M8.2 Flashcards
(173 cards)
1
Q
What is the definition of aerodynamics?
A
The study of the properties of moving air and the integration between the air and moving bodies
2
Q
What is said about air in the subsonic region?
A
The air is incompressible
3
Q
How are streamlines layered out when there isn’t any disturbance?
A
They’re parallel to each other
4
Q
What does the continuity equation state?
A
The speed of airflow is inversely proportional to the area of cross section
5
Q
What is the equation for the continuity equation?
A
V1 x A1 = V2 x A2
6
Q
What does the term diffuser outlet mean?
A
The tube diameter increases and the speed decreases
7
Q
What does the term jet outlet mean?
A
The tube diameter decreases and the speed increases
8
Q
What does Bernoulli’s equation state?
A
Total pressure is always the sum of static pressure and dynamic pressure
9
Q
If airflow speed increases what happens to static pressure and the dynamic pressure?
A
Static pressure decreases and dynamic pressure increases
10
Q
What is up-wash?
A
When some of the lower streamlines get pulled up and over the profile
11
Q
What is down-wash?
A
When the streamlines on top of the profile get pushed down after leaving the profile
12
Q
What happens to lift if you have no differential pressure?
A
You have no lift
13
Q
What is the Magnus effect?
A
Lift caused by rotation
14
Q
What is meant by a profile?
A
The cross section of a wing
15
Q
What is the chord line?
A
It is a straight line from the leading edge to the trailing edge
16
Q
What is the mean camber line?
A
It is a line drawn halfway between the upper and lower surfaces of the profile
17
Q
Why is the mean camber line important?
A
Because it helps determine the aerodynamic characteristics
18
Q
What is the camber?
A
It is the distance between the mean camber line from the chord line
19
Q
Where is the location of max camber?
A
Where the camber is at it widest
20
Q
What is flight path velocity?
A
The speed of the aircraft in a certain direction
21
Q
What is relative wind?
A
The speed and direction of the air acting on the aircraft
22
Q
What direction does relative wind tend to act in?
A
The opposite to flight path velocity
23
Q
What is the angle of attack?
A
The angle of the chord line and relative wind
24
Q
What is the angle of incidence?
A
The angle between the chord line and the longitudinal axis of the aircraft
25
How is angle of attack denoted?
By the symbol of alpha (a)
26
How is angle of incidence denoted?
By the symbol of gamma (Y)
27
Is the fuselage area included in the wing area?
Yes
28
How is wing area calculated?
Wing span X chord line
29
What is the root chord?
The chord at the root of the aircraft
30
What is the tip chord?
The chord at the tip of the wing
31
How is a tapered wing area calculated?
Wing span X average chord
32
What is the taper ratio?
The ratio between tip chord and root chord
33
How is the aspect ratio calculated?
- wing span / average chord
| - wing span squared/ wing area
34
How is the sweep angle measured?
It is a line from the root to tip taken from 25% of the chord
35
What direction is a positive sweep?
Backwards
36
What direction is a negative sweep?
Forwards
37
What happens when the wing gets more swept back?
It becomes more stable on the roll axis
38
What will a shock wave cause the aircraft to do?
Reduce lift and increase drag on the wing
39
What is it called when the shock wave begins to appear?
Critical mach number
40
What is span wise flow?
When the airflow is perpendicular to the chord line
41
What happens to airflow parallel to the chord line?
It accelerates
42
What happens to airflow that is perpendicular to the chord line?
It reduces the amount of acceleration
43
Why would you want reduced acceleration on your wing?
Because it delays your critical mach number
44
What is the purpose of span wise flow?
To delay your critical mach number
45
What is the benefit of having a delayed critical mach number?
You can fly at a high mach number before you start to create wave drag
46
What is the disadvantage of having swept wings?
Reduces lift so you’ll need to have bigger wings (poor lift to drag ratio)
47
What is an dihedral angle (positive dihedral)?
When the wings are pointing upwards
48
What is a anhedral angle (negative dihedral)?
When the wings are pointing downwards
49
What is the reason for dihedral angles?
It increases roll stability
50
When is a positive dihedral more commonly used?
On larger commercial aircraft
51
Why do military combat aircraft have small dihedral?
To increase manoeuvrability but reduces stability
52
What types of aircraft use anhedral wings?
Fighter aircraft
53
Why are anhedral wings used?
To increase manoeuvrability
54
What type of pressure is at the front and back of the profile?
