4 Primary Forces Flashcards
1
Q
During unaccelerated flight, the four main forces are said to be
A
in a state of equilibrium
2
Q
The product of mass and gravitational force is called
A
Weight
3
Q
What is the centre of gravity?
A
The point through which the weight of a body acts
4
Q
Wing loading is calculated how?
A
Weight of aircraft / Wing area
5
Q
Wing loading is simply the
A
Weight supported per unit area of wing
6
Q
The Bernoulli Principle
A
High flow gives low pressure
7
Q
What term is given to layer of air closest to an aerofoil’s surface?
A
Boundary layer
8
Q
What term is given to the point at which air within the boundary layer becomes turbulent and thickens significantly?
A
Transition point
9
Q
When an airflow no longer follows a streamlined flow pattern, it has become..?
A
Turbulent
10
Q
What term is given to the point at which the boundary layer separates from the aerofoil and becomes turbulent?
A
Separation point
11
Q
The separation point is where what leaves the aerofoil?
A
Boundary layer
12
Q
Describe the venturi effect in terms of pressure?
A
Pressure energy decreases, kinetic energy increases
13
Q
Dynamic pressure equation
A
1/2 x rho x V-squared
14
Q
Bernoulli’s principle states that increased velocity means
A
Decreased static pressure
15
Q
The angle-of-attack is simply the,..
A
The angle at which the aerofoil is presented to the airflow
16
Q
Camber is a term for what?
A
Curvature
17
Q
Increasing the camber does what to airflow?
A
Airflow accelerates and generates greater lift
18
Q
What causes the air to accelerate as it flows over an aerofoil?
A
An upwash is created and the air flows through a more constricted area
19
Q
What term is given to the straight line between the ends of the camber line?
A
Chord line
20
Q
The chord line connects the ends of what?
A
Mean camber line
21
Q
What is the name of the measurement of a chord line’s length?
A
Chord
22
Q
The distance between the mean camber line and chord lines called the?
A
Camber
23
Q
The camber is the distance between what?
A
Mean camber line and chord line
24
Q
What is the camber of a symmetrical aerofoil?
A
Zero
25
Lift's equivalent of CoG is called what?
Centre of Pressure
26
The centre of pressure is...
The point at which the total reaction of the aerodynamic forces of an aerofoil act through
27
Total reaction has which two components?
Lift and drag
28
Lift and drag combine to form what force that acts through the centre of pressure?
Total reaction
29
Lift acts at what relation to the relative airflow?
Perpendicular
30
Drag acts at what relation to the relative airflow?
Parallel
31
What angle of the wing is AoA measured from?
Chord line
32
What is the angle of incidence?
Angle at which the wing is fixed to the airframe relative to longitudinal axis
33
What is the term given to the angle at which the wing is fixed to the airframe relative to longitudinal axis?
Angle of incidence
34
What term is given to the point at which the airflow comes to rest relative to the wing?
Stagnation point
35
If the Centre of Pressure moves forward, what is occurring?
AoA is increasing
36
AoA increasing has what effect on the Centre of Pressure's position?
It moves forward
37
Air density is given what Greek letter?
Rho
38
The coefficient of lift is considered what?
Lifting ability of a wing at a given AoA
39
Equation of lift
Coefficient of Lift x 1/2 x Rho x V-Squared x Wing Surface Area
40
As wing shape is fixed, any change in Coefficient of Lift only occurs when what changes?
AoA
41
When is the Centre of Pressure at its furthest point forward?
Stalling AoA
42
The lift curve for a symmetrical aerofoil will give a Coefficient of Lift of 0 at what AoA?
0 degrees Angle of Attack
43
For a symmetrical aerofoil, 0 degrees AoA equattes to what Coefficient of Lift?
0
44
A laminar flow wing has what properties?
Low curvature that allows air to retain laminar flow over more of its surface than a cambered aerofoil
45
Laminar essentially means what in terms of airflow?
Streamlined
46
Laminar flow wing's advantages over cambered aerofoil?
Same lift produced for less drag at cruise speed
47
The higher stalling speed of a laminar flow wing can be explained how?
The Maximum Coefficient of Lift is a lower value than the C-Lift Max for a well-cambered aerofoil
48
Longitudinal axis of the aircraft is important for what angle?
Angle of incidence
49
Air resistance is commonly known as what?
Drag
50
Types of drag can be split into what two categories?
Induced drag
Parasite drag
51
Induced drag is...
Drag associated with production of lift
52
Drag associated with production of lift is known as..?
Induced drag
53
Parasite drag consists of what 3 sub-categories?
Skin friction
Form
Inteference
54
For skin friction drag, what occurs within an increase in airspeed?
Increase of skin friction drag
55
For skin friction drag, what occurs within an increase in AoA?
