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M8 > 8.2 > Flashcards

8.2 Flashcards

1
Q

In what region is the air incompressible?

A

Subsonic region

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2
Q

What does the continuity equation state?

A

The speed of the airflow is inversely proportional to the area of the cross section of the tube as long as the density remains constant.

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3
Q

What term is used when the diameter increases for the continuity equation?

A

Diffuser outlet.

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4
Q

What term is used when the diameter decreases for the continuity equation?

A

Jet outlet.

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5
Q

What is Bernoulli’s principle?

A

The total pressure is always the sum of static pressure and dynamic pressure.

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6
Q

What happens to the static and dynamic pressure when the valve is open?

A

Static pressure decreases

Dynamic pressure increases.

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7
Q

How does the dynamic pressure change with a change in speed?

A

Changes with the square of change in speed.

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8
Q

What results in lift?

A

Difference in pressure.

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9
Q

What is an up-wash?

A

When some streamlines approach the profile in a low position slope upwards in front of the wing.

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10
Q

What is down-wash?

A

When some streamlines of the upper surface flow downwards when leaving.

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11
Q

What is the Magnus effect?

A

When a body is rotating and it creates an increase of speed on the upper surface and a decrease in speed on lower surface

(Something rotating creating lift)

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12
Q

What is the profile on a wing?

A

The cross section.

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13
Q

What is the chord line on a wing?

A

A straight line connecting the leading edge and the trailing edge.

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14
Q

What is the mean chamber line?

A

A line drawn halfway between the upper and the lower surface of the wing

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15
Q

What is the chamber of the wing?

A

The displacement of the mean chamber line from the chord line.

(Quantities expressed as a fraction or % of basic chord dimension)

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16
Q

What would a typical low speed profile have a maximum camber loft?

A

5% located 45% aft of the leading edge.

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17
Q

What is the maximum thickness of a profile as a fraction also known as?

A

Fineness ratio

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18
Q

What is the flight path velocity?

A

Speed of the aircraft in a certain direction through the air.

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19
Q

What is the relative wind?

A

Speed and direction of the air acting on the aircraft which is passing through it.

(Opposite in direction to the flight path velocity)

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20
Q

What is the angle of attack?

A

The angle between the chord line of the profile and the relative wind.

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21
Q

What is the angle of attack denoted by?

A

Alpha.

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22
Q

What is the angle of incidence?

A

Angle between the chord line and the longitudinal axis of the aircraft.

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23
Q

What is the angle of incidence denoted by?

A

y (gamma)

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24
Q

What is the maximum thickness of low speed profile?

A

18% of chord line.

Located 30% aft of the leading edge.

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25
Q

What is the wing area?

A

The projection of outline on the plane of the chord. Includes area of fuselage between the wings.

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26
Q

What is the formula for wing area?

A

Wing area = wing span (b) x chord of the wing (c)

Wing span x average chord of the wing (C)

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27
Q

How is the taper ratio (lambda) of a wing found?

A

Tip chord/ root chord

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28
Q

What is the aspect ratio?

A

Wing span / average chord

Wing span squared / wing area

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29
Q

What are typical aspect ratios?

A

35 for high performance sail plane

3.5 for jet fighter plane.

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30
Q

What is the sweep angle?

A

The angle between the line of 25% chords and a line perpendicular to the root chord.

(Positive sweep = backwards)

(Negative sweep = forwards)

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31
Q

What is the dihedral angle of the wing?

A

Formed between the wing and the horizontal plane passing through the root of the wing.

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32
Q

What is the aerodynamic force?

A

The resultant of all forces on a profile in an airflow acting on the centre of pressure.

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33
Q

What is the centre of pressure?

A

The point on which all pressure and forces act.

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34
Q

What does the aerodynamic forces of lift and drag depend on?

A

Dynamic pressure
Surface area of profile
Shape of profile
Angle of attack

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35
Q

What is the formula for theoretical lift?

A

Theoretical lift = 1/2 x air density x velocity squared x surface area

Or

Theoretical lift = dynamic pressure x surface area

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36
Q

How do you measure the actual lift?

A

Using a wind tunnel

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37
Q

What scales are attached to a universal joint in a wind tunnel?

A

Horizontal scale measuring drag

Vertical scale measuring lift

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38
Q

What is the coefficient of lift?

