How the Airspeed Indicator Operates

Whether you are driving an automobile or piloting a passenger aircraft, being aware of your current speed while traveling is paramount to safety, navigation & route planning, and much more. For the measurement of aircraft speed, such vehicles rely on a flight instrument known as an airspeed indicator. As a part of the pitot-static system, the airspeed indicator is a required installation mandated by the FAA to ensure proper speeds while taking off, descending, landing, and cruising.

While the speedometer of an automobile is often sufficient enough to discern current speeds for drivers, an aircraft has to take into account wind, the density of the surrounding atmosphere, possible instrument errors, and other factors that can make the measurement of aircraft speed more complicated. With four types of airspeed obtainable from instruments and calculations, pilots can find the indicated airspeed, true airspeed, calibrated airspeed, and groundspeed of their aircraft during operations.

With the base measurements provided by the airspeed indicator, pilots can find the indicated airspeed of the aircraft. While indicated airspeed is a measurement garnered from the pitot-static system, it is a reading that has not been adjusted for any standard errors. As such, pressure and temperature variables are used to correct the indicated airspeed to find true airspeed. With both measurements, pilots can oversee the general performance of their aircraft throughout a flight operation.

Beyond indicated airspeed and true airspeed, pilots can also calculate calibrated airspeed by utilizing standard position and instrumentation errors in order to correct the indicated airspeed value. For groundspeed, true airspeed is adjusted for wind to achieve a value. Through instrument measurements, adjustments for errors, and various calculations, pilots can find each of the four types of airspeed to safely travel. Before pilots can receive indicated airspeed to find the other three types, however, they must first measure and compare air pressure through instrumentation. While the assembly of instrumentation and pitot-static lines may vary from aircraft to aircraft, all airspeed indicators will rely on static ports, static lines, pitot tubes, pitot lines, cases, pressure diaphragms, and instrument faces.

With the static port, areas that exhibit fairly undisturbed airflow can be used to gather air at ambient pressures. Through static lines, static pressure can be transferred from ports to the instrument, and a line is required for each port that is present on the fuselage. With the pitot tubes, on the other hand, relative wind is captured and collected for ram air pressure measurements. Generally, pitot tubes are specifically placed and aligned with the surrounding airflow, ensuring that the pressure is relative to the moving speed of the aircraft. Once air enters the inlets, it will then move through pitot lines to the airspeed indicator instrument. Unlike static pressure, the pressure captured by pitot tubes is transported into the housed pressure diaphragm to create a reading that may be displayed on the instrument face.

For the operation of an airspeed indicator, the air pressure differential is measured. To carry out such measurements, air is provided to the airspeed indicator from both the pitot and static tube. As ram air from the pitot tube enters the diaphragm, the difference between air pressures will cause the diaphragm to either expand or retract. As the diaphragm adjusts, the needle on the face of the instrument will move in unison to denote the indicated airspeed. Unlike other instruments such as the altimeter and vertical speed indicator that only rely on static ports, airspeed indicators require a functional and unblocked pitot-static system to operate.

With a functional and well-maintained airspeed indicator and pitot-static system, pilots can safely traverse the skies while following safe speeds for their various operations. When you are in search of aircraft instrumentation and other aerospace components, let the experts at ASAP NSN Hub help you secure everything you need with ease. Explore our expansive offerings and begin the purchasing process today when you fill out and submit an Instant RFQ form as provided on our website.


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