EXAM ( WEATHER, AERODYNAMIC ) Flashcards
What does the high dew point spread mean ?
That the air is dryer
What does prevailing wind mean ?
A wind that blows permanently from a perticular direction
Wind circle: What does the red hash mean ?
2 min avarage of prevailing wind
Name the wind speed from top to bottom
Wind calm
5 kts
10 kts
50 kts
How often is a METAR issued ?
every hour on the hour
When can a SPECI be issued and why ?
Any time during the current METAR, when there is a significant change to the exciting conditions
What periode of the year is daylight saving ?
How much does the time change ?
2nd sunday in march to 1st sunday in november
+1 hour
When is VV used ?
When clouds or a weather phenomena at the surface is obscuring the sky from view.
The altitude given is the height the observer can see upward.
When is “CLR” used ?
No clouds below 12.000 ft (automated observation)
When is “SKC” used ?
No clouds at a manned station (not automated)
Name the two cloud layers and two ceilings
Layer: FEW, SCT
Ceiling: OVC, BKN
What does the following abbreviations signify? :
AO
AO1
AO2
AO2A
AO Automated observation
AO1 Automated no PD
AO2 Automated with PD
AO2A Automated with PD and human controlled
PD = Precipitation determinator (speed and type)
When is RVR reported ?
What does P & M indicate in this regard
If prevailing visability has been cut down on the active runway.
(Mist, haze ect.)
M: Less than the distance shown
P: Greater than the distance shown *They can't measure more precis due to distance between the sensors on the RW.
When can gust spread speed reliably be determined ?
When the spread is > 10 kts
What does the following abbreviations mean and signify ?
On station
VC
DSTN
Weather observed
On station: 0-5 NM
Vicinity: 5-10 NM
Distance: +10 NM
What is “obscurations” ?
Any phenomenon ( other than Precipitation ) that obscures the horizontal visibility
How far out does the TAF cover the weather ?
5 mile radius from the center of the RW complex
Which forecast/observation display visability in meters/SM ?
Metar/TAF
Metar: SM
TAF: meters
How many SM is visability 9999 (TAF)
7 SM or greater
How big of a dew point spread results in posible visible moister in the air ?
2 degrees
Change groups meaning:
FM
BECMG
TEMPO
PROP
FM : Rapid change of conditions
BECMG : Gradual change of conditions
TEMPO : Between the hours listed
PROP : Between the hours listed a percentage og probability exists
What does the following mean ?
TX35/0518ZTN22/0509Z
Represent the end of the validity - there will be no more reporting lines
TX = max temp
TN = min temp
What does the following signify ?
P6SM
Visability +7 SM (9999)
Temperature and pressure are the two most critical factors with ____ being the most critical
Temperature
What are the 3 components of atmospheric density ?
Temperature, pressure and humidity
If temperatures are colder than standard, what are TA and DA in regards to PA?
Lower than standard
If temperatures are warmer than standard, TA & DA are always ___ ?
Higher than standard
Which is more favorable for aviation:
Higher or lower pressure ?
Higher pressure
high pressure pushes air down and keep moister from raising = no clouds, rain, storms + sunny weather
What DA follows with higher pressure
Lower density altitude
= better a/c performance
colder, dryer air
What’s standard pressure laps rate ?
1 inch / 1000 ft
= 1000' altitude - 28.92 inches of mercury (standard day)
What’s standard temperature laps rate ?
2º / 1000’
At what altitude (standard atmosphere) does temperature become minus degrees ?
7500’
If the static pressure system fails which instruments fail ?
IAS, VSI and ALT
What altitude do you set in the kollsman window ?
Pressure altitude -> corrected for non-standard pressures (MSL)
How often should you attempt to get current altimeter setting ?
Every 50 NM ( not exceeding 100 NM )
What’s the purpose of the kollsman window ?
Corrects for atmospheric pressure changes
(non standard pressure at the surface. If we have a low pressure day the a/c will be lower than what it's supposed to be if not corrected in the window)
What’s: True altitude ?
Height above MSL (QNH)
What’s: Absolute altitude ?
Height above the ground - AGL (QFE)
What’s: Pressure altitude ?
Altitude above the standard datum plane
( 29.92, 1013.5)
MSL at a standard day (15 degrees celcius, 29.92 at seal level)
What’s: Density altitude ?
PA corrected for non standard temperatures
“Density corresponding to a given altitude in a standard atmosphere”
What altitude do you set > 18.000’
Pressure altitude
What pressure altitude is altimeter setting and what happens in air if the raise pressure (altimeter) ?
