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POF Flashcards

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1
Q

A symmetrical aerofoil has a mean chord line that is ______

A

Straight

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2
Q

AoA of an aerofoil is measured between the mean chord line of the aerofoil and the ______

A

Relative AF

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3
Q

What are the characteristics of the fully articulated rotor head

A

They are extremely complex and heavy

The freedom of movement provided my mechanical

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4
Q

Characteristics of rigid main rotor head

A

Simple design, cheaper

Uses flexible structures to allow blade movement in one or more directions

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5
Q

Characteristics of teetering main rotor head

A

Simple design

Prone to mast bumping

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6
Q

The manufactured twist in rotor blades to distribute lift is called:

A

Washout

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7
Q

Asymmetrical aerofoil rotor blade can be described as_____

A

Having a curved mean chord line

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8
Q

A vector differs from a line as it has both

A

Direction and magnitude

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9
Q

The angle between chord of aerofoil and relative airflow is termed ______

A

Angle of attack

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10
Q

Elaborate the lift equation terms

A

Cl= coefficient of lift
S=wing surface area
p= air density
V = wing speed over aerofoil

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11
Q

Angle of attack is between aerofoil chord line and ______

A

Relative Air Flow

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12
Q

Rotor disc is best described as

A

Circular area swept by the main rotors

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13
Q

Relative Airflow vector is made up of______

A

Rotational airflow
Induces Flow

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14
Q

Increasing the rotor speed will _____ the amount of lift

A

Increase

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15
Q

Will a wider or thinner blade of equal length create the most lift?

A

Wider

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16
Q

Will a helicopter at sea level generate equal lift to helicopter at 28,000ft

A

No (air density)

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17
Q

Induced flow is caused by drawing air from _____ the rotor

A

Above

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18
Q

The combination of IF and rotational AF creates _____

A

RAF

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19
Q

The path described by the tips of the rotor blades during rotation is the _____

A

Tip path plane

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20
Q

TR is the vector or rotor thrust and

A

Rotor drag

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21
Q

The force opposing rotor drag is?

A

Torque

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22
Q

The ability of a wing to provide lift increases with_____ until ______ is reached

A

Angle of attack

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23
Q

To lift off the ground TRT must be ____ all up weight (AUW)

A

Greater than

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24
Q

In the BVD when IF increases the AoA _____. Why?

