Air data computer

An air data computer (ADC) is an essential avionics component found in modern aircraft. This computer, rather than individual instruments, can determine the calibrated airspeed, Mach number, altitude, and altitude trend data from an aircraft's pitot-static system. [1][2] In some very high speed aircraft such as the Space Shuttle, equivalent airspeed is calculated instead of calibrated airspeed.

The first air data computer patented in the US was developed by John H. Andresen in February, 1971.[3]

Air data computers usually also have an input of total air temperature. This enables computation of static air temperature and true airspeed.

From the late 1980s much of the USAF and USN aircraft fleets were retrofitted with the GEC Avionics Rochester developed Standard Centralised Air Data Computer (SCADC). Aircraft fitted included the A-4 Skyhawk, A-6 Intruder, A-7 Corsair, C-5A/B Galaxy, EA-6B Prowler, F-111 Aardvark, F-4 Phantom, S-3 Viking, C-141 Starlifter, C-135 Stratolifter, C-2 Greyhound, and E-2 Hawkeye [4], for which the company received the Queens Award for Technological Achievement[5].

In Airbus aircraft the air data computer is combined with altitude, heading and navigation sources in a single unit known as the Air Data Inertial Reference Unit (ADIRU) this has now been replaced by the Global Navigation Air Data Inertial Reference System (GNADIRS).

In simpler aircraft including helicopters the Air Data Computers, generally two in number, and smaller, lighter and simpler than an ADIRU, may be called Air Data Units, although their internal computational power is still significant. They commonly have the pitot and static pressure inputs, as well as outside air temperature from a platinum resistance thermometer and may control heating of the pitot tube and static vent to prevent blockage due to ice. As on simpler aircraft there is usually not a fly by wire system, the outputs are typically to the cockpit altimeters or display system, flight data recorder and autopilot system. Output interfaces typically are ARINC 429, Gillham or even IEEE1394 (Firewire). The data provided may be true airspeed, pressure altitude, density altitude and Outside Air Temperature (OAT), but with no involvement in aircraft attitude or heading, as there are no gyroscopes or accelerometers fitted internally. These devices are usually autonomous and do not require pilot input, merely sending continuously updated data to the recipient systems while the aircraft is powered up. Some, like this ESCADU (Enhanced Software Configurble Air Data Unit) are software configurable to suit many different aircraft applications.

Apart from commercial ADCs implementation, there are available do-it-yourself, and Open implementations.[6]

See also


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