Temperature

Question 1

Definition of ISA:

Answer 1

• 1013.25 hPa
• 15°C
• Lapse Rate is 1.98°C per 1000’ up to 36 090’ then –56.5°C
• Density is 1.225 kg/m3

Question 2

Temperature at 39 000’?

Answer 2

• -56.5°C

Question 3

Aircraft maintains a constant IAS in the climb, what happens to TAS & LSS?

Answer 3

• Constant IAS – TAS will increase & LSS will decrease

Question 4

How does temperature affect the speed of sound?

Answer 4

• The speed of sound is directly proportional to the square root of the absolute temperature (the speed of sound will increase with an increase in temperature).
• LSS = 38.94√K
• At sea level ISA: LSS = 661kts.
• At 35,000’ ISA: LSS = 575kts.

Question 5

Airspeed in the climb – at a constant TAS / IAS / Mach No. what do each do?

Answer 5

• Constant IAS – Both TAS & Mach No. increase
• Constant Mach No – Both IAS & TAS decrease
• Constant TAS – Mach No. increases, IAS decreases

Question 6

Cruise Mach No. is more limiting when

Answer 6

• In warm temperatures

* The higher the aircraft flies