ToF Flashcards
(101 cards)
1
Q
What is the Troposphere?
A
Lowest layer of atmosphere up to 36,090 ft.
2
Q
What is the Stratosphere?
A
Isothermic layer of atmosphere from Tropopause to Stratopause (164000 ft).
3
Q
What are the 4 layers of the Atmosphere in ascending order?
A
Troposphere, Stratosphere, Mesosphere, and Thermosphere.
4
Q
Lapse rate of pressure in Troposphere?
A
1 hPa/30ft
5
Q
Lapse rate of temp in Troposphere?
A
1.98C/1000ft
6
Q
ICAO ISA at MSL (pressure, temp and density)?
A
1013.5 hPa, +15C, 1.225kg/m^3
7
Q
What happens to density as alt increases?
A
Decreases
8
Q
State Newton’s 3 laws.
A
Inertia, Force, and Action/Reaction
9
Q
What is Bernoulli’s Theorem?
A
Pressure + Kinetic = Constant (Energy Conservation)
Static Pressure + Dynamic Pressure = Total Pressure
10
Q
What are the four forces acting on an aircraft in steady flight?
A
Weight, Lift, Thrust, and Drag.
11
Q
Define Aerofoil.
A
A surface designed to gain lift from the airflow that moves over it.
12
Q
What is the Leading Edge Radius?
A
The shape of the leading edge.
13
Q
What is the Chord Line and Cord?
A
Cord Line - A line joining the leading and trailing edges of an Aerofoil section.
Cord - The distance between leading and trailing edge measured along the Cord Line.
14
Q
What is C(L) and C(D)?
A
Coefficient of Lift and Coefficient of Drag.
15
Q
What is Camber and the Mean Camber Line?
A
The curvature of the aerofoil above and below the chord line.
A line equidistant between the upper and lower surfaces of an aerofoil section.
16
Q
What is the Angle of Incidence?
A
The angle at which the aerofoil is attached to the fueslage. (Angle between the chord line and longitudinal fuselage datum).
17
Q
What is the term RAF?
A
Relative Airflow - Direction of the airflow remote from the aircraft and unaffected by it’s presence.
18
Q
What is AoA?
A
Angle of Attack - The angle between the chord line and the relative airflow (RAF).
19
Q
What is Freestream Flow?
A
Air in the region where pressure, temp and relative velocity is unaffected by the passage of the aerofoil through it.
20
Q
What is the Boundary Layer and where can the Transition Point be found?
A
Boundary Layer - The layer of airflow close to the aerofoil surface which has affected velocity due to viscosity.
Transition Point - The point on the aerofoil where the boundary layer becomes turbulent and thickens.
21
Q
Where can laminar and turbulent flow be found?
A
Laminar flow - Smooth, parallel layers of air found at the front of an aerofoil.
Turbulent flow - Airflow is rough and movement of air particles is unpredicted. Found after the Transition Point.
22
Q
How is Lift/Drag generated from an Aerofoil?
A
A reaction to the movement of air over the surface of the airflow. This is resolved into two compoents.
Lift - Force perpendicular to RAF.
Drag - Force parallel to the RAF, opposing motion.
23
Q
What is the resultant force called acting on an Aerofoil?
A
Total Aerodynamic Reaction.
24
Q
Define Wing Shape, Wing Area and Aspect Ratio.
A
Wing Span - Max lateral dimension of a wing.
Wing Area - Planform area of the wing.
Aspect Ratio - Wing Span divided by Mean Chord Length.
25
Characterise Classical Linear Flow, Controlled Separated Flow and Unsteady Flow.
Classical Linear Flow - Low AoA, Streamlines follow contour of the aerofoil, No serparation of the flow from surface.
Controlled Separated Flow - Halfway stage between steady streamline and unsteady flow. Transition Point present.
Unsteady Flow - Flow varies with time and cannot be represented by streamlines, fully turbulent behind object.
26
Describe the pressure distribution on an aerofoil as AoA increases.
Low AoA - Small areas of positive pressure at leading and trailing edge of aerofoil. negative pressure on both sides of the wing.
Medium AoA - Positive pressure increases at the leading edge, angled below the aerofoil. Negative pressure increases greatly above the aerofoil.
High AoA - Positive pressure greatly increases at leading edge and under aerofoil. Negative pressure drops off above the aerofoil section. Stall imminent.
27
Describe Three Dimensional Flow.
A wing of finite length when creating lift produces a differential pressure that tries to equalises around the wing tip. Outwards under the wing and inwards above the wing, resulting in spanwise flow.