Altimeter setting is the pressure at MSL (true altitude).
Turning the knob and raising pressure at sealevel, raises our altimeter setting. We would have to desent to get same altitude as before correcting.
If temperatures are warmer than standard the a/c will be:
higher/lower ?
than standard altitude
Higher
How do you determine the accuracy of the a/c altimeter
Set field elevation, then true altitude (QNH).
max +- 75’ deviation
What’s impact pressure ?
Static + dynamic pressure
What’s atmospheric pressure ?
The force exerted by the weight og a column of air
Define static pressure
Ambient pressure
What’s IAS ?
Shown on the dial of the instrument, uncorrected
What’s TAS
CAS corrected for nonstandard pressure and temperature
What’s CAS
IAS corrected for instrument and position error
Name and explain the 3 errors in the airspeed indicator
- Installation error (misalignment of the pitot tube + placement of static vents)
- Density error (Pressure and temperature changes in the atmosphere)
- Instrument error (Friction in the instrument)
Define altimeter setting
Station pressure corrected for MSL
Is DA higher/lower than PA when temperature is higher than standard
Higher
If temperature decreases below standard temp. where is DA in relation to PA ?
Lower
Does high DA and low air density mean the same thing ?
Yes
What’s true airspeed ?
CAS corrected for density error
How does humidity affect air pressure ?
High relative humidity = lower pressure
(cause the water absorbed is lighter than air, but takes op the air molekyle space = lighter pressure in a column of air)
Fill in the boxes
Which of newtons laws of motion applies:
Torque effect
Action/Reaction
Which of newtons laws of motion applies:
More power needed to obtain a desired RPM than is need to maintain the RPM
Inertia
Which of newtons laws of motion applies:
Greater load, less acceleration
Acceleration
Define center of pressure
The point along the chord line of an airfoil through which all aerodynamic forces are considered to act
If airflow atop of an airfoil increases, what happens to static pressure ?
Decreases
List the two basic types of airfoils
Symmetrical & nonsymmetrical
Define: Rotational relative wind
That flow of air parallel and opposite to the flight path of a rotating airfoil (produced by the rotor blades turning about the mast)
Which rotational relative wind arrorw fit the airfoil movement:
A. Rotation only
B. Rotation and flapping up
C. Rotation and airspeed
D. Rotation and flapping down
A:2
B:1
C:4
D:3
Rotational relative wind to airfoil movement: Parallel and opoosit
Define induced flow
Downward flow of air through the rotor blades
downwash
Define reultant relative wind
Rotational wind modified by induced flow
Between what is AOA measured ?
Resultant relative wind and chord line
Between what is AOI measured ?
helicopter
Chord line and plane of rotation relative wind (tip path plane)
What 3 events affect the rotor blades when passing through the 6 o’clock position ?
- The baldes advance into a relative wind
- The balde begins to speed up
- The blade beginds to flap up (max flap is at the 3 o’clock position)
The 3 o'clock position is the only place where the blades have the rounded leading edge into the relative wind
What happens to the airflow over the blade when entering the retreading half ?
An increase in reverse flow
When in the rotor cycle does max reverse flow accur?
Max flap down ( 9 o’clock )
rotor blade is slower at the root than the tip
What is induced flow ?
Washdown
Air flowing vertically through the rotor system
Results from production of lift
Which angle is the mechanical angle ?
AOI (controled by the fight controls)
Which angle is the aerodynamic angle ?
AOA
As induced flow increases, AOA ____ and ____ lift is produced
Decreases, less
The only way to reduce the effects of induced flow is with ____
Forward airspeed
What are the 2 components of TAF ?
Lift and drag
Induced drag ____ with ____ airspeed
decreases with forward
what is “induced drag” ?
A result from the production of lift
Higher AOA = Higher induced drag
When do we have symmetry of lift ?
no wind hover
= no blade flapping
Where does retreating blade stall initiate ?
From the hub and outboard(first 25% has zero span velocity at 9 o'clock)
Why does blades flap ?
To equal the dissymmetry of lift
To increase induced flow AOA must be ____ ?
Decreased
What is the most dominant force in turning the rotor system ?
Centrifugal force
Where are centrifugal forces the greatest ?
Where most lift is produced - just outside the rotor tips
What’s rotor balde coning ?
Upward flexing of the blades
Upward coning is a compromise of ____
Lift and centrifugal forces
What factors can result in blade coning ?
