1
Q
Lateral (Transverse) axis:
A
Parallel to wings running from pilots left to right.
2
Q
Longitudinal (Roll) axis:
A
Drawn through body of vehicle from tail to nose.
3
Q
Vertical (Yaw) axis:
A
Drawn from top to bottom, perpendicular to the other axes.
4
Q
Frames of reference/axis rules:
A
Mutually orthogonal
Fixed in the aircraft
Moves with the aircraft (translation and rotation)
5
Q
Mutually orthogonal definition:
A
At right angles to each other.
6
Q
Control surface used for pitch manoeuvre:
A
Elevators
7
Q
Control surface used for roll manoeuvre:
A
Ailerons
8
Q
Control surface used for yaw manoeuvre:
A
Rudder
9
Q
What is a standard atmosphere?
A
It relates fight tests, wind tunnel tests and general airplane design to a common reference.
10
Q
Standard sea-level pressure:
A
101.325 kPa; 2116.7 lbf /ft^2
11
Q
Standard sea-level density:
A
1.225 kg/m^3; 0.002378 slug/ft^3
12
Q
Standard sea-level temperature:
A
15°C; 288.15 K; 59°F
13
Q
What are standard values?
A
Values at sea level.
14
Q
How are ratios presented in altitude tables?
A
local value / “standard” value
15
Q
Forces acting on an aircraft:
A
Lift (upwards)
Weight [gravity] (downwards)
Drag [slows aircraft down] (backwards)
Thrust [pushes aircraft forward] (forwards)
16
Q
What are aerofoil sections used for?
A
Aerofoil sections are used to generate a lift force efficiently (i.e. low drag).
17
Q
Leading edge
A
The foremost edge of an aerofoil.
18
Q
Trailing edge
A
The rear edge of an aerofoil.
19
Q
Chord
A
The line connecting the
leading edge and trailing edge.
20
Q
Angle of attack (a)
A
The angle between the relative wind (or
freestream) and the chord.
21
Q
Aerofoil lift (L)
A
A force generated by the aerofoil which is perpendicular to the relative wind direction.
22
Q
Aerofoil drag (D)
A
A force generated by the aerofoil which is parallel to the relative wind direction.
23
Q
Aerofoil Normal Force (N)
A
A force which is perpendicular to the chord.
24
Q
Aerofoil axial force (A)
A
A force which is parallel to the chord.
25
Angle of attack
Angle between the flight direction and chord.
26
Pitch angle
Angle between the chord and horizontal axis.
27
Flight path angle
Angle between the flight direction and horizontal axis.
28
Non-dimensional meaning
No units
29
Why are non-dimensionalised parameters used to present data?
Allows "performance" from different flight conditions (altitude, speed etc.) to be directly compared.
In aerodynamics, parameters such as lift, drag and pressure are commonly presented in the form of coefficients.
30
Dynamic pressure definition
The kinetic energy per unit volume of a fluid element.
31
True Air Speed (TAS) definition
The actual relative speed of the aircraft to the air through which it is flying - the speed of the air over the wing.
32
Equivalent Air Speed (EAS) definition
The air speed at sea level density, that would give the same dynamic pressure that is produced at the true air speed (TAS) and altitude at which the aircraft is flying.
33
What is Equivalent Air Speed (EAS) useful for?
Useful for predicting aircraft handling, aerodynamic loads, stall etc. in varying atmospheric conditions (and altitude).
34
Indicated Air Speed (IAS) definition
Speed shown in cockpit. Level, constant speed flight, will be same as EAS.
35
Calibrated Air Speed (CAS) definition
Indicated airspeed corrected for instrument, sensor location and position error. More accurate measure of the aircraft's speed relative to the air.
(EAS is CAS corrected for compressibility effects).
36
What is the speed of sound also known as?
Sonic velocity
37
What is the Mach number (M)?
A common non-dimensional parameter to describe flight velocity.
The local Mach number is the ratio between the local airspeed (or local freestream velocity) and the local speed of sound.
38
What does 1 knot mean?
1 nautical mile / hr
39
What does deflecting a control surface do?
Changes the local angle of attack and the local lift and drag.
40
Downward deflection of ailerons…
Increases local angle of attack => increase lift.
41
Upward deflection of ailerons…
Reduces local angle of attack => reduce lift.
42
What happens if the aileron at one side shows upward deflection and another side shows downward deflection?
The net effect is the generation of rolling moment.
43
What do leading edge slats and trailing edge flaps do?
Increase lift.
