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B Licence M8 > Aerodynamics > Flashcards

Aerodynamics Flashcards

1
Q

What gases make up the atmosphere?

A

78% Nitrogen
21% Oxygen
1% Traces of neon, argon, krypton & carbon dioxide

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2
Q

Height of the troposphere?

A

28,000ft - 54,000ft

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3
Q

Height of the tropopause?

A

Averages 36,000ft

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4
Q

Height of the stratosphere?

A

31 Miles

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5
Q

Temperature at the tropopause?

A

-56.5 degrees Celsius

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6
Q

The average pressure at sea level is …..

A

1013.25 millibars or 29.92 inches mercury

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7
Q

How does the density of gases change with pressure and temperature?

A
  • Varies directly in proportion with pressure

- Varies inversely with temperature

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8
Q

At what rate does temperature fall when altitude increases?

A

Temperature falls at a rate of 6.5 degrees celsius for every 1,000m or 2 degrees celsius for every 1000ft

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9
Q

How do you measure water vapour in the air?

A

Using a hydrometer

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10
Q

Dew point:

A

The temperature at which a body of air must be lowered before the water vapour condenses out and becomes liquid vapour

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11
Q

Boundary layer:

A

A thin layer of viscous fluid close to the solid surface of a wall in contact with a moving stream in which the flow velocity varies from zero at the wall

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12
Q

Transition region:

A

The area at which the boundary layer changes from laminar to turbulent

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13
Q

Bernoulli’s Principle:

A

Any increase in velocity will cause a decrease in its pressure

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14
Q

Mean Camber:

A

A line drawn midway between the upper and lower camber

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15
Q

Maximum Camber:

A

The maximum distance of the mean camber line from the chord line

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16
Q

Maximum thickness:

A

The maximum distance of the lower surface from the upper surface

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17
Q

Fineness ratio:

A

The ratio of length to maximum thickness. (For best results it should be about 4 to 1

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18
Q

Angle of attack:

A

The angle between the airfoil and airflow

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19
Q

Upwash:

A

The airfoil, just before it reaches the leading edge, is sucked into the low pressure area

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20
Q

Aerofoil, where is the high and low pressure?

A

Low pressure on the upper surface, high pressure on the lower surface

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21
Q

Total drag:

A

The sum of all types of drag

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22
Q

Induced drag:

A

Drag due to lift

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23
Q

Parasite drag:

A

Drag due to the viscosity of the air

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24
Q

Three types of parasite drag:

A

Form drag, interference drag & skin friction

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25
Q

What happens on the wing tip with induced drag?

A

High pressure air below the wing spills over to the low pressure air above the wing and causes vortexes

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26
Q

Form drag:

A

The drag caused by the separation of the boundary layer from a surface and the wake created by that separation

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27
Q

Interference drag:

A

Drag that is generated by the mixing of airflow streamlines between airframe components such as the wing and the fuselage

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28
Q

Friction drag:

A

The resistant force exerted on an object moving in a fluid. Skin friction drag is caused by the viscosity of fluids and is developed from laminar drag to turbulent drag as a fluid moves on the surface of an object

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29
Q

Induced drag equation

A

Induced drag (N) = drag coefficient X dynamic pressure (N/m^2) X wing area (m^2)

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30
Q

Five factors that affect aerodynamic lift and induced drag:

A
  • Shape of the aerofoil section
  • Area of the aerofoil
  • Air density
  • Speed of the air relevant to the airfoil surface
  • Angle of attack
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31
Q

Centre of pressure:

A

The point on the chord line where the aerodynamic forces are concentrated

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32
Q

The centre of pressure of a subsonic airflow is typically located:

A

30%-40% of the chord line back from the leading edge

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33
Q

How does the centre of pressure move as the angle of attack increases?