Increase of skin friction drag
56
Form drag is created how?
Airflow separates from the surface
Eddies are formed
Streamline flow distrubed and thus increases drag
57
Skin friction drag is essentially the...
Friction forces between an object and air
58
How do designers reduce form drag?
Delay separation of the boundary layer from the surface
59
How does form drag result in stalling on a wing at high AoAs?
Pressure gradient on upper surface is too severe
Boundary layer no longer adheres to the surface
Separation occurs well forward near the leading edge
60
If you streamline a surface and decrease its curvature, what effect is had on the boundary layer?
Delaying separation of the boundary layer and reducing eddying
61
Interference drag can be thought of as drag occuring from..
Combined parts of an aircraft as a whole
62
Parasite drag's relationship with airspeed
An increase in airspeed will increase parasite drag
63
Parasite drag increases in what manner with increased airspeed
As a square rule (V-squared)
64
Spanwise flow of induced drag on lower surface of wing?
Outwards from fuselage
65
Spanwise flow of induced drag on upper surface of wing?
Inwards towards fuselage
66
Why are wingtip vortices greatest at high values of C-Lift?
The pressure difference between upper and lower wing surfaces are greatest
67
Aspect ratio equation (span, chord)
Span / Chord
68
Aspect ratio equation (wing arrea, chord)
Area / Chord-squared
69
Why do tapered wings have weaker wingtip vortices?
Relatively, there is less wingtip so the induced drag is less
70
A wing whose AoA differs at the wingtip and wing root possesses what?
Washout
71
How does inbuilt washout reduce induced drag?
Wingtip AoA is lower than wing root AoA
72
Inbuilt washout means lift is produced where on a wing?
Predominantly by the inner part of the wing
73
WInglets or wing fences can reduced induced drag how?
Spanwise flow is reduced so induced drag is less
74
Why is induced drag greater at lower airspeeds?
AoA must increase to maintain given lift
Slower passage of air rearwards forms greater vortices and greater downwash
Greater downwash inclines local airflow downwards further
Lift force tilted further back
Stronger component of lift force is in the drag direction
75
Relationship between lift and induced drag
The greater the lift produced, the greater the induced drag
76
What occurs in a total drag graph
As airspeed increases:
Induced drag reduces
Parasite drag increases
Total drag initially decreases then increases
77
What drag predominates at low speeds?
Induced drag
78
What drag predominates at high speeds?
Parasite drag
79
Total drag is least when what is equal?
Parasite and induced drag
80
Minimum drag speed is where on a total drag graph?
Where the parasite drag and induced drag lines intersect
81
The point at which parasite drag and induced drag intersect on a total drag graph (and equal zero) is known as what?
Minimum drag speed
82
Minimum drag speed is considered the speed at which...
The wings produce lift to balance weighht but with minimum amount of drag possible
83
Drag equation
Coefficient of Drag x 1/2 x rho x V-Squared x S
84
The only difference between the equations for drag and lift are the presence of?
The respective coefficients (of lift or drag)
85
Lift/Drag Ratio is calculated how?
C-Lift / C-Drag
86
The AoA at the highest point of a Lift/Drag ratio curve can be described as
The most efficient angle of attack
87
With decreasing weight and flying at the same IAS, what happens to the AoA?
It decreases
88
With decreasing weight and flying at the same AoA, what happens to the airspeed?
It decreases
89
Using the AoA and C-lift equation, explain how IAS remains constant but TAS changes at different airspeeds?
Rho is less at higher altitudes, so V (in V-squared) must increase to maintain IAS
90
What type of airspeed is most important for AoA and lift considerations?
IAS
91
Why is IAS the most significant airspeed for AoA and lift considerations?
IAS is related to dynamic pressure, thus impacting aerodynamics
92
What does S denote in drag calculations?
Wing area
93
Wing area is denoted by what term in drag equations?
S
94
The axis upon which a propeller rotates is called the...?
Plane of rotation
95
Static pressure situation surrounding a propeller blade?
The static pressure ahead of the blade is less than that behind
96
Name of angle between chord line of a propeller and the plane of rotation?
Blade angle
97
The blade angle is the angle between what?
Propeller chord line and plane of rotation
98
Name of cambered side of propeller blade?
Blade back
99
Name of flat side of propeller bade?
Blade face
100
Name of angle between the resultant veolicty of the propeller blade and the plane of rotation?
Helix angle
101
The Helix angle is the angle between what?
Resultant velocity of the propeller blade and the plane of rotation
102
What two angles combine to form the blade angle of a propeller?
AoA + Helix angle
103
The AoA + Helix angle forms what angle for a propeller?
Blade angle
104
How does blade angle change from the hub of a propeller to its tip?
