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Basic Aerodynamics > Aerodynamics > Flashcards

Aerodynamics Flashcards

1
Q

What is aerodynamics?

A

The study of the properties of moving air and the interaction between the air and the solid bodies moving through it

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2
Q

What is the continuity equation?

A

As speed increases, the cross sectional area decreases so long as density remains constant

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3
Q

What is the relationship between the velocity and the cross-sectional area in the continuity equation?

A

They are inversely proportional to one another

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4
Q

Give the continuity equation formula

A

A1V1 = A2V2

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5
Q

What is the property of air in the subsonic region?

A

Incompressible

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6
Q

Why is air incompressible in the subsonic region?

A

The flying body does not attain speeds necessary to compress the air

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7
Q

If there is no disturbance, air streamlines are what to one another?

A

Parallel to each other

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8
Q

When the diameter increases and speed decreases, what type of outlet is this classed as?

A

A diffuser outlet

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9
Q

What is a jet outlet?

A

An outlet where the diameter decreases and the speed increases

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10
Q

What does Bernoulli’s Principle state?

A

Total Pressure = Static Pressure + Dynamic Pressure

Total Pressure is always constant

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11
Q

If the valve is closed, describe static, dynamic and total pressure

A

Static pressure is at its maximum
Dynamic pressure is 0
Total pressure is at its maximum

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12
Q

As a valve starts to open, describe what happens in relation to pressure

A

Static pressure decreases as dynamic pressure increases

Total pressure remains at its maximum

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13
Q

What is the Point of Stagnation?

A

The point on the leading edge where dynamic pressure is 0 or the total pressure is equal to the static pressure

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14
Q

How do you calculate the total pressure?

A

Total pressure = Static Pressure + Dynamic Pressure

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15
Q

How is lift produced?

A

Higher pressure below the wing
Lower pressure above the wing
The difference in static pressure acts on the surfaces of the wing to create a lifting force

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16
Q

What is up-wash?

A

The upward flow of air directly ahead of the Leading Edge

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17
Q

What is down-wash?

A

The downward flow of air directly ahead of the Trailing Edge

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18
Q

What is the Magnus Effect?

A

Mechanically induced circulation

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19
Q

Describe the pressure waves using the Magnus effect when the cylinder is stationary

A

Static pressure on the upper surface of the cylinder is equal to the static pressure on the lower surface
No differential pressure means no lift

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20
Q

Describe the pressure waves using the Magnus Effect on a rotating cylinder

A

The circulatory flow causes an increase in local speed on the upper surface and a decrease in local speed on the lower surface
Difference in pressure generates lift

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21
Q

If the cylinder rotates at a higher speed, what happens to the pressure?

A

Decrease

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22
Q

What relation does speed have to pressure?

A

They are inversely proportional

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23
Q

What is the general rule for vortices?

A

They come in a pair, clockwise and anti-clockwise

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24
Q

What is a wing profile?

A

A cross-section of a wing

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25
Q

What line connects the leading edge to the trailing edge?

A

Chord line

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26
Q

Describe the mean camber line

A

The line drawn halfway between the upper and lower surfaces of the profile

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27
Q

What is the displacement of the mean camber line from the chord line called?

A

Camber

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28
Q

What is a maximum camber and where is it located in a typical low speed profile?

A

5% of the chord line

45% aft of the Leading Edge

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29
Q

What is the fineness ratio?

A

The ratio of the length to diameter on a wing profile
Or
Maximum thickness as a fraction

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30
Q

What is the maximum thickness of a typical low speed profile and where is it located?

A

18% of the chord

30% aft of the Leading Edge

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31
Q

What is the Flight Path Velocity?

A

The speed of the aircraft in a certain direction through the air

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32
Q

What is relative wind?

A

The speed and direction of the air acting against the aircraft which is passing through it

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33
Q

What does the relative wind depend on?

A

The flight velocity therefore it is not always horizontal

E.g banking

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34
Q

What symbol is used for the angle of attack?

A

Alpha

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35
Q

What is the angle of attack?

A

The angle between the chord line and the relative wind

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36
Q

What is the angle of incidence?

A

The angle between the chord line and the longitudinal axis of the aircraft

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37
Q

What is the symbol used for the angle of incidence?

A

Gamma

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38
Q

What is the wing area?

A

The projection of the outline on the plane of the chord

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39
Q

What does the wing area include?

A

The fuselage between the wings

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40
Q

How do you calculate the wing area?

