Pressure error question
TOTAL PRESSURE ERROR
"As an aircraft moves through the air, a static pressure disturbance is generated in the air, producing a static pressure field around the aircraft. At subsonic speeds, the flow perturbations due to the aircraft static pressure field are nearly isentropic and do not affect the total pressure. As long as the total pressure source is not located behind a propeller, in the wing wake, in a boundary layer, or in a region of localized supersonic flow, the pressure errors due to the position of the total pressure source are usually negligible. Normally, the total pressure source can be located to avoid total pressure error."
"As an aircraft moves through the air, a static pressure disturbance is generated in the air, producing a static pressure field around the aircraft."
What is this static pressure field around the aircraft i would of thought this was just the free air around the aircraft, the air which is not impacted by the aircraft which would be then dynamic pressure right?
It then goes on to say: "at subsonic speeds, the flow perturbations due to the aircraft static pressure field are nearly isentropic and do not affect the total pressure."
I understand that isentropic basically means the same all round though i can't grasp what this paragraph mean either can anyone simplify it?