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M8 > M8.2 > Flashcards

M8.2 Flashcards

1
Q

Why is the air in the subsonic region incompressible?

A

Because the flying body does not reach the speeds necessary

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2
Q

What is the continuity equation?

A

V1A1=V2A2

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3
Q

What is a jet outlet?

A

When the diameter decreases and the speed increases

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4
Q

What is a diffuser jet?

A

When the diameter increase the speed decreases

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5
Q

What is Bernoulli’s principle?

A

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

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6
Q

What is the point of stagnation?

A

The speed of airflow falls to zero and the static pressure equals the total pressure.

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7
Q

What happens in the Venturi tube?

A

The velocity increases and pressure decreases as the cross sectional are decreases

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8
Q

What is up wash?

A

When some streamlines approaching the edge in the low position slope upwards and pass on top of the aero foil

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9
Q

What is down wash?

A

Some streamlines of the upper surface flow downwards when leaving the aero foil

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10
Q

What is the Magnus effect?

A

Mechanically induced circulation

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11
Q

What is a profile?

A

The cross-section of a wing

Sometimes call an aerofoil section

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12
Q

What is the chord line?

A

This is a straight line connection the leading edge and the trailing edge

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13
Q

What is the mean chamber line?

A

Is a line drawn halfway between the upper and lower surfaces of the profile

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14
Q

What is the chamber of the profile?

A

It is the displacement of the mean camber line from the chord line

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15
Q

What is the fineness ratio?

A

The maximum thickness of a profile is defined as a fraction or a percentage of the chord

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16
Q

What is the flight path velocity?

A

It is the speed of the aircraft in a certain direction through the air

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17
Q

What is the relative wind?

A

It is the speed and direction of the air acting on the aircraft which is passing through it

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18
Q

What is the angle of attack?

A

The angle between the chord line of the profile and the relative wind
(Signified by alpha a)

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19
Q

What is the angle of incidence?

A

It is the angle between the chord line of the profile and the longitudinal axis of the aircraft
(Signified by gamma Y)

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20
Q

How do you work out the wing area?

A

Wing span x the wing chord

if the wings are tapered then take an average wing chord

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21
Q

What is the aspect ratio?

A

It is the wing span divided by the average chord

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22
Q

What is the taper ration?

A

It is the chord tip divided by the chord root

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23
Q

What is the average chord?

A

It is the geomatics average of all the chords

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24
Q

Does a higher or lower aspect ratio cause more drag?

A

Lower aspect ratio has more drag

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25
Q

What is the sweep angle?

A

It is the angle of the wings taken from 25% of the wing

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26
Q

What is the dihedral angle?

A

It is the angle between the wing and the horizontal line of the aircraft

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27
Q

What is a positive and negative dihedral?

A

-Positive is when the wings point upwards -negative is when the wings point downwards

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28
Q

What is the finesses ratio?

A

The ratio between thickens and length of a profile

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29
Q

What is centre pressure?

A

This is where all forces on a profile connect

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30
Q

What four things affect lift and drag?

A
  • dynamic pressure
  • surface area
  • shape of profile
  • angle of attack
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31
Q

Why is calculating lift difficult?

A

The profile has different pressure due to different aircraft area

(Must use a wind tunnel)

32
Q

What is interference drag?

A

Is the turbulence in the airflow caused by sharp corners which comes from parts being added together
(Can be reduced by fairings)

33
Q

Where does compressible drag occur?

A

Transonic and supersonic

34
Q

How is compressible drag caused?

A

By shock waves on an aircraft approaching the speed of sound

35
Q

When is static pressure at the highest point

A

Point of stagnation where the air comes to a stop

36
Q

At what points do we have maximum air velocity and minimum static pressure

A

Point near maximum thickness of the profile

37
Q

What is aerodynamic force

A

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

38
Q

What four factors does lift and drag depend on:

A
  • Dynamic Pressure
  • Surface Area
  • Shape of profile
  • Angle of attack
39
Q

What are the four wing types?

A
  • elliptical
  • rectangular
  • tapered
  • swept
40
Q

What are the two types of wing design?

A
  • geometrically twisted wing

- aerodynamically twisted wing

41
Q

What is the difference between the two types of wing designs?