A

Wing span x average chord

b x c

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41
Q

What is the taper ratio?

A

The ratio between the tip chord and the root chord

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42
Q

How do you calculate he taper ratio?

A

Tip chord / root chord

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43
Q

What symbol is given to the taper ratio?

A

Lambda

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44
Q

What is the average chord?

A

The geometric average of all the chords

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45
Q

What is the aspect ratio?

A

The ratio between the wing span and the average chord

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46
Q

How do you calculate the aspect ratio?

A

Wing span / average chord

b / c

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47
Q

What is another way to calculate the aspect ratio?

A

AR = b^2/A

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48
Q

What is the meaning of a high aspect ratio?

A

It has longer and narrower wings

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49
Q

What is the angle between the line 25% chord and a line perpendicular to the root chord known as?

A

Sweep angle

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50
Q

What is dihedral?

A

The increase of the angle attack for lateral stability

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51
Q

What is a positive dihedral wing?

A

When the wing tips are higher than the wing base

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52
Q

What is a negative dihedral wing known as and what are they?

A

Anhedral

When the wing tips are below the wing base

53
Q

What is the span wise flow?

A

The air flow that moves from the leading edge to the trailing edge

54
Q

Airflow flowing what to the chord line accelerates?

A

Parallel

55
Q

What are some disadvantages of a swept wing?

A

Reduce amount of lift produced for a given flight speed, wing area and angle of attack
Contribute to drag

56
Q

What are some advantages of a swept wing?

A

Designed to fly close to or above the speed of soung

Provides stability

57
Q

What does a small dihedral allow?

A

More manoeuvrability

58
Q

Give the 2 aerodynamic forces

A

Lift and drag

59
Q

What is the center of pressure?

A

The point at which all pressures and forces act on

60
Q

What do lift and drag depend on?

A

Shape of the aerofoil
Angle of attack
Surface area
Dynamic pressure

61
Q

Give the equation for theoretical lift

A

Dynamic pressure x surface area

62
Q

What is the coefficient of lift?

A

Measured lift/ theoretical lift

63
Q

What is the coefficient of drag?

A

Measured drag / theoretical drag

64
Q

Why can one not rely on only the theoretical lift?

A

Too many variables changing

65
Q

If the measured lift is less than the theoretical lift, how do we account for the difference?

A

Introduce the Coefficient of lift to the lift equation

66
Q

What is the difference between the theoretical lift and the. Lift equation?

A

The lift equation includes the coefficient of lift which makes it more reliable

67
Q

What happens if the maximum angle of attack is exceeded?

A

Stall happens due to flow separation

68
Q

Two profiles have the same camber but different thickness. How are they affected by the Coefficient of lift?

A

Same coefficient of lift but at a lower angle of attack

Higher coefficient of like when the angle of attack exceeds 10 degrees

69
Q

Two profiles have the same thickness but different camber. How are they affected by the coefficient of lift?

A

Higher coefficient of lift at very low angle of attacks

Higher maximum coefficient of lift at lower maximum angle of attack

70
Q

What is the advantage/disadvantage of an aircraft flying at a high maximum Coefficient of lift?

A

Adv - aircraft able to fly slower

Disadv - may produce high drag and low critical mach

71
Q

How can ice on the surface be formed?

A

Change in temperature, pressure, density or humidity

72
Q

What effect can ice formation on the surface on the wing have?

A

Reduce maximum coefficient of lift and the maximum angle of attack if it forms on the LE

73
Q

Give the 2 dimensionless coefficients that can be combined to give information about the performance of profiles

A

Coefficient of drag

Coefficient of lift

74
Q

What is the Polar Diagram?

A

A lift vs drag graph which gives the best glide ratio

75
Q

What is needed in the Polar Diagram to find the angle for the best glide ratio?

A

Coefficient of lift

Coefficient of drag

76
Q

What is the meaning of the best glide ratio?

A

The best angle for the aircraft to fly efficiently

77
Q

What is induced drag?

A

Drag caused by lift

78
Q

What is the drag caused by pressure distribution known as?

A

Form Drag

79
Q

On a finite wing, what are the ends called?

A

Wing tips

80
Q

What happens on the wing tips of a finite wing?

A

Turbulence at the wingtips causes wingtip vortices

81
Q

What is the circulation around the profile causing upwash and downwash known as?

A

The bound vortex

82
Q

What does a finite wing have in comparison to an infinite wing?

A

Wing tip vortices and the bound vortex

83
Q

What is induced drag affected by?

