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UH 72 > EXAM ( WEATHER, AERODYNAMIC ) > Flashcards

EXAM ( WEATHER, AERODYNAMIC ) Flashcards

1
Q

What does the high dew point spread mean ?

A

That the air is dryer

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2
Q

What does prevailing wind mean ?

A

A wind that blows permanently from a perticular direction

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3
Q

Wind circle: What does the red hash mean ?

A

2 min avarage of prevailing wind

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4
Q

Name the wind speed from top to bottom

A

Wind calm
5 kts
10 kts
50 kts

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5
Q

How often is a METAR issued ?

A

every hour on the hour

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6
Q

When can a SPECI be issued and why ?

A

Any time during the current METAR, when there is a significant change to the exciting conditions

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7
Q

What periode of the year is daylight saving ?

How much does the time change ?

A

2nd sunday in march to 1st sunday in november

+1 hour

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8
Q

When is VV used ?

A

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.

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9
Q

When is “CLR” used ?

A

No clouds below 12.000 ft (automated observation)

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10
Q

When is “SKC” used ?

A

No clouds at a manned station (not automated)

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11
Q

Name the two cloud layers and two ceilings

A

Layer: FEW, SCT
Ceiling: OVC, BKN

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12
Q

What does the following abbreviations signify? :
AO
AO1
AO2
AO2A

A

AO Automated observation
AO1 Automated no PD
AO2 Automated with PD
AO2A Automated with PD and human controlled

PD = Precipitation determinator (speed and type)

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13
Q

When is RVR reported ?
What does P & M indicate in this regard

A

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.

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14
Q

When can gust spread speed reliably be determined ?

A

When the spread is > 10 kts

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15
Q

What does the following abbreviations mean and signify ?

On station
VC
DSTN

A

Weather observed

On station: 0-5 NM
Vicinity: 5-10 NM
Distance: +10 NM

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16
Q

What is “obscurations” ?

A

Any phenomenon ( other than Precipitation ) that obscures the horizontal visibility

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17
Q

How far out does the TAF cover the weather ?

A

5 mile radius from the center of the RW complex

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18
Q

Which forecast/observation display visability in meters/SM ?

Metar/TAF

A

Metar: SM
TAF: meters

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19
Q

How many SM is visability 9999 (TAF)

A

7 SM or greater

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20
Q

How big of a dew point spread results in posible visible moister in the air ?

A

2 degrees

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21
Q

Change groups meaning:
FM
BECMG
TEMPO
PROP

A

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

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22
Q

What does the following mean ?
TX35/0518ZTN22/0509Z

A

Represent the end of the validity - there will be no more reporting lines

TX = max temp
TN = min temp

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23
Q

What does the following signify ?
P6SM

A

Visability +7 SM (9999)

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24
Q

Temperature and pressure are the two most critical factors with ____ being the most critical

A

Temperature

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25
Q

What are the 3 components of atmospheric density ?

A

Temperature, pressure and humidity

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26
Q

If temperatures are colder than standard, what are TA and DA in regards to PA?

A

Lower than standard

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27
Q

If temperatures are warmer than standard, TA & DA are always ___ ?

A

Higher than standard

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28
Q

Which is more favorable for aviation:
Higher or lower pressure ?

A

Higher pressure

high pressure pushes air down and keep moister from raising = no clouds, rain, storms + sunny weather

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29
Q

What DA follows with higher pressure

A

Lower density altitude
= better a/c performance

colder, dryer air

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30
Q

What’s standard pressure laps rate ?

A

1 inch / 1000 ft

= 1000' altitude - 28.92 inches of mercury (standard day)

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31
Q

What’s standard temperature laps rate ?

A

2º / 1000’

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32
Q

At what altitude (standard atmosphere) does temperature become minus degrees ?

A

7500’

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33
Q

If the static pressure system fails which instruments fail ?

A

IAS, VSI and ALT

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34
Q

What altitude do you set in the kollsman window ?

A

Pressure altitude -> corrected for non-standard pressures (MSL)

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35
Q

How often should you attempt to get current altimeter setting ?

A

Every 50 NM ( not exceeding 100 NM )

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36
Q

What’s the purpose of the kollsman window ?

A

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)

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37
Q

What’s: True altitude ?

A

Height above MSL (QNH)

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38
Q

What’s: Absolute altitude ?

A

Height above the ground - AGL (QFE)

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39
Q

What’s: Pressure altitude ?

A

Altitude above the standard datum plane
( 29.92, 1013.5)

MSL at a standard day (15 degrees celcius, 29.92 at seal level)

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40
Q

What’s: Density altitude ?

A

PA corrected for non standard temperatures

“Density corresponding to a given altitude in a standard atmosphere”

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41
Q

What altitude do you set > 18.000’

A

Pressure altitude

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42
Q

What pressure altitude is altimeter setting and what happens in air if the raise pressure (altimeter) ?