44
What do simple trailing edge flaps do to the aircraft angle of attack?
Reduce the angle of attack
45
What do simple leading edge slats do to the aircraft angle of attack?
Increase the angle of attack
46
Angle of attack and lift relationship?
Greater angle of attack => greater lift (until a certain point)
47
Is the lift lesser or greater with flaps down?
Greater lift.
48
How to produce constant lift?
Need to reduce the angle of attack.
49
What happens to lift and angle of attack in flaps down condition?
AoA flaps down> AoA flaps up
Lift flaps down > Lift flaps up
50
What is the ratio between lift and drag called?
The lift-to-drag ratio (L/D).
Cl/Cd has only one maximum value at one angle of attack.
L/D is also called the Glide Ratio
51
What happens when an aircraft’s engines turn off?
No thrust is generated so the aircraft starts gliding.
52
What is the objective when gliding?
Maximise the range, which means need to minimise the glide angle (y).
The aircraft is tilted downwards so gravity can make the aircraft travel at constant speed.
The lower the glide angle, the further the aircraft will fly, therefore, the greater the range.
53
How do we minimise the glide angle?
Maximise the lift-to-drag ratio (L/D).
54
When is the range at a maximum?
When the lift-drag ratio is maximum.
55
Types of Total Aircraft Drag:
Profile (parasitic) Drag
Lift Induced Aircraft Drag
-At high speed the penalty associated
with generating air is lower.
56
Types of Profile (parasitic) Drag:
Form (pressure) Drag - Aircraft pushing through air.
Skin Friction
(Profile drag = Form drag + skin friction)
*as speed increases, these also increase*
57
What is form drag/pressure drag?
Due to the shape of the aircraft: the resistance an object experiences due to its overall shape as it moves through a fluid.
At higher speed more work required to push through the air. Hence, higher drag.
Also higher skin friction at higher flight speed.
58
What is Induced drag/drag-due-to-lift?
Induced by the lift generated by the aircraft.
Harder to generate lift force at low speed.
Proportionally takes more energy out of freestream air.
Hence higher drag at low speed.
59
Drag speed relationship with Wing Area
The minimum drag speed decreases with the wing area S.
The bigger the wing area, the lower the drag speed.
60
When does maximum L/D speed occur?
At the point when the profile drag is equal to the induced drag.
61
What is the speed for minimum power-to-speed ratio equal to?
The minimum drag speed.
62
What is range?
How far an aircraft can fly on the available fuel. (units: m)
63
What is endurance?
How long an aircraft can stay airborne given the available fuel. (units: s)
64
For a jet aeroplane, what is fuel flow proportional to?
Thrust
In steady flight, thrust = drag, so fuel flow is proportional to drag.
65
For a jet aeroplane, where does best range occur?
Best range occurs at speed where the drag-to-speed ratio is minimum (i.e. lowest fuel flow (or drag) at the highest speed).
66
For a jet aeroplane, where does best endurance occur?
Best endurance occurs at speed where drag is minimum (lowest fuel flow).
67
What is fuel flow?
Amount of fuel going into the engine.
68
For a propeller, what is fuel flow proportional to?
Engine power.
69
For a propeller, where does best range occur?
Best range occurs at speed where the power-to-speed ratio is
minimum (i.e. lowest fuel flow at the highest speed).
70
For a propeller, where does best endurance occur?
Best endurance occurs at speed where power is minimum (lowest fuel flow).
71
Why do long-range aircraft climb as they burn fuel?
Aircraft get lighter during flight - fuel is being used.
72
Why do long-range aircraft need to climb as they burn fuel?
As an aeroplane burns fuel, its weight (W) decreases.
This means lift coefficient decreases. Therefore operation moves away from the best lift to drag ratio point.
NOTE: Weight change only affects lift, DRAG of aircraft is unchanged.
73
How to maintain operation at best CL/CD?
Lift should be maintained at best CL/CD angle of attack (i.e. CL, needs to be constant).
* Hence, dynamic pressure needs to change, so either
i. reduce the flight speed, U
ii. reduce the air density p (i.e. climb to higher altitudes)
ill. do both.
(Or aircraft could fly at a different AoA)
74
What happens when an aircraft climbs in the Troposphere?
Climbing in Troposphere means a local temperature reduction. Hence, reduces local speed of sound (a) and hence, increases the local Mach number (M).
Increased flight Mach number will increase compressibility drag.
Shock waves may appear when the critical
Mach number is reached.
First Year Aeronautical Engineering
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