Low RPM, high GW, High G, Turbulent air
How is gyroscopic percession actuated ?
Mechanically
Why are the baldes twisted at the factory ?
To distribute the lifting forces more evenly along the blade
How are the rotor balde twisted ?
High pitch angle at the root decending to lower pitch at the tips
Torque effect is ____ (direction)
clockwise ( to the right )
Tail rotor thrust is ____ torque
opposite
What is translating tendency
a/c tendency to drift to the right (effects of torque and tail rotor thrust)
What’s the relationship of lift to resultant relative wind ?
Perpendicular
What’s the relationship of drag to resulatant relative wind ?
Parallel to and in the same direction
How does a helicoper compensate for unequal lift ?
Blade flapping
How does a pilot control blowback ?
Forward cyclic feathering
The velocity of the relative wind increase when the airfoil produces ____ lift
more
Relative wind = velocity of airflow over wing
What temp, pressure and humidity will produce the most lift ?
(high/low)
High pressure, low temp, low humidity
Centrifugal force is ____ to rotational velocity
proportional
Where is coning angle the greatest and why ?
At the tips because of the greates blade velocity (greatest lift at tip)
How is precession overcome ?
Offsetting the linkage in the cyclic pitch control system to create an input 90 degreese ahead of the desired action
Where is the pitch angle highest ( along the blade ) and why ?
At the root - blade twisting - equal distribution of lift
What requires more power: turning left/right ?
Turning left
How can you determine DA ?
By correcting PA for non-std. temperature
Does upward or downward flapping cause increased lift ?
Downward flapping
What’a the mean camber line ?
A line dividing the airfoil equally in a upper and lower part
What’s the disadvantages of a symmetrical airfoil ?
Less lift at a AOA
bad stall characteristics
What’s the advantages of a nonsymmetrical airfoil ?
More lift at a given AOA
Increased lidt/drag ratios
better stall characteristics
What’s the advantages of a symmetrical airfoil ?
Constant center of pressure
Easy construction
Lower cost
Relative wind ____ velocity on the retreating side, which can lead to ____ at the hub
Reduces, no lift area
Semi-rigid rotor system tilts .. ?
Disk tilts relative to the mast
When will the baldes cone upward ?
When lift is stronger than centrifugal force
What are the 4 types of rotor blade actions ?
Rotation
Flapping
Feathering
Hunting (articulated/rigid)
What is cyclic feathering
Incresed pitch of one rotor blade while simultaneously decreasing the pitch of the others
Tilts the rotor disk for directional control and control of dissummetry of lift
Doesn’t change overall lift, but increases lift in one half while simultaneously decreasing lift in the other half
What does collective feathering mean ?
A pitch change to all rotor blades that affects the overall lift of the rotor system and provides vertical control
What’s the purpose of (rotor blade) hunting ?
Relieves the stress forces on the blade caused by flapping
If the tip path plane is ____ by the ____ control, the total force will incline in the ____ the rotor is tilted
tilted, cyclic pitch, same direction
What are the two components of total force when til tip path plane is tilted ?
Vertical acts as lift (opposes weight)
Horizontal acts as thrust (opposes drag)
How is thrust produced (total force and tip path)
By tilting the tip path plane
ETL:
Relative wind becomes more ____ which results in: ?
Horizontal
- More vertical lift
- Less induced drag
- Increased AOA
What causes blowback
Dissymmetry og lift and gyroscopic pressesion
What is transverse flow effect ?
Forward movement
Resultant wind hits the rotor different
vertically front/horizontal back
Fwd = Less induced drag = more AOA + Lift
Gyroscopic preccession = effect are felt 90 degress later
More lift left than right
Helicopter drift right
10-20 kts
What determine the max rotor RPM limit ?
Centrifugal forces - due to structural limitations on the main rotor system
When does rotor blade coning start to occur ?
When the rotor begins to develope lift
DA affects what in regards to the a/c ?
Max TQ available
Max GW
Performance
1
Tip path plane/Plane of rotation
2
Chord line
3
Axis of rotation
4
Rotational relative wind
5
Induced flow
6
AOA
7
Resultant relative wind
8
AOI
9-10-11
Lift-Drag-TAF
Loss or apparent loss of ground effect is caused by ?
- Altitude greater than rotor diameter
- Trees and bushes
- Tall grass and uneven terrain
- Hovering over water
- Begining translational movement
- Hovering into a wind
