Total Air Temperature (TAT) is calculated by adding the temperature increase caused by an aircraft's speed to the Static Air Temperature (SAT).
Understanding Total Air Temperature (TAT)
TAT, also known as Ram Air Temperature (RAT), represents the temperature an aircraft experiences due to both the still air outside and the compression of air as the aircraft moves through it. In essence, it is the temperature measured by a sensor on the aircraft that is exposed to the "ram air" – the air forced into the sensor by the aircraft's forward motion.
The Formula: A Breakdown
While a precise formula might involve more complex aerodynamic considerations, the core concept is represented as:
TAT = SAT + Temperature Increase due to Flight
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SAT (Static Air Temperature): This is the actual temperature of the air undisturbed by the aircraft's presence. It's the temperature you would measure if you were stationary relative to the air mass.
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Temperature Increase due to Flight: As an aircraft flies, the air ahead of it is compressed. This compression heats the air. The faster the aircraft flies, the greater the compression and the greater the temperature increase.
Why is TAT Important?
TAT is crucial for several reasons:
- Engine Control: Aircraft engines, particularly turbine engines, are highly sensitive to air temperature. TAT is a critical input for engine control systems to optimize performance and prevent damage.
- Ice Detection: TAT helps in detecting icing conditions. If the TAT is near freezing, and other conditions are met, the aircraft's anti-icing or de-icing systems may need to be activated.
- Performance Calculations: Air temperature affects air density, which in turn affects aircraft performance (lift, drag, thrust). TAT is used in performance calculations and flight planning.
In Summary
To calculate the total air temperature, you add the temperature increase resulting from the aircraft's motion through the air to the static air temperature. This provides a more accurate temperature reading for various aircraft systems and calculations.