A

The centre of pressure moves forward as the angle of attack increases and backwards as the angle of attack decreases

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34
Q

Lift equation:

A

Aerodynamic lift = lift coefficient X dynamic pressure X airfoil surface

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35
Q

Dynamic pressure equation:

A

Dynamic pressure = 0.5 X air density X airspeed^2

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36
Q

Wing span:

A

The maximum distance from tip to tip

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37
Q

Wing Area:

A

The surface of the plan view of the wing (including the parts covered such as the fuselage, engines and others)

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38
Q

Angle of incidence:

A

Acute angles formed between the chord of the wing and a line drawn parallel to the longitudinal axis of the aircraft

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39
Q

Mean chord equation:

A

Mean chord = wing area (s) / wing span (b)

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40
Q

Mean aerodynamic chord (MAC):

A

The distance between the leading and trailing edge of the wing, measured parallel to the normal airflow over the wing, is known as the chord. The position fo the MAC is important for aircraft stability.

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41
Q

Aspect ratio:

A

The ratio of its span to its mean chord

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42
Q

Aspect ratio equation:

A

Wing span^2 / wing area

Or

Wing span / mean chord

43
Q

What type of wing has a minimum trailing vortex (induce drag)?

A

Long span with a small chord (glider)

44
Q

Aspect ratio of a: glider, fast jet & commercial aircraft?

A

Glider = 40
Fast jet = 3.5
Commercial aircraft = 5-8

45
Q

What is the effect of reducing the aspect ratio?

A

Reduces induced drag

46
Q

Washout:

A

Aircraft designed with a greater angle of incidence at the root of the wing than the tip. (This imposes stability of the aircraft as it approaches the stall condition) This will cause the root to stall before the tips allowing better control.

47
Q

Washin:

A

A wing designed so that the angle of incidence is greater at the tip that at the root.

48
Q

Rime Ice:

A

Forms a rough surface on the leading edge (water freezes before it can flow)

49
Q

Glaze ice:

A

Forms a smooth thick coating over the leading edges (when the temperature is slightly below freezing and the water can flow before freezing)

50
Q

How much can ice on the wing effect drag and lift?

A

Reduces lift by 30% and increases drag by 40%

51
Q

If the centre of pressure is acting behind the centre of gravity, how will the aircraft act?

A

It will cause a nose down pitching moment

52
Q

If the centre of pressure is acting forward of the centre of gravity, how will the aircraft act?

A

A nose up pitching moment will occur

53
Q

If the thrust line is below the centre of gravity, how will the aircraft act?

A

The aircraft will give a nose up pitching moment

54
Q

Lateral axis:

A

A straight line passing through the centre of gravity parallel to the wing span (Pitch axis)

55
Q

Longitudinal axis:

A

A straight line passing straight through the fuselage of the aircraft from nose to tail, passing through the centre of gravity (Roll axis)

56
Q

Vertical axis:

A

A straight line running vertically through the centre of gravity (Yaw axis)

57
Q

Motion about the lateral axis is referred to as…..

A

Longitudinal control or longitudinal stability

58
Q

Motion about the longitudinal axis is referred to as……

A

Lateral control or lateral stability

59
Q

Motion about the vertical axis is referred to as…..

A

Directional control or directional stability

60
Q

Glide ratio:

A

The ratio of every unit of vertical distance an aircraft descends to the horizontal distance it travels while gliding

61
Q

How does a higher lift/drag ratio affect glide ratio?

A

The higher the lift/drag ratio the smaller the gliding angle, thus increasing the glide ratio

62
Q

What does the glide angle depend on?

A

The glide angle depends on the ratio of lift to drag and is independent of weight

63
Q

Wing loading:

A

This is the all up weight of the aircraft divided by the wing area. (Usually given in kg/m^2)

64
Q

Load factor:

A

The ratio of the weight of the aircraft to the load imposed during a manoeuvre.

65
Q

How does the stall speed change with an increase in the wing loading?

A

The stalling speed increases as wing loading increases

66
Q

Wing loading stall equation:

A

V2=V1 x square root of(w1/w2)

V2 = New stalling speed
V1 = Original stalling speed
w2 = new weight
w1 = Original weight
67
Q

Three effects of additional weight (same as an increase in altitude):

A
  • Slight reduction in maximum speed
  • Large reduction in rate of climb
  • Increase in stalling speed
68
Q

High lift devices:

A

Used to provide extra lift when the aircraft is at low air speeds or high angle of attacks (Slats, slots, flaps)

69
Q

Slats:

A
  • Increase stalling speed

- Prolongs the lift curve by delaying the stall until a higher angle of attack

70
Q

Static Stability:

A

The means when disturbed from its flight path, forces will be activated which will initially tend to return the aircraft to its original position

71
Q

Dynamic Stability:

A

Determines the way the aircraft will return. It is the property that dampens the oscillations set up by a statically stable aircraft.