Static pressure
55
What type of pressure is on top and bottom of the profile?
Dynamic pressure
56
Where is static pressure highest?
At the point of stagnation where the air comes to a stop
57
What happens to the profile around the camber?
Max air velocity and minimum static pressure
58
What is aerodynamic force?
It is the resultant of all forces on a profile in an airflow acting on the centre of pressure
59
What are the two components to aerodynamic force?
Lift and drag
60
What is centre of pressure?
The point on which all pressures and forces act
61
Where is the centre of pressure located?
Where the chord intersects with the resultant of aerodynamic forces
62
What does aerodynamic forces of lift and drag depend on?
- dynamic pressure
- surface area of profile
- shape of profile
- angle of attack
63
What is the calculation for theoretical lift and drag?
1/2xqxV2xA
64
How do you calculate actual lift?
You cant you have to use a wind tunnel
65
How is the coefficient of lift measured?
Measured lift
——————
theoretical lift
66
What is the lift equation when you have the coefficient of lift?
Coefficient of lift X dynamic pressure X surface area
67
How is the coefficient of drag measured?
Measured drag
———————
theoretical drag
68
Why is a coefficient lift and drag used?
To account for the difference between theoretical figures and actual figures
69
What is the drag equation when you have the coefficient of drag?
Coefficient of drag X dynamic pressure X surface area
70
What is alpha max?
The maximum angle of attack
71
What happens after alpha max?
A stall occurs
72
What is an advantage of having a high maximum lift coefficient?
It can fly slowly
73
What will ice and frost do to the coefficient of lift and angle of attack?
It will be reduced
74
What happens to the coefficient of drag when you increase the angle of attack?
It increases
75
What does a stall produce?
A large increase in drag
76
What is a polar diagram used for?
To figure out the best glide ratio
77
What information does the polar diagram use?
Coefficient of lift and coefficient of drag
78
Who invented wind tunnel tests?
Otto Lilienthal in the 19th century
79
Name the variation of polar diagram?
Lift drag ratio diagram
80
What happens to lift as climb increases?
It decreases therefore the pilot increases thrust
81
What is drag parallel with?
Relative wind
82
What is drag opposite to?
Thrust
83
What are the different categories of drag?
- induced drag
- parasite drag
- compressible drag
84
What causes induced drag?
Lift
85
How are wing tip vortices created?
The high pressure underneath ‘spills over’ onto the the top low pressure causing turbulence
86
What is bound vortex?
The up-wash ad down-wash affect
87
What creates the up-wash and down-wash on the wings?
Bound vortex and wing tip vortices
88
What are the gutters inline with?
They are in line with the flow pattern of the airstream around the wing
89
What are the gutters above the door designed for?
To reflect the up-wash and down-wash
90
What directions are the gutters facing that reflect up-wash?
They’re sloped upwards
91
What directions are the gutters facing that reflect down-wash?
They’re sloped downwards
92
What affects the induced drag?
- aspect ratio
- wing tip design
- aircraft speed
93
How do you reduce wing tip vortices?
By using wing tip fences or winglets
94
If an aircraft has a high angle of attack what is also high?
The lift coefficient
95
What are the different types of parasite drag?
- form
- friction
- Interference
96
What causes form drag?
Distribution of pressure
97
What causes friction drag?
Skin friction
98
What is interference drag?
The difference between individual drag and total drag from the indivuals
99
What causes compressible drag?
Shockwaves when the aircraft approaches the speed of sound
100
What does form drag depend on?
The frontal area and the speed of airflow
101
How is form drag reduced?
By streamlining
102
What is form drag on the wing called?
Wing drag or profile drag
103
What is the retarded air called?
The boundary layer
104
How is a boundary layer created?
By having a rough surface layer causing airflow particles to stop
105
What are the two types of boundary layer?
- laminar boundary layer
| - turbulent boundary layer
106
Where is the laminar boundary layer located?
Immediately down stream of the leading edge until the point of maximum thickness
107
In the laminar boundary layer the air particles don’t move from one layer to another, what’s this called?
Laminar flow
108
Where is the turbulent boundary layer located?
Downstream of the laminar boundary layer
109
What happens when air particles travel from one layer to another?
There is an energy exchange
110
How much more drag does the turbulent boundary layer produce?
Three times more
111
What boundary layer is the thickest?
The turbulent boundary layer
112
The turbulent boundary layer produces higher kinetic energy, what does this reduce?
