Second Year Semester 1 Flashcards
(122 cards)
1
Q
Name the properties indicated in this picture:
A
b = span
s = semi-span
cr = chord root
ct = chord tip
C~ = mean chord
Cl = centre line
Ωle = leading edge angle
Ωte = trailing edge angle
Ωqc = quarter chord
2
Q
What is the mach number? (Ma)
A
fluid velocity / sonic velocity
sub < sonic (1) < super
3
Q
What is the aspect ratio?
A
AR = span / chord
=span ^2 / planform area(S)
4
Q
What is taper ratio?
A
Ɣ = chord tip / chord root
5
Q
What is the thickness chord ratio?
A
= thickest width / chord length
6
Q
What is a camber line?
A
Same as Chord Line
The line which ic is the centre beteen the top and bottom surface in an aerofoil
will be curved if the wing is cambered
7
Q
What does camber do?
A
Alows lift to be produced at zero angle incidence
Changes pitching moment
8
Q
What can this be named?
A
incidence, alpha or angle of attack
It is the angle relative to the local wind vector (not horizon)
Angle between chord line of aerofoil and airflow
9
Q
What can this be described as?
A
Yaw, Beta, or angle of sideslip
Attitude relative to local wind vector
Angle between vertical centreline and wind vector
10
Q
What are the three moments generated by aerodynamic forces?
A
Pitch, yaw, roll
11
Q
What are the three areodynamic forces?
A
Lift, Drag, Sideforce
12
Q
How do the aerodynamic forces appear in cruisng flight?
A
13
Q
What do the ailerons controll and where are they located?
A
They controll Roll
Located at the back of the wings
14
Q
What do the elevators controll and where are they located?
A
Controll Pitch
Back of tailplane
15
Q
What does the rudder controll and where is it located?
A
Controlls Yaw
Back of fin
16
Q
What gives the aircraft stability?
A
Tilplane (in pitch)
Fin (stability in Yaw)
like a dart ken
17
Q
What happens as the incidence of an aerofoil is increased?
A
Pressure reduction on upper surface increases
Stagnation point moves back on lower surface
Positive pressure area larger on lower surace
pressure reduction on lower surface decreases
LIFT INCREASES
18
Q
What is the stall angle?
A
The angle of incidence at which point the lift generated peaks and begins to decrease.
This is because of the flow seperatin on the upper surface
19
Q
What are the 2 aerodynamic forces present on a body?
A
Pressure differences normal to surface
friction forces tangental to surface (because air is viscous)
20
Q
What are the differences in viscous and inviscous flow? (how they look)
A
21
Q
What is a boundry laye, how is it formed?
A
Flow at surface
Slow moving flow close to surface slows the flow next to it, increasing the size of the boundry layer as it moves along a surface
22
Q
How does the pressure look over an aerofoil?
A
23
Q
How does the pressure GRADIENT change over an aerofoil?
A
24
Q
What are favourable and adverse pressure gradients?
A
Favourable = negative gradient
Adverse = positive gradient
25
How des the boudry layer affect stall? (using gradients)
At the tup rear of a wing the pressure gradient is adverse (positive)
The adverse pressure gradient slows the flow down at the surface, thickening the boudry layer
If the gradent is too large then the flow will seperate
26
What is the seperation point?
Where the velocity of the flow just beside the surface is also zero
27
What happens as the incience is increased after the stall angle?
The spereation point moves forward
The lift generated reduces
When the seperation point moves into the high adverse pressure region the lift reduces significantly.
28
What is the difference between laminar and turbulent flow?
LAminar is smooth and attached
Turbulent is rough and chaotic
29
What is the Reynolds number?
Re = density \* Velocity \* Trasition distance /
Viscosity of water
= ρ V x / μ
30
Will laminar or turbulent flow seperate quicker and why?
Laminar seperates quicker becuase turbulant flow allows enery from the free stream to be passed into the lower layers of the boundry layer "energysing the flow"
This increases the velocity gradient closer to the wall
31
How do you calculate the force acting on a body?