A

CL

Account for difference between measure lift and theoretical lift

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39
Q

What is the formula for coefficient of lift?

A

CL = measured lift / theoretical lift

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40
Q

What is the lift equation?

A

Coefficient of lift x dynamic pressure x surface area

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41
Q

How is the coefficient of drag measured?

A

Drag / theoretical drag

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42
Q

When does a stall occur?

A

When the airflow cannot follow the upper surface of the profile and there is an airflow separation.

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43
Q

What is an advantage of a high maximum lift coefficient?

A

Aircraft can fly slowly

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44
Q

What is a disadvantage of a high maximum lift coefficient?

A

The thickness and camber necessary for profiles may produce high drag and low critical Mach number.

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45
Q

What does upper surface frost do to the maximum coefficient of lift and maximum angle of attack?

A

Reduces it.

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46
Q

Who invented the method of evaluating wind tunnel tests?

A

Otto Lilienthal

47
Q

What does a polar diagram plot?

A

The lift and drag coefficients

48
Q

What is the lift-drag ratio?

A

Lift/Drag

49
Q

When an aircraft is in a steeper climb, what must happen to thrust?

A

Must be increased

50
Q

What must the thrust equal to maintain a constant speed on climb?

A

Not only the drag but also the rear wards acting weight W Sin 0

51
Q

When climbing, will the lift generated be less or more than the aircraft weight?

A

Less than.

Must increase thrust

52
Q

What are the 3 categories of drag?

A

Induced drag
Parasite drag
Compressible drag

53
Q

What is induced drag?

A

The drag on the wing caused by lift.

54
Q

What is parasite drag?

A

Not related to lift. Can cause drag caused by distribution of pressure, friction drag caused by skin friction, or interference drag caused by aerodynamic interference.

55
Q

What is compressible drag?

A

Caused by shock waves on an aircraft approaching the speed of sound.

56
Q

What does the turbulence at wing tips form?

A

Vortices

57
Q

What do vortices at wing tips cause?

A

Drag and a loss of lift.

Induced drag

58
Q

What is a bound vortex?

A

If a wing span is infinite the circulation around the profile causes an upward wash on leading edge and down wash on trailing edge

59
Q

On a finite wing span, what vortices do we have?

A

Wing tip vortices and the bound vortex.

60
Q

What is the induced drag affected by?

A

Aspect ratio, wing tip design and aircraft speed.

61
Q

What aircraft use wing tip fences and winglets?

A

Small aircraft- wing tip fences

Large aircraft- winglets

62
Q

What type of drag is form drag?

A

Parasite drag caused by pressure distribution on body.

63
Q

What would an airflow with friction cause?

A

More drag, pressure at front of cylinder is not the same as the pressure behind the cylinder.

64
Q

How does the shape of the nose affect drag?

A

Disc form- very high drag

Bullet nose- drag decreases to 20%

Bullet nose with streamline tail- decreases to less than 10%

65
Q

What does high form drag equal to in form of fiction drag?

A

High form drag = low friction drag

66
Q

What does the ratio for friction drag range from?

A

1 at top and 10 at bottom.

67
Q

What is the retarded air called?

A

Boundary layer.

68
Q

What does retarded airflow mean?

A

Surface of aircraft is quite rough and velocity of some trapped air particles is reduced to zero.

69
Q

What are the 2 basic types of boundary layer?

A

Turbulent boundary layer

Laminar boundary layer

70
Q

What is the laminar boundary layer?

A

Immediately downstream of leading edge.

Air particles do not move from one layer to another.

71
Q

What is turbulent boundary layer?

A

Downstream of laminar boundary layer.

Laminar flow breaks down and we get turbulent flow.

(Air particles travel from one layer to another and produces energy exchange)

72
Q

What is the thickness difference between turbulent and laminar boundary?

A

Turbulent boundary much thicker and produces 3 times more friction drag.

73
Q

Which boundary layer produces more kinetic energy?

A

Turbulent boundary layer next to surface and reduces tendency for flow separation.

74
Q

Why is the area of the laminar boundary kept smooth and clean?

A

Because small disturbances in the laminar boundary bring it into the turbulent boundary or produce flow separation.

75
Q

What boundary has the lowest static pressure?

