POF Flashcards
A symmetrical aerofoil has a mean chord line that is ______
Straight
AoA of an aerofoil is measured between the mean chord line of the aerofoil and the ______
Relative AF
What are the characteristics of the fully articulated rotor head
They are extremely complex and heavy
The freedom of movement provided my mechanical
Characteristics of rigid main rotor head
Simple design, cheaper
Uses flexible structures to allow blade movement in one or more directions
Characteristics of teetering main rotor head
Simple design
Prone to mast bumping
The manufactured twist in rotor blades to distribute lift is called:
Washout
Asymmetrical aerofoil rotor blade can be described as_____
Having a curved mean chord line
A vector differs from a line as it has both
Direction and magnitude
The angle between chord of aerofoil and relative airflow is termed ______
Angle of attack
Elaborate the lift equation terms
Cl= coefficient of lift
S=wing surface area
p= air density
V = wing speed over aerofoil
Angle of attack is between aerofoil chord line and ______
Relative Air Flow
Rotor disc is best described as
Circular area swept by the main rotors
Relative Airflow vector is made up of______
Rotational airflow
Induces Flow
Increasing the rotor speed will _____ the amount of lift
Increase
Will a wider or thinner blade of equal length create the most lift?
Wider
Will a helicopter at sea level generate equal lift to helicopter at 28,000ft
No (air density)
Induced flow is caused by drawing air from _____ the rotor
Above
The combination of IF and rotational AF creates _____
RAF
The path described by the tips of the rotor blades during rotation is the _____
Tip path plane
TR is the vector or rotor thrust and
Rotor drag
The force opposing rotor drag is?
Torque
The ability of a wing to provide lift increases with_____ until ______ is reached
Angle of attack
To lift off the ground TRT must be ____ all up weight (AUW)
Greater than
In the BVD when IF increases the AoA _____. Why?
Decreases
The RAF vector changes position the lessen the angle between RAF and chord line
HIGE requires less power as the IF vector is reduced which _____ the AoA, hence creating more lift
Increases
4 factors that effect the amount of HIGE
Height above ground, weight, wind and nature of surface
Recirculated air is likely to be induced when the ACFT is ____
Hovering near:
- building,
- solid fences,
- cliff faces,
- near other helicopters
- over long grass
Reduced power required to hover due to ground effect is experienced at ______
Half rotor diameter
Recirculation causes a reduction in lift generated due to an ______ in the IF vector
Increase
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
4 factors
Ligma
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
ETL causes the ACFT to ______
Balloon
As the helicopter transitions and accelerates, what aerodynamic structure helps compensate the ACFTs tendency to pitch nose down?
The horizontal stabiliser
Induced Flow Roll is exhibited at slow speed due to?
Difference in magnitude of the IF experienced by portions of the rotor disc
IFR is due to the IF experienced by the front half of the rotor being ____ then the back
Less
During flapback the advancing blade flaps _____ and the retreating blade flaps _____
Up
Down
Order of forward flight transition effects
1) initial height loss
2) flapback and IFR
3) ETL
4) Torque reduction
Source of low frequency lateral vibs
Main rotor blades out of balance
Low freq vertical vibes cause
Rain rotor blades out of track
Medium freq vibration due to?
Downwash from main rotor impinging on the structure
High frequency vibes due to
Engines, gearbox and hydraulic pumps
To dampen vertical vibrations the the rotor system and dampening mass vibrate with the same frequency but _____
180• out of phase
Parasite Power is?
The power required to overcome parasite drag
Power available is?
The maximum power the engines can deliver under particular conditions
Power required is:
The power required to climb,hover, accelerate, turn or maintain speed at a AUW in particular conditions
When does over pitching occur?
When collective pitch is applied to the rotor blades without having sufficient engine power to overcome increased rotor drag
Density altitude is pressure altitude adjusted for _____
Temperature
Over pitching will result in ______
RPM decay until collective lowered
What unit disconnects to allow rotors to spin freely?
Free wheeling
Instead of IF during autorotations we have _____ airflow moving through rotor system
Rate of descent
Why does forward auto rotations have reduced RoD
- Forward airspeed increases descent airflow
- which increases AoA
-which increases TRT
-which reduces RoD
3 benefits of flare
- decelerates
- increases thrust
- increases rotor RPM
Dead man’s curve depicts flight regimes to avoid relative to
Height and airspeed
Stability is classified as either? Subcategories
Dynamic or static
Positive (stable), neutral or negative (unstable)
An ACFT that returns to it original attitude after being disturbed is said to be statically _____
Stable or have positive static stability
An ACFT that remains in its new attitude after being disturbed is said to be statically ____
Neutral or have neutral static stability
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
Lateral, longitudinal and directional stability is stability in
Lat: roll
Long: pitch
Directional:yaw
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
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
What are the 3 stability aids on the EC135
- horizontal stabiliser
- vertical stabiliser
- automatic flight control system
Retreating blade stall would be exhibited in the EC135 by?
Nose pitching up
Roll to the left
What factors can lead to RBS
High forward speed
AUW
HIGH DA
excessive movements
High G manoeuvres
Turbulence
Ground resonance occurs primarily with _____ rotor heads
Fully articulated
Helicopters with a _____ undercarriage are more prone to ground resonance
Wheeled
3 areas contributing to ground resonance
- rotor systems
- landing gear
- construction of landing platform
Static roll over angle
45•
Static roll over occurs when___
CoG moves outside base of support
Conditions for static roll over
-slope
-soft ground/undercarriage sinks
-undercarriage failure
-structure failure of landing platform
- ship exceeds critical roll angle
For dynamic roll over to occur the rotors must be ____ and generating _____ and have a wheel or skid _____
Turing
Lift
Fixed to ground
Recovery from dynamic roll over
Lower collective
Balance/level the rotor disk
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
Symptoms of vortex ring state
- vibes
- pitching rolling
-Fluctuating power and torque - decrease in flight controls
- rapid descent
- random yawing
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
Recovery from VRS
Increase forward air speed THEN increase collective. Can enter auto rotation if you have the height
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
Main Rotor Vortex Intefernce is most likely to occurs in which position?
10-11 o’clock
How to counter loss of tail rotor effect
- don’t initiate
- gently use pedals to turn
- be prepared for tail “Flick”