F = 0.5 ρ\*V^2\*S\*Cf
Where V = velocity of fluid
S = Wing area
Cf = force coefficient
(Cf becomes Cd or Cl for drag and lift)
32
How do you calculate moment coefficients?
M = 0.5 ρ V^2 S c Cm
c = mean span
33
How do you calculate pressure coessificients?
P - P. = 0.5 ρ V^2 Cp
34
How do you work out the minimum speed an aircraft can go at a constant altitude?
Lift = weight
use lift coefficient formula and Cl max
rearrange
35
What are trailing edge devices and what do they do?
NAme different types ad general info on each
They increase the camber , zero lift incidence and max lift
36
What are slotted flaps and what do they do?
Name different types and some info on each
They utilise the high pressure underneath the wing to keep the boundry layer atached on the upper surface by re energysing it.
Delay the stall of the angle
37
What are leading edge devices and what do they do?
Sots (gap) and Slats (small aerofoil)
energising boundry layer and delay stall angle
38
What are the two main sets of Drag?
Induced (ACl^2)
Parasite (Cd.)
39
What is Wave drag?
When shock waves, caused by travelling close to and above the speed of sound, instantaneously slow the flow down causing boundry layers to thicken.
40
What is induced drag?
Results from the generation of a trailing vortex
41
What are trailing vorteces?
caused by the air at a higher pressure under the wing leaking upwards into the low pressure region on the upper surface of the wing.
Two large vortices are formed by the combination of individulal vortices on each wing.
42
How to trailing vortices effect drag?
They create a downwash behind the wing, this tilts the reaction force backwards giving a component horizontally called drag.
43
What is drag produced by vortices called?
trailing vortex, lift induced
or just induced drag.
44
What is the induced drag dependant on?
The amount of lift being generated by the wing.
This may account for 80% of the total drag!
45
How is the induced drag spread across the wing?
Increases towards centre as forces combine.
46
How can induced drag be minimised?
By having eliptical lift distribution across the wing!
This can be done by having an eliptical planform wing or have linear tapered wings or by reducing camber from root to tip, or twisting the wing (washout). In practice a mixture of these are used.
Using Winglets.
47
What are winglets?
Surfaces fitting at the end of wings to prevent the flow "spilling" from the bottom to the top of the wing. Thus reducing the strength of the trailing vortex and induced drag.
48
How is induced drag related to aspect ratio?
Inversly proportional
Thats why gliders have large aspect ratios
(some up to 50 +)
49
What is form drag?
Also called pressure drag
Cause by flow seperating as it travels around a body, leaving a low pressure wake.
50
What is profile drag?
Due to a loss of momentum within the boudry layer. creating a wake if seperation does not occur.
51
What type of wings have larger profile drag?
Thicker wings
52
What is skin friction drag?
Cause by shear stresses in boundry layer.
Donimates at high velocities.
53
How is drag broken down when plotted against air speed velocity?
54
What renolds number (very roughly) does transition occur?
10^5
But highly suseptable to surface roughness and turbulence.
55
How is the shear stress and viscosity related?
τ = μ\*Velocity gradient
56
How can skin friction drag be claculated?
Laminar: 1.328Re^-1/2
Turbulent: 0.455(ln(Re))^-2.58
Hence laminar drag is much less (85% less)
57
Why would we want boundry layer removal? How could we do it?
By using suction devices to create a smoth surface for laminar flow.
However these devices are heavy and unreliable.
58
What is interference drag?
When pressure fields and boundry layers interfere at sharp junctions. These cause the boundry layers to thicken, increasing skin friction and pressure drag and may lead to flow seperation.
59
How can interference drag be reduced?
B using fillets and careful design.
Placing the wings high on the fuselage is the best for this. Miggle wings are the worst option.
60
What is trim drag?
Down force caused by tail plane means that a larger lift from the wing is needed to balance the moments around the COG.
This produces more induced drag from the main wing and also from the tail plane.
61
How can trim drag be reduced?
