Rotary Wing, Weather Exam Flashcards
The METAR is a report that is issued ____.
Hourly
What kind of report is made anytime there is a significant change in the weather at the observation station?
SPECI
The wind direction is given in degrees from ____ north and wind speed is always in ____.
TRUE, Knots
METAR KOZR 100955Z would indicate an hourly report for what time on the current date?
10 o`clock
What is atmosspheric pressure?
The force excerted by the weight of a column of air.
What is standard sea level pressure in inches of mercury?
29.92 INS
What is standard sea level temperature in °C?
15°C
What is the standard temperature lapse rate with altitude?
2°C/ 1000ft
A change in one inch of mercury pressure is equal to approx. _____ feet of altitude.
1000
Define impact pressure.
Static pressure plus dynamic pressure.
Define static pressure.
Ambient pressure.
Which instruments depend on static pressure only?
IVSI, altimeter
Which instrument depends on both impact (dynamic) and static pressure?
Airspeed indicator
What pressures affect the pitot static system?
Static and Dynamic
Name and define the three types of airspeed
IAS (read from the dial on the face of the instruments)
Calibrated (IAS corrected for instrument and position error)
True (CAS corrected for density error)
Name and explain the three errors in the airspeed indicator
Installation Error (Misalignment of the Pitot tube with the relative wind and position of the static vents)
Density Error (Caused by pressure and temperature changes, air less dense as altitude increases)
Instrument error (Caused by friction in the instrument)
Is the instantaneous vertical speed indicator (IVSI) a pressure differential measuring instrument)
Yes
What does the setting knob on the altimeter change when it is turned?
Kollsman setting and position of the needles
A change if 0.15 inch of mercury pressure is equal to ___ feet
150
Define Indicated Altitude
Altitude as read on the dial with a current altimeter setting
Define True Altitude
Altitude above MSL
Define Pressure Altitude
Altitude above the standard datum plane (29.92 HG or 1013.25 hPa)
Define absolute Altitude
Altitude above terrain (AGL)
Define altimeter setting
Station pressure corrected to MSL
Why is the altimeter setting necessary?
To correct for pressure changes
What is the maximum allowable error in the altimeter?
Plus or minus 75` (FAA), check specific manual for specific Airframe
The ______ (instrument) stops functioning properly due to pitot icing.
Airspeed indicator
What is the recommended corrective action when the static system is clogged?
Switch to an alternate source
High DA and low air density mean nearly the same thing (True or false)?
True
What causes density errors?
Nonstandard pressure and temperature
Define true airspeed
CAS corrected for density error
Which of Newtons Laws is involved?
Torque effect
Action/ Reaction
Which of Newtons Laws is involved?
More power needed to obtain a desired RPM than is need to maintain the RPM
Inertia
Which of Newtons Laws is involved?
Greater load, less acceleration
Acceleration
If the airflow atop the airfoil increases, static pressure will ___ and dynamic pressure will _____.
Decrease, Increase
Define Center of pressure
The point along the chord line of an airfoil through which all aerodynamic forces are considered to act
Define airfoil
Any surface designed to produce lift when air is passed over it
List two basic types of airfoil
Symmetrical and Asymmetrical
Define rotational relative wind as applied to an airfoil
That flow of air parallel and opposite to the flight path of rotating airfoil produced by the rotor blades turning about the mast
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 a/c?
The angle between the chord line of an airfoil and the plane of rotation (tip path plane [TPP])
Define angle of attack (AoA)
The angle between the chord line of an airfoil and the resultant relative wind
Which flight control changes the angle if incidence differentially around the rotor system?
Cyclic pitch control
With an increase in the speed of air over a surface, what happens to dynamic and static pressure?
Dynamic pressure increases while static pressure decreases
Time TAF
Issued every 6 hours, Valid (Military) for 30 hours
Most critical atmospheric parameters
Temperature (most critical) and Pressure
Components of atmospheric air density
Pressure, Temperature, Humidity
Standard Temperature Rule
If temperatures are colder than standard temperature, than true Altitude and DA are always lower and vice versa!
Density Altitude Rule
Higher Pressure equals more dense air, but equals low DA and vice versa!
The four forces of flight
Lift, Weight, Thrust and Drag
Lift as it opposes Weight and Thrust as it opposes Drag
Newtons First Law
Inertia
“A body at rest will remain at rest and a body in motion will remain in motion at the same speed and in the same direction unless acted upon by an external force”
Example: “Requires more torque to accelerate to 100% RPM than to maintain 100% RPM”
Newtons 2nd Law
Acceleration
“A change in velocity with respect to time
F=m*a”
Example: “Rate of acceleration to 100% RPM from Engine Idle dependent upon amount of force applied through introduction of fuel and oxygen”
Newton 3rd Law
Action/ Reaction
“For every Action the is an equal and opposite Reaction”
Example: “Main rotor turns counterclockwise forcing the nose of helicopter to turn clockwise.”
Bernoullis Principle
Within a confined system (with a incompressible fluid or gas), total energy remains the same.
