Aerodynamics Flashcards
(103 cards)
1
Q
What gases make up the atmosphere?
A
78% Nitrogen
21% Oxygen
1% Traces of neon, argon, krypton & carbon dioxide
2
Q
Height of the troposphere?
A
28,000ft - 54,000ft
3
Q
Height of the tropopause?
A
Averages 36,000ft
4
Q
Height of the stratosphere?
A
31 Miles
5
Q
Temperature at the tropopause?
A
-56.5 degrees Celsius
6
Q
The average pressure at sea level is …..
A
1013.25 millibars or 29.92 inches mercury
7
Q
How does the density of gases change with pressure and temperature?
A
- Varies directly in proportion with pressure
- Varies inversely with temperature
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
9
Q
How do you measure water vapour in the air?
A
Using a hydrometer
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
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
12
Q
Transition region:
A
The area at which the boundary layer changes from laminar to turbulent
13
Q
Bernoulli’s Principle:
A
Any increase in velocity will cause a decrease in its pressure
14
Q
Mean Camber:
A
A line drawn midway between the upper and lower camber
15
Q
Maximum Camber:
A
The maximum distance of the mean camber line from the chord line
16
Q
Maximum thickness:
A
The maximum distance of the lower surface from the upper surface
17
Q
Fineness ratio:
A
The ratio of length to maximum thickness. (For best results it should be about 4 to 1
18
Q
Angle of attack:
A
The angle between the airfoil and airflow
19
Q
Upwash:
A
The airfoil, just before it reaches the leading edge, is sucked into the low pressure area
20
Q
Aerofoil, where is the high and low pressure?
A
Low pressure on the upper surface, high pressure on the lower surface
21
Q
Total drag:
A
The sum of all types of drag
22
Q
Induced drag:
A
Drag due to lift
23
Q
Parasite drag:
A
Drag due to the viscosity of the air
24
Q
Three types of parasite drag:
A
Form drag, interference drag & skin friction
25
What happens on the wing tip with induced drag?
High pressure air below the wing spills over to the low pressure air above the wing and causes vortexes
26
Form drag:
The drag caused by the separation of the boundary layer from a surface and the wake created by that separation
27
Interference drag:
Drag that is generated by the mixing of airflow streamlines between airframe components such as the wing and the fuselage
28
Friction drag:
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
29
Induced drag equation
Induced drag (N) = drag coefficient X dynamic pressure (N/m^2) X wing area (m^2)
30
Five factors that affect aerodynamic lift and induced drag:
- Shape of the aerofoil section
- Area of the aerofoil
- Air density
- Speed of the air relevant to the airfoil surface
- Angle of attack
31
Centre of pressure:
The point on the chord line where the aerodynamic forces are concentrated
32
The centre of pressure of a subsonic airflow is typically located:
30%-40% of the chord line back from the leading edge
33
How does the centre of pressure move as the angle of attack increases?
The centre of pressure moves forward as the angle of attack increases and backwards as the angle of attack decreases
34
Lift equation:
Aerodynamic lift = lift coefficient X dynamic pressure X airfoil surface
35
Dynamic pressure equation:
Dynamic pressure = 0.5 X air density X airspeed^2
36
Wing span:
The maximum distance from tip to tip
37
Wing Area:
The surface of the plan view of the wing (including the parts covered such as the fuselage, engines and others)
38
Angle of incidence:
Acute angles formed between the chord of the wing and a line drawn parallel to the longitudinal axis of the aircraft
39
Mean chord equation:
Mean chord = wing area (s) / wing span (b)
40
Mean aerodynamic chord (MAC):
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.
41
Aspect ratio:
The ratio of its span to its mean chord
42
Aspect ratio equation:
Wing span^2 / wing area
Or
Wing span / mean chord
43
What type of wing has a minimum trailing vortex (induce drag)?
Long span with a small chord (glider)
44
Aspect ratio of a: glider, fast jet & commercial aircraft?
Glider = 40
Fast jet = 3.5
Commercial aircraft = 5-8
45
What is the effect of reducing the aspect ratio?
Reduces induced drag
46
Washout:
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
Washin:
A wing designed so that the angle of incidence is greater at the tip that at the root.
48
Rime Ice:
Forms a rough surface on the leading edge (water freezes before it can flow)
49
Glaze ice:
Forms a smooth thick coating over the leading edges (when the temperature is slightly below freezing and the water can flow before freezing)
50
How much can ice on the wing effect drag and lift?
Reduces lift by 30% and increases drag by 40%
51
If the centre of pressure is acting behind the centre of gravity, how will the aircraft act?
It will cause a nose down pitching moment
52
If the centre of pressure is acting forward of the centre of gravity, how will the aircraft act?
A nose up pitching moment will occur
53
If the thrust line is below the centre of gravity, how will the aircraft act?