A

Laminar boundary layer between the leading edge and the point of maximum thickness.

76
Q

When does the air particle lose energy due to friction?

A

As it enters the turbulent boundary layer after the point of maximum thickness.

77
Q

What does the slot do?

A

Helps to regenerate the flow of air from low pressure to high pressure at the trailing edge.

78
Q

What does the slot prevent?

A

Flow separation.

79
Q

What friction would a profile with a greater low drag laminar region have?

A

Lower friction.

Known as a laminar profile

80
Q

What is the interference drag?

A

The sum of all drags from the wing, strut and engine is greater than the drag of all individual components.

81
Q

What can interference drag be reduced by?

A

Fairings.

82
Q

When does compressible drag only occur?

A

Transonic and supersonic.

83
Q

What is compressible drag caused by?

A

Shock waves on aircraft approaching speed of sound.

84
Q

What is compressible drag sometimes called?

A

Wave drag.

85
Q

What is a Lillenthal diagram?

A

Graph plotting the co-efficient of lift against of coefficient of drag for each angle of attack.

Best glide ratio can be found.

86
Q

What is the advantage of a thicker wing?

A

Raises coefficient of lift at higher angles of attack and raising alpha max.

87
Q

What are the 3 main categories of parasite drag?

A

Form, friction and interference.

88
Q

What is an advantage of a cambered wing?

A

Increases coefficient of lift at low angles of attack.

89
Q

What speeds is induced drag highest?

A

Low speeds

90
Q

At What speeds does parasitic drag increase?

A

Parasitic drag increases with increase in speed.

91
Q

What does a high down wash produce?

A

Low local angle of attack.

92
Q

When does an elliptical wing stall?

A

Stalls at the same time everywhere.

93
Q

When does a rectangular wing start to stall?

A

At the root.

Tip last.

94
Q

What stalls first on a tapered wing?

A

Tip before the root.

95
Q

What stalls first on a swept wing?

A

Tip section first.

Dangerous implications for the lateral control and stability of the aircraft

96
Q

What wings are used on most aircraft?

A

Swept wing.

97
Q

What is geometric twisting?

A

Designing the wing so that the root stalls before the tip

Angle of incidence greater at root than tip, camber remains constant

98
Q

What is aerodynamic twisting?

A

Camber at the root is greater than at the tip.

Angle of incidence is constant.

99
Q

What is MAC?

A

Mean aerodynamic chord..

(Chord line through the centre of lift)

(Approx 30% centre of lift)

100
Q

When is the aircraft in level flight?

A

When the position of the centre of lift is in the same position of the centre of gravity and no aircraft rotation.

101
Q

When the position of the centre of the lift moves forward of the position of centre of gravity, what happens to the nose?

A

Nose up reaction.

102
Q

When there is flow separation at the root of the wing, where does the centre of lift move to?

A

Towards the tip and behind the centre of gravity.

Nose down, airspeed increases and angle of attack decreases

103
Q

What stall does the aircraft recover from the stall without pilot input?

A

Wing root stall.

104
Q

What is wing tip stall?

A

Flow separation at tip of wing, centre of lift moves towards the root and forward of centre of gravity.

(Nose up)

105
Q

What is a device on smaller aircraft which prevents the wing tip form stalling first?

A

A stall strip

Mounted at leading edge of root of wing

106
Q

What is a disadvantage of the stall strip?

A

Disturbs the lift.

107
Q

What are used to prevent wing tip stall on some larger aircraft?

A

Slats

108
Q

Where are slats located?

A

Leading edges of wing tips.

109
Q

What happens at the point of stagnation?

A

Speed of airflow falls to zero and static pressure equals total pressure.

110
Q

What is a spanwise flow?

A

Air particles splitting, some at right angles to leading edge and others follow leading edge

111
Q

What effect does a spanwise flow have on the boundary layer towards the wing tip?

A

Thickening it, especially during low speed flight.

112
Q

What reduces the effect of spanwise flow?

A

Wing fences.

Or saw tooth leading edge

113
Q

What does a vortex generator used for?

A

Improve boundary layer control.

114
Q

What is a vortex generator?

A

Small, low aspect ratio wing placed vertically on surface of large wing.

Produces lift.

M8 (4 decks)

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