C09 - 3D Flow

Question 1

Define Spanwise?

Answer 1

Flow over the wing perpendicular to the Relative Airflow.

Question 2

Name two factors which influence the Spanwise Airflow?

Answer 2

• Inertia of the Air Mass Flow.

- Local Pressure differences around the Aircraft.

Question 3

An Aerofoil has a region of relatively ‘____’ pressure over the upper surface and a region of relatively ‘____’ pressure lower surface?

Answer 3

• Low.

- High.

Question 4

True or False. At the Wingtip, the relatively high pressure doesn’t whip around to the relatively low pressure air?

Answer 4

False. It does.

Question 5

When the relatively high pressure of the lower upper surface of an Aerofoil mixes with the low pressure on the upper surface, what is the resulting action of the Airflow?

Answer 5

A Vortex is created.

Question 6

When viewed from behind, the Vortex is ‘____’ around the left Wing Tip and ‘____’ around the right Wing Tip (2)?

Answer 6

• Clockwise.

- Anti-Clockwise.

Question 7

Name two factors affecting the intensity of the Vortex?

Answer 7

• Pressure differential between the upper and lower surfaces (the driving force).
• Amount of time the driving fore is given to operate on the air mass.

Question 8

The greater the pressure differential, the ‘____’ the driving force?

Answer 8

Greater.

Question 9

A tip Vortex can only form when the Wing is producing what?

Answer 9

Lift.

Question 10

Tip Vortices decrease with ‘____’ forward speed?

Answer 10

Increasing.

Question 11

A low Aspect Ratio Wing produces ‘____’ tip Vortices than a High Aspect Ratio Wing?

Answer 11

More Intense.

Question 12

Name three factors which reduce the intensity of tip Vortex?

Answer 12

• Aircraft speed increases.
• Wing Aspect Ratio increases.
• Amount of Lift being produced reduces.

Question 13

Name two other effects of tip Vortices?

Answer 13

• Downwash.

- Drag.

Question 14

At the Trailing Edge, Airflow over the Upper Surface turns slightly ‘____’ and the Airflow under the Lower Surface turns slightly ‘____’. What is the name which causes this Vortices (3)?

Answer 14

• Inboard.
• Outboard.
• Trailing Edge Vortices.

Question 15

Vortices give a ‘____’ velocity to the air leaving the Trailing Edge?

Answer 15

Downward.

Question 16

True or False. The upwash is greater than the downwash when Vortices are created?

Answer 16

False. Downwash is greater.

Question 17

Define Induced Drag?

Answer 17

Accompanies the production of Lift.

Question 18

Lift is the component of the vector ‘____’ to the Relative Airflow?

Answer 18

Perpendicular.

Question 19

Induced Drag is the component of the vector ‘____’ to the Relative Airflow?

Answer 19

Parallel.

Question 20

Name two factors which affect the level of Induced Drag?

Answer 20

• Induced Angle of Attack.

- Intensity of Vortices (Downwash).

Question 21

Define Angle of Attack in 3D Flow?

Answer 21

The angle between the Aircraft’s Longitudinal Axis and the Relative Airflow.

Question 22

Define Induced Angle of Attack?

Answer 22

The angle between the effective and relative airflows.

Question 23

Induced Angle of Attack is larger when (2)?

Answer 23

• The Aircraft is flying at lower TAS.

- The Vortices are stronger which produces greater Downwash.

Question 24

Define Effective Angle of Attack?

Answer 24

The angle between the Effective Airflow and the Chord Line of the Wing.

Question 25

The Angle of Attack is the sum of what AoAs?

Answer 25

Induced AoA + Effective AoA.

Question 26

Weaker Vortices result in a ‘____’ Effective Angle of Attack and a ‘____’ Induced Angle of Attack?

Answer 26

• Larger.

- Smaller.

Question 27

Strong Vortices result in a ‘____’ Effective Angle of Attack and a ‘____’ Induced Angle of Attack?

Answer 27

• Smaller.

- Larger.

Question 28

What strength of Vortices results in a better proportion of Lift to Induced Drag?

Answer 28

Weaker.