The aircraft will give a nose up pitching moment
54
Lateral axis:
A straight line passing through the centre of gravity parallel to the wing span (Pitch axis)
55
Longitudinal axis:
A straight line passing straight through the fuselage of the aircraft from nose to tail, passing through the centre of gravity (Roll axis)
56
Vertical axis:
A straight line running vertically through the centre of gravity (Yaw axis)
57
Motion about the lateral axis is referred to as.....
Longitudinal control or longitudinal stability
58
Motion about the longitudinal axis is referred to as......
Lateral control or lateral stability
59
Motion about the vertical axis is referred to as.....
Directional control or directional stability
60
Glide ratio:
The ratio of every unit of vertical distance an aircraft descends to the horizontal distance it travels while gliding
61
How does a higher lift/drag ratio affect glide ratio?
The higher the lift/drag ratio the smaller the gliding angle, thus increasing the glide ratio
62
What does the glide angle depend on?
The glide angle depends on the ratio of lift to drag and is independent of weight
63
Wing loading:
This is the all up weight of the aircraft divided by the wing area. (Usually given in kg/m^2)
64
Load factor:
The ratio of the weight of the aircraft to the load imposed during a manoeuvre.
65
How does the stall speed change with an increase in the wing loading?
The stalling speed increases as wing loading increases
66
Wing loading stall equation:
V2=V1 x square root of(w1/w2)
```
V2 = New stalling speed
V1 = Original stalling speed
w2 = new weight
w1 = Original weight
```
67
Three effects of additional weight (same as an increase in altitude):
- Slight reduction in maximum speed
- Large reduction in rate of climb
- Increase in stalling speed
68
High lift devices:
Used to provide extra lift when the aircraft is at low air speeds or high angle of attacks (Slats, slots, flaps)
69
Slats:
- Increase stalling speed
| - Prolongs the lift curve by delaying the stall until a higher angle of attack
70
Static Stability:
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
Dynamic Stability:
Determines the way the aircraft will return. It is the property that dampens the oscillations set up by a statically stable aircraft.
72
Two factors that will affect longitudinal stability:
- Position of the centre of gravity
| - Pitching moment on the wings
73
The amount of horizontal stabiliser restoring moment will depend on:
- The area of the stabiliser (a larger area will provide more force)
- The length of the fuselage
74
In a slide slip, what happens to the angle of attack and lift on the lower wing?
The lower wing has an increased angle of attack and greater lift (The greater lift will restore level flight)r
75
What are the two purposes of swept wings?
- Delay the formation of sonic shockwaves
| - Improves lateral stability
76
Dutch roll:
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
Longitudinal Stability:
Pitch stability, relation of the wing and tail effect this stability
78
Lateral stability:
Roll stability, positive lateral stability helps stabilise the rolling effect when one wing gets lower than the other
79
Directional stability:
Yaw stability, The tendency to return to initial equilibrium when yawing
80
Yaw Damper:
An automatic flight control device that senses the Dutch roll and applies corrective rudder action to prevent or at least greatly attenuate it
81
Passive stability:
The aircrafts natural aerodynamic stability
82
Active stability:
Computer enhanced stability (Yaw damper)
83
Keel effect:
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
Sideslip:
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
Longitudinal axis:
Nose to nose, aileron roll movement
86
Vertical axis:
Top to bottom, directional stability, rudder yaw movement
87
Lateral axis:
Wing tip to wing tip, elevator pitch movement
88
For the same angle of attack, how does the lift compare of a delta wing and a high aspect ratio wing?
The lift on a delta wing is lower than the lift on a high aspect ratio wing
89
Neutral Static Stability:
When a ball is displaced and shows no tendency to roll back to its original position
90
Positive Static Stability:
The tendency to return to equilibrium
91
Negative static stability:
The tendency to continue in the displacement direction
92
Dynamic Stability:
Refers to how the continuous motion of a body varies over time (only applies if we have positive static stability)
93
Undamped oscillation:
The ball theoretically oscillates forever after initial displacement
94
If the pivot point is below the centre of gravity what type of stability is there?
Negative static stability
95
If the pivot point is above the centre of gravity, what type of stability is there?
Positive static stability
96
The relationship between induced drag and airspeed is .......
Inversely proportional to the square of the speed
97
Angle of incidence:
The angle the chord of the mainplane or tailplane makes with the horizontal
98
Compressible drag:
Caused by the shock wave on an aircraft approaching the speed of sound
99
Down-wash:
Trailing vortices produce a downward flow of air behind the wing
100
Wing fences:
Reduce the effects of spanwise flow
101
Effect of spanwise flow?
It has the effect of thickening the boundary layer towards the wing tip (Especially during low speed flight with high angle of attack)
102
Vortex generator:
Used to improve boundary layer control, produces lift and has an associated tip vortex which is comparable to induced drag
103
Stall strip:
Used to prevent the wing tips from stalling first