28
Describe the required Lift to allow level flight.
Lift force generated equals the force of gravity.
29
What Lift is dependent on?
Freestream Velocity, Air Density, AoA, Wing Shape, Wing Planform, Speed of Sound, and Coefficient of Lift.
30
What factors affect the Coefficient of Lift?
Wing Section, Aspect Ratio, Planform Profile, Wing Surface Condition.
31
What is Downwash?
The idea that an Aerofoil adjusts the RAF after moving through it, thus retrospectively adjusting the AoA. This is turn will tilt Lift and Drag rearwards, reducing the amount of Lift generated.
32
What are the two types of Drag?
Zero Lift Drag (ZLD) - Known as 'profile drag'
Lift Dependent Drag (LDD) - Known as 'induced drag'
33
What is included in the Drag Formula?
Density, Velocity, Wing Area, and Coefficient of Drag.
34
What does ZLD comprise of and what are their definitions?
Surface Friction Drag - Aerodynamic resistance due to contact of RAF with surface of the aircraft.
Form Drag - Drag created due to the profile of the object in the RAF.
Interference Drag - Created by the result of flow interference at: wing/fuselage, wing/nacelle, and wing/wing loadout.
35
What is Induced Drag?
Drag caused by airflow splitting from the wing tip and trailing edge, forming vortices. These intensify under high lift conditions.
36
List methods to reduce Induced Drag.
Winglet, Tip tank/missle, Taper, High Aspect Ratio, Washout, and Change of Aerofoil Section.
37
Why is Lift/Drag Ratio important?
It will highlight at which AoA the most efficient lift/drag performance occurs (usually at 4degrees).
38
Why is the Total Drag Curve important?
It will highlight at which airspeed we find the best lift/drag ratio (V imd) and max speed/drag for best range setting (1.32 x V imd).
39
Which axis is Pitch and what control surface primarily affects it?
Lateral and Elevators (trailing edge of tailplane).
40
Which axis is Roll and what control surface primarily affects it?
Longitudinal and Aileron (outboard trailing edge of wing).
41
Which axis is Yaw and what control surface primarily affects it?
Normal and Rudder.
42
What are the 3 Control Requirements?
Control Force - Effort required to manoeuvre the aircraft.
Control Movement - Sensitivity of control column movement.
Control Harmony - Ratio of aileron, elevator and rudder per unit movement.
43
What do Ailerons do to change movement?
Up-going wing deflects down to produce an effective increase in camber, therefore increasing lift. Down-going wing deflects up to produce an effective decrease in camber, therefore decreasing lift.
44
Do all controls become more effective with increased speed?
Yes.
45
Describe what happens if I push on my right rudder pedal.
This will cause the rudder to move to the right altering the camber of the fin/rudder combination. This will in-turn move the nose of the aircraft to the left.
46
List the secondary effects of the 3 controls.
Elevator - Height/speed interchange.
Ailerons - If roll is unchecked, insufficient lift will occur and the aircraft will sink. Airflow across the side of the aircraft now comes into play, called sideslip. The aircraft will yaw.
Rudder - Extra speed over the outside wing will induce extra lift, thus creating roll. If left unchecked the extra yaw from the ailerons alongside the roll from the rudder will cause a cycle to happen which if left becomes dangerous.
47
List the 4 Secondary Controls.
Flaps, Spoilers, Airbrake, and Trim tabs.
48
How does a Flap work?
The Flap provides extra lift by adjusting the shape of the aerofoil (camber) and the wing area. However, they also induce extra drag.
Drag increases greater than lift, therefore the Life/Drag ratio decreases.
Pitch attitude will also be affected by the change in CoG.
49
What are Spoilers?
Flat plates located on the wing that can raise at right angles to the airflow. They induce drag on a wing resulting in roll.
At low speeds spoilers will dump significant lift from the wing.
50
What are Air Brakes?
An extension from the aircraft to increase drag to reduce speed. Very similar to spoilers but normally located centrally on the fueslage.
Poorly designed airbrakes will call unwanted pitch change.
51
What role do Trim Tabs play?
A small hinged surface forming part of the trailing edge of the primary control surface
Work opposite to the elevators to allow trim to be set, reducing the need for constant input through the control column.
Fixed trim tab on the rudder allows for alignment of control surface.
52
What is RoC?
Rate of Climb - An aircraft's vertical speed; altitude change with respect to time.
53
What is AoC?
