Segment V3.4: Air Speed Indicator

(Related to Textbook Section 3.5 - Static, Stagnation, Dynamic, and Total Pressure)

The stagnation pressure at the tip of a Pitot tube is greater than the static pressure by an amount equal to one-half times the fluid density times the speed squared. Thus, the speed can be determined by measuring the pressure difference.

The Pitot tube on an aircraft is connected to the air speed indicator, a pressure transducer calibrated to read in knots or miles per hour rather than psi. Because the air density varies with temperature, pressure, and altitude, the speed displayed on the air speed indicator (termed the indicated air speed) equals the actual speed at which the airplane is flying through the air only for standard density conditions.