How does a pitot tube work? --- Bala, Chennai, India
Marshall Brain Answered:
Pitot tubes were in the news recently because of the Airbus accident over Brazilian waters. It is thought that a faulty pitot tube reading may have confused the computer that controlled the aircraft. You can see a pitot tube in the following video:
The basic idea behind a pitot tube is very simple. A pitot tube detects airspeed by sticking a hollow tube into the air stream. As air jams into the end of the tube, it creates pressure. By comparing the pressure inside the tube with the natural pressure of the air around the tube (the static pressure), you get an accurate measure of airspeed. Obviously when the plane is sitting still on the ground, there is no air jamming into the end of the tube, so the pressure inside the tube is the same as static pressure and the airspeed is zero. As the plane starts moving, the pressure in the tube rises with the airspeed.
Since pitot tubes are so important in flight, most planes have more than one. Pitot tubes also have heaters to keep them from clogging with ice at high altitudes.
For more info see: How does a speedometer in an airplane work?