A

Aspect Ratio
Speed of the aircraft
Wing tip design

84
Q

If the aspect ratio is high, what happens to the bound vortex and wing tip vortices?

A

They decrease

85
Q

What is the drag caused by skin friction known as?

A

Friction Drag

86
Q

What are the 3 types of Parasite drag?

A

Form
Friction
Interference

87
Q

What factors affect form drag?

A

Area of the wing

Aircraft speed

88
Q

What is the retarded air hitting the surface of the wing known as?

A

Boundary layer

89
Q

What is compressible drag?

A

Drag caused by shockwaves approaching the speed of sound

90
Q

What is compressible drag also known as?

A

Wave drag

91
Q

How do heavy birds reduce drag?

A

Use their feathers - act as wingtips

92
Q

What happens to an aircrafts angle of attack and lift coefficient during low speed and high speed flights?

A

Low speeds - higher angle of attack and lift coefficient

High speeds - lower angle of attack and lift coefficient

93
Q

What is used to reduce form drag on aircraft

A

Make the profile more streamlined

94
Q

What is the relationship between form and friction drag?

A

Inversely proportional

95
Q

How much is the form drag on the profile with the highest length to diameter ratio?

A

Has the lowest form drag but the highest friction drag

96
Q

What is the length to diameter ratio known as?

A

Fineness ratio

97
Q

What is friction drag?

A

Air particles that get trapped on the skin of the wing

98
Q

What is the boundary layer?

A

Where the air thickens and becomes retarded

Where the air moves from high pressure to low pressure areas and back again

99
Q

How is friction drag minimised?

A

Higher form

Making the skin surface smoother

100
Q

What are the two types of boundary layers?

A

Laminar

Turbulent

101
Q

Where is the laminar boundary layer located on the wing?

A

From the leading edge to the maximum thickness

102
Q

What does an increase in angle of attack do to the laminar boundary layer?

A

The laminar boundary layer comes earlier due to a faster airflow

103
Q

Which type of boundary layer encounters an energy exchange?

A

Turbulent

104
Q

How much friction is produced in the turbulent boundary layer compared to the laminar?

A

3x more than the laminar

105
Q

What are the roles of a slot in a profile?

A

To assist air particles reach high pressure areas at the trailing edge
To transfer air with the high energy to the lower side

106
Q

How can flow separation be prevented on the profile?

A

Slots

107
Q

What is interference drag?

A

Pressure caused by shockwaves

108
Q

How can we reduce interference drag?

A

Fearings

109
Q

What is compressible drag?

A

Shockwaves formed by the aircraft approaching the speed of sound

110
Q

What is the cause of flow separation in the compressible drag?

A

Boundary layers thickening

Adverse pressure gradient across shockwaves

111
Q

What are the 4 different types of wing shapes?

A

Tapered
Rectangular
Square
Swept

112
Q

How is the wing designed so that the root can stall before the tips?

A

Geometric and aerodynamic twists

113
Q

What is the difference between the geometric and the aerodynamic twist?

A

Geometric twist - where the angle of incidence is greater at the root than the tip

Aerodynamic twist - where the camber is greater at the root than in the tip

114
Q

Where does the total wing lift act?

A

The center of lift

115
Q

What does MAC stand for?

A

Mean Aerodynamic Chord

116
Q

Where is the MAC located?

A

30% from the leading edge

117
Q

Where does the total weight of the aircraft act?

A

The center of gravity

118
Q

What happens if the position of the center of lift is the same as the center of gravity?

A

Straight and level flight

119
Q

When there is flow separation, at the root of the wing, where will the center of lift be?

A

In front of the center of cravity

120
Q

When does the aircraft experience a nose up reaction?

A

When the center of lift is in front of the center of gravity

121
Q

What is the device used on small aircraft to prevent the wing tip from stalling?

A

Stall strips

Vortex generator

122
Q

What is the disadvantage of the stall strip being mounted at the leading edge of the wing root?

A

Stall strips disturb lift

123
Q

What are slats used for?

A

Prevent wingtip stall on large aircraft

124
Q

What is span wise flow?

A

The air flow from the leading edge to the trailing edge

125
Q

What is the effect of span wise flow?

A

Boundary layer thickens towards the wing tip

126
Q

What are wing fences used for?

A

To keep the air particles in a straight line direction

127
Q

What are boundary layer fences?

A

Wing fences

128
Q

What is another device used to improve boundary layer control?

A

Saw toothed leading edges

Basic Aerodynamics (3 decks)

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