Helicopters Flashcards
Name 4 types of Helicopters
Gyroplane - has a freely rotating wing supplying the aerodynamic force for lift; all forward thrust is supplied by a separate propeller as in a conventional aircraft.
Pure helicopter - Has powered rotating wings supplying all lift
Compound Helicopter - main lift supplied by rotor, supplemented by power units or stub wings
Convertible Helicopter - modifies config during flight (Vtol)
4 Mainly used Heli configs
Single rotor with tail rotor
Tandem
coaxial contrarotating
NOTAR
4 Controls used by the pilots
Collective Lever - Simultaneously Alter the pitch of all the blades by the same amount
Cyclic - Varied pitch of each blade cyclically
yaw pedals - Varies the force produced by the tail rotor to oppose torque reaction
throttle - Controls the throttle of RRPM
What are the 3 ways that engine or rotor revolutions are controlled
Mechanical engine and rotor speed governing
Hydro mechanical engine and rotor speed governing
FADEC (Fully automatic digital engine control)
4 Main types of rotor heads
Teetering Rotor
Fully articulated rotor head
Semi rigid
fully rigid
Teetering Rotor
2 Blades rigidly connected to each other with a built in coning angle and gimble mounted rotor shaft
fully articulated rotor head
3 hinges (3 axis)
Flapping hinge - Allows for verticle flap
Dragging hinge - Move in the plane of rotation
Feathering hinge - Allows for change in pitch
3 flapping constraints:
Droop restrainer - Limits droop of blade when rotating below normal speeds
Flapping Restrainer - Prevents flapping in gusty conditions
Delta 3 hinges
Designed to improve stability of the Rotor head.
Flap hinge mounted at right angles to span of blade, pitch doesnt change during flapping instead the flapping hinge can be set at an angle, pitch angle reduced, reducing angle of attack.
semi rigid rotor head
Has only feathering hinge, flapping and dragging allowed for by the flexing of the arms.
What is the coning angle
The coning angle is measured between the spanwise length of the blade and the blades’ tip path plan
Will vary when the rotor RRPM and thrust from the rotor blades vary
if thrust is increased but RRPM constant, the blades will cone upwards
If RRPM is reduced but thrust stays the same, the coning angle in increase upwards due to centrifugal force
what is wash out
The dispersion of root stresses throughout the rotor blade, stress increases as you move up the blade
Verticle Movement
increase the pitch of each blade by the same amount at the same time, increases Angle of attack (Collective pitch change), done by raising the collective
this causes the blades to cone up increasing TR and drag. therefore more engine power will be required to maintain this rpm
When a helicopter is hover at 200ft what state is it in?
HOGE -Hover outside of ground effect
Ground descent
Collective pitch lever lowered, Angle of attack is reduced.
Airflow resulting will oppose induced airflow through the disc, resultant will change in direction of the RAF to the blade, increasing the AOA
When AOA reaches 4 degrees, rotor thrust will equate to the weight and downwards acceleration will be a steady rate.
Ground effect.
Hovering the helicopter near the ground in still air will require less power than is required at 50ft or 100ft. this is ground effect.
Hovering near the ground creates a divergent duct causing an increase of pressure.
4 factors that affect ground effect
Height
slope
nature of ground
wind
what two components does a helicopter need to move horizontally
A verticle component - must be equal to the weight of the helicopter to hold the aircraft in level flight
A horizontal component - must be equal to total drag of the helicopter for constant speed in level flight
how is horizontal movement done
Tilt disc, done by increasing pitch on one side, increasing AOA and Lift, causing rise on flapping hinge has the opposite effect on opposite side (decrease AOA, decrease lift) Known as cyclic pitch change, done with the cyclic pitch stick
what is torque reaction
MRB Makes fuselage want to move one way, tail rotor moves it in the opposite direction. So if MRB is going CW, then Tail rotor is going ACW.
What is tail rotor drift
When the helicopter has a tendency to move sideways in relation to the Tail rotor. corrected by the pilot with an opposing cyclic stick input
How to correct for tail rotor drift
Mount the main rotor gearbox on the tilt
rigging the controls - set a new normal for the AC
How to stop tail rotor roll
Set the tail rotor to be in line with the MRB when the helicopter is in forwards flight
Describe flapping to equality
When the pilot changes the angle of the rotor disc, the blade positions change by flapping. Blades that flap down have an increase on Angle of attack and lift while reducing the acceleration. it reduces the value of the IAF
The blade that flaps up has an increased value of IAF therefore the angle of attack and lift decrease.
This creates the same values for when the rotor disc in level, providing the same results.
