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Module 8: Aerodynamics > 8.2 > Flashcards

8.2 Flashcards

1
Q

Dynamic pressure

A

The pressure on the surface of a body, which causes moving air to stop.

Depends of density and velocity.

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2
Q

Flow continuity

A

When water flows through a duct, mass flow is the same at any point.

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3
Q

Convergent duct

A

Velocity increases
Pressure and temperature decreases

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4
Q

Divergent duct

A

Velocity decreases
Pressure and temperature increases

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5
Q

Bernoullis principle

A

Total pressure is constant if no work is done to it

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6
Q

Stagnation point

A

Point where the air separates over and below the wing

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7
Q

Airspeed indicator

A

Uses pitot pressure inside capsule and static pressure outside capsule to measure dynamic pressure.

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8
Q

Indicated airspeed

A

Speed of aircraft measured by its pitot static system and displayed on the airspeed indicator.

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9
Q

Calibrated airspeed

A

Indicated airspeed corrected for instrument and position error

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10
Q

Equivalent airspeed

A

Calibrated airspeed corrected for compressibility

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11
Q

True airspeeed

A

Equivalent airspeed corrected for density

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12
Q

Ground speed

A

Airspeed minus windspeed

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13
Q

What displays display what airspeeds?

A

PFD displays IAS and Mach number

ND displays GS and TAS

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14
Q

Mean camber line

A

Line joining leading and trailing edge curving at the very middle.

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15
Q

Fineness ratio

A

Ratio of the chord to the thickness

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16
Q

Camber

A

Different between mean camber line and chord line

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17
Q

Relative airflow

A

Vector sum of aircraft forward speed and airflow resulting from any vertical of the aerofoil.

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18
Q

Angle of attack

A

Angle between chord line and relative airflow.

If aerofoil is descending, relative airflow will flow upward increasing the angle of attack.

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19
Q

Newton’s third law

A

Every action has an equal and opposite reaction

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20
Q

Drag

A

Parallel with relative airflow.

If thrust is greater than drag, aircraft will accelerate to where they equal again causing a steady state.

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21
Q

Aerodynamic resultant

A

Sum of lift and drag

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22
Q

Dorsal fin

A

Vertical stabiliser is above the fuselage

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23
Q

Wash out

A

Decrease in wing angle of incidence from root to tip.

Improves stability.

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24
Q

Wash in

A

Increase angle of incidence from root to tip.

Decrease stability of wing.

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25
Q

Mean Aerodynamic chord (MAC)

A

Wing area over wing span

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26
Q

Aspect ratio

A

Span over chord

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27
Q

Dihedral

A

Upward angle of wing increasing stability

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28
Q

Wing loading

A

Weight of aircraft divided by wing area

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29
Q

Angle of incidence

A

Angle between chord line and a reference axis along fuselage.

If aircraft is flying straight and level, the AOI will equal the AOA.

30
Q

Two types of Boundary layers

A

Laminar flow: layers move smoothly in parallel

Turbulent flow: irregular pattern of flow

31
Q

Laminar vs Turbulent

A

Laminar is thinner and smoother producing less drag.

Turbulent contains more energy as turbulent molecules interact with free stream air and gain energy.

32
Q

Upwash

A

Air flows upwards just before leading edge due to the boundary layer.

33
Q

Downwash

A

Downward movement of air over wing.

Decreases angle of attack.

34
Q

Vortices

A

Formed when air flows from higher pressure (under) to low pressure (upper).

Any two flows of air meet at an angle forms a vortex.

35
Q

Reynolds number

A

Determines wether a flow is laminar or turbulent.

36
Q

When does boundary layer separation occur?

A

High speeds - turbulent separation close to trailing edge.

Low speeds - separation is moved forward, causing stall.

37
Q

3 types of Profile drag (parasite)?

A

Skin Friction drag
Form drag
Interference drag

38
Q

Skin friction drag

A

Caused by friction of fluid against the surface of an object.

Reduced by smoothing the surfaces and polishing.

