Theory of flight Flashcards
List the two components of total aerodynamic force
Lift and drag
Describe the relationship of lift to resultant relative wind
Perpendicular
Describe the relationsship between drag and resultant wind
Drag is parallel to and in the same direction of the resultant wind
Which type of drag decreases with an increase in airspeed?
Induced
Which type of drag increases with an increase in airspeed
Parasite
Define dissymmetry of lift
Differential (unequal) lift between advancing and retreating halves of the rotor disk
Relative wind velocity on the advancing blade equals blade speed _________ airspeed
plus
Relative wind velocity on the retreating blade equals blade speed ___________ airspeed
minus
What causes the advancing blade to flap uo?
An increase in lift
What causes the retreating blade to flap down?
A decrease in lift
How does the helicopter compensate for dissymmetry of lift?
Flapping
How does the pilot control dissymmetry of lift?
Cyclic feathering
Define blowback
Change in the attitude of the rotor system
How does the pilot correct for blowback?
Cyclic feathering
Which forces in the lift equation can the pilot control?
Coefficient of lift and airspeed
What are the three factors in air density (1/2 rho) tha will affect lift?
Pressure, temperature and humidity
A semi-rigid disk tilts relative to the_____
Mast
An articulated disk tilts relative to the _______
Hub
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 compromise between which two forces?
Lift and centrifugal force
Define gyroscopic precession
When a force is applied to a rotating body, it will manifest 90 degrees after application in the direction of rotation
Why is blade twisting necessary?
To distribute the lifting force more evenly along the blade
A pedal turn to the right requires __________ (more/less) power than a pedal turn to the left.
Less
Define translating tendency
Tendency of a single rotor helicopter to drift right while hovering
List four methods used to overcome translating tendency in single rotor helicopters
Rigging the cyclic Tilting the mast Left cyclic Automated flight-control/stabilization augmentation system
List the four rotor blade actions
Rotation Flapping Feathering Hunting
Describe the relationship of total force to the tip path plane?
Perpendicular
When the rotor disk is tilted, what are the two components of total force?
Lift and thrust
What are the two flight conditions
Balanced and unbalanced
At what altitude would the aircraft be in ground effect?
Less than one rotor diameter
Loss or apparent loss, of ground effect is caused by? a____________ b____________ c____________ d____________ e____________ f____________
a. An altitude greater than one rotor diameter b. Trees and bushes c. Tail grass and uneven terrain d. Hovering over water e. Beginning of translational movement f. Hovering into the wind
Define effective translational lift (ETL)
When the rotor completely outruns the recirculation of old vortices and begins to work in relatively undisturbed air
Effective translational lift occurs at an airspeed of?
16-24KTS
Transvers flow effect is noticeable at an airspeed of
10-20KTS
Label the components
- Tip path plane / plane of rotation
- Chord line
- Axis of rotation
- Rotational relative wind
- Induced flow
- AOA
- Resultant relative wind
- Angle of incidence
- Lift
- Drag
- TAF (resultant force)
List the three simultaneous conditions required for settling with power
Vertical or near vertical descent of at least 300 fpm
/ 20-100% engine power
/ slow airspeed less than ETL
Required recovery procedure for setlling with power
Increase airpseed with power
/ Reduce collective as altitude permits
/ Adjust rotor RPM to normal operating range
Define autorotation
The flight condition which no engine power is supplied and the main rotor is driven only by the action of the relative wind
Dynamic rollover occurs due to a combination of which two factors
Human and physical
Operating at what speed is most likely to produce retreating blade stall
High forward speed
Symptoms of retreating blade stall
Abnormal vibration, pitch-up and left roll
Describe the recovery procedure from retreating blade stall
Reduce collective pitch
/ regain control of the aircraft
Define true airspeed
CAS corrected for density error
Define rotational relative wind
The flow of air parallel and opposite the direction of the flight path
Define resultant relative wind
Rotational relative wind modified by induced flow
Define induced flow
Downward flow of air through the rotor blades
How is the angle of incidence measured
Between the chord of an airfoil and the plane of rotation
Define angle of attack
The angle between the chord of an airfoil and the resultant relative wind
Takeoff to a hover is an example of which of Newtons three laws?
Action/reaction
What is total force a component of?
Lift and thrust
How do you obtain ETL?
Horizontal flight or hovering in a headwind
What happens at max flap up at 3 o’clock in relation to induced flow and AOA?
Induced flow increases and AOA decreases
List the four causes for excessive coning
Low RPM’s / High gross weight / high G maneauvers / turbulent air
Three adverse effects to excessive coning
Loss of disk area / loss of total lift / stress on the blades
What happens to the fwd half of the disk at the transverse flow effect?
Induced flwo decreases, AOA increases
