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XPrinciples of Flight > Lesson 2 > Flashcards

Lesson 2 Flashcards

1
Q

Lift is a pressure gradient pushing…

A

upwards

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2
Q

Pressure drag is?

A

an aerodynamic force created downstream of an object in the aerofoil

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3
Q

CL represents

A

Coefficient of lift

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4
Q

CL MAX describes?

A

Max lift an aerofoil can produce

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5
Q

αCRIT describes?

A

AoA critical = stall

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6
Q

CL / α graph:
line crosses zero alpha and zero Coefficient of lift
would be what type of aerofoil?

A

symmetrical

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7
Q

CL / α graph:
line crosses +4 alpha and zero Coefficient of lift
would be what type of aerofoil?

A

positive camber aerofoil

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8
Q

CL / α graph:
line crosses -4 α and zero CL
would be what type of aerofoil?

A

negative camber aerofoil

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9
Q

What is the lift equation

A

Lift = 1/2 x Density x Velocity2 x Surface area x Coefficient of lift

Lift = 1⁄2 ρ V2 S CL

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10
Q

Air is fluid, How would you describe its compressibility?

A

Incompressible

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11
Q

Equation of continuity:
Mass flow and a streamtube
tell me more

A

Mass flow of incompressible fluid through a streamtube must be constant at all points

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12
Q

Mass flow equation is:

A

m = ρ (density) x velocity x cross-sectional area of the flow

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13
Q

PTOT represents

A

Total pressure

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14
Q

PSTAT represents

A

Static pressure

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15
Q

the letter
‘q’
represents

A

Dynamic pressure

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16
Q

When streamlines converge static pressure does what?

A

Decreases

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17
Q

A pressure gradient is…

A

A change in static pressure over a distance

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18
Q

Describe the pressure gradient force

A

Acts on an object inside a pressure gradient. The force acts in the high to low direction.

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19
Q

Which two things determine the pressure gradient force strength?

A

The difference in the static pressure
The distance over which that difference is acting.

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19
Q

Drag acts in the opposite to which direction.

A

Flight.

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20
Q

2D airflow works in which two dimensions?

A

Up and down
forward and aft

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21
Q

3D air flow ads which dimension?

A

Left to right
Spanwise flow

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22
Q

What are the two types of two dimensional drag?

A

Form (pressure drag)
Skin friction drag

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23
Q

What causes form drag

A

Form drag is caused by asymmetry in the areas of high pressure in front of and behind the aerofoil. The static pressure to the rear is lower than the static pressure around the front stagnation point. This causes a net force rearwards dash the ultimate cause of form drag.

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24
Q

How do you minimise form drag

A

Reduce frontal surface area
Minimised by changing shape of the object

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25
Q

In which direction does form drag act?

A

Opposite to the direction of flight.

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26
Q

Turbulent flow behind an object is indicative of which type of drag?

A

Form drag

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27
Q

How would you define freestream airspeed?

A

The Airflow completely unaffected by the aerofoil and aircraft

28
Q

What is the name of the layer which changes the speed of the free stream air up to 99%?

A

The boundary layer

29
Q

Is skin friction drag a large value?

A

Negative, but it acts over the entire aircraft so can become significant.

30
Q

What are the two types of boundary layer?

A

Laminar boundary layer
Turbulent boundary layer

31
Q

Does the laminar boundary layer or the turbulent boundary layer present a smooth velocity increase?

32
Q

Does the laminate boundary layer or the turbulent boundary layer present a steep velocity gradient?

A

Turbulent boundary layer

33
Q

Turbulent boundary layer or laminar boundary layer resist separation more?

A

turbulent boundary layer

34
Q

Which of these is more prone to separation [stall ] Laminar boundary layer or turbulent boundary layer

A

Laminer boundry layer

35
Q

would the laminar boundary layer be measured in millimetres or centimetres

A

millimetres

36
Q

would the turbulent boundary layer be measured in millimetres or centimetres

A

centimetres

37
Q

The transition point of an aerofoil marks the difference between what?

A

Laminar and turbulent boundary layers

38
Q

The separation point marks the difference between what?

A

Turbulent and a stalled condition
Where the boundary layer separates from the surface

39
Q

Where on the aerofoil are you most likely to see laminar flow

A

On the top front edge

40
Q

At what point of the aerofoil is laminar flow physically unable to pass?

A

The thickest point of the aerofoil

41
Q

The adverse pressure gradient describes the pressure gradient in which location of an aerofoil

A

The adverse pressure gradient is caused because of the static pressure distribution, it causes pressure to flow against the direction of for air flow over the air of foil, it prevents the laminate flow going past the thickest point.

42
Q

What happens to the energy of the air flow once it moves aft of the adverse pressure gradient

A

Loses energy

43
Q

Which type of boundary layer requires a smooth clean surface forward of the thickest point?

A

laminar boundary layer

44
Q

How can you extend the laminar boundary layer on the top front of an aerofoil

A

Move the thickest point of the aerofoil aft

45
Q

What type of aircraft are you more likely to see turbulent boundary layer on

A

Slower training aircraft

46
Q

Role operates about which axis

A

Longitudinal

47
Q

Pitch operates about which axis

48
Q

Yaw Operates about which axis

49
Q

An aircraft will pitch roll and yaw about which point?

A

Centre of gravity

50
Q

What word describes the top down shape of the wing

51
Q

Give four examples of wing shape

A

Rectangular Tapered elliptical swept

52
Q

What is used for the taper ratio of a wing

A

Tip chord divided by root chord

53
Q

What is used for the aspect ratio of a wing

A

Span divided by chord

54
Q

What is used for the thickness of a wing

A

Maximum thickness divided by chord length multiplied by 100 to get a percentage

55
Q

How would you describe the mean geometric chord

A

The average chord length

56
Q

The mean aerodynamic chord could be described as what

A

The cord of an imaginary rectangular wing with the same span as the swept or tapered wing that creates the same pitching moment as the wing. The position of things like scent of gravity and scent of pressure are given as percentages of MAC

57
Q

Describe sweep angle of a wing

A

The angle between the leading edge and a line perpendicular to the fuselage

58
Q

Describe rigging angle when it comes to a wing

A

Rigging angle for the angle of incidence is the angle between the aircraft’s longitudinal axis and the wing cord at the wing root

59
Q

Describe a dihedral wing

A

The wing tips are higher than the wing root

60
Q

And describe a dihedral wing

A

The wing tips are lower than the wing root

61
Q

Why does span wise flow occur in three dimensional aerodynamics?

A

The elliptical lift distribution across the span of the wing

62
Q

What direction to spanwise flow run in

A

Towards the tip of the wing beneath and then towards the root on top.
This creates a port clockwise rotation when viewed from behind and they starboard anticlockwise rotation

63
Q

What causes tip vortices

A

The combination of forward motion through the air and the span wise flow

64
Q

What affects wing tip vortices

A

Tip chord length
Aircraft speed(A lower speed allows the spam wise flow to add a greater vortex to the incoming air flow)

65
Q

Where do vortices come from

A

Wing tip
Trailing edge

66
Q

What is the effect of spoilers on the angle of attack and stall speed at a constant mass

A

with increasing spoilers both the angle of attack and stall speed increase

XPrinciples of Flight (5 decks)

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