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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
What is the positive and negative Dihedral angle?
Positive dihedral - wings upwards | Negative dihedral - wings downwards
26
What is the aerodynamic force?
The resultant of all forces on a profile in an airflow acting on the centre of pressure
27
What are the two components that make up aerodynamic forces?
Lift - perpendicular to relative wind | Drag - parallel to relative wind
28
What is the equation of lift/drag (Theoretical lift/drag)?
Lift/Drag Force = Dynamic Pressure x Area | F = 1/2PV^2 x A
29
What is the centre of pressure?
The point at which all pressures and forces act
30
What are the 4 things that affect lift and drag?
- Dynamic Pressure - Surface Area - Shape of Profile - Angle of Attack
31
How is the Coefficient of lift (CL) calculated?
Measured lift —————— Theoretical lift
32
It is not possible to calculate actual lift. What is used to measure this?
A wind tunnel with two scales: - horizontal = drag - vertical = lift
33
How is the Coefficient of drag (CD) calculated?
Measured drag ——————— Theoretical drag
34
If the angle of attack increases above amax (alpha max) what happens?
The airflow cannot follow the upper surface of the profile and an airflow separation called a “stall” occurs
35
If a profile has a larger camber, what increases?
The Coefficient of lift at a smaller angle of attack
36
If a profile has a larger thickness, what increases?
- higher max coefficient of lift - higher amax (alpha max) - higher angle of attack
37
What are the disadvantages of creating a profile with a larger camber or thickness?
- more drag | - low critical Mach number
38
How is the angle for the best glide ratio calculated?
Using a graph, drawing a tangent from the intersection of the axis to the graph
39
What is the same as the ratio of lift and drag?
The ratio of lift coefficient to the drag coefficient
40
What is the glide ratio?
The best possible lift for the least possible drag
41
What are the three categories of drag?
- induced - parasite - compressible
42
What is induced drag?
Drag on the wing caused by the lift
43
What is parasite drag?
Drag not related to the lift. Can be due to distribution of pressure, friction or aerodynamic interference.
44
What is compressible drag?
Drag caused by shockwaves on an aircraft approaching the speed of sound
45
What is drag?
It is the aerodynamic force which is parallel to the relative wind. It is opposite force to thrust
46
What is the turbulence at the wing tips called?
Wing tip vortices
47
What is the circulation of air (up-wash and down-wash) called around the wings causing drag?
The bound vortex
48
What is important about the door gutters design?
They reflect the up-wash and down-wash caused by the vortices. They are in line with the flow pattern
49
What are the 3 types of PARASITE drag?
- form - friction - interference
50
What is form drag?
A parasite drag caused by the pressure distribution on a body
51
How is form drag reduced?
Streamlining of an object
52
What is the relationship between form drag and friction drag?
If the form drag is low, the friction drag is high | If the form drag is high, the friction drag is low
53
What is the name of the area of air on top of a wing, with friction drag, causing it to retard?
The boundary layer
54
What are the two types of boundary layer?
- laminar boundary layer | - turbulent boundary layer
55
How much more friction drag does the turbulent boundary layer produce than the laminar boundary layer?
3 times more friction
56
Where is the laminar boundary?
Immediately downstream from the leading edge (up to the minimum static pressure/maximum thickness)
57
Where is the turbulent boundary?
Immediately downstream of the laminar boundary layer (starting where the static pressure is minimum/maximum thickness)
58
What can be introduced to a wing to prevent flow separation?
A slot | - high energy air moved from bottom of the wing up to the top through the slot
59
A lower profile wing is known as?
The laminar profile
60
How is interference drag reduced?
By using fairings
61
What is interference drag?
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
When does compressible drag occur?
Only in transonic and supersonic flight
63
What is total drag?
The combination of induced drag and parasite drag
64
What are the four types of wing shapes?
- elliptical - rectangular - tapered - swept
65
What type of wings stall at the tip?
- Swept | - Tapered
66
What type of wing does the stall start at the root?
Rectangular wings
67
What type of wing does the stall occur spanning across the wing?
Elliptical
68
What is geometric twist?
The camber is constant throughout the span but the angle of incidence is greater at the root than the tip
69
What is aerodynamic twist?
The camber is greater at the root than at the tip but the angle of incidence is instant across the span
70
Where does the total wing lift act?
It acts on the centre of lift
71
What is MAC?
The mean aerodynamic chord | - the chord line through the centre of lift
72
Where is the centre of lift located?
At 30% MAC
73
Where do the streamlines above and below the wings bend?
Above - towards the centre | Below - towards the wing tips
74
What is induced drag affected by?
The aspect ratio, aircraft speed and the wing tip design
75
How do you measure the theoretical lift/drag of a profile?
Dynamic pressure x area
76
If airflow over a wing increases in velocity, what happens to induced drag and parasite drag?
Induced drag decreases | Parasite drag increases
77
What is the equation for the AREA of a tapered wing?
Wing span x average chord
78
What boundary layer would you find the most amount of kinetic energy?
The turbulent layer
79
What is another name for the polar diagram?
Lilienthal diagram
80
What is the polar (Lilienthal) diagram used for?
To find the angle for the best glide ratio | The most efficient operation of the profile
81
Is the induced drag LARGER on a low aspect ratio or a high aspect ratio?
Induced drag is less on a high aspect ratio
82
What can be added to wing profiles to reduce induced drag?
- Winglets | - Wing tip fences
83
Where does an aircrafts total weight act?
The centre of gravity
84
What type of stall would an aircraft recover without pilot input?
A wing root stall
85
What type of stall is the most dangerous?
A wing tip stall as the aircraft rotates in the nose-up position
86
What is used on a small aircraft to prevent wing tip stall?
A stall strip (knife edge device on the leading edge of the wing root) -disadvantage is that it disturbs the lift
87
What are used on larger aircraft to prevent wing tip stall?
Slats on the leading edge - giving the boundary layer more energy preventing flow separation
88
What is spanwise flow?
Airflow over a swept wing - air following the leading edge - air at right angles to the leading edge
89
How can spanwise flow be reduced?
- wing fences (boundary layer fences) | - saw tooth leading edge
90
What determines the number and location of vortex generators?
The flight test investigations
91
What is the purpose of a vortex generator?
It improves the boundary layer control by producing lift
92
How do you calculate the aspect ratio?
``` Wing span (b) —————— Average chord (c) ``` (Or the span squared over the area)
93
What would an average high performance sail plane’s aspect ratio be?
35
94
What would a jet fighter’s average aspect ratio be?
3.5
95
When is an aircraft in level flight?
When the CofG is in the same position as the centre of lift

Module 8 (4 decks)

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