6. Anemometer Application in Aeronautical Field
Airspeed tube on aircraft is a typical pitot tube anemometer, which is an extremely important measuring tool on aircraft.
Its installation position must be in the area outside the aircraft where airflow is less affected by the aircraft, generally in front of the nose, vertical tail or wing tip.
When the aircraft 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, i.e. the dynamic pressure.
The faster the plane flies, the greater the dynamic pressure. If you compare the static pressure of the air with the dynamic pressure, you can know how fast the air rushes in, that is, how fast the plane flies.
The tool for comparing the two pressures is a hollow circular box with corrugated surface made of two thin pieces of metal, called a diaphragm box.
If the aircraft is fast, the dynamic pressure will increase, the pressure in the diaphragm box will increase, and the diaphragm box will bulge up. This is the simplest airspeed meter for an aircraft.
The static pressure measured by the airspeed tube can also be used as the calculation parameters of the altimeter.
If the diaphragm box is completely sealed, the pressure inside will always be equal to the pressure of air on the ground.
In this way, when the aircraft flies into the air, the altitude increases and the static pressure measured by the airspeed tube decreases, the diaphragm box will bulge up, and the altitude of the aircraft can be measured by measuring the deformation of the diaphragm box.
This altimeter is called a barometric altimeter.
The speed measured by the airspeed tube is not the real speed of the aircraft relative to the ground, but the speed relative to the atmosphere, so it is called airspeed.
If there is wind, the speed of the aircraft relative to the ground (terrestrial speed) should also be added to the wind speed (downwind flight) or subtracted from the wind speed (upwind flight).