Deck 1 Flashcards
What are the 4 main helicopter configurations
Single rotor with Tail rotor
Tandem rotor
Contra-rotating rotor
NOTAR
What are the 4 pilots controls
Collective pitch lever
Cyclic pitch column
Yaw pedals
Throttle
What 5 control systems are used to control throttle
Manual
Hydro-mechanical
ESU
FCU
FADEC
What are the 4 types of rotor head
Teetering
Fully Articulated
Semi-Rigid
Rigid(theoretical)
How does a teetering rotor head operate
Two blades rigidly connected by coning hinges, held by a teetering hinge. A weighted bar below the rotor aids in stability and automatically corrects unwanted tilt of the rotor.
What 3 hinges are present on a fully articulated rotor head and what do they do
Flapping hinge - allows the blade to move vertically about the hinge to relieve stress
Dragging hinge - allows the blade to move horizontally through the plane of rotation
Feathering hinge - allows blade to change pitch
What restrainers are there and what do they do
Droop restrainer - limits droop of blade when at low rpm or stationary
Flapping restrainer - stops blade from flapping violently when at low rpm or stationary
How does a fully articulated rotor head work
Allows the rotor blades to rotate about 3 hinges to reduce stress in all axis
How does a semi rigid rotor head work
Has a cruciform shaped rotor head where there is only a feathering hinge. Requires high strength materials such as titanium
What is the tip path plane
The perimeter of the area in which the main rotors spin, as viewed from above
What is the axis of rotation
The point in the rotor head about which the blades spin
What is the rotor disk?
Area marked by the tip path plane
What is the coning angle
Angle between the tip path plane and the rotor head
What are the 3 constants of a coning angle
-Will vary when RRPM and rotor thrust vary
-If rotor thrust is increased but RRPM stays the same, blades will cone upwards
-If RRPM is reduced but thrust stays the same, blades will cone upwards
What is over pitching
Extra application of pitch to the rotor blades without sufficient engine power to compensate for the extra drag
Describe a vertical climb
Collective pitch lever raised
Pitch and thrust increased
Increase in TR and rotor drag
More engine power required
TRT will overcome the weight force + drag and take off
What are the 7 factors affecting max forward speed
Compressibility of advancing blade tip
Retreating blade tip stall
Air reversal on retreating blade root
Altitude
Structural limitations
Cyclic limitations
Power availability
Weight
What is ground effect?
Hovering a helicopter at 50-100ft will cause a downwash of air to collide with the ground and escape to horizontally, causing an increase in pressure below the rotor disc
Describe vertical descent
Collective lowered
Angle of attack on all blades will reduce and so will total thrust
Aircraft will begin to accelerate vertically downwards
Opposite airflow will cause AoA to increase
Rate of descent becomes steady at 4•
What 4 factors affect the ground affect
Height
Slope
Nature of ground
Wind
What components are involved in horizontal movement
Vertical and horizontal
What is tail rotor roll and how can it be avoided
When the tail rotor thrust acts above or below the side thrust from the main rotor, causing the helicopter to hover/skid to one side. This can be avoided by setting the tail rotor in line with the main rotor
What is a fenestron
The the aerofoil shape on the vertical stabiliser on the gazelle helicopter that encloses the tail rotor, and aids in anti-torque forces
How does a NOTAR work
Uses an engine driven fan to force air under pressure through a hollow tail boom and out of a grille creating opposing force to TR
What are the 3 causes of drag
Coriolis effect
Hookes joint effect
Periodic drag changes
What is the coriolis effect
Fluctuation of speed of the blades is allowed by a dragging hinge
What is hookes joint effect
Movement of blades to reposition themselves relative to others following cyclic input
What are drag dampers
Drag dampers control the drag movement of blades and stop excessive swinging and absorb and shock loads
What types of drag dampers are there
Elastomeric
Hydraulic
Friction pads
What is phase lag / gyroscopic precession
Where the output from cyclic or collective is felt 90 degrees after the input
What is a swash plate / star plate
The still plate and rotating plate above it that connect to the pilots controls and the rotor blades to change the pitch of the blades
What is flapping to equality
When blades being pitched by different amount last naturally flap back and equalise the lift on the rotor disk.
The descending blade will increase its AoA and raise, the ascending blade will lower its AoA and will drop
What is flapback
When the cyclic is pushed forward, the retreating and advancing blades experience dissymmetry of lift and the rotor disc will try to level out. To compensate for this the cyclic must have an increased input
What factors affect maximum forward speed
Reversal of Airflow over blade root
Retreating blade stall
Compressibility of advancing blade
Cyclic limits
Power available
Blade pitching
Structural limits
What are the 4 methods of increasing max forward speed
Swept blade tips
Compound helicopters
ABC rotor
BERP blades
What are BERP blades made from
Glass and carbon fibre, with erosion shields made from titanium and nickel
What is the flare manoeuvre
Cyclic stick moved backwards during forward flight to decelerate and and increase total rotor thrust and an increase in RRPM
What is autorotation
The automatic rotation of the rotor head and blades without engine input to allow toe helicopter to descend without falling out of the air. Controlled crash
What is the minimum height from which to auto rotate
400ft
What is ground resonance
The violent undampened vibration of the aircraft on contact with the ground
What are the 4 rotor causes of ground resonance
Faulty dampers
Faulty tracking
Blade imbalances
Nr effect
What are the 5 non rotor causes of ground resonance
Pilot mishandling
Rough taxiing
Incorrect tire pressures
Incorrect oleo pressures
Troops disembarking
How can a pilot recover from ground resonance
Immediate take off if RRPM permits
Change RRPM
Shut down, lower collective, shut down engine and apply rotor brake
What conditions will lead to a vortex ring
More than 20% available power supplies to rotors, Be descending at 300ft and little to no engine power
May occur during flare manoeuvre at 500ft/min through 30 knots
How would you recover from vortex rings
Disengage engine and autorotate
Lower collective and push cyclic forward
Vuichard manoeuvre
What is rotor profile power
Power required to drive the rotors at a set RRPM for a minimum collective setting along with all ancillaries
What is induced power
Power required to induce flow through the disc
What is parasite power
Power required to overcome the form drag of the rotors
