Lesson 206 Turbulence

Question 1

What is turbulence?

Answer 1

An irregular motion of the air resulting from the formation of eddies and/or vertical currents of air.

Question 2

What are the four types of turbulence?

MSCW

Answer 2

Mechanical
Shear
Convective
Wake

Question 3

What are the three intensities of turbulence?

Answer 3

Light
Moderate
Severe

Question 4

What three factors control the evolution of mechanical turbulence?
RSS

Answer 4

Roughness of terrain
Strength of winds
Stability of the air

Question 5

What are the five causes of wake turbulence?

Answer 5

Wing tip vortices 
Rotor tip vortices 
Jet blast
Rotor down wash
Prop wash

Question 6

Factors that control the evolution of convective turbulence are:
STTDD

Answer 6

Stability of the air - more unstable = more turbulence
Degree of difference in unequal heating
Time of year (seasonal differences in heating)
Time of day - late afternoon early evening
Degree of temperature contrast associated with cold air advection.

Question 7

What factors control the evolution of wake turbulence?

Answer 7

Weight and speed of the aircraft
Lighter crosswinds = more longevity, crosswinds >5 Kt break up vortices.
Stable air increases longevity
Strength of jet engines
Rotor blade vortices are greatest at lower speeds and with fewer blades.
Rotor down wash depends on weight, speed air density and rotor diameter.

Question 8

Wind associated with mechanical turbulence occurs in the PBL due to friction and we can quantify their effects by applying the following table:

Answer 8

Non-existent: very light (less than 10 KT)
Light: (10-12 KT without gusts)
Moderate: (wind or gust > 15 KT)
Severe: (wind or gust > 20 KT)

Question 9

The 3 criteria that are used to establish the possibility of turbulence in the free atmosphere are:

Answer 9

Vertical wind shear in knots/1000’

• light <5 knots
• Moderate 5 to 9 Knots
• Severe 10 knots or more