Theory Of Rotary Wing Flashcards
Define settling with power?
A condition of powered flight in which the helicopter settles in its own downwash.
List the three simultaneous conditions required for settling with power.
a. Vertical or near vertical descent of at least 300 FPM
b. 20% to 100% engine power
c. Slow airspeed less than ETL
List the required recovery procedures for settling with power.
Increase airspeed with cyclic.
Reduce collective as altitude permits.
Adjust rotor RPM to normal operating range.
Define autorotation
The flight condition during which no engine power is supplied and the main rotor is driven only by the action of the relative wind.
Describe how a pilot prevents a rotor R.P.M. over speed during an autorotation with turn.
The pilot must prevent rotor RPM over speed with collective control.
List the three conditions required for dynamic rollover to occur.
a. Pivot point
b. Rolling motion
c. Exceed critical angle
Dynamic rollover occurs due to a combination of which two factors?
Physical and human
Which control input is required to recover from dynamic rollover on level ground?
Smooth, moderate collective reduction
Operating at what speed is most likely to produce retreating blade stall?
High forward speed
Describe the symptoms of retreating blade stall in a single rotor helicopter.
Abnormal vibration,
pitch-up of the nose,
and left roll.
Describe the recovery procedure from retreating blade stall.
Reduce collective pitch, regain control of the aircraft, reduce airspeed, increase rotor RPM to normal operation range, minimize maneuvering, and descend to a lower altitude.
Listed below examples of Newton’s Laws of Motion. To the right of each example, indicate which law is involved
A. Torque effect - Action / Reaction
B. More power is needed to obtain a desired RPM than is need to maintain the RPM - Inertia
C. Greater load, less acceleration
- Acceleration
If the airflow atop the airfoil increases, static pressure will
…decrease and dynamic pressure will increase
Define center of pressure
The point along the chord line of an airfoil through which all aerodynamic forces are considered
Define airfoil.
..any surface designed to produce lift when air is passed over it
List two basic types of airfoils.
A. Symmetrical
B. Non-symmetrical
Six descriptions of airfoil (blade) sections
Match the descriptions to the airfoil terms
Chord - Straight line from the leading edge to the trailing edge
Rounded edge - leading edge
Upper curvature - Upper camber
Lower shape - Lower camber
The length of the rotor blade from the point of rotation to the tip of the blade
- Span
Trailing edge - Tapered edge
Define rotational relative wind as applied to an airfoil.
The flow of air parallel and opposite to the flight path of an airfoil
Descriptions of airfoil movements. Match these movements to the rotational relative wind arrows.
Rotation only - look for a straight line Rotation and flapping up - look for and decline arrow Rotation and airspeed - look for a double headed arrow Rotation and flapping down - look for a ascending arrow
Define Induced flow.
…Downward flow of air through the rotor blades
Define resultant relative wind.
…Rotational relative wind modified by induced flow
How is the angle of incidence measured in a rotary-wing aircraft?
…The angle between the chord of an airfoil and the plane of rotation (tip path plane)
Define angle of attack?
…the angle between the chord of an airfoil and the resultant relative wind
Which flight control changes the angle of incidence differentially around the rotor system?
…the cyclic pitch control
With an increase in speed of air over a surface, what happens to dynamic and static pressure?
…dynamic pressure increases, static pressure decreases
List the two components of total aerodynamic force.
Lift and drag
Describe the relationship of lift to resultant relative wind.
Perpendicular
Describe the relationship between drag and resultant relative wind.
Drag is parallel to and in the same direction of the resultant relative wind
Listed below are descriptions of various types of drag. To the right of each description, indicate whether the drag is induced, parasitic, or profile.
a. Rotor-tip vortices-
b. Lift and total aerodynamic force tilting rearward on the airfoil -
c. Skin friction on the fuselage -
d. Skin friction on the airfoil -
e. Non-streamlined fuselage -
a. Rotor-tip vortices- induced
b. Lift and total aerodynamic force tilting rearward on the airfoil - induced
c. Skin friction on the fuselage - parasitic
d. Skin friction on the airfoil - profile
e. Non-streamlined fuselage - parasitic
Which type of drag decreases with an increase in airspeed?
Induced drag
Which type of drag increases with an increase in airspeed?
Parasite drag
Define dissymmetry of lift.
Differential (unequal) lift between advancing and retreating halves of the rotor blade
Relative wind velocity on the advancing blade equals blade speed
Plus
Relative wind velocity on the retreating blade equals blade speed
Minus
What causes the advancing blade to flap up?
An increase of 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 altitude of the rotor system
How does the pilot correct for blowback?
Cyclic feathering
Which forces in the lift equation can the pilot control?
Coefficient lift and airspeed
What are the three factors in air density (1/2 rho) that 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 flexing of the rotor blades.
Define rotor blade coning.
Upward flexing of the rotor blade
Rotor blade Koning is a compromise between which two forces?
Lift and centrifugal force.
Define gyroscopic procession.
When force is applied to a rotating body, it will manifest 90 degrees after application.
Why is blade twisting necessary?
To distribute the lifting force more evenly along the blade
A pedal turn to the right requires_______( less) power than a pedal turn to the left.
Less
Define translating tendency.
…translating tendency is the tendency of a single rotor helicopter to drift right while hovering.
List four methods used to overcome translating tendency in single rotor helicopters.
a. Rigging the cyclic
b. Tilting the mast
c. Left cyclic
d. Automatic 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. An altitude greater than one rotor diameter
b. Trees and bushes
c. Tall grass and uneven terrain
d. Hovering over water
e. Beginning of translational movement
f. Hovering into a wind
Define effective translational lift
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
Approximately 16-24 KTS
Transverse flow effect is noticeable at an airspeed of
10-20 KT
Label the components of the Basic Aerodynamic Model.
- Tip path plane/plane of rotation
- Chord line
- Axis of rotation
- Rotational Relative Wind
- induced flow
- Angle of attack
- Resultant Relative Wind
- Angle of Incidence
- Lift
- Drag
- TAF (Resultant Force)
METAR is done how often
Routine hourly report
METAR contains
Type of report Station identifier Date and time of observation Winds Visibility Precipitation and obscurations Sky condition Temperature and dew point Altimeter setting and remarks
Observation station are showed in four-letter identification system
i.e. KOZR- Cairns AAF
Two factors must be considered when converting Zulu / Local time.
Must know time zone you are located in. Ref. FIH E-4
Daylight savings time begins second Sunday in March.
Standard time begins on first Sunday in November.
AUTO in METAR means
In automated observation. Most military sites in many civilian sites are automated.
In A02A would indicate that the observer has augmented the observation.
Wind direction is in reference to
True north and is reported to the nearest 10°.
Wind speed is reported…
two minute average reported to the nearest knot
Calm wind
00000KT
Gust - fluctuations
Gust fluctuations in wind speed of 10 KTS or more between peaks in LULLS
VRB
Variable is used when direction is variable and speed is
V is used when
Wind varies 60° or more and the wind is > 6 knots
When is Peak wind reported
Peak wind is reported in remarks when instantaneous speed is over > 25 KTS
Visibility
The greatest horizontal distance specified objects can be seen and identified. Reported in miles in fractions of miles.
Prevailing visibility
The greatest horizontal distance that specified objects can be seen over at least one half (1/2) of the horizontal, not necessarily continuous.
Prevailing visibility
3/4 SM
1 1/2 SM
7/8 SM
1/2 SM
