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Module 8 > 8.2 Aerodynamic Principles > Flashcards

8.2 Aerodynamic Principles Flashcards

1
Q

Where is the air incompressible?

A

In the subsonic region

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2
Q

What is the continuity equation?

A

A1 V1 = A2 V2

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3
Q

What does the continuity equation state?

A

The speed of airflow is inversely proportional to the area of the cross-section of the tube as long as the density remains the same

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4
Q

What are the terms used for:

  • tube diameter increasing and speed decreases
  • tube diameter decreasing and speed increases
A
  • diffuser outlet

- jet outlet

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5
Q

What does Bernoulli’s principle state?

A

The total pressure is equal to the sum of the static pressure and the dynamic pressure
The total pressure remains constant

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6
Q

What is IAS?

A

Indicated air speed

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7
Q

What is the point of stagnation?

A

The speed of the airflow = zero

The static pressure is equal to the total pressure

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8
Q

What is the Magnus effect?

A

The mechanically induced circulation around an object

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9
Q

What is the rule of vortices?

A

They always form in pairs and rotate counter-clockwise

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10
Q

What is up-wash and down-wash?

A

Streamlines approaching or leaving the wing flow upwards or downwards

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11
Q

As the speed increases, what happens to the static and dynamic pressure?

A

Static - decreases

Dynamic - increases

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12
Q

What is a profile?

A

A cross-section of a wing

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13
Q

What is the chord line?

A

A straight line that connects the leading edge to the trailing edge

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14
Q

What is the mean camber line?

A

A line drawn half-way between the upper and the lower surfaces of the profile

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15
Q

What is the camber?

A

The displacement between the mean camber line and the chord line

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16
Q

What is the maximum camber of a low-speed profile?

A

Maximum camber of 5% located 45% aft of the leading edge

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17
Q

What is the maximum thickness of a low-speed profile?

A

Maximum thickness of 18% located 30% aft of the leading edge

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18
Q

What is the maximum thickness (as a fraction) of a profile also known as?

A

The fineness ratio

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19
Q

What is the flight path velocity?

A

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

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20
Q

What is the relative wind?

A

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

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21
Q

What is the angle of attack?

A

The angle between the chord line of the profile and the relative wind (a - alpha)

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22
Q

What is the angle of incidence?

A

The angle between the chord line of the profile and the longitudinal axis of the aircraft (y - gamma)

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23
Q

What is the equation for taper ratio?

A

n (lambda) = Ct (tip) / Cr (root)

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24
Q

How is the sweep angle measured?

A

The angle between 25% from the leading edge and the perpendicular line, both measured from the root chord
Positive (backwards)
Negative (forwards)

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25
Q

What is the positive and negative Dihedral angle?

A

Positive dihedral - wings upwards

Negative dihedral - wings downwards

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26
Q

What is the aerodynamic force?

A

The resultant of all forces on a profile in an airflow acting on the centre of pressure

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27
Q

What are the two components that make up aerodynamic forces?

A

Lift - perpendicular to relative wind

Drag - parallel to relative wind

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28
Q

What is the equation of lift/drag (Theoretical lift/drag)?

A

Lift/Drag Force = Dynamic Pressure x Area

F = 1/2PV^2 x A

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29
Q

What is the centre of pressure?

A

The point at which all pressures and forces act

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30
Q

What are the 4 things that affect lift and drag?

A
  • Dynamic Pressure
  • Surface Area
  • Shape of Profile
  • Angle of Attack
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31
Q

How is the Coefficient of lift (CL) calculated?

A

Measured lift
——————
Theoretical lift

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32
Q

It is not possible to calculate actual lift. What is used to measure this?

A

A wind tunnel with two scales:

  • horizontal = drag
  • vertical = lift
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33
Q

How is the Coefficient of drag (CD) calculated?

A

Measured drag
———————
Theoretical drag

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34
Q

If the angle of attack increases above amax (alpha max) what happens?

A

The airflow cannot follow the upper surface of the profile and an airflow separation called a “stall” occurs

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35
Q

If a profile has a larger camber, what increases?

A

The Coefficient of lift at a smaller angle of attack

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36
Q

If a profile has a larger thickness, what increases?

A
  • higher max coefficient of lift
  • higher amax (alpha max)
  • higher angle of attack
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37
Q

What are the disadvantages of creating a profile with a larger camber or thickness?

A
  • more drag

- low critical Mach number

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38
Q

How is the angle for the best glide ratio calculated?

A

Using a graph, drawing a tangent from the intersection of the axis to the graph

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39
Q

What is the same as the ratio of lift and drag?

A

The ratio of lift coefficient to the drag coefficient

40
Q

What is the glide ratio?

A

The best possible lift for the least possible drag

41
Q

What are the three categories of drag?

A
  • induced
  • parasite
  • compressible
42
Q

What is induced drag?

A

Drag on the wing caused by the lift

43
Q

What is parasite drag?

A

Drag not related to the lift. Can be due to distribution of pressure, friction or aerodynamic interference.

44
Q

What is compressible drag?

A

Drag caused by shockwaves on an aircraft approaching the speed of sound

45
Q

What is drag?

A

It is the aerodynamic force which is parallel to the relative wind. It is opposite force to thrust

46
Q

What is the turbulence at the wing tips called?