72
Q

Two factors that will affect longitudinal stability:

A
  • Position of the centre of gravity

- Pitching moment on the wings

73
Q

The amount of horizontal stabiliser restoring moment will depend on:

A
  • The area of the stabiliser (a larger area will provide more force)
  • The length of the fuselage
74
Q

In a slide slip, what happens to the angle of attack and lift on the lower wing?

A

The lower wing has an increased angle of attack and greater lift (The greater lift will restore level flight)r

75
Q

What are the two purposes of swept wings?

A
  • Delay the formation of sonic shockwaves

- Improves lateral stability

76
Q

Dutch roll:

A

The tendency to roll as the aircraft yaws as a result of increased velocity of the forward moving wing and decreased velocity of the backward moving wing

77
Q

Longitudinal Stability:

A

Pitch stability, relation of the wing and tail effect this stability

78
Q

Lateral stability:

A

Roll stability, positive lateral stability helps stabilise the rolling effect when one wing gets lower than the other

79
Q

Directional stability:

A

Yaw stability, The tendency to return to initial equilibrium when yawing

80
Q

Yaw Damper:

A

An automatic flight control device that senses the Dutch roll and applies corrective rudder action to prevent or at least greatly attenuate it

81
Q

Passive stability:

A

The aircrafts natural aerodynamic stability

82
Q

Active stability:

A

Computer enhanced stability (Yaw damper)

83
Q

Keel effect:

A

The result of side-force generating surfaces being above or below the centre of mass. (Also known as the pendulum effect or pendulum stability)

84
Q

Sideslip:

A

A movement fo an aircraft in which relative airflow of air moves along the lateral axis, resulting in a sideways movement from a projected flight path

85
Q

Longitudinal axis:

A

Nose to nose, aileron roll movement

86
Q

Vertical axis:

A

Top to bottom, directional stability, rudder yaw movement

87
Q

Lateral axis:

A

Wing tip to wing tip, elevator pitch movement

88
Q

For the same angle of attack, how does the lift compare of a delta wing and a high aspect ratio wing?

A

The lift on a delta wing is lower than the lift on a high aspect ratio wing

89
Q

Neutral Static Stability:

A

When a ball is displaced and shows no tendency to roll back to its original position

90
Q

Positive Static Stability:

A

The tendency to return to equilibrium

91
Q

Negative static stability:

A

The tendency to continue in the displacement direction

92
Q

Dynamic Stability:

A

Refers to how the continuous motion of a body varies over time (only applies if we have positive static stability)

93
Q

Undamped oscillation:

A

The ball theoretically oscillates forever after initial displacement

94
Q

If the pivot point is below the centre of gravity what type of stability is there?

A

Negative static stability

95
Q

If the pivot point is above the centre of gravity, what type of stability is there?

A

Positive static stability

96
Q

The relationship between induced drag and airspeed is …….

A

Inversely proportional to the square of the speed

97
Q

Angle of incidence:

A

The angle the chord of the mainplane or tailplane makes with the horizontal

98
Q

Compressible drag:

A

Caused by the shock wave on an aircraft approaching the speed of sound

99
Q

Down-wash:

A

Trailing vortices produce a downward flow of air behind the wing

100
Q

Wing fences:

A

Reduce the effects of spanwise flow

101
Q

Effect of spanwise flow?

A

It has the effect of thickening the boundary layer towards the wing tip (Especially during low speed flight with high angle of attack)

102
Q

Vortex generator:

A

Used to improve boundary layer control, produces lift and has an associated tip vortex which is comparable to induced drag

103
Q

Stall strip:

A

Used to prevent the wing tips from stalling first

B Licence M8 (1 decks)

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