2 minute read
Fig.4 Example of Probes location in an A380
2.5.1 Onboard information sources
Service aircraft integrate a few number of sensors, commonly used for navigation purposes and to provide environment information to the pilot. The Air Data and Inertial Reference System (ADIRS) calculates flight parameters (Indicated Airspeed, position, etc) directly from probe measurements and supplies with air data a large number of critical aircraft systems (like FMS). The probes network, used for navigation, includes the following sensors: - Pressure sensors (Pitot probes, Pitot-static probes and static pressure probes) - Temperature sensors (total air temperature probes) - Angle of Attack sensors
Figure 1 presents the main location of the previous sensors. For integration purposes, new generation of sensors have been developed. Those multi-function probes (MFP) are able to measure more than one parameters (A380 MFP measure the angle of attack, the total pressure and the temperature).
Fig.4 Example of Probes location in an A380
2.5.1.1 Pressure
Pressure sensors measure various type of pressures, depending on their position and type: - The static pressure sensor, which measures the static pressure - The Pitot sensor, which measure the total pressure - The Pitot-static sensor, which measure both static and total pressure The statics pressure sensor is used to determine the statics pressure. This information is crucial since, combined with Pitot sensors measurements, it is used to calculates the aircraft velocity (the Indicated Air Speed, which leads to the True Air Speed) and wind speed (combined with inertial data). The number of integrated static pressure sensors varies by manufacturer and aircraft model. Airbus commercial aircrafts are commonly equipped with 6 pressure sensors (3 on each side of the aircraft) while Boeing usually use 3 probes per aircraft. The Pitot sensor provides the aircraft with the total pressure (sum of dynamic pressure and static pressure). The probe is an opened trend tube, parallel with the air flow. The delta between total pressure and static pressure provides the dynamic pressure, required to determine the relative wind speed and the Mach number.
2.5.1.2 Temperature
The total air temperature probes sense total air temperature (TAT), used to calculate the static air temperature (SAT or outer air temperature OAT). The TAT (see Fig. 4) is directly sent to the ADIRS and used (with static and total pressure) to compute the true air speed (TAS). The information is also displayed to the pilot on the electronic flight instrument system (EFIS). The temperature sensors tolerance is ± 0.25°C plus 0.5% percent of the magnitude of the temperature in degrees Celsius, with a response time in the air around 1 second.
2.5.1.3 Multi-function probe
The Multi-Function Probe (MFP) combines two or more sensors. This type of probes does not provide any new weather parameter to the aircraft but reduce the number of probes integrated in the fuselage for cost efficiency, and drag reducing purposes. The MFP does not refer to a clear need, and each aircraft and manufacturer integrate different functionalities to the sensor, depending on the aircraft need. The MFP integrated in the A380 and A350 (provided by Goodrich) supply total pressure, total air temperature and angle of attack data (Fig. 5). The static pressure is measure by dedicated probes located on each side of the