Chord
Provides longituidinal dimension and is contained in the airfoil section
Chord line
Imagninary line which extends through the leading edge on which all angles and winds are measured
Effects regarding relative wind on the advancing blade after 6 o’clock
Advances into the relative wind
Blade speeds up
Blade flaps up, max. 3 o’clock
Effects regarding relative wind on the retreating blade after 12 o’clock
blade retreats from relative wind
blade begins to slow down
blade begins to flap down, max. flap down 9 o’clock
Induced Flow/AoA Rule
As induced Flow increases, AoA decreases and less Lift is produced and vice versa!
List the two components of aerodynamic Force
Lift and Drag
Describe the relationship of lift and resultant relative wind
Perpendicular
Describe the relationship between Drag and resultant relative wind
Drag is parallel to and in the same direction as the resultant relative wind
Match with type of drag
Rotor-tip vortices
Lift and total aerodynamic force tilting rearward on the airfoil
Skin friction of the fuselage
Skin friction of the airfoil
Non-streamlined fuselage
induced
induced
parasitic
profile
parasitic
Which type of drag decreases with increasing airspeed
induced
Which type of drag increases with increasing airspeed
Parasite
Define Dissymmetry of lift
Differential lift between advancing and retreating halves of the rotor disk
What causes the advancing blade to flap up
increase in lift
How does the helicopter compensate for dissymetry of lift?
Flapping
How does the pilot compensate dissymmetry of lift
cyclic feathering
Define blowback
Change in attitude of the rotor system
Which of forces of the lift equation can the pilot control?
Coefficent of lift thru angle of attack and relative wind velocity or airspeed
What are the three factors in air density that will affect lift?
Pressure, Temperature, Humidity
A semi-rigid disk tilts relative to the ____
Mast
A 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 to forces
Lift and Centrifugal forces
Define gyroscopic precession
When a force is applied to a rotating body, it will manifest 90 degrees after application in the direction of the rotation
Why is blade twisting necessary?
To distribute the lifting force more evenly along the blade
Define translating Tendency
The Tendency of a single main rotor helicopter to drift laterally in the direction of tail rotor thrust
Lift four methods to overcome translating tendency
Mast/ Transmission tilting
Cyclic rigging
Pilot induced left cyclic
Automatic/ Electronic, preprogrammed stability measures
List the four rotor blade actions
Rotating, Flapping, Hunting, Feathering
Describe the relationship of total force to the TPP (tip path plane)?
Perpendicular
When the rotor disk is tilted, what are the two components of total force
Lift, Thrust
What are the two flight conditions
Balanced/ Unbalanced
At what altitude would the aircraft be in ground effect
Less than one rotor diameter (Ground to Rotor disk)
Loss, or apparent loss, of ground effect is caused by?
An altitude greater than one rotor diameter
Trees, bushes
Tall grass or uneven terrain
Hovering over water
Beginning of translational movement
Hovering into the wind
Define effective translational lift
When the rotor completely outruns the reciculation of old vortices and begins to work in relatively undisturbed air
Effective translational lift occurs at an airspeed of ____
16 - 24 KIAS
Transverse Flow effect occurs at an airspeed of ____
10 - 20 KIAS
- Tip path plane or Plane of rotation
- Chord line
- Axis of Rotation
- Rotational relative wind
- Induced Flow
- Angle of Attack
- Resultant relative wind
- Angle if Incidence
- Lift
- Drag
- TAF (Resultant Force)
Define settling with power
A condition of powered flight in which the helicopter settles in its own downwash (vortices)
List the three simlutaneous conditions required for settling with power
A vertical or near vertical descent esceeding 300 ft/min
20 - 100% Power used by engines
Airspeed less than ETL
List the required recovery of settling with power
Increase airspeed with cyclic
Reduce collectiv as altitude permits
Adjust rotor RPM to normal operating range
Define autorotation
Flight condition with no power supplied and the main rotor is driven only by the relative wind
Describe how the pilot prevents a rotor rpm overspeed during an autorotation with turn
Raise the collective
List the three conditions required for a dynamic rollover
Pivot Point
Rolling motion
Exceeding the critical angle
Dynamic rollovers 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?
Excessive Speed
Describe the symptoms of retreating blade stall in a single rotor helicopter
Pitch nose up
Roll towards left
Describe the recovery procedure from retreating blade stall
Reduce collective
Regain A/C control
Retreating blade stall and excessive coning share which causes?
High GW
High “G” maneuvers
Low Rotor RPM
Turbulances
Cyclic feathering does what?
Does NOT change overall lift of the rotor system (increases one half, decreases other)
Collective Feathering is what?
Pitch changes applied equally and simultaneously to all blades
What reduces impact of Induced Flow?
Airspeed
Hunting does?
Reduces stress of the blades caused by flapping
Define Total force
Single Force emitted troughout the center of the rotor disk
Define Ceiling
Lowest Layer of Broken or Overcast or vertical visibility if sky is obscured
Three cockpit setting of METAR
Ceiling, wind, visibility
Atmospheric Pressure is changed by
Temperature, Pressure and Humidity
What is and what provides the most dominant force for the rotor system?
It is the centrifugal force and it provides rigidity
Regarding advancing and retreating blade:
Max. Flap Up/ down applied at 3 and 9 o’clock
Components of TAF
Lift and Drag
Components of Total Force
Lift and Thrust
Pressure table
Pressure temperature conversion table
