Theory Of Rotary Wing Flight Flashcards
Define center of pressure.
The point along the chord line of an air foil through which all aerodynamic forces are considered to act.
Define airfoil.
Any surface designed to produce lift when air passes over it.
List two basic types of airfoils.
Symmetrical
Non-symmetrical
Define rotational relative wind as applied to an airfoil.
The flow of wind parallel and opposite to the flight path of an airfoil.
Define induced flow.
Downward flow of air through the rotor blades.
Define resultant relative wind
Rotational relative wind modified by induced flow.
How is angle of incident measured.
The angle between the chord line of an airfoil and the plane of rotation.
Define angle of attack
The angle between the chord line of an airfoil and the resultant relative wind.
Centrifugal force…
The outward force produced whenever a body moves in a curved path
Provides rigidity to the rotor blades
Three adverse effects of coning
Loss of disk area
Loss of total lift
Stress on blades
Why is blade twisting necessary?
To distribute the lifting forces more evenly along the blade
How is the rotor blade twisted?
Higher AOI at the base and decreases towards the end
List the two components of total aerodynamic force.
Lift and drag
Describe the relationship of lift to the resultant relative wind.
Perpendicular
Describe the relationship between drag and resultant relative wind.
Parallel and in the same direction
Which type of drag decreases with an increase of airspeed?
Induced Drag
Which type of drag increases with an increase in airspeed.
Parasite drag
Define dissymmetry of lift
Dissymmetry of lift is the differential lift between advancing and retreating halves of the rotor disk caused by the different wind flow velocity across each half
What causes the advancing blade to flap up
An increase in lift.
Define blowback
Change in the attitude of the rotor system
Which forces in the lift equation can the pilot control
Coefficient of lift
Airspeed
Define centrifugal force
Outward force produced whenever a body moves in a curved path
Define rotor blade coning
Upward flexing of the rotor blades
Rotor blade coning is a compromised between which two forces
Lift
Centrifugal force
Define gyroscopic precession
When a force is applied to a rotating body it will manifest 90 degrees after the application in the direction of rotation
Why is blade twisting necessary
To distribute the lifting forces more evenly along the blade
Define translating tendency
Tendency of a single rotor helicopter to drift to the right
List 4 methods used to overcome translating tendency in single rotor helicopters.
Rigging the cyclic
Tilting the mast
Left cyclic
Automatic flight controls and SAS
Describe the relationship of total force to the tip path plane
Perpendicular
And the rotor disc is tilted what are the two components of total force
Lift
Thrust
What are the two flight conditions
Balanced
Unbalanced
List the 4 rotor blade actions
Rotation
Flapping
Feathering
Hunting
Define effective translational lift
When the rotor completely outruns the recirculation of old vortices and begins to work in relatively undisturbed air
ETL occurs at what speed
16-24
Transverse flow effect occurs at what speed
10-20
Define settling with power
When I helicopter settles into its own downwash
Where is the three simultaneous conditions required for settling with power
Vertical decent speed of at least 300 fpm
20% to 100% of engine power
Slow airspeed less than ETL
What is the required recovery procedures for settling with power
Increase airspeed with cyclic
Reduce collective (altitude permitting)
Adjust RPM to normal range
Define autorotation
No engine power is given and main rotor is driven only by the relative wind
Describe how to prevent a rotor RPM over speed during auto rotation with turns
Collective control
Describe the symptoms of her treating blade stall
Abnormal vibrations
Pitch up attitude
Left roll
Describe the recovery procedure from retreating blade stall
Reduce collective pitch Regain control Reduce airspeed Increase rotor rpm to normal operating range Minimize maneuvering Descend to a lower altitude