A

Decreases

The RAF vector changes position the lessen the angle between RAF and chord line

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25
HIGE requires less power as the IF vector is reduced which _____ the AoA, hence creating more lift
Increases
26
4 factors that effect the amount of HIGE
Height above ground, weight, wind and nature of surface
27
Recirculated air is likely to be induced when the ACFT is ____
Hovering near: - building, - solid fences, - cliff faces, - near other helicopters - over long grass
28
Reduced power required to hover due to ground effect is experienced at ______
Half rotor diameter
29
Recirculation causes a reduction in lift generated due to an ______ in the IF vector
Increase
30
IAW BVD how does recirculation impact TRT
As air passes through the system a second time the V increases As V increases so does IF and therefore a reduction in TRT
31
4 factors
Ligma
32
The increased rotor thrust due to forward speed during transition from hover to toward flight is refereed to as _____ and occurs at____
ETL - Effective translational lift 10-20k
33
ETL causes the ACFT to ______
Balloon
34
As the helicopter transitions and accelerates, what aerodynamic structure helps compensate the ACFTs tendency to pitch nose down?
The horizontal stabiliser
35
Induced Flow Roll is exhibited at slow speed due to?
Difference in magnitude of the IF experienced by portions of the rotor disc
36
IFR is due to the IF experienced by the front half of the rotor being ____ then the back
Less
37
During flapback the advancing blade flaps _____ and the retreating blade flaps _____
Up Down
38
Order of forward flight transition effects
1) initial height loss 2) flapback and IFR 3) ETL 4) Torque reduction
39
Source of low frequency lateral vibs
Main rotor blades out of balance
40
Low freq vertical vibes cause
Rain rotor blades out of track
41
Medium freq vibration due to?
Downwash from main rotor impinging on the structure
42
High frequency vibes due to
Engines, gearbox and hydraulic pumps
43
To dampen vertical vibrations the the rotor system and dampening mass vibrate with the same frequency but _____
180• out of phase
44
Parasite Power is?
The power required to overcome parasite drag
45
Power available is?
The maximum power the engines can deliver under particular conditions
46
Power required is:
The power required to climb,hover, accelerate, turn or maintain speed at a AUW in particular conditions
47
When does over pitching occur?
When collective pitch is applied to the rotor blades without having sufficient engine power to overcome increased rotor drag
48
Density altitude is pressure altitude adjusted for _____
Temperature
49
Over pitching will result in ______
RPM decay until collective lowered
50
What unit disconnects to allow rotors to spin freely?
Free wheeling
51
Instead of IF during autorotations we have _____ airflow moving through rotor system
Rate of descent
52
Why does forward auto rotations have reduced RoD
- Forward airspeed increases descent airflow - which increases AoA -which increases TRT -which reduces RoD
53
3 benefits of flare
- decelerates - increases thrust - increases rotor RPM
54
Dead man’s curve depicts flight regimes to avoid relative to
Height and airspeed
55
Stability is classified as either? Subcategories
Dynamic or static Positive (stable), neutral or negative (unstable)
56
An ACFT that returns to it original attitude after being disturbed is said to be statically _____
Stable or have positive static stability
57
An ACFT that remains in its new attitude after being disturbed is said to be statically ____
Neutral or have neutral static stability
58
An ACFT that continues to move away from its original attitude after being disturbed is said to be statically ______
Unstable or have negative static stability
59
Lateral, longitudinal and directional stability is stability in
Lat: roll Long: pitch Directional:yaw
60
What do vertical stabilisers do?
Assist by dampening yawing movements in the hover and forward flight Reduces power required for anti torque in forward flight
61
What do horizontal stabilisers do
Provide static stability in pitch and assist in dampening the pitching movements of the fuselage in response to wind gust Add to dynamic stability End plates aide in anti torque during forward flight
62
What are the 3 stability aids on the EC135
- horizontal stabiliser - vertical stabiliser - automatic flight control system
63
Retreating blade stall would be exhibited in the EC135 by?
Nose pitching up Roll to the left
64
What factors can lead to RBS
High forward speed AUW HIGH DA excessive movements High G manoeuvres Turbulence
65
Ground resonance occurs primarily with _____ rotor heads
Fully articulated
66
Helicopters with a _____ undercarriage are more prone to ground resonance
Wheeled
67
3 areas contributing to ground resonance
- rotor systems - landing gear - construction of landing platform
68
Static roll over angle
45•
69
Static roll over occurs when___
CoG moves outside base of support
70
Conditions for static roll over
-slope -soft ground/undercarriage sinks -undercarriage failure -structure failure of landing platform - ship exceeds critical roll angle
71
For dynamic roll over to occur the rotors must be ____ and generating _____ and have a wheel or skid _____
Turing Lift Fixed to ground
72
Recovery from dynamic roll over
Lower collective Balance/level the rotor disk
73
3 conditions for vortex ring state
- be in powered flight, generating IF -descending with rate of descent airflow -must be operating at a low forward airspeed
74
Symptoms of vortex ring state
- vibes - pitching rolling -Fluctuating power and torque - decrease in flight controls - rapid descent - random yawing
75
Flight situations that induce a Vortex Ring State
-pulling power during auto rotations - too steep and angle of approach -RoD increase in a low air speed descent -landing or operating at low toward speed in a downwind situation -allowing RoD to develop in a harshly executed quick-stop
76
Recovery from VRS
Increase forward air speed THEN increase collective. Can enter auto rotation if you have the height
77
Loss of Tail Rotor effectiveness (LTE) is generally caused by one of the three events. Name them
Weathercock effect Tail Rotor Vortex wind state Main rotor vortex interference
78
Main Rotor Vortex Intefernce is most likely to occurs in which position?
10-11 o’clock
79
How to counter loss of tail rotor effect
- don’t initiate - gently use pedals to turn - be prepared for tail “Flick”

POF pp Qs (1 decks)

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