An aircraft at rest on the ground in still air is subject to normal atmospheric pressure, which bears equally on all parts of the aircraft. This ambient pressure is known as static pressure.
An aircraft in flight, whilst still subject to the static pressure at its flight level, experiences an additional pressure on the leading edges due to the resistance of the air to the aircraft’s movement.
This additional pressure is dynamic pressure, and its value depends on the speed of the aircraft through the air and on the density of the air. The leading edges, therefore, encounter a total pressure consisting of static plus dynamic pressures. This total pressure is also known as pitot pressure. It is not possible to isolate dynamic pressure by direct measurement because it cannot be separated from the associated static pressure. The instruments which require dynamic pressure therefore measure total (pitot) pressure and also static pressure and then subtract static from pitot within the instrument to derive dynamic pressure.
PITOT = STATIC + DYNAMIC
DYNAMIC = PITOT – STATIC
The following instruments require inputs of static and pitot:
Inside an aircraft, pressure and temperature are seldom the same as outside the aircraft so pitot and static pressures must be sensed by devices mounted on the outside of the aircraft.