Static System
All aircraft are equipped with a small hole in the surface of the aircraft called the static port. The air pressure in the vicinity of the static port is conveyed by a conduit to the altimeter and the airspeed indicator. This static port and the conduit constitute the aircraft's static system. The objective of the static system is to sense the pressure of the air at the altitude at which the aircraft is flying. In an ideal static system the air pressure fed to the altimeter and airspeed indicator is equal to the pressure of the air at the altitude at which the aircraft is flying.
As the air flows past an aircraft in flight, the streamlines are affected by the presence of the aircraft and the speed of the air relative to the aircraft is different at different positions on the aircraft's outer surface. In consequence of Bernoulli's principle, the different speeds of the air result in different pressures at different positions on the aircraft's surface. The ideal position for a static port is a position where the local air pressure in flight is always equal to the pressure remote from the aircraft, however there is no position on an aircraft where this ideal situation exists for all angles of attack. When deciding on a position for a static port aircraft designers attempt to find a position where the error between static pressure and free-stream pressure is a minimum across the operating range of angle of attack of the aircraft. The residual error at any given angle of attack is called the position error.
Position error affects the indicated airspeed and the indicated altitude. Aircraft manufacturers use the aircraft flight manual to publish details of the error in indicated airspeed and indicated altitude across the operating range of speeds. In many aircraft, the effect of position error on airspeed is shown as the difference between indicated airspeed and calibrated airspeed. In some low-speed aircraft, the position error is shown as the difference between indicated airspeed and equivalent airspeed.
Read more about this topic: Position Error
Famous quotes containing the word system:
“When the finishing stroke was put to his work, it suddenly expanded before the eyes of the astonished artist into the fairest of all the creations of Brahma. He had made a new system in making a staff, a world with full and fair proportions; in which, though the old cities and dynasties had passed away, fairer and more glorious ones had taken their places.”
—Henry David Thoreau (1817–1862)