Temperature

Question 1

Temperature

Answer 1

Is the measure of the concentration of thermal energy in an object

Question 2

Celsius (C)

Answer 2

Absolute Zero: -273C
Freezing Point of water in ISA: 0C
Boiling point of water in ISA: 100C

Question 3

Kelvin (K)

Answer 3

Same units as C but referenced to absolute zero (0K).

To convert C to K, add 273
To convert K to C, subtract 273

Question 4

Fahrenheit (F)

Answer 4

Freezing point of water in ISA: 32F
Boiling point of water in ISA: 212F
1C or K = 1.8F

To convert C to F: multiply by 1.8 and then add 32

To convert F to C: subtract 32 and then divide by 1.8

Question 5

Outside Air Temperature (OAT)

Answer 5

Is measured at a point not in direct sunlight

Question 6

Static Air Temperature (SAT)

Answer 6

The inferred temperature outside an aircraft for air which is not affected by movement

Question 7

Total Air Temperature (TAT)

Answer 7

The sensed temperature outside an aircraft which is affected by adiabatic heating as the air, relative to the aircraft, its slowed to zero

Question 8

Ram Rise

Answer 8

The difference between SAT and TAT caused by adiabatic heating.

SAT=TAT-ram rise

Ram rise also approximately =(TAS/100)^2

Question 9

Why is TAT useful to the ADC?

Answer 9

TAT is used to derive TAS. On CAT aircraft it is usually displayed

Question 10

Direct Reading Temperature Probe

Answer 10

• Simple dial connected to a probe passing through the skin of the aircraft near the windshield
• Position error can be significant because of airflow disturbances at the front of the aircraft, and sunlight can affect the sensed temperature
• Instrument error can be significant because of its very basic construction

Question 11

Indirect temperature probe

Answer 11

• Electrical TAT measurement giving accurate data to the ADC, which calculates SAT and sends TAT and SAT to systems and displays
• Position error is minimised by placement on the fuselage where the airflow is stable. The probe has a strut to position it out of the boundary layer
• The sensor is inside the probe body to protect it from sunlight

Question 12

Sensor icing protection

Answer 12

• Without special design measures this would cause the sensor to heat up, making measurement inaccurate
• Effect on TAT sensor is minimal because heat-shield and airflow are between the probe body. This relies on airflow, which requires the aircraft to be in motion or an aspirated probe (eg. using air from the APU)