A

Wing tip vortices

47
Q

What is the circulation of air (up-wash and down-wash) called around the wings causing drag?

A

The bound vortex

48
Q

What is important about the door gutters design?

A

They reflect the up-wash and down-wash caused by the vortices. They are in line with the flow pattern

49
Q

What are the 3 types of PARASITE drag?

A
  • form
  • friction
  • interference
50
Q

What is form drag?

A

A parasite drag caused by the pressure distribution on a body

51
Q

How is form drag reduced?

A

Streamlining of an object

52
Q

What is the relationship between form drag and friction drag?

A

If the form drag is low, the friction drag is high

If the form drag is high, the friction drag is low

53
Q

What is the name of the area of air on top of a wing, with friction drag, causing it to retard?

A

The boundary layer

54
Q

What are the two types of boundary layer?

A
  • laminar boundary layer

- turbulent boundary layer

55
Q

How much more friction drag does the turbulent boundary layer produce than the laminar boundary layer?

A

3 times more friction

56
Q

Where is the laminar boundary?

A

Immediately downstream from the leading edge (up to the minimum static pressure/maximum thickness)

57
Q

Where is the turbulent boundary?

A

Immediately downstream of the laminar boundary layer (starting where the static pressure is minimum/maximum thickness)

58
Q

What can be introduced to a wing to prevent flow separation?

A

A slot

- high energy air moved from bottom of the wing up to the top through the slot

59
Q

A lower profile wing is known as?

A

The laminar profile

60
Q

How is interference drag reduced?

A

By using fairings

61
Q

What is interference drag?

A

Turbulence in the airflow caused by sharp corners from when components are joined together (engines on wings etc)

  • The total drag of the joined components is GREATER than the total drag of the individual components
62
Q

When does compressible drag occur?

A

Only in transonic and supersonic flight

63
Q

What is total drag?

A

The combination of induced drag and parasite drag

64
Q

What are the four types of wing shapes?

A
  • elliptical
  • rectangular
  • tapered
  • swept
65
Q

What type of wings stall at the tip?

A
  • Swept

- Tapered

66
Q

What type of wing does the stall start at the root?

A

Rectangular wings

67
Q

What type of wing does the stall occur spanning across the wing?

A

Elliptical

68
Q

What is geometric twist?

A

The camber is constant throughout the span but the angle of incidence is greater at the root than the tip

69
Q

What is aerodynamic twist?

A

The camber is greater at the root than at the tip but the angle of incidence is instant across the span

70
Q

Where does the total wing lift act?

A

It acts on the centre of lift

71
Q

What is MAC?

A

The mean aerodynamic chord

- the chord line through the centre of lift

72
Q

Where is the centre of lift located?

A

At 30% MAC

73
Q

Where do the streamlines above and below the wings bend?

A

Above - towards the centre

Below - towards the wing tips

74
Q

What is induced drag affected by?

A

The aspect ratio, aircraft speed and the wing tip design

75
Q

How do you measure the theoretical lift/drag of a profile?

A

Dynamic pressure x area

76
Q

If airflow over a wing increases in velocity, what happens to induced drag and parasite drag?

A

Induced drag decreases

Parasite drag increases

77
Q

What is the equation for the AREA of a tapered wing?

A

Wing span x average chord

78
Q

What boundary layer would you find the most amount of kinetic energy?

A

The turbulent layer

79
Q

What is another name for the polar diagram?

A

Lilienthal diagram

80
Q

What is the polar (Lilienthal) diagram used for?

A

To find the angle for the best glide ratio

The most efficient operation of the profile

81
Q

Is the induced drag LARGER on a low aspect ratio or a high aspect ratio?

A

Induced drag is less on a high aspect ratio

82
Q

What can be added to wing profiles to reduce induced drag?

A
  • Winglets

- Wing tip fences

83
Q

Where does an aircrafts total weight act?

A

The centre of gravity

84
Q

What type of stall would an aircraft recover without pilot input?

A

A wing root stall

85
Q

What type of stall is the most dangerous?

A

A wing tip stall as the aircraft rotates in the nose-up position

86
Q

What is used on a small aircraft to prevent wing tip stall?

A

A stall strip (knife edge device on the leading edge of the wing root)
-disadvantage is that it disturbs the lift

87
Q

What are used on larger aircraft to prevent wing tip stall?

A

Slats on the leading edge - giving the boundary layer more energy preventing flow separation

88
Q

What is spanwise flow?

A

Airflow over a swept wing

  • air following the leading edge
  • air at right angles to the leading edge
89
Q

How can spanwise flow be reduced?

A
  • wing fences (boundary layer fences)

- saw tooth leading edge

90
Q

What determines the number and location of vortex generators?

A

The flight test investigations

91
Q

What is the purpose of a vortex generator?

A

It improves the boundary layer control by producing lift

92
Q

How do you calculate the aspect ratio?

A 
Wing span (b)
——————
Average chord (c)

(Or the span squared over the area)

93
Q

What would an average high performance sail plane’s aspect ratio be?

A

35

94
Q

What would a jet fighter’s average aspect ratio be?

A

3.5

95
Q

When is an aircraft in level flight?

A

When the CofG is in the same position as the centre of lift

Module 8 (4 decks)

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