Pitot-Static Tubes
Can someone explain why a pitot-static tube would be used instead of a conventional pitot tube?
The conventional pitot tube measures total pressure and sends this to the ASI, the static pressure from the static ports on the side of the aircraft is then fed to the ASI and whatever the static pressure is, it then offsets this (cancels) what the static pressure is when it came through the front of the pitot tube to give us dynamic pressure.
The pitot-static tube has the holes in the side of the tube 90 degrees to the airflow to obviously measure static pressure I presume then to calculate the dynamic pressure? Is this the case? If so what's the point of the static ports on the side of the aircraft for the ASI if the static pressure is known from the pitot-static tube?