Turbulence

Question 1

Describe convection in regards to turbulence

Answer 1

•Air heated by conduction will be less dense and will rise
•Produces up currents called thermals or convection currents
•Air cooled will also sink but this is not as strong as updraughts

Question 2

Describe mechanical processes in regards to turbulence

Answer 2

Caused by physical obstructions to the normal flow of air such as hills, mountains, coasts, trees and buildings

Question 3

Describe clear air turbulence in regards to turbulence

Answer 3

• Can be in cloud or in clear air
• Clear air turbulence (TURB) occurs around the boundaries of jet streams because of the large horizontal and vertical wind-shears

-Feels like driving over cobblestones

Question 4

Describe wake turbulence

Answer 4

•Disturbance in the atmosphere behind an aircraft when it is in the air caused by creating lift

•Spreads out like a boat wake behind the aircraft and sinks with gravity

•Strongest with heavy aircraft in clean configuration and low speed

Question 5

Describe the effects of atmospheric stability on turbulence

Answer 5

(a) Convective turbulence stronger when atmosphere is unstable as more air can rise

•(b) Mechanical turbulence stronger with unstable atmosphere as larger vertical extent

•(c) CAT strongest when atmosphere is unstable as more small changes in wind-shear

Question 6

Describe the effects of surface roughness on turbulence

Answer 6

(a) Convective turbulence stronger when surface is rough as it heats unevenly creating sporadic thermals

•(b) Mechanical turbulence stronger with increased roughness

•(c) CAT strongest when mountains are rough due to mountain waves

Question 7

Describe the effect of wind speed/direction on turbulence

Answer 7

(a) Convective turbulence stronger when speed is high

•(b) Mechanical turbulence stronger with high wind speed 90° to mountain or object

•(c) CAT strongest when wind speed is high as horizontal and vertical wind-shear is increased

Question 8

Describe the effects of vertical wind-shear on turbulence

Answer 8

•(a) Convective turbulence weaker with increased vertical wind-shear as reduces vertical currents and mixes cold air with warm air

•(b) Mechanical turbulence stronger with vertical wind-shear as it encourages mountain waves

•(c) CAT stronger when any wind-shear is increased

Question 9

Describe effects of surface friction on turbulence

Answer 9

The rougher the surfaces the greater the surface friction

•Can reduce speed at surface to almost stationary creating vertical wind-shear with free flowing air above

•Will cause wind to veer towards the low due to pressure gradient force being stronger than Coriolis

Question 10

Describe effects of thunderstorms on turbulence

Answer 10

Downdraughts during the mature stage create a gust front increasing both horizontal and vertical wind-shear

•Microbursts can create horizontal wind-shear

•Up draughts and down draughts in mature stage can create horizontal wind-shear

Question 11

Describe effect of temperature inversions on turbulence

Answer 11

Will separate the fast moving air above from the cold slower moving air below

•At the boundary between these two turbulence is generated

Question 12

Describe the effects of frontal activity on turbulence

Answer 12

• Wind direction and temperature change as front passes

•Creates large amounts of wind-shear and turbulence

Question 13

Describe the effects of wake turbulence from fixed and rotary winged aircraft on turbulence

Answer 13

Rotary wing aircraft create wake from blades spinning
•Large helicopters create similar wakes to commercial jets
•Fixed wing aircraft create a rotational wind-shear that can invert smaller aircraft caught in their wake

Question 14

Describe techniques used to avoid turbulence/low level wind shear (5)

Answer 14

•Use altitude/fly higher to reduce effects
•Fly above turbulent cloud
•Select route on the windward side of mountains or ridges, this increases up draughts increasing lift and less turbulence
•Slow down below VA
•Read the clouds (cumulus = turbulence)

Question 15

Describe light turbulence

Answer 15

• Turbulence that momentarily causes slight, erratic changes in altitude and/or attitude (pitch, roll, yaw)

•IAS fluctuates 5 - 15 kt. (<0.5 g at the aircraft’s centre of gravity) Report as ‘Light Turbulence’

Question 16

Describe moderate turbulence

Answer 16

•Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times

•IAS fluctuates 15 - 25 kt. (0.5 - 1.0g at the aircraft’s centre of gravity). Report as ‘Moderate Turbulence’

Question 17

Describe severe turbulence

Answer 17

• Causes large, abrupt changes in altitude and/or attitude. Aircraft may be momentarily out of control

•IAS fluctuates more than 25 kt. (>1.0 g at the aircraft’s centre of gravity). Report as ‘Severe Turbulence’