is above the propeller stream or engine exhaust and well outside the local boundary layer. The pitot tube is connected to the airspeed indicator, and the same instrument also uses the static port, a small hole on the side of the fuselage near the rear of the airplane, typically on the side of the empennage near the tail. The static port supplies the reference pressure for the altimeter and vertical speed indicator as well.. Because pitot-static system errors pose danger as the information is safety-critical, many manufacturers include an alternate static port so that if the static port becomes blocked, the crew will still receive reliable static pressure.
What is the left and right pitot for on the aircraft?
Multiple pitot tubes and static ports are placed symmetrically on both sides of the fuselage for redundancy and balance. The left and right pitot-static systems supply identical data to the captain's and first officer's instruments. If one side fails, the flight crew can select the alternate source so that no airspeed, altitude, or vertical-speed information is lost.. Separate static ports on either side of the fuselage measure static pressure, feeding the airspeed indicator, altimeter, and vertical-speed indicator on each panel. The balanced location lets the two sets of instruments agree even when the aircraft yaws or sideslips. Pitot heat prevents visible moisture from freezing inside each pressure chamber, ensuring the left and right systems remain unobstructed in icing conditions.