It decreases
105
Why does blade change decrease from the hub to tip of a propeller?
Greater velocity meeans less AoA needed
106
Approximately where on the propeller blade is thrust produced effectively?
Between 60% and 90% of the tip radius
107
Why is the direction of the relative airflow on a propeller and the direction of flight not parallel?
Rotational velocity offsets the forward motion of the aircraft
108
In theory, it is assumed that the direction of flight is what relation to the plane of propeller rotation?
Perpendicular
109
In theory, it is assumed that the direction of flight is perpendicular to what?
Plane of propeller rotation
110
Propeller torque is...?
Resistance to motion in the plane of rotation
111
For propellers, total reaction is divided into what two components?
Propeller torque force
Thrust
112
For the components of propeller torque force and thrust, which is related to the plane of rotation?
Propeller torque force
113
For the components of propeller torque force and thrust, which is related to the direction of flight?
Thurst
114
What is the angle between propeller torque force and thrust?
Perpendicular
115
Lift/drag comparative forces for propellers?
Lift is enngine torque and drag is propelller torque
116
Why does RPM increase in a dive with constant throttle position?
Relative airflow is changed
Forward speed increases
Propeller torque is reduced
117
Why does a propeller blade's AoA decrease as speed increases at constant RPM?
Forward motion component is greater so the relative airflow hits the blade at a shallower angle
118
Why does a propeller blade's AoA increase as speed decreases at constant RPM?
Forward motion component is less so the relative airflow hits the blade at a higher angle
119
At constant speed, why does a propeller blade's AoA increase as the RPM increases?
Rotational motion component is greater so the relative airflow hits the blade at a higher angle
120
At constant speed, why does a propeller blade's AoA decrease as the RPM decreases?
Rotational motion component is less so the relative airflow hits the blade at a shallower angle
121
For variable-pitch propellers, what pitch is optimum for lower airspeeds?
Fine pitch
122
For variable-pitch propellers, what pitch is optimum for higher airspeeds?
Coarse pitch
123
Fine pitch means what kind of pitch for a propeller?
Low pitch
124
Coarse pitch means what kind of pitch for a propeller?
High pitch
125
What happens to the AoA as RPM remains constant in a variable-pitch propeller?
It remain constant
126
Variable-pitch propellers are also known by what other name?
Constant-speed propellers
127
What kind of speed is referred to in the term 'constant-speed' for variable-pitch propellers?
RPM
128
Feathering a propeller does what?
Aligns the blades with the airflow
129
Slipstream effect causes an AoA to be created where?
Between the tailfin and slipstream airflow
130
Name of effect that occurs with propellers under high power conditions?
Slipstream effect
131
A clockwise-rotating propeller will possess effects that will yaw an aircraft in what direction?
Left
132
When discussing fine and coarse pitch, these terms are described relative to what?
Plane of rotation
133
For a propeller diagram, what is represented by the x-axis?
Forward motion of a propeller blade
134
For a propeller diagram, what is represented by the y-axis?
Rotational motion of a propeller blade
135
For a propeller diagram, a higher airspeed does what to the 'triangle'?
Lengthens its base
Hypotenuse strikes blade at reduced angle
136
For a propeller diagram, a higher RPM does what to the 'triangle'?
Lengthens its height
Hoptenuse strikes blade at greater angle
137
For a propeller diagram, what two 'triangle' transformations will increase the AoA?
Reducing the base (reducing the forward speed)
Increasing the height (increasing the RPM)
138
For a propeller diagram, what is the hypotenuse?
Resultant velocity of propeller blade through the air
139
What is the influence of wing aspect ratio on induced drag?
High aspect ratio (long thin wing) = less induced drag
140
Relationship between wake vortices and induced drag
The smaller the vortices, the lower the drag
141
Why does smaller width of a wing reduce induced drag?
There is less spillage of high pressure beneath the wing onto the lower pressure above the wing
142
Name the two types of boundary layer associated with an aerofoil?
Laminar and Turbulent
143
As speed increases, what happens to the Transition Point?
It moves forward towards the leading edge
144
The transition point moving forward (as speed increases) has what effect?
More turbulent flow and increased drag
145
What are the key differences between the laminar boundary layer and turbulent boundary layer?
The turbulent layer is thicker
The turbulent layer has high skin friction drag
The turbulent layer is more resistant to separation whereas the laminar layer is very unstable
146
What three effects are experienced by the aircraft in ground effect?
Aerofoil produces more lift since the Total Lift Vector is more perpendicular to the ground
Induced drag vector is reduced
Wingtip vortices are reduced
147
Why does an aerofoil produce more lift during ground effect?
Relative airflow becomes flatter and the Total Lift Vector maintans its perpendicular angle by angling forward
