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CAT B- Mod 8 Aerodynamics > 8.3- Theory of Flight > Flashcards

8.3- Theory of Flight Flashcards

1
Q

How does an aircraft overcome the effects of gravity?

A

Producing a lifting force greater than or equal to its weight.

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2
Q

What are the four fundamental forces?

A

Lift
Drag
Weight
Thrust

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3
Q

Why is force a vector quantity?

A

Because it has magnitude and direction.

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4
Q

What is the weight of the aircraft?

A

The weight of the aircraft is the gravitational pull of the earth acting on the aircraft’s mass.

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5
Q

What is the centre of mass?

A

Location at which the aircraft would remain balanced if suspended from that point.

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6
Q

What is lift?

A

A force vector which acts perpendicular to the direction of flight.

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7
Q

How is drag overcome?

A

Thrust force of the engines.

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8
Q

What is the total aircraft drag proportional too?

A

Square of the aircrafts flying velocity

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9
Q

What is the glide ratio?

A

The ratio of distance forward to the distance down.

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10
Q

What effect does weight have on the glide ratio?

A

It only effects the time the aircraft will glide for.

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11
Q

If two aircraft have the same Lift-to-Drag ratio but weigh differently, and begin a glide from the same altitude, the heavier aircraft gliding at a higher airspeed arrives where?

A

The same touch down point but sooner.

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12
Q

What is used to calculate the best glide ratio?

A

The lift to drag ratio and polar diagrams.

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13
Q

What is the optimum angle of attack?

A

4 degrees

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14
Q

What dictates the lift drag ratio for an aircraft?

A

Its role

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15
Q

What is the lift drag ratio of a glider?

A

Between 25 and 60

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16
Q

What is a larger aircrafts lift drag ratio?

A

12-20

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17
Q

What is a small piston aircrafts lift drag ratio?

A

10-15

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18
Q

In steady flight what is the sum of all the forces?

A

0

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19
Q

Where in the aircraft does lift and drag act?

A

Centre of pressure.

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20
Q

Where does the thrust act on an aircraft?

A

Parallel to the aircrafts longitudinal axis.

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21
Q

What is the moment value equal too?

A

Force x moment arm

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22
Q

What is the moment arm?

A

Shortest distance between the point of rotation and the line of action of the force.

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23
Q

What causes the centre of pressure on the wing to move?

A

When the angle of attack is altered.

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24
Q

How can the pitching moment be measured?

A

Experimentally by direct measurement on a balance or by pressure plotting.

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25
Q

What is the aerodynamic centre?

A

The centre of pressure and gravity where coefficient of lift is highest… often 25% of the chord from leading edge.

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26
Q

What is key about the aerodynamic centre?

A

It is a fixed point.

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27
Q

What are some of the factors effecting performance?

A

Take off and landing distance
Rate of climb
Ceiling
Payload
Range
Speed
Manoeuvrability
Stability
Fuel economy

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28
Q

What causes parasite drag to increase?

A

Speed

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29
Q

Why is total drag high at low speed?

A

High induced drag

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30
Q

What is the difference between power and thrust?

A

Thrust is a force or pressure exerted on an object.

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31
Q

Which part of flying is the aircraft potential energy?

A

Aircraft position

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32
Q

What happens to power with an increase of altitude?

A

It decreases.

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33
Q

What is specific range?

A

The NM of flying distance vs the amount of fuel consumed.

34
Q

What three factors effect specific range vs speed?

A

Aircraft weight
Altitude
Aerodynamic config

35
Q

What is banking?

A

Makes the aircraft turn caused by the ailerons.

36
Q

What is the force that pulls the aircraft from a straight flight path to make a turn.

A

Horizontal component of lift (centripetal).

37
Q

What is the equal and opposite reaction of the horizontal component of lift?

A

Centrifugal.

38
Q

What would happen if the angle of bank were held constant and the angle of attack decreased?

A

The rate of turn would decrease.

39
Q

How is equilibrium between the horizontal lift component and centrifugal force re-established?

A

By either decreasing the bank, increasing the rate of turn or a combination of the two.

40
Q

What does a skidding turn result in?

A

Excess centrifugal force pulling the aircraft to the outside of the turn.

