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ATPL POF > 2D / 3D Flow > Flashcards

2D / 3D Flow Flashcards

1
Q

What is skin friction

A

Friction cause by the viscosity of air

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2
Q

What is a free stream flow

A

The airflow not affected by the aircrafts surface

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3
Q

What happens to the airflow in the boundary layer

A

Slowed down by aircrafts surface

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4
Q

After what height does the boundary layer not take effect anymore

A

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

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5
Q

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

A

0 m/s

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6
Q

Why does smooth laminar flow change to turbulent flow

A

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

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7
Q

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

A

Transition point

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8
Q

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

A

Rapid increase

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9
Q

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

A

Very easy

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10
Q

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

A

Very difficult

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11
Q

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

A

Turbulent

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12
Q

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

A

Transition point moves forward

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13
Q

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

A

Laminar flow : late transition point

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14
Q

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

A

Turbulent flow : early transition point

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15
Q

What happens With the stagnation points with a increased AOA

A

Pressure gradient increases therefor stagnation points increase

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16
Q

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

A

Closer to leading edge

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17
Q

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

A

Further back towards the trailing edge

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18
Q

What does an adverse pressure gradient do

A

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

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19
Q

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

A

30% of the chord

20
Q

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

A

50-60% of the chord

21
Q

What affect does AOA have on the pressure gradient

A

Higher AOA means higher pressure gradient

22
Q

What is the separation point

A

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

23
Q

What are the effects of the separation point

A

Air behind separation point is turbulent

Consequently large reduction in life and large increase in drag

24
Q

What is the taper ratio

A

Top chord

—

25
Q

What is the aspect ratio

A

Wingspan^2/ area

Or
Span/chord

26
Q

What is the sweep angle

A

The angle from the lateral axis to the centre of pressure

737 = 25°
747= 35°
27
Q

What is the mean aerodynamic chord (MAC)

A

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

28
Q

What is the rigging angle

A

The angle between the wing root and the longitudinal axis

29
Q

What is washout

A

Where the angle of incidence decreases along wing root

30
Q

What is the angle of incidence

A

The angle between the chord line and the aircrafts longitudinal axis

31
Q

What is a dihedral angle

A

The angle between the wingtip and the lateral axis

When the wingtip is higher than the root

32
Q

What is the anhedral angle

A

The angle between the wing tip and lateral axis

when wingtip is lower than the root

33
Q

How is a wing tip vortex created

A

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

34
Q

How does speed effect span wise flow

A

The slower you go the greater the spanwise flow

35
Q

When does tip vortex decrease?

A

If:

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

36
Q

What are the effects of a tip trailing vortex

A

Downwash

Drag

37
Q

How are trailing edge vortices created

A

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

38
Q

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

A

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

39
Q

What is effective airflow

A

RAF adjusted for downwash

40
Q

What is the induced angle of attack

A

The angle between relative air flow and effective airflow

41
Q

In 3D flow what is induced drag

A

The component of the vector parallel to the relative airflow

42
Q

What is the angle of attack in a 3D flow

A

The angle between the aircrafts longitudinal axis and the relative airflow

43
Q

How does angle of attack effect lift to induced drag proportion

A

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

44
Q

How does speed affect the effective angle of attack

A

Bigger when faster

45
Q

How does being closer to the tip affect the EAF

A

EAF moves closer to chord line as downwash is greater

46
Q

What is dynamic pressure equal to?

A

Half density x true airspeed^2

47
Q

What forces predominate in w laminar flow

A

Viscous forced predominate

ATPL POF (12 decks)

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