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Define Airfoil
Coverts the movement of air over its surface into a force useful for lift
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Define Lift
Force produced by airfoil, perpendicular to relative windand opposes graviety
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Define Drag
force acting on a body and opposite to relative wind. resistenace of the atmosphere to the motion of the aircraft
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Define Thrust
Force developed by the rotor bllades, parallel to relative wind, opposes weight and drag
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Define Chord
distance from leading edge to trailing edge
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Define Span
Distance from root of blade to tip
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Define angle of attack
Angle of Chord relative to the relative wind
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Define relative wind
opposes direction of airfoil movement
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Define Stall
When the angle of attack is exceeded, to low of airspeed
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Define Centre of Pressure
the point on the airfoil where lift is produced
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Define Pitch angle
The angle the blade is making to a reference point
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What causes Coning
Lift and centifugal force or weight
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What controls Vertical movement
and how-collective, changes blade pitches equally
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What provides directional control, how is this accomplished?
Cyclic, changes pitches of blades opposite to each other
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What provides Yaw control, and hows is this done?
Tail rotor pedals, collectivly changes pitch on the tail rotor pedals
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Define Translating tendency
when you add or reduce power, it wants to move the nose of the aircraft
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how is the a/c designed to compensate for translating tendency
mast is tilted 2 deg
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Which was does the main rotor head rotate on a European a/c
CW When viewed from above
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How is pitch changed on a individual rotor blade, which axis?
the feathering axis
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why are the blades washed out
to comp for the lift across the lenght of the blade
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Define Dissymmertery of lift
difference between the amount of lift on the advancing and retreating blades of the rotor system due to airspeed
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what is it called when the blades flap up and down
Corilious effect
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how do you comp for corrilious effect, (what is adjusted)
lead-lag hinge, allows the blade to move fore and aft
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Name 3 types of rotor heads
- RigidSemi
- RigidFully
- Articulated
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what direction can blades move in a rigid rotor system
only movement is pitch, blades can flex
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What design feature is incorperated into some semi rigid rotor systems
under sliging comp for corrilious effect
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what direction can blades move in a FullyArticulated rotor system
feathers flaps lead-lags
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explain the transfer of motion that the swashplate provides
transfers movement of cyclic and collective from stationary push pull movements to rotating push pull movements in the rotor system
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What does charactistic of a spinning rotor does the swashplate comp for
Gyroscopic precession
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Define Translational Lift
Increase in lift as the rotor enters horzional flighthigher airflow velocity supplies a greater mass of air per unit of time
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"A condition of increased drag and loss of lift at the aft portion of the rotor disc" is defined by what term
- Transvers Flow-Caused by the air having a greater induced velocity and angle
- -More lift in the front than the back
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Self excitied viberations occurs on the ground is defined by what term?
Ground resonance
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What rotor head system is most seceptiable to ground resonance?
Fully Ariticulated, if out of phase
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If the skid gear catches on a root or freezes to the ground before you try to take off,what would this condition be defined as?
Dynamic Rollover
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What are the two primary reasons for blade stall?
- Insufficient airspeed
- Too great angle of attack
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What would be an indicator of a blade about to stall
viberation of the main rotor head
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What must the pilot do if he/she sences retreating blade stall?
- Unload rotor system
- slow down
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Name the 2 Viberations that occour to the main rotor head?
- Lateral-out of balance
- Vertical-out of track
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Name 3 types of viberations found in a helicopter
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When dynamically balancing the main rotor, which should be balanced first? Balance or track?
Track then balance
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'Lifting rotors are driven by the action of the air moving through the blades as the a/c decends' What term is used to describe this?
Autorotation
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Name two different types of Freewheel unit?
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What two procedures would require adjusting the lenght of the pitch links ?
- for autorotation
- for out of track
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Condition of powered flight where the helicopter settles into its own downwash, (settling with power) -What is the proper name for this definition?
Vortex ring state
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Name some conditions that can result in the Loss of Tail Rotor Effectiveness (LTE)?
- requires high power
- low airspeeed
- unanticipated manuevers
- No translational lift in main rotor-robs power from tail rotor resulting in LTE
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Name 3 different types of tail rotor designs?
- Traditional design of two or more blades
- fenstrom
- Notar
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What hinge is incorperated into the design of the rotor system to counter the efferct of dissymmerty of lift?
Teetering Hinge
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in a Notar helicopter, a design feature incorperated into the tail boom takes advantage of what aerodynamic princpal?
Cowanda effect
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What is one of the main purposes of strakes on the tail boom?
help counter main rotor torque
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Define engine derating, and why is it done?
- de-rated by making 100% torque at less power than the engine can produce
- because the power output decreases at altitude
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name two types of clutches?
- belt tightener
- centrifugal
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What type of helicopter needs clutches?
Recip or fixed shaft, free turbines don't need a clutch
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With regaurds to a tail rotor drive shaft, what are the two most important design considerations?
- Shaft must be flexiable (torque from tail boom)
- Must be driven when a/c is in autoration
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Why is the vertical fin offset?
offset to move the tail rotor sideways, takes over for tail rotor at airspeed
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Why is the horizontial stabilizer an inverted airfoil?
Holds the nose up in forward flight to reduce drag
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How is the direction changed in a tandem rotor helicopter?
by changing the direction of thrust from each rotor system
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Why is a stabilizer bar used on some two bladed rotor systems?
to increase dynamic stabability
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