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  • The Airspeed is a measurement of the plane's speed relatives to the air around it. The pitot-static tube system is an ingenious device used by airplanes and boats for measuring forward speed.
  • The device is really a differential pressure gauge and was invented by Henri Pitot in 1732, The air speed indicator actually measures the difference between a static-sensor not in the air stream and a sensor (pitot tube) in the air stream.
  • When the airplane is standing still, the pressure in each tube is equal and the air speed indicator shows zero. The rush of air in flight causes a pressure differential between the static-tube and the pitot-tube. The pressure differential makes the pointer on the air speed indicator move.
  • An increases in forward speed raises the pressure at the end of the pitot tube. In turn, the air pressure pushes against a flexible diaphragm that moves a connected mechanical pointer on the face of the indicator.
  • The indicator is calibrated to compensate for winds in the air or the speed of the opposing current in the water. In airplanes, electronics also compensate for altitude and air #temperature to make the airspeed measurement accurate.

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