2. The Flying Environment

Question 1

What are the three critical quantities?

Answer 1

p = Pressure (Pa, Nm^-2, bar, atm, psi, inches of mercury)
T = Temperature (K, °C, °F)
ρ = Density (kgm^-3) ρ = m/V

Question 2

What is the equation of state?

Answer 2

p = ρRT

R = Ideal gas constant = 287.1 Nmkg^-1K^-1

Question 3

Troposhere

Answer 3

0 to 11 km AMSL
- The temperature decreases with increasing altitude.
- Warmer near the surface because low altitude water and CO2 absorb heat radiated from the surface.
- Tropos: Greek for turning/mixing. Air is generally turbulent. Most weather occurs here.

Question 4

Stratosphere

Answer 4

11 to 50 km AMSL
- The boundary between the troposphere and the stratosphere is the tropopause.
- Much less water at lower levels so absorptivity from the ground is lower.
- Ozone levels increase over this region, which encompasses the ozone layer, increasing absorption from ultraviolet radiation.
- Relatively little vertical mixing observed on this region.
- Stratos: Latin for ‘Stratus’ meaning layered.
- Almost all flight is in the stratosphere or below.

Question 5

Mesosphere

Answer 5

50 to 80 km AMSL
- The boundary between the stratosphere and mesosphere is the stratopause.
- The temperature decreases decreases with increasing altitude due to the decreasing levels of solar heating and increasing cooling by CO2 radiating emission.
- Mesos: Greek for middle.

Question 6

Thermosphere

Answer 6

80 to 800 km AMSL
- Temperature increases rapidly to 100 km AMSL, then constant above 100 km upwards. Density and pressure are very low.
- Thermos: Greek for hot.
- Atmospheric gases separate by molecular mass.
- The Karman line (at 100 km AMSL) is considered the edge of space.
- A typical low earth orbit satellite orbits at roughly 300 km or higher.

Question 7

Exosphere

Answer 7

Everything else
- Forms boundary with empty space.
- Exo: Greek for outside.

Question 8

What is the rate of change of temperature in the Troposphere?

Answer 8

λ0 = -6.5 K/km

Question 9

What is the temperature in the lower Stratosphere?

Answer 9

216.65 K from 11 to 20 km

Question 10

What is the temperature change in the middle Stratosphere?
And the rate of this change?

Answer 10

216.65 K at 20 to 228.65 K at 32 km
λ2 = 1 K/km

Question 11

What is the temperature in the ith layer?

Answer 11

T(z) = Ti + λi(z - hi)

Question 12

Where do the values for the sea level come from?

Answer 12

Comes from mean values at sea level at 45° latitude

Question 13

What happens at the equator?

Answer 13

• The distance from the centre of the earth to the equator is higher therefore g(equator) < g(pole)
• The centrifugal force tends to reduce at the equator

Question 14

How are true and geopotential heights related?

Answer 14

PE = g0*h = integrate( g(z) dz ) between ht and 0

Question 15

What is p/p0?

Answer 15

p/p0 = ( 1 + (λ0h) / T0 )^( - g0 / ( Rλ0 ) )

Question 16

What is ρ/ρ0?

Answer 16

ρ/ρ0 = ( 1 + (λ0h) / T0 )^(( - g0 / ( Rλ0 ) ) - 1)

Question 17

What is the speed of sound (cs)?

Answer 17

cs = sqrt(γRT)

Where γ is the ratio of the specific heats, γ = 1.4 for air

cs = cs0 * sqrt(Θ)

Question 18

What is δ?

Answer 18

Relative pressure
δ = p/p0

Question 19

What is σ?

Answer 19

Relative density
σ = ρ/ρ0

Question 20

What is Θ?

Answer 20

Relative temperature
Θ = T/T0

Question 21

What equation relates δ, Θ and σ?

Answer 21

δ = σ*Θ