The pitot-static system of instruments uses the principle of air pressure gradient. It works by measuring pressures or pressure differences and using these values to assess the speed and altitude. The static pressure is used in all measurements, while the pitot pressure is used only to determine airspeed.

The pitot-static tube is based on Bernoulli’s principle, where the increase in speed of a fluid is directly related to pressure variations. The fluid itself exerts pressure on the surroundings, called static pressure. If the speed of the fluid is zero, the static pressure is at its maximum.

In aircraft, the static pressure is generally measured using the static ports on the side of the fuselage. The dynamic pressure measured can be used to determine the indicated airspeed of the aircraft.

A Pitot tube measures total pressure and static pressure to determine the velocity pressure from which air velocity can be derived. The Pitot tube is inserted into the duct with the tip pointed toward the airflow. Accurate readings cannot be taken in a turbulent air stream.

In a pitot-static tube, we have two different pressure, the static pressure ps and the total pressure p0=ps+12ρv2, which comes from the Beroulli equation for incompressible flows.

A clogged pitot tube affects only the airspeed indicator. One or more clogged static ports will affect the airspeed indicator, the vertical speed indicator, and the altimeter. The airspeed indicator will continue to operate, but it won’t be accurate.

So, there is three flight instruments that ultimately use this pitot-static system – the airspeed indicator, the altimeter, and the vertical speed indicator. Starting from the airspeed indicator, we see here that I’ve kind of illustrated that the airspeed indicator uses both the pitot source and the static source.

In fluid dynamics, a stagnation point is a point in a flow field where the local velocity of the fluid is zero. (In compressible flows, stagnation pressure is also equal to total pressure providing the fluid entering the stagnation point is brought to rest isentropically.)

The Pitot tube (named after Henri Pitot in 1732) measures a fluid velocity by converting the kinetic energy of the flow into potential energy. The conversion takes place at the stagnation point, located at the Pitot tube entrance (see the schematic below).

In fluid dynamics, stagnation pressure (or pitot pressure) is the static pressure at a stagnation point in a fluid flow. At a stagnation point the fluid velocity is zero. In an incompressible flow, stagnation pressure is equal to the sum of the free-stream static pressure and the free-stream dynamic pressure.

The pressure at a point in a fluid is called the ‘static pressure’. The ‘stagnation pressure’ is the pressure that the fluid would obtain if brought to rest without loss of mechanical energy. The difference between the two is the ‘dynamic pressure’.

Fan static pressure can be described in a number of ways, but in simplest terms it is the resistance pressure the fan has to blow against in order to move air in the desired direction. If the fan is blowing against a high resistance pressure, it requires more horsepower and delivers less air.