A

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.

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43
Q

If temperatures are warmer than standard the a/c will be:
higher/lower ?
than standard altitude

A

Higher

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44
Q

How do you determine the accuracy of the a/c altimeter

A

Set field elevation, then true altitude (QNH).

max +- 75’ deviation

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45
Q

What’s impact pressure ?

A

Static + dynamic pressure

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46
Q

What’s atmospheric pressure ?

A

The force exerted by the weight og a column of air

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47
Q

Define static pressure

A

Ambient pressure

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48
Q

What’s IAS ?

A

Shown on the dial of the instrument, uncorrected

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49
Q

What’s TAS

A

CAS corrected for nonstandard pressure and temperature

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50
Q

What’s CAS

A

IAS corrected for instrument and position error

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51
Q

Name and explain the 3 errors in the airspeed indicator

A
  1. Installation error (misalignment of the pitot tube + placement of static vents)
  2. Density error (Pressure and temperature changes in the atmosphere)
  3. Instrument error (Friction in the instrument)
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52
Q

Define altimeter setting

A

Station pressure corrected for MSL

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53
Q

Is DA higher/lower than PA when temperature is higher than standard

A

Higher

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54
Q

If temperature decreases below standard temp. where is DA in relation to PA ?

A

Lower

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55
Q

Does high DA and low air density mean the same thing ?

A

Yes

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56
Q

What’s true airspeed ?

A

CAS corrected for density error

57
Q

How does humidity affect air pressure ?

A

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)

58
Q

Fill in the boxes

A
59
Q

Which of newtons laws of motion applies:

Torque effect

A

Action/Reaction

60
Q

Which of newtons laws of motion applies:

More power needed to obtain a desired RPM than is need to maintain the RPM

A

Inertia

61
Q

Which of newtons laws of motion applies:

Greater load, less acceleration

A

Acceleration

62
Q

Define center of pressure

A

The point along the chord line of an airfoil through which all aerodynamic forces are considered to act

63
Q

If airflow atop of an airfoil increases, what happens to static pressure ?

A

Decreases

64
Q

List the two basic types of airfoils

A

Symmetrical & nonsymmetrical

65
Q

Define: Rotational relative wind

A

That flow of air parallel and opposite to the flight path of a rotating airfoil (produced by the rotor blades turning about the mast)

66
Q

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

A:2
B:1
C:4
D:3

Rotational relative wind to airfoil movement: Parallel and opoosit

67
Q

Define induced flow

A

Downward flow of air through the rotor blades

downwash

68
Q

Define reultant relative wind

A

Rotational wind modified by induced flow

69
Q

Between what is AOA measured ?

A

Resultant relative wind and chord line

70
Q

Between what is AOI measured ?

helicopter

A

Chord line and plane of rotation relative wind (tip path plane)

71
Q

What 3 events affect the rotor blades when passing through the 6 o’clock position ?

A
  1. The baldes advance into a relative wind
  2. The balde begins to speed up
  3. 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

71
Q

What happens to the airflow over the blade when entering the retreading half ?

A

An increase in reverse flow

72
Q

When in the rotor cycle does max reverse flow accur?

A

Max flap down ( 9 o’clock )

rotor blade is slower at the root than the tip

73
Q

What is induced flow ?

A

Washdown
Air flowing vertically through the rotor system
Results from production of lift

74
Q

Which angle is the mechanical angle ?

A

AOI (controled by the fight controls)

75
Q

Which angle is the aerodynamic angle ?

A

AOA

76
Q

As induced flow increases, AOA ____ and ____ lift is produced

A

Decreases, less

77
Q

The only way to reduce the effects of induced flow is with ____

A

Forward airspeed

78
Q

What are the 2 components of TAF ?

A

Lift and drag

79
Q

Induced drag ____ with ____ airspeed

A

decreases with forward

80
Q

what is “induced drag” ?

A

A result from the production of lift

Higher AOA = Higher induced drag

81
Q

When do we have symmetry of lift ?

A

no wind hover
= no blade flapping

82
Q

Where does retreating blade stall initiate ?

A

From the hub and outboard
(first 25% has zero span velocity at 9 o'clock)

83
Q

Why does blades flap ?

A

To equal the dissymmetry of lift

84
Q

To increase induced flow AOA must be ____ ?

A

Decreased

85
Q

What is the most dominant force in turning the rotor system ?

A

Centrifugal force

86
Q

Where are centrifugal forces the greatest ?

A

Where most lift is produced - just outside the rotor tips

87
Q

What’s rotor balde coning ?

A

Upward flexing of the blades

88
Q

Upward coning is a compromise of ____

A

Lift and centrifugal forces

89
Q

What factors can result in blade coning ?

