2D / 3D Flow

Question 1

What is skin friction

Answer 1

Friction cause by the viscosity of air

Question 2

What is a free stream flow

Answer 2

The airflow not affected by the aircrafts surface

Question 3

What happens to the airflow in the boundary layer

Answer 3

Slowed down by aircrafts surface

Question 4

After what height does the boundary layer not take effect anymore

Answer 4

Once speed is over 99% of the free stream flow speed

Question 5

What is the speed of the bottom layer of the boundary layer

Answer 5

0 m/s

Question 6

Why does smooth laminar flow change to turbulent flow

Answer 6

Because skin friction causes the laminar layer to slow down and lose energy which causes the air to tumble over itself

Question 7

What is the name of the point in which laminar flow changes into turbulent flow

Answer 7

Transition point

Question 8

What is the rate of speed increase through the boundary layer with turbulent flow

Answer 8

Rapid increase

Question 9

How easy is it for laminar flow to detach from the wing

Answer 9

Very easy

Question 10

How easy is it for turbulent flow to be detached from the wing

Answer 10

Very difficult

Question 11

What boundary layer produces the most friction; laminar or turbulent?

Answer 11

Turbulent

Question 12

As the curve of the airflow increases what happens to the transition point

Answer 12

Transition point moves forward

Question 13

What does a low Reynolds number mean? (Anything below 500,000)

Answer 13

Laminar flow : late transition point

Question 14

What does a high Reynolds number mean? (Anything greater than 10,000,000)

Answer 14

Turbulent flow : early transition point

Question 15

What happens With the stagnation points with a increased AOA

Answer 15

Pressure gradient increases therefor stagnation points increase

Question 16

At slow speeds where is the transition point in relation to leading edge / training edge

Answer 16

Closer to leading edge

Question 17

At high speeds where is the transition point in relation to leading edge/ trailing edge

Answer 17

Further back towards the trailing edge

Question 18

What does an adverse pressure gradient do

Answer 18

Try and push air round the trailing edge and against the airflow

Question 19

Where is the point of maximum thickness usually on a low speed aerofoil

Answer 19

30% of the chord

Question 20

Where is the point of maximum thickness usually in a modern airliner

Answer 20

50-60% of the chord

Question 21

What affect does AOA have on the pressure gradient

Answer 21

Higher AOA means higher pressure gradient

Question 22

What is the separation point

Answer 22

The point at which the turbulent air loses enough kinetic energy so that it is overcome by the adverse pressure gradient resulting in separation as the boundary layer rides above the adverse pressure gradient flow

Question 23

What are the effects of the separation point

Answer 23

Air behind separation point is turbulent

Consequently large reduction in life and large increase in drag

Question 24

What is the taper ratio

Answer 24

Top chord

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Question 25

What is the aspect ratio

Answer 25

Wingspan^2/ area Or Span/chord

Question 26

What is the sweep angle

Answer 26

The angle from the lateral axis to the centre of pressure ``` 737 = 25° 747= 35° ```

Question 27

What is the mean aerodynamic chord (MAC)

Answer 27

The chord of an imaginary rectangular wing with similar longitudinal stability properties to the actual wing

Question 28

What is the rigging angle

Answer 28

The angle between the wing root and the longitudinal axis

Question 29

What is washout

Answer 29

Where the angle of incidence decreases along wing root

Question 30

What is the angle of incidence

Answer 30

The angle between the chord line and the aircrafts longitudinal axis

Question 31

What is a dihedral angle

Answer 31

The angle between the wingtip and the lateral axis | When the wingtip is higher than the root

Question 32

What is the anhedral angle

Answer 32

The angle between the wing tip and lateral axis | when wingtip is lower than the root

Question 33

How is a wing tip vortex created

Answer 33

When the high pressure air from beneath the wing tries to “flow” to the low pressure area on top of the wing but because the wing is moving, by the time the air reaches the top of the wing, it’s already not there, meaning the air has no where to go causing vortex

Question 34

How does speed effect span wise flow

Answer 34

The slower you go the greater the spanwise flow

Question 35

When does tip vortex decrease?

Answer 35

If: Aircraft speed increases Wing aspect ratio increases Amount of lift being produced decreases

Question 36

What are the effects of a tip trailing vortex

Answer 36

Downwash | Drag

Question 37

How are trailing edge vortices created

Answer 37

When lower wing air going towards wing tip meets over wing air going towards wing root At trailing edge these are going different directions but collide causing a vortex

Question 38

How does vortices affect upwash and downwash in a 3D flow

Answer 38

Upwash decreases and downwash increases (compared to a 2d flow)

Question 39

What is effective airflow

Answer 39

RAF adjusted for downwash

Question 40

What is the induced angle of attack

Answer 40

The angle between relative air flow and effective airflow

Question 41

In 3D flow what is induced drag

Answer 41

The component of the vector parallel to the relative airflow

Question 42

What is the angle of attack in a 3D flow

Answer 42

The angle between the aircrafts longitudinal axis and the relative airflow

Question 43

How does angle of attack effect lift to induced drag proportion

Answer 43

Lower angle of attack = smaller vortices = lower effective angle of attack = larger induced angle of attack = lower lift to drag proportion

Question 44

How does speed affect the effective angle of attack

Answer 44

Bigger when faster

Question 45

How does being closer to the tip affect the EAF

Answer 45

EAF moves closer to chord line as downwash is greater

Question 46

What is dynamic pressure equal to?

Answer 46

Half density x true airspeed^2

Question 47

What forces predominate in w laminar flow

Answer 47

Viscous forced predominate