The tendency for flow separation
113
How does flow separation occur?
When the air particles are unable to reach the high pressure because they stop moving
114
How is flow separation prevented?
By a slot in the profile
115
How does the slot in a profile work?
It allows high energy from the lower side to give stationary air energy
116
How can Interference drag be reduced?
By fairings
117
Where does compressible drag occur?
Transonic and supersonic
118
What happens to the boundary layer as it passes through the shockwave?
It thickens
119
What occurs when the boundary layer thickens?
Flow separation
120
What makes up total drag?
Induced drag and parasite drag
121
When is the induced drag high?
At low speeds (decreases as speed increases)
122
When does parasite drag increase?
When speed increases
123
When is total drag high?
When either induced or parasite drag is high
124
What are the four types of wing shapes?
- elliptical
- rectangular
- tapered
- swept
125
What is induced drag sometimes called?
Trailing vortex drag
126
Where does stall begin on an elliptical wing?
All over
127
Where does stall begin on a rectangular wing?
At the root
128
Where does stall begin on a tapered and swept wing?
At the tip
129
What is the reason for different stall characteristics?
The down-wash changes the angle of attack
130
What does a high down-wash produce?
A low local angle of attack
131
What does a low down-wash produce?
A high local angle of attack
132
What does an elliptical wing constantly have?
Down-wash
133
What does the constant down wash on the elliptical wing produce?
Constant flow separation
134
Why does the rectangular wing have a large tip vortex?
Because it has a larger down-wash at the tip than the root
135
What does the stall at the wing tip have dangerous implications on?
Lateral control and stability
136
How do you make sure the root stalls first?
By geometrically or aerodynamically twisting the wing
137
What is it called when you geometrically twist the wing?
Washing out
138
What does it mean by geometrically twisted?
The camber is the same but the angle of incidence changes
139
What does it mean by aerodynamically twisted?
The camber gradually gets smaller
140
How are the chord lines layed out on an geometrically twisted wing?
Not in parallel
141
How are the chord lines layed out on an aerodynamically twisted wing?
Are in parallel
142
On a twisted wing, where does flow separation occur first?
At the root
143
When increasing the angle of attack, what happens to the centre of pressure?
It moves towards the leading edge
144
What does the total weight of the aircraft act on?
The centre of gravity
145
What does the aircraft rotate round?
The centre of gravity
146
What happens when the position of the centre of gravity is the same as the centre of lift?
Nothing the aircraft is in steady flight
147
What happens when the position of the centre of gravity is behind the centre of lift?
The aircraft goes nose up
148
What happens when the position of the centre of gravity is in front of the centre of lift?
The aircraft goes nose down
149
Where does the total wing lift act on?
The centre of lift
150
What is the mean aerodynamic chord (MAC)?
The chord line through the centre of lift
151
How is the centre of lift on the wing described?
In percentages (0 from leading edge to 100 at the trailing edge
152
What happens to the centre of lift when flow separation occurs next to the root of the wing?
It moves to the tip of the wing
153
Will an aircraft recover from a root stall without pilot input?
Yes it will
154
What happens to the centre of lift at a root stall?
It moves behind the centre of gravity
155
What happens to the centre of lift at a tip stall?
It moves in front of the centre of gravity
156
Is pilot input needed to recover from a wing tip stall?
Yes it is
157
What is a stall strip?
A knife edge on the leading edge that prevents wing tip stalls occurring first
158
What is the disadvantage of a stall strip?
It disturbs lift
159
What are slats used for?
To prevent wing tip stall
160
Where would you find stall strips?
On the leading edge of wing root on small aircraft
161
Where would you find slats?
On the leading edge of the wing tips on larger aircraft
162
How do slats work?
It alters the profile to allow the boundary layer to receive more energy
163
What do slats prevent?
Flow separation at the wing tip
164
What do wing fences do?
Reduce spanwise flow
165
What are wing fences also known as?
Boundary layer fences
166
What has the same affect as a saw tooth leading edge?
Wing fences
167
What is a vortex generator?
A small low aspect ratio wing on top of the wing
168
What do vortex generators do?
It produces lift by taking air from above the boundary layers and adding it to the boundary layer
169
Why is the vortex large compared to the vortex generator?
Because of the aspect ratio
170
What is the temperature at sea level?
288k
171
What is the density at seal level?
1.225 kg/m3
172
What is the pressure at sea level?
1013.25 hecto pascals
173
what is the fineness ratio?
Length x thickness
