Pitot Static System In Aircraft

Pitot static system , device for
measuring the rate at which a fluid
flows. Among the principal
applications of the device are an
airspeed indicator for aircraft and a
distance and speed indicator for ships. The device contains a short tube with
one open end that faces directly
toward the stream of air or other fluid.
When no fluid is moving into the
opening, a minimum pressure, called
the static pressure, is exerted against it. When a stream is flowing into it, the
pressure rises by an amount that
depends on the velocity of the stream.
Behind this tube is another tube with a
number of small vents at right angles
to the direction of the first tube. When a stream raises the pressure against
the opening of the first tube, the
pressure against the vents is still equal
to the static pressure. A suitable gauge
compares these pressures, using the
static pressure as a reference, and gives a reading in units of velocity. For
an aircraft this reading is called
"indicated airspeed" ; "true airspeed"
requires a correction, made
automatically by some airspeed
indicators, for the local density of the air. Because of winds, neither reading
accurately measures the speed in
relation to a point on the surface of the
earth. That value is known as
groundspeed. Although airspeed is
normally given in knots or miles per hour, for supersonic aircraft it may be
given in Mach numbers, which give the
ratio of the aircraft's speed to the
speed of sound. For navigational
purposes Mach numbers are
converted to true airspeed.