Pitots

Pitots, or Pitot tubes, are measurement devices used to determine the velocity of a fluid by converting the kinetic energy in the flow into potential energy. They consist of a tube pointing directly into the flow, which captures stagnation pressure as the fluid is brought to rest inside the tube. A separate static port measures the ambient static pressure. The difference between stagnation pressure and static pressure, called dynamic pressure, is related to flow velocity through Bernoulli’s principle.

Pitot tubes are named after Henri Pitot, who described the device in the 18th century. In aviation, a Pitot-static system combines a Pitot tube and static ports to feed an airspeed indicator, allowing the cockpit to display indicated airspeed. Subsystems may include a standby tube or multiple sensing points to reduce errors from yaw or flow distortion.

There are several forms: the simple Pitot tube, and the Pitot-static tube, which integrates both the stagnation and static pressure measurements. Multi-hole Pitot probes are used in wind tunnels and profiling to detect directional components of the flow and to reduce measurement errors due to flow distortion.

Limitations and sources of error include icing and blockages in the intake, misalignment with the flow, flow separation, pressure port blockages, and calibration drift. In high-speed compressible flows, the relationship between dynamic pressure and velocity depends on Mach number and air properties; modern aircraft use compensation and calibration to derive true airspeed from indicated readings.

Pitot devices are also used in water and other fluids for flow measurement, hydraulic research, and industrial instrumentation.