A

Low RPM, high GW, High G, Turbulent air

90
Q

How is gyroscopic percession actuated ?

A

Mechanically

91
Q

Why are the baldes twisted at the factory ?

A

To distribute the lifting forces more evenly along the blade

92
Q

How are the rotor balde twisted ?

A

High pitch angle at the root decending to lower pitch at the tips

93
Q

Torque effect is ____ (direction)

A

clockwise ( to the right )

94
Q

Tail rotor thrust is ____ torque

A

opposite

95
Q

What is translating tendency

A

a/c tendency to drift to the right (effects of torque and tail rotor thrust)

96
Q

What’s the relationship of lift to resultant relative wind ?

A

Perpendicular

97
Q

What’s the relationship of drag to resulatant relative wind ?

A

Parallel to and in the same direction

98
Q

How does a helicoper compensate for unequal lift ?

A

Blade flapping

99
Q

How does a pilot control blowback ?

A

Forward cyclic feathering

100
Q

The velocity of the relative wind increase when the airfoil produces ____ lift

A

more

Relative wind = velocity of airflow over wing

101
Q

What temp, pressure and humidity will produce the most lift ?

(high/low)

A

High pressure, low temp, low humidity

102
Q

Centrifugal force is ____ to rotational velocity

A

proportional

103
Q

Where is coning angle the greatest and why ?

A

At the tips because of the greates blade velocity (greatest lift at tip)

104
Q

How is precession overcome ?

A

Offsetting the linkage in the cyclic pitch control system to create an input 90 degreese ahead of the desired action

105
Q

Where is the pitch angle highest ( along the blade ) and why ?

A

At the root - blade twisting - equal distribution of lift

106
Q

What requires more power: turning left/right ?

A

Turning left

107
Q

How can you determine DA ?

A

By correcting PA for non-std. temperature

108
Q

Does upward or downward flapping cause increased lift ?

A

Downward flapping

109
Q

What’a the mean camber line ?

A

A line dividing the airfoil equally in a upper and lower part

110
Q

What’s the disadvantages of a symmetrical airfoil ?

A

Less lift at a AOA
bad stall characteristics

111
Q

What’s the advantages of a nonsymmetrical airfoil ?

A

More lift at a given AOA
Increased lidt/drag ratios
better stall characteristics

112
Q

What’s the advantages of a symmetrical airfoil ?

A

Constant center of pressure
Easy construction
Lower cost

113
Q

Relative wind ____ velocity on the retreating side, which can lead to ____ at the hub

A

Reduces, no lift area

114
Q

Semi-rigid rotor system tilts .. ?

A

Disk tilts relative to the mast

115
Q

When will the baldes cone upward ?

A

When lift is stronger than centrifugal force

116
Q

What are the 4 types of rotor blade actions ?

A

Rotation
Flapping
Feathering
Hunting (articulated/rigid)

117
Q

What is cyclic feathering

A

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

118
Q

What does collective feathering mean ?

A

A pitch change to all rotor blades that affects the overall lift of the rotor system and provides vertical control

119
Q

What’s the purpose of (rotor blade) hunting ?

A

Relieves the stress forces on the blade caused by flapping

120
Q

If the tip path plane is ____ by the ____ control, the total force will incline in the ____ the rotor is tilted

A

tilted, cyclic pitch, same direction

121
Q

What are the two components of total force when til tip path plane is tilted ?

A

Vertical acts as lift (opposes weight)
Horizontal acts as thrust (opposes drag)

122
Q

How is thrust produced (total force and tip path)

A

By tilting the tip path plane

123
Q

ETL:
Relative wind becomes more ____ which results in: ?

A

Horizontal

  1. More vertical lift
  2. Less induced drag
  3. Increased AOA
124
Q

What causes blowback

A

Dissymmetry og lift and gyroscopic pressesion

125
Q

What is transverse flow effect ?

A

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

126
Q

What determine the max rotor RPM limit ?

A

Centrifugal forces - due to structural limitations on the main rotor system

127
Q

When does rotor blade coning start to occur ?

A

When the rotor begins to develope lift

128
Q

DA affects what in regards to the a/c ?

A

Max TQ available
Max GW
Performance

129
Q

1

A

Tip path plane/Plane of rotation

130
Q

2

A

Chord line

131
Q

3

A

Axis of rotation

132
Q

4

A

Rotational relative wind

133
Q

5

A

Induced flow

134
Q

6

A

AOA

135
Q

7

A

Resultant relative wind

136
Q

8

A

AOI

137
Q

9-10-11

A

Lift-Drag-TAF

138
Q

Loss or apparent loss of ground effect is caused by ?

A
  1. Altitude greater than rotor diameter
  2. Trees and bushes
  3. Tall grass and uneven terrain
  4. Hovering over water
  5. Begining translational movement
  6. Hovering into a wind

UH 72 (42 decks)

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