39
Q

Transition point

A

Point where laminar turns to turbulent

40
Q

Form drag

A

Also known as pressure drag.

Separation of the boundary layer from a surface and the wake created by the separation.

Reduced by streamlining (fairings).

50% of total drag.

41
Q

Interference drag

A

Caused by the mixing of airflow streams between airframe components e.g. wing and fuselage.

Reduced by using fairings and fillets.

42
Q

Drag coefficient

A

Lower drag coefficient means less drag

43
Q

Induced drag

A

Where high pressure below and low pressure above meets at the wing tip causing vortexes producing drag.

Larger the lift, larger the pressure difference meaning greater vertexes.

Proportional to lift, inversely proportional to the square of speed.

44
Q

Induced downwash

A

Effect of vortex deflects air downwards creating additional downwash.

Increased downwash at trailing edge reduces angle of attack reducing lift.

45
Q

Span effect

A

Higher the aspect ratio, less induced drag.

Greater the cord length at wing tip the more intense the vortex becomes.

46
Q

Induced drag and lift

A

As angle of attack increases the induced drag increases

47
Q

Profile drag and induced drag in relation to speed

A

Profile drag increase with speed.

Induced drag decreases with speed.

48
Q

Wave drag

A

Retards forward movement of the plane.

Caused by the formation of shock waves.

49
Q

Does an aerofoil produce more lift or drag

A

Produces more lift many times greater than drag.

50
Q

Angle of attack will cause…

A

Centre of pressure to move forward
Transition point to move forward
Separation point to move forward
Stagnation point to move down and aft

51
Q

When does windspeed move quicker? (Pressure)

A

Low pressure

52
Q

Symmetrical vs cambered (centre of pressure?

A

Symmetrical remains constant

Cambered varies with angle of attack

53
Q

Centre of pressure in terms on location?

A

Small angles of attack 40-50% of chord, doesn’t exceed 25%.

Moves forward as angle of attack increase but rapidly moves back when stalling.

54
Q

Stalling angle?

A

16 degrees

55
Q

Dynamic pressure formula?

A

1/2 pV^2

56
Q

At zero angle of attack (Cambered vs Symmetrical), lift?

A

Cambered produces some lift and some drag.

Symmetrical produces no lift but some drag. (Stalls at a higher angle of attack)

57
Q

How to maintain altitude with decreasing air density?

A

Increase angle of attack

Increase airspeed

58
Q

What happens to the camber and AOA when flaps are deployed?

A

They’re both increased

59
Q

What happens to camber and AOA when leading edge slats are deployed?

A

Camber is increased

AOA is decreased

But when the slats are deployed with the flaps they increase AOA

60
Q

Lift/drag ratio

A

Steady increase up until 4 degrees
(Most amount of lift with least amount of drag also known as the optimum angle of attack).

Deteriorates up until 15 degrees then it stalls.

61
Q

Polar curves

A

Coefficient of lift vs coefficient of drag

62
Q

Can vortexes generate lift?

A

Yes, the energy in a vortex’s can be extremely high

63
Q

How does a stall happen?

A

When airflow has broken away from most of the upper surface.

64
Q

Where does the separation point move as AOA increases?

A

Starts at trailing edge and progressively moves forward.

65
Q

What does stall depend on?

A

Only on AOA

66
Q

How to maintain level flight with heavy aircraft?

A

Amount of lift must be equal to weight.

Increase AOA.

It will therefore stall at a higher airspeed.

67
Q

Load factor

A

Total lift over aircraft weight.

Ratio of load acting on aircraft during a manoeuvre vs straight and level flight.

68
Q

Stalls during manoeuvres due to an increased load factor?

A

Accelerated stall

69
Q

How to maintain altitude on low density?

A

AOA is increased.

Higher airspeed.

70
Q

What happens if speed increases past mach number?

A

Cause a stall due to shockwaves

71
Q

Coffin corner

A

Altitude where stall speed is equal to critical Mach number

Module 8: Aerodynamics (2 decks)

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