A

Geometrically twisted:
-the camber is constant across the span
-angle of incidence is greater at the root than tip
-chord lines are not parallel
Aerodynamically twisted:
-the camber is greater at the root than the tip
-angle of incidence is constant across the span
-chord is parallel

42
Q

What does Mean aerodynamic chord (MAC) mean?

A

It is the chord line through the centre of its lift

43
Q

How do you work out theoretical lift?

A

0.5 x density x velocity^2 x area

44
Q

How do you work out the coefficient lift?

A

Measured lift/Theoretical lift

same for coefficient drag

45
Q

What is alpha max?

A

The maximum angle to get the most lift before stall is created

46
Q

What will a high camber produce?

A

It will have a much higher coefficient of lift at the zero angle of attack

47
Q

What is a polar diagram (Lilienthal Diagram)?

A

It is a diagram that compares the coefficient of lift and coefficient of drag to give information about the performance of the profiles

48
Q

What are the three main types of drag?

A
  • Induced drag (Lift)
  • Parasite drag (Form, Friction, Interference)
  • Compressible drag (Shockwaves)
49
Q

What is induced drag

A

Drag on the wing caused by lift

50
Q

What is parasite drag?

A
  • drag caused by the distribution of pressue
  • drag caused by skin friction
  • aerodynamic interference
51
Q

What is compressible drag?

A

Drag caused by shock waves on an aircraft approaching the speed of sound

52
Q

What causes wing tip vortex’s?

A

Wing tip vortex’s are caused by turbulence at the wing tips

53
Q

How do wing tip vortex’s affect the aircraft?

A

The turbulence absorbs energy and increases drag

54
Q

What type of drag are wing tip vortex’s?

A

Induced drag

55
Q

What direction do the streamlines go when they go over the wing profile?

A

They go over and then head inwards towards the fuselage

Outward if under wing profile

56
Q

What is used to reduce wing tip vortex’s?

A

Winglets or a wing tip fence

57
Q

What is a bound vortex?

A

It is the circulation of up-wash and down-wash

58
Q

What is trapped (retarded) air called?

A

The boundary layer

59
Q

What does the boundary layer do to the streamlines?

A

It slows down the layer above it which slows the layer above that and so on until the free stream velocity is restored

60
Q

What are the two basic boundary layers?

A
  • laminar boundary layer

- turbulent boundary layer

61
Q

What happens to the layers of air in the laminar boundary layers and the turbulent boundary layer?

A
  • In the laminar boundary layer they do not move from layer to layer
  • in the turbulent boundary layer they move from layer to layer (produces an exchange of energy)
62
Q

Why is there a slot in a profile?

A

It transfers air with high energy from the lower side to the upper side that gives trapped air energy to reduce air separation

63
Q

How much more drag is in the turbulent boundary layer compared to the laminar boundary layer?

A

3 times the amount

63
Q

What is the laminar boundary layer?

A

It is the immediate downstream of the leading edge

63
Q

What is the turbulent boundary layer?

A

The immediate downstream of the laminar boundary layer

64
Q

What is total drag?

A

Induced drag (Lift) and Parasite drag (Form, Friction, Interference)

65
Q

What happens if the centre of lift is equal to the centre of gravity?

A

The aircraft will have a steady level flight

66
Q

What happens when the centre of lift is in front of the centre of gravity?

A

The aircraft will point upwards

67
Q

What happens when the centre of lift is behind of the centre of gravity?

A

The aircraft will point downwards

68
Q

What happens when the root of the wing stalls?

A

The centre of lift on the wing heads to the wing tips which puts it behind of the centre of gravity this puts the nose down. A pilot input is not required

69
Q

What happens when the tips of the wing stalls?

A

The centre of lift on the wing heads to the root which puts it in front of the centre of gravity this puts the nose up. A pilot input is required

70
Q

What type of stall is the most dangerous?

A

Wing tip stall

71
Q

What does a small aircraft use to prevent wing tip stalling?

A

A stall strip (it also disturbs lift)

72
Q

What does a large aircraft use to prevent wing tip stalling?

A

Slats

73
Q

What is the job of a wing fence or saw-tooth wings?

A

They keep air particles going in a straight line by reducing the effects of span-wise flow (when air flows on the wing and towards the span)

74
Q

What is a vortex generator?

A

It is a small blip on the wing that is used to improve boundary layer control

M8 (4 decks)

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