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→How to measure pressure
=== How to measure pressure ===
A '''pitot tube''' is a device used to measure total pressure. It works by pointing a bent tube directly into flow so that the flow is brought to a rest when the bend is reached (i.e. stagnated). As a result, the static pressure raises to the total pressure value of the free stream. A pitot tube is usually found at the nose of an aeroplane (e.g. the K-21s), but it can be elsewhere. There are designs where the pitot tube sticks out of the vertical stabliser (the fin) or on the side of the fuselage.
A '''static port''' is used to measure static pressure. This port must be located on an aeroplane where the pressure coefficient is zero. In addition, it needs to be perpendicular to the flow so that no dynamic pressure is converted into static pressure by the slowing down of the flow. On an aeroplane a static port (a small hole) is usually found on the side of the fuselage. You can ask an instructor to show you where this is.
The difference between the pitot tube reading and the static port reading is the dynamic pressure.
Note that there are restrictions on both of these regarding the relative direction with respect to the flow. Given that most of the times an aeroplane flies straight and level, the designers will use this attitude to design the pitot tube and the static port. If a significant amount of yaw is present, or if the angle of attack is extreme (such as when an aeroplane is stalled), these pressure readings will be unreliable.
For reasons that should be obvious by now, it is important that the pitot tube and the static port are not blocked. This should be a part of the daily inspection of an aeroplane. Furthermore, there is a chance that the pitot tube may ice up in flight, for example, if the aeroplane is flown in rain at low temperatures.
== Atmosphere ==
