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PPL Principles of Flight > Stability > Flashcards

Stability Flashcards

1
Q

Which pair of forces are greater in the magnitude than the other?

A

Lift/Weight

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2
Q

If CP is behind the CG, what pitching motion occurs?

A

Nose-down

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3
Q

If CP is in front of the CG, what pitching motion occurs?

A

Nose-up

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4
Q

If the drag line is above the thrust line, what pitching motion occurs?

A

Nose-up

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5
Q

If the drag line is below the thrust line, what pitching motion occurs?

A

Nose-down

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6
Q

In a standard designed aircraft, what moment does the thrust-drag couple have?

A

Nose-up

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7
Q

In a standard designed aircraft, what moment does the lift-weight couple have?

A

Nose-down

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8
Q

Function of the tailplane?

A

To counteract the residual pitching moments from the two main couples

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9
Q

Why is the area and size of the tailplane small compared with the mainplanes?

A

Its moment arm is long so can provide significant pitching effect

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10
Q

Generally, where does the CP and CG lie relatively?

A

The CP is behind the CG

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11
Q

Generally, what aerodynamic force does the tailplane provide?

A

Downwards

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12
Q

What does stability refer to?

A

Natural ability of aircraft to return to its original condition

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13
Q

The natural ability of aircraft to return to its original condition after being disturbed is given what term?

A

Stability

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14
Q

What is the trade-off for stability?

A

Controllability

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15
Q

A highly controllable aircraft will possess poor…?

A

Stability

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16
Q

An aircraft in trim is different from the state of equilibrium how?

A

Its pitch, roll and yaw moments are zero, not the aerodynamic forces or turning moments

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17
Q

Movement around the longitudinal axis is known as…

A

Rolling

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18
Q

Rolling’s axis

A

Longitudinal axis

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19
Q

Stability around the longitudinal axis is known as?

A

Lateral stability

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20
Q

Lateral stability is related to what motion?

A

Roll

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21
Q

Movement around the lateral axis is called?

A

Pitch

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22
Q

Pitch’s axis?

A

Lateral axis

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23
Q

Stability around the lateral axis is known as?

A

Longitudinal stability

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24
Q

Longitudinal stability is related to what motion?

A

Pitch

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25
Q

Movement about the normal axis is known as?

A

Yaw

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26
Q

Yaw’s axis

A

Normal axis

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27
Q

What is the third axis alongside the lateral and longitudinal axis?

A

Normal axis

28
Q

Stability around the normal axis is known as?

A

Directional stability

29
Q

Directional stability is related to what motion?

A

Yaw

30
Q

Rotation around a point or axis is called?

A

Angular motion

31
Q

The speed at which rotation occurs around a point or axis is called?

A

Angular velocity

32
Q

The number of degrees that rotation occurs by is called?

A

Angular displacement

33
Q

What is the key term used when discussing a rotation around a point or axis?

A

Angular

34
Q

A body that returns to its original position after being disturbed is said to possess….

A

Static stability

35
Q

A body that does not return to its original position after being disturbed is said to possess….

A

Dynamic stability, dynamic instability or neutral dynamic stability

36
Q

Neutral dynamic stability is when what remains constant?

A

Amplitude and period of oscillation

37
Q

If the departure of a body from its original position increases over time, it is said to have

A

Dynamic instability

38
Q

A nose-up disturbance results in a nose-down moment how?

A

Greater AoA on tailplane
Tailplane rises and nose falls

39
Q

What aircraft part provides the greatest contribution to longitudinal stability?

A

Tailplane

40
Q

Relation of CG position and turning effect of tailplane

A

Further forward the CG, the greater the moment arm of the tailplane

41
Q

High AoA are detrimental to longitudinal stability in what way?

A

High AoA may shield the tailplane or cause turbulent airflow and reduce tailplane effectiveness

42
Q

What aircraft part provides the greatest contribution to directional stability?

A

Vertical fin

43
Q

During a sideslip or yawing motion, a vertical fin experiences what to provide it with directional stability?

A

AoA

44
Q

What power-related force can affect a fin’s effectiveness as a vertical stabiliser?

A

Propeller slipstream

45
Q

A dihedral means the lower wing in a turn will experience what?

A

A greater AoA than the upper wing so there is a lift imbalance and a rolling moment is produced

46
Q

What is a negative dihedral called?

A

Anhedral

47
Q

High keel surfaces correct disturbances in roll how?

A

Their high position with a lower CG will create a restoring moment

48
Q

Dihedral helps increas what in roll?

A

AoA on lower banked wing

49
Q

In roll, what is essential for lateral stability to work?

A

Sideslip

50
Q

Directional stability in a roll means the aircraft will…

A

Yaw its nose into the relative airflow

51
Q

An aircraft is in a roll and yaws its nose into the relative airflow. What has ocurred?

A

Sideslip has exerted a force on the keel surfaces and given it directional stability

52
Q

Directional stability essentially points an aircraft’s nose towards what?

A

Into the relative airflow

53
Q

In a roll, the greater the directional stability of an aircraft, the greater the..

A

Tendency to turn away from the original heading in the direction of the lower wing

54
Q

Relationship between directional stability strength and yaw

A

The greater the directional stability, the greater the yaw

55
Q

Why does the nose drop in a roll with good directional stability?

A

Outside wing is moving faster and generates greater lift

56
Q

What aerodynamic conflict occurs in a roll followed by yaw?

A

Directional stability wants to steepen the turn and drop the nose further
Lateral stability wants to level the wings

57
Q

What counteracting force occurs during a roll as directional stability steepens the turn?

A

Lateral stability uses the dihedral to level the wings

58
Q

Directional stability > lateral stability =

A

Spiral instability

59
Q

Directional stability < lateral stability =

A

Dutch roll

60
Q

Dutch roll is what experience?

A

Aircraft shows no tendency to turn in the direction of the sideslip

61
Q

In a yaw followed by roll, directional stability < lateral stability =

A

Significant yaw, sideslip and resulting banked turn away from sideslip

62
Q

In a yaw followed by roll, directional stability > lateral stability =

A

Sideslip towards lower wing occurs

63
Q

On the ground, a low-thrust line has effect in high-power situations?

A

Lower tendency to pitch onto its nose

64
Q

What two aerodynamic design features means crosswinds have a greater destabilising effect?

A

High keel surfaces
Dihedral

65
Q
A

PPL Principles of Flight (6 decks)

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