Decreasing the tail arm (moving it clocer to the COG so that less downfore required for the same moment to be produced.)
Using a flight controll system.
Installing a canard system (so that trimming force in same direction as lift)
62
What is Base drag?
When a blunt rear seperates the flow creating a pressure drag
63
What is Cooling drag?
Cause by the engine istallation including the engine and its enclosure
64
What is a Townend ring and how is it useful?
An air cooled engine enclosed in an aerodynamic cowling at the front of the plane rather than in the free stream. Has less drag and better cooling effect.
65
What is a secondary surface radiator?
A well designed duct, well placed under the wings that can produce a little thrust as well as effeectively cool the engines.
F = m (Vout - Vin)
66
What does ASI stand for?
Air speed indicator
67
How can the velocity be calculated using pressures?
Where
Pt = Total pressure
P.. = Static presure
68
What is a Pitot Tube?
Simply a tube open at one end to measure the total pressure (or Pitot Pressure)
69
What is a static port?
A hole in the surface adjacet to the flow.
No dynamic pressure is measured, only Static pressure!
70
How is airspeed measured?
By combining the Static and Pitot probes into a device that flexed due to the delta P. This flex is transformed into a dial to show the ASI
71
What is ISA?
International Standard Atmosphere
Standard condition to use and compare things
72
What is IAS? (no not ASI...)
Indicated Air Speed...
Needs to be calibrated as it is based on density which changes with altitude and region
73
What is the true airspeed?
The speed that the air is actually passing over the aircraft. This will only be shown if the density of air is at what it was calibrated and there are no errors.
74
Why is IAS useful?
It is useful to see the stall speed.
This is based on the initial density and so is not effected by altitude.
75
What is the relationship between ground speed and TAS?
The ground speed = TAS if no wind
Ground speed = TAS - Wind Speed (If headwind)
Ground Speed = TAS + WInd Speed (if tailwind)
76
What is an Altimeter?
A device that shows the altitude of the plane based on static pressure
77
How does an altimeter work?
It expands a case due to pressure which turns a dial.
Calibrated for ISA
Can be changed / re calibrated as datums vary
78
What value is ISA?
1013 mbar
79
What is ATC?
Air Traffic Controll
80
What is QFE?
Static pressure at airport
Given to pilot so that they can calibrate Altimeter to read 0 when landed.
81
What is QNH?
The altimeter setting for latitude from sea level.
82
What is SAS?
Standard Altimeter Setting
Gives a datum for long distance flights to ensure aeroplanes dont crash!
Measured in Fliegh Levels of 100 ft
ie. 10000ft = FL100
83
What is a VSI?
Vertical Speed indicator
Works similar to ASI but has static pressure fed to both sides of captule and case. A matering unit causes a time delay in the pressures equalising, casing the dial to move only when altitude is changing and then settle as altitude settles.
84
What is a Mach meter?
Indicated the Mach number the aircraft is flying at
85
Why would the pilot need to know the Mach Number?
At roughly 0.5Mach the properties of ari change.
Compressability apparent, density changes happen, and pitot pressures may be wrong.
Pilot may need to know max Mach to fly at.
Commercial = 0.85M
86
What is a turn and slip indicator?
It is an artificil horizon for when visibility low.
87
What are VFR conditions?
Visual Flight Rules (can see horizon)
88
What are IMC conditions?
Instrument Meterological Conditions (cant see)
89
What are IFR conditions?
Instrument Flight Rules ( rely on artificial horizon)
90
What does the slip ball show?
Shows if the turn is coordinated or if there is slip present
91
How does the turn indicator work?
A gyro is spun a high speeds (electronically or pnumatically) which does not want to change motion. Hence it can show turn when capsule and plane turn.
92
What is an Attitude Indicator?
If two gyros are used then the aircrafts attitude in three axes can be displayed
93
What is a FMS?
Flight Management System
Gives all of the information to the piolets dgitally so that there is no need for a flight engineer
94
What does EFIS stand for?
Electronic Fight Instrumentation System
95
What does CRT stand for?