Angle of Climb - The ratio between distance travelled over the ground with altitude gained.
54
What determines the RoC?
The rate of climb is determined by the amount of excess power.
Rate of Climb = (V (Thrust - Drag)) / Weight
55
What determines the AoC?
The angle of climb is determined by the excess thrust after opposing drag.
56
When is the best RoC met?
When there is the greatest difference between Power Available to Drag.
57
For a jet aircraft, what is the best speed for max AoC?
Min Drag Speed.
58
What is the Absolute Ceiling?
Max Power available curve touches the power required curve, therefore sustained RoC is no longer possible.
59
What is a Glide Descent?
The distance of forward travel divided by the altitude lost in that given distance.
60
What is Powered Descent?
Reducing the descent angle and therefore increasing the distance travelled over the ground, increasing the range from a given altitude.
61
What conditions must be met for a steady descent?
Weight force is balanced by resultant lift and drag. To maintain air speed, energy must be expended to overcome drag. When the engine provides no thrust, energy is sourced from the potential stored energy due to altitude.
62
What is the condition required for Max Endurance Gliding?
The rate of descent is least at the speed where the power required is least.
63
What condition is required for Max Glide Range?
For max distance the aircraft should be flown for min drag. The best angle of glide depends on an angle of attack that gives the best lift/drag ratio.
64
List the effects of Wind and Weight on descending.
Wind does not affect Max Glide Endurance but does have significant impact on the Max Glide Range.
Weight does not affect the Max Glide Range but does impact the Max Glide Endurance.
65
What happens to the Lift force during a banked turn?
Lift is vectored, perpendicular to the wings while weight continues to act from the CoG to the ground. Lift now has a horizontal component that creates the turning effect. If the AoA remains constant, the lift force opposing the weight of the aircraft is now less therefore the aircraft will descend.
66
What are the 3 limits to a turn?
Aircraft reaches stall due to AoA increasing to maintain level flight.
G threshold of pilot is reached.
G limit of aircraft is reached.
67
Why will heavier aircraft have the same angle of bank as lighter aircraft?
As weight increases, the vertical lift component required to counter it increases, but the centripetal force to maintain the same radius of turn also increases in proportion.
68
What criteria must be met to achieve a minimum radius turn?
Wing loading as low as possible.
Air as dense as possible (lowest Alt).
Maximum value of the product of C(L) and angle of bank.
69
Describe what happens leading to a stall.
Power reduced, speed decreases: less lift, Aircraft would descend.
To maintain height, AoA increases, lift increases but speed further decreases due to more drag: less lift.
This continues until critical AoA is reached when aircraft stalls.
70
When is the Max Coefficient of Lift achieved?
Immediately prior to a stall.
71
What determines the nature of the Boundary Layer?
Maximum lift coefficient
Stalling characteristics of a wing.
Value of form drag.
Certain high-speed characteristics of an aircraft.
72
What are the key factors in regards to Stalling Speed?
Change in Weight. Increase in weight = increase in stall speed.
Manoeurve (load factor). Increase in g load will increase the stall speed.
Configuration (changes in C(L)). If C(L) increases, both stall speed and AoA reduce.
Power and Slipstream. Excess power makes noticing the signs on a imminent stall harder. Excess power will reduce the stalling speed and increase pitch attitude.
73
What does Static Stability describe?
The immediate reaction of a body after an external force has been removed. Straight line displacement is characteristic of this.
74
What does Dynamic Stability describe?
The subsequent reaction of a body after an external force has been removed. Oscillating displacement is characteristic of this.
75
Define Stability.
The tendency of an aircraft to return to a steady state of flight, after being disturbed by an external force, without correction from the pilot.
76
Describe the Ball and Bowl analogy.
Positive Stability - Ball in a round bowl, always returning the centre.
Neutral Stability - Ball on a flat plane, will remain in new position once external force removed.
Negative Stability - Ball on top of a dome, will further displace after disturbance has been removed.
77
List the 5 types of Dynamic Stability.
Negative Dynamic Stability - The body oscillates about the equilibrium with increasing amplitude.
Negative Dynamic Stability (Divergence) - The body returns to equilibrium but then continues to diverge through the axis.
Neutral Dynamic Stability - The body oscillates about the equilibrium with constant amplitude.
Positive Dynamic Stability (Damped Phugoid) - The body oscillates about the equilibrium with decreasing amplitude.
Postive Dynamic Stability (Dead Beat Convergence) - Motion heavily damped - oscilliations cease and motion becomes 'dead beat'.