41
Q

What happens in a slipping turn?

A

The aircraft is not turning at the required rate, its banked too much meaning the horizontal lift component is greater than the centrifugal force.

42
Q

At 400mph what angle must an aircraft be banked at to turn 3 degrees per second?

A

44 degrees

43
Q

At bank angle of 44 degrees what percentage of the lift of the aircraft compromises the vertical component of lift?

A

79%

44
Q

What is the load factor?

A

The ratio of lift to it weight.

45
Q

What unit is given too load factor?

A

g

46
Q

What does load factor 3 mean?

A

Total load felt on the aircraft is 3 times its weight.

47
Q

What is a limit load factor?

A

The force that an aircraft structure must be able to withstand for safety reasons.

48
Q

How is load factor worked out?

A

Lift divided by weight

49
Q

At zero degrees of bank angle what is the load factor?

A

1

50
Q

At 45 degrees of bank what is the load factor?

A

1.41

51
Q

At 60 degrees of bank what is the load factor?

A

2

52
Q

At 70 degrees of bank what is the load factor?

A

3

53
Q

At 75 degrees of bank what is the load factor?

A

4

54
Q

A study of the effect that load factor has on aircraft revealed what?

A

That an aircrafts stall speed increases in proportion to the square root of the load factor.

55
Q

What is a V-n diagram?

A

Plots load factor against Equivalent airspeed (EAS)

56
Q

What are some of the adverse effects of an aircraft flying above its limit range?

A

Destructive flutter, aileron reversal and wing divergence.

57
Q

What does a lower amount of g loading lead too?

A

Metal fatigue.

58
Q

What is an aeroelastic limit?

A

Defines the max operating speeds in both knots, airspeed and indicated mach number.

59
Q

What is aeroelasticity?

A

The interaction between the inertial, elastic and aerodynamic forces that occur when a body is exposed to fluid flow.

60
Q

What is redline airspeed?

A

Aeroelastic limit.

61
Q

What is the ultimate structural limit compared to the structural limit?

A

150%

62
Q

What are lift augmentation systems?

A

Devices installed on wings to produce lift.

63
Q

What are the principle lift augmentation devices?

A

Flaps
Slats and slots
Boundary layer control

64
Q

What is a plain flap?

A

Hinged flap, providing 50-55% increase in the maximum lift.

65
Q

What is a split flap?

A

Upper and lower section of trailing edge, lower is the flap, provides 60-65% increase.

66
Q

What is a slotted flap?

A

Similar to a plain flap, but with a gap to reduce flow separation. Single slotted provides 65-70% whereas multi slotted provides 70%.

67
Q

What is a fowler flap?

A

Used on modern aircraft. Provides 95% at 15 degrees.

68
Q

What is the issue with leading edge devices?

A

They cause a increase in the stalling angle.

69
Q

What is a krueger flap?

A

Deploy down and forwards, found on swept wing airliners.

70
Q

What is LE cuff?

A

They are fixed aerodynamic cuffs.

71
Q

What are slats?

A

Small auxiliary aerofoil that can be extended forward.

72
Q

How do slats prevent flow separation?

A

They supply more energy to the boundary layer.

73
Q

How is the boundary layer re-energised by slats?

A

The added camber increases the air velocity over the upper surface and this is assisted by the flow from lower to upper through the slot.

74
Q

What is a slot?

A

Similar to a slat but fixed.

75
Q

How much does a slot increase the max lift coefficient?

A

40%

76
Q

What are vortex generators used for?

A

Help control the boundary layer by adding kinetic energy from the high energy free stream air into the lower energy boundary layer.

77
Q

What is adverse pressure gradient?

A

The pressure decreases before and up to the centre of lift the after it increases again.

78
Q

What is a winglet?

A

Small upturned structure at the end of the wings.

79
Q

How do winglets prevent loss of lift due to vortex’ at the tip of the wing?

A

The vortex of induced drag is torn apart and distributed vertically.

80
Q

What do winglets do due to the relative wind?

A

Bend towards the fuselage.

81
Q

What are the benefits of winglets?

A

Reduced fuel consumption
Increased range
Improved performance
Lower emmisions

CAT B- Mod 8 Aerodynamics (4 decks)

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