Heli Final Flashcards
what are the four blade movements
feathering
teetering
flapping
lead/lag
what are the three basic types of rotor heads
rigid
semi-rigid
fully articulated
what is the main rotor strap? what purpose does it serve
they are wraps fine steel wire between two bearings.
they are designed to retain the rotor blades while still allowing for movement of the blade
what is a droop stop? what type of rotor heads will they be found on
droop stops limit how far down a blade will settle, eliminating any damage to the airframe.
will be found on rotor heads that flap
what are teeter stops? what are the two types
stops that limit the downward travel of semi rigid rotor heads
static and dynamic stops
what are the different ways a main rotor head can be lubricated
oil or grease
self lubricated components
life lubricated components
what is an example of a self lubricated component
Teflon Bearing
what does the term life lubricated mean
the component is lubricated by the manufacturer and will not be re-lubricated for the usable life of the component
what is a rotor disc
the total surface area occupied by the main rotor assembly while in motion
what is coning
the upwards angle of the rotor blades while in flight. resultant of the creation of lift
what is an autogyro? how does it differ from a helicopter
an autogyro uses an un controlled / unpowered rotor system to produce lift. can only produce lift during forward flight
what effect does centrifugal force have on rotor blades in motion
it will cause the rotor blades to stay flat until lift is increased
what is Nr
rotor RPM
when lift is increased, what happens to the rpm of the main rotor
the RPM always stays constant at 100%. all flight inputs are done by changing blade pitch, not blade speed
what defines a hover
all forces are equal
zero movement relative to wind speed
what is gyroscopic precession
any blade pitch adjustment made during directional flight must occur 90 degrees early
how will the airframe react to the torque forces of the main rtor
the airframe will always react in the opposite direction of the main rotor
what is induced flow
the direction of airflow through the rotor blades during directional travel
what is translational lift
the transition from hover to directional flight. reduces the induced flow angle and causes light airframe buffeting
why is there no ground effect when flying frward at low altitude
the rotor downwash is propelled to the rear of the aircraft and does not create an air cushion for the aircraft to rest on
what is dissymmetry of lift
difference in blade speeds while in directional flight
what are the solutions for dissymmetry of lift
flapping hinge
differential cyclic
what is differential cyclic
a difference in blade pitch dependent of position
what is the law of conservation of angular momentum
when the centre of mass of a rotating object moves towards the centre of rotation, the object will accelerate
what are the solutions for the law of conservation of angular momentum problem
lead lag hinge
underslung mounting
what is mast bumping
the rotor head striking the mast. only occurs in underslung rotor heads
what pilot input controls yaw? how is yaw controlled
anti torque pedals at the pilots feet
controlled by changing the pitch angle of the tail rotor blades
what control devices are incorporated into the tail rotor system
push pull tubes or teleflex cables connected to bell cranks which move walking beams to change pitch
what are some examples of additional controls located on the collective
landing lights start switch governor controls idle release throttle twist grip pop out float trigger
what are some additional controls that are located on the cyclic
push to talk radio
cargo hook release
trim
what is the purpose of the mixing unit
converts individual cyclic and collective input into a common set of outputs
prevents collective inputs from altering cyclic position
what is centrifugal twisting force? what is used to combat it
a force acting on a rotor blade attempting to return it to a low pitch angle
counterweights and collective spring
what is aerodynamic twisting force
forces acting on rotor blades to return them to a higher pitch
what are hydraulic servos used for
provides flight control boost and eliminates rotor system feedback
what are the different types of gearboxes
main rotor
tail rotor
intermediate
combining
how is the main rotor gearbox mounted on a bell 206
using 2 a-frame support links to hold the gearbox and still allow movement
when is a clutch required on a helicopter
for all piston engine aircrafts and all direct drive turbine engine aircrafts
what are the two types of turbine engine
free turbine and direct drive turbine
what type of helicopters have freewheeling untis? are any of them manual
all helicopters have freewheel units and they are all automatic
what two measurements are displayed on a dual tach
engine RPM and rotor RPM measured in percent
what are drive shaft couplings
they are flexible metal plates or greased bearings that allow the drivetrain to move with the airframe without being damaged
what is a side effect of tail rotor anti-torque forces
translating tendency (lateral drift)
how do you counteract translating tendency
Pilot
mixing unit which applies slight lateral cyclic when collective is moved
why mount the tail rotor higher on the vertical stab
more ground clearance
brings the tail rotor in line with CofG
what is a delta hinge
the teeter hinge on a tail rotor that is not at a right angle with the blades. causes blades angle of attack to lower when flapping up
what do strakes do
the eliminate the ow pressure zone on one side of the tailboom which increases tail rotor efficiency
what is autorotation
the state of flight where the main rotor system is being turned by the action of relative wind instead of engine power
what are the different regions of the rotor disc duriong autorotation
stall region
from centre to 25% of the blade
autorotation region
25 - 75% of blade
driven region
75% - blade tip
what are the different multi rotor configurations
co-axial (stacked)
Tandem (one in front of the other)
Synchrocopter (intermeshing)
what is a design feature that helps to overcome nose down tendency
forward tilt of mast or horizontal stabilizers
what is the purpose of a synchronized elevator
changes the CofG
during start up, fully articulated rotor blades will have a tendency to what?
lag
how are coning stresses reduced in rotor blades
pre coning angles
what must be recorded during autorotational rigging
a/c weight
pressure altitude
temperature
rotor rpm