Cathode Ray Tube displays
(mini Tvs in the cocpit displaying all information
96
What does INS stand for?
Internal Navigation System
| (Navaids)
97
What does FADEC stand for?
Fully uthority Digital Electronic Controll
98
How do navaids work?
MEasure 3 component accelerations on a known mass, and use newtons laws to calculate the displacement.
If origional point known then location can be calculated.
99
What is a Ring Laser Gyro?
Same idea as Navaids, however using lazers and mirrors in a triangular shape. These expand with acceleration and so cause different interference patterns.
Computer calulated acceleration and displacement to find location.
100
What is DME
Ulra high frequency signals sent and recieved to a ground station. The aircraft works out the distance to ground station based on sending and recieving times.
GS has delay of 50 microseconds to not cause an interference.
s = time\*Vsingal / 2
101
What is VOR?
Very High Frequecy Omnidirectional Range
Transmits information for the INS
102
What is DME?
Distance Measuring Equipment
Information based on location normauult used for landing /taking off
103
How does GPS work?
Triangulates 3 satelite signals to locate an exact point. (from time taken for signal to reach reciever)
A fouth satelite verifies if this is correct.
If wrong the GPS will adjust its clock to make sure it aligns.
104
What are EHSI's?
Electronic Horizontal Situation Indicator
Shows all navigation information on a CRT
105
What is the EADI?
Electronic Attitude Data Indicator
Displays all information based on plane attitude on a CRT
106
What is the EICAS?
Electronic Indication and Crew Alerting System
Displays Engine information and gives warning of faults etc on CRT
107
What are the four regions within a fully developed boundry layer?
Laminar boundry
Transition
Turbulent boundry
Laminar Sub Layer
108
What happens to the flow around a body as Re changes?
It is altered, transition point can change, or sub layer can be reoved
109
What do the flow patterns around a sphere look at Re\<0.5
Flow is dominated by viscous forces, no seperation
Stokes Flow
110
What do the flow patterns around a sphere look at 2
Seperation occurs creating two stable vortices
111
What do the flow patterns around a sphere look at 90
Vortices are shed asymetrically creating oscilation forces around a cylinder.
Von Karman Vortex
112
How do you find the shredding frequency of a shedding vortex?
Strouhal Number
S = fd/V
113
What are the effects of Vortex shedding?
Telegraph produce whistling sound
In near resonance frequency the wire / object will vibrate
114
Why do flags flutter even in steady winds?
Because of the Von Karmen Vortex being shed on the pole
115
Why do chimney stacks have a thread on the outside of them?
Because the Von Karmen Vortex that can be shed from it could make it vibrate.
If it oscilated at natural frequency it would quickly collapse.
If not hen it could fatigue the root of the structure
Thread disturbs this process!
116
What is the difference between laminar and turbulant flow around a sphere?
Laminar is mooth and straight so will seperate at the top and bottomw of the ball (causing a large wake)
Turbulent is not smooth but will flow/stick around the ball better, seperate later and produce a smaller wake
117
Why are golf balls dimpled?
The rough surface of the gold ball creates an early transition to turbulent flow, which flows around the ball better causing a small wake and less of a pressure difference, and hence less drag! (goes further)
118
How can bolwers make a ball curve in the air?
One side of ball is smooth and the other is rough.
This creates a difference in seperation points as the flow travels over the ball.
This causes a difference in pressures and so a sidewards force!
119
What is Galloping?
When a downforce producing device moves upwards, the relative wind is now at a negative angle of attack, which produces a lift in the direction of movement.
This is unstable.
This can lead to large oscilations and distruction
120
What is flutter?
When two degrees of freedom (rotation and vertical displacement) couple together to produce an unstable oscilation.
121
What are the 3 forces occuring in flutter?
Aerodynamic
Structural resistance
Inertia
122
How does flutter work?
As wing moves up, forces puch wing up
Resistance slows movement and pushes wing back, creating downwards lift force
Resistance doest the same again sending wing back up
Repetative and can be distructive
