Sensors play an important role in modern aviation. A typical airplane has hundreds or even thousands of sensors, each of which collects valuable data. Among these sensors are total air temperature probes.
The Basics of Total Air Temperature Probes
Total air temperature probes are devices that measure the total air temperature. They feed this data to multiple aircraft systems that use it for performance, efficiency and navigation purposes.
Common locations for total air temperature probes include the following:
- The nose
- The front of the fuselage
- The sides or perimeter of cockpit windows
Understanding Total Air Temperature
Not to be confused with static air temperature, total air temperature is the temperature of the air after it’s been affected by an airplane’s forward motion.
Air temperature changes in response to an airplane’s movement. When an airplane moves forward, the surrounding air will move to its flight surfaces. As the airflow slows, some of this kinetic energy will turn to heat. Therefore, total air temperature is typically higher than the surrounding atmospheric air temperature or static air temperature. Total air temperature takes into account these small differences.
How Total Air Temperature Probes Work
Total air temperature probes rely on several components to accurately measure the total air temperature. They feature an air inlet that directs air into the probe itself; a chamber where the air slows down; a sensor that senses the temperature of the air; and electrical connections that send the corresponding data to various aircraft systems.
Air will initially enter the probe via the inlet. Once inside the inlet, it will move to the airflow chamber. The sensor will then sense the air temperature, after which the data will be transmitted to the aircraft systems.
Why Airplanes Use Total Air Temperature
Airplanes use total air temperature for several reasons. Jet engines, for instance, use it for thrust and performance. They rely in heavily on atmospheric data. Temperature affects the density of air. Even small changes in air temperature can affect their thrust, fuel consumption and maximum temperature limits.
Flight management systems (FMSs) also use total air temperature for routing and efficiency purposes. FMSs are designed to set the optimal altitude and speed. To perform this task, they must know the total air temperature.
Another reason airplanes use total air temperature is to protect against icing. Ice can form when airplanes move through moisture-containing clouds at temperatures below freezing. With total air temperature probes, pilots can avoid this hazard.