78
List design features to affect Stability.
Directional Stability - Fin Size, Moment Arm.
Longitudinal Stability - Size of Horizontal Tailplane, Moment Arm.
Lateral Stability - Fin Size, Diheadral, Sweep Back, High Wing.
79
Describe 'Flying for Range'.
Achieving the most efficient fuel economy per distance. It is now flying slowly, as this requires high power due to the large amount of lift dependant drag. It is also not min power as the low speed is also uneconomical. It is achieved by obtaining IAS when total drag is least.
80
Describe 'Flying for Endurance'.
Achieving the longest air time. Maximum fuel economy is obtained using the lowest power output of the engine (lowest Gross Fuel Consumption).
81
What is SFC?
Specific Fuel Consumption = amount of fuel used to generate a unit of thrust over a time unit.
82
What factors effect SFC?
RPM - Jet engines are designed to run at high RPMs, this is achieved at high alts and reduces SFC.
Temp - Colder temperatures reduce SFC.
Altitude - Temp decreases and forces RPM up, this improves thermal efficiency and SFC reduces.
83
What governs the maximum permissible take-off weight?
Certificate of Airworthiness
Weight-Amplitude-Temperature
Field length requirements
Take-off net flight path
En route terrain clearance
Landing distance requirements
84
List the factors affecting the length of take-off run required.
All-Up Weight (AUW)
Amount of flap used
Engine power
Wind velocity
Runway gradient
Runway contamination
Air Temp
Airfield Elevation
85
What effects do flaps have on landing?
A steeper descent path at a given speed and power setting and consequently, a better view for the pilot over the nose.
A lower approach airspeed (as the stalling airspeed is reduced) and hence, a shorter landing run.
86
What characteristics do engine-assisted approaches have?
It is possible to regulate the angle of approach despite varying wind strength.
The change of alt when rounding out is small compared with that for a glide approach.
The use of power reduces the stalling speed and thus a lower approach speed can be used.
87
List the 2 main Lift Augmentation Devices.
Slats and Flaps.
88
What does a Slat do?
It flattens the marked peak of the low-pressure envelope at high angles of attack and changes it to be more gradual. This flattening means that the boundary layer retains it's energy for longer, penetrating almost the full chord of the wing.
89
What do Flaps do and list the main types.
Flaps vary the camber, increasing C(L) but decreasing the stalling Angle of Attack.
Types: Plain, Split, Slotted, Double-slotted, Zap, Fowler, and Triple-slotted.
90
What is the Helix Angle?
Angle between plane of rotation and the vector which the blade travels through the RAF.
91
What is the Prop Pitch Angle (Blade Angle)?
Prop AoA + Helix Angle.
Angle between camber centre line of prop and the rotational velocity vector.
92
What is Prop AoA?
Angle between camber centre line of prop to the vector which the blade travels through the RAF.
93
Why are props twisted?
Rotational velocity depends on radius from the centre point. Therefore a reduced blade AoA is required towards the tip, maintaining efficiency.
94
When would 'fine' and 'coarse' pitch be required?
Fine pitch used during low air speeds.
Coarse Pitch used during cruising/high alt.
95
Describe 'Windmilling'.
RPM reduced > Rotational velocity decreases. Airspeed remains the same by dipping nose. Angle between the RAF Vector and the rotational velocity increases so much that Prop AoA becomes inverted (negative). This results in negative torque and negative thrust (drag), maintaining the prop spinning clockwise.
96
Describe 'Feathering'.
Power loss. Increase Prop AoA to almost 90degree from rotational velocity. This will ensure no thrust is produced, but also no drag is produced. Prop has little effect on flight.
97
How does 'Reverse Thrust' differ to 'Windmilling'?
Prop is in the same position, negative Prop AoA but engine torque is applied. This allows for controlling of the negative thrust being created, until 'Windmilling'.
98
What is Solidity?
(Number of Blades x Chord at Radius) / Circumference at Radius.
Area filled out by a prop in its given circle of influence.
99
What is CTM?
Centrifugal Twisting Moment - Due to camber of blade, leading and trailing edges are in different planes. The centrifugal force applies force in these which create a moment, causing the prop to twist.
100
What is ATM?
Aerodynamic Twisting Moment - Twisting due to Pitch Change Axis being behind the centre of pressure.
101
Why does Swing occur during Take-Off?
Slipstream created by prop acts on the fin and rudder of the aircraft causing rotation. Assuming prop rotates clockwise, aircraft will yaw to the left.
