Wind speed sensor in aviation field

The "airspeed tube" on an airplane is a typical Pitot tube wind speed sensor and an extremely important measurement tool on the airplane. It must be installed in an area outside the aircraft where the airflow is less affected by the aircraft, generally in front of the nose, vertical tail or wingtip. When the airplane is flying forward, the airflow rushes into the airspeed tube, and the sensor at the end of the tube will feel the impact force of the airflow, that is, dynamic pressure. The faster the plane flies, the greater the dynamic pressure. If you compare the static pressure and the dynamic pressure when the air is at rest, you can know how fast the air is rushing in, that is, how fast the airplane flies. The tool for comparing the two pressures is a hollow circular box with corrugated surfaces made of two thin metal sheets, called a bellows. The box is sealed, but there is a tube connected to the PTS. If the airplane is fast, the dynamic pressure will increase, the pressure in the bellows will increase, and the bellows will bulge. A device composed of small levers and gears can measure the deformation of the bellows and display it with a pointer. This is the simplest airplane airspeed indicator.

The static pressure measured by the pitot tube can also be used as the calculation parameter of the altimeter. If the bellows is completely sealed, the pressure inside will always be equal to the pressure of ground air. In this way, when the aircraft flies into the air, the altitude increases, and the static pressure measured by the airspeed tube drops, and the bellows will bulge, and the height of the airplane can be measured by measuring the deformation of the bellows. This altimeter is called a barometric altimeter.

The speed measured by the airspeed tube is not the actual speed of the aircraft relative to the ground, but only the speed relative to the atmosphere, so it is called airspeed. If there is wind, the speed of the aircraft relative to the ground (called ground speed) should also be added to the wind speed (flying downwind) or minus the wind speed (flying upwind).