Final Exam for METR 122

LOCK INN!!

What is viscosity?

Viscosity is the slight resistance to deformation under force.

What is drag?

Drag is the interaction between the surface of a moving object and viscosity of the air.

What is pressure?

Pressure is a force applied perpendicular to the surface of an object.

What is Density Altitude?

Density Altitude is Pressure Altitude adjusted for T and humidity.

What impact does low air density have on an aircraft

It causes the aircraft to fly at higher pressure altitude while decreasing power, thrust, and lift due to thin air.

What impact does high air density have on an aircraft?

It causes the aircraft to fly at a lower pressure altitude.

What are some of the ways density altitude can change?

1. As T ↑, density ↓

2. As humidity ↑, density ↓

3. As altitude ↑, density ↓

What is Bernoulli’s Principle of Differential Pressure?

As velocity of a moving object ↑, the P of the fluid ↓

How does Bernoulli’s Principle of Differential Pressure “cause” lift?

It works with Newton’s Laws of Motions to produce lift.

• The air moving over the wing moves faster to account for the longer distance (Lowering P)

• Since P is now lowered at the top (Bernoulli), lift is produced since P moves from H to L

What are the four main forces acting on an aircraft?

1. Thrust

2. Drag

3. Lift

4. Weight

How do changes in thrust, lift, drag, and weight yield changes in lift?

• When engine power ↑, thrust > drag + speed ↑

• When engine power ↓, thrust < drag + speed ↓

• If thrust ↓ and airspeed ↓, lift < weight, and the aircraft descends

How does an aircraft accelerate?

An aircraft accelerates when thrust > drag. It will continue to accelerate until thrust = drag

Describe how AOA can be used to adjust lift

The AOA determines how air flows over the wing to generate lift.

• At a constant airspeed, an ↑ in AOA = ↑ lift

• An increase after max AOA = rapidly diminishing lift (stalling AOA)

How should the AOA be adjusted at low airspeeds?

The AOA must be high to maintain balance between lift and weight.

How should be the AOA be adjusted when thrust ↓?

If thrust ↓, airspeed will also ↓, so the AOA must be ^^ or the aircraft will lose altitude.

How should the AOA be adjusted when thrust ^^?

If thrust ^^, speed and lift will ^^ too unless the AOA is decreased enough to maintain balance.

How does an aircraft maintain lift at higher altitudes?

An aircraft must fly at a greater true airspeed at any AOA (also applies for warm, humid days) since air is less dense.

What is Roll?

Roll is side to side motion controlled by ailerons on the wings

• Wings move up and down

What is Pitch?

Pitch is up and down motion controlled by the elevator on the tail.

• Nose moves up and down

What is Yaw?

Yaw is rotation along the vertical axis controlled by the rudder.

• Nose moves side to side

Explain how AOA, thrust, and banking need to be managed to successfully maintain altitude

To maintain altitude while banking, ^^ AOA until lift = weight. Since ^^ AOA = ↓ airspeed + ^^ drag, you need to ^^ thrust also.

Describe how different atmospheric conditions may influence aircraft performance.

Landing + takeoff are affected if atmosphere varies from standard atmosphere. Also affected from tailwinds and water on runway.

Determine how pressure altitude may change.

Changes if T and/or SLP varies from standard

What is banking?

Banking is tilting an aircraft to its side to change heading of an aircraft.

List out the gases of the atmosphere by volume

1. Nitrogen (N2) - 78%

2. Oxygen (O2) - 21%

3. Argon (Ar) - .93%

4. CO2 - .043%

5. WV (H20) - 0-4%

What is the importance of greenhouse gases with respect to atmospheric Ts?

Greenhouse gases absorb SWR and radiate heat.

What are the layers of the atmosphere?

exosphere

thermosphere

mesosphere

stratosphere

troposphere

Troposphere

• Highest in summer and tropics

• Lowest in winter and arctics

• Almost all weather occurs here

• Almost all WV held here

• Extends to 36,000 ft

Stratosphere

• Contains the ozone layer

• Isothermal at bottom and T inversion w height

• Commercial airlines fly at bottom

• Severe turb can occur from overshooting cumulus tops

• 36k - 164k

Mesosphere

• 164k - 278k

• Slows down meteorites

• Less density lowers warming from UV

Thermosphere

• Exceedingly hot at top

• Only UV and x-ray absorbed

Exosphere

• Atoms escape into space

• Satellites orbit here

What are the three ways heat is transferred?

1. Conduction

2. Convection

3. Radiation

What is Conduction?

Conduction is the transfer of heat energy from molecule to molecule (solids)

What is Convection?

Transfer of heat energy by mass movement of molecules (fluids)

What is Radiation?

Heat transfer from electromagnetic radiation.

• Sun emits SWR

• Earth absorbs SWR and emits LWR

What controls the seasonal T variations?

Earth’s tilt (23.5 degrees) and peak zenith days

What controls the diurnal cycle?

Peak insolation hours and T lag

• Peak heat occurs 3-4 hours later bc SWR is still > than LWR

• As sun sets, insolation ↓ and LWR > SWR, so T ↓

What controls T inversions?

Fog and pollution

What is Pressure?

Pressure is the force per unit area exerted by the mass of the atmosphere

How does P + D vary in cold air columns?

Cold air has a low height and more dense (trough + LP)

• As P ↑, D ↑

• As T ↓, D ↑

How does P + D vary in warm air columns?

Warm air has a high height and less dense (ridge + HP)

• As P ↓, D ↓

• As T ↑ , D ↓

What is Indicated Altitude?

Reading from altimeter

• if P is 29.92’’, PA = IA = 0 ft.

What is True Altitude?

The actual vertical distance above sea level

What is Absolute Altitude?

The actual vertical distance above the ground

• TA - terrain elevation = AA

What is Transition Altitude?

The altitude where pilots transition to flying via flight levels

What happens when PA ↓ en route?

Your true altitude is lower than indicated

What impact does high density altitude (or low density) have on aspects of flight?

1. Reduces power to engines

2. Reduces lift bc ↓↓ rate of climb

3. Reduces thrust

4. Increased runway for takeoff and landing because of increased groundspeed

What are some wind directions based off of degrees and cardinal directions?

1. ENE = 67.5º

2. E = 90º

3. SSE = 157.5º

4. S = 180º

5. SW = 225º

6. W = 270º

7. NW = 315º

What are the four forces that effect wind flow?

1. PGF

2. Coriolis

3. Centrifugal

4. Friction

What is PGF?

Wind is driven by P differences across an area

• Flows from H → L P in an attempt to equalize

• Strength of wind is proportional to distance between isobars

What is the Coriolis Force?

Apparent force that acts on objects moving in a rotating reference frame

• Curves right in NH

• Curves left in SH

• 0 at ITCZ, max at poles

• As wind speed ^^, CF ^^

What is Centrifugal Force?

Apparent force that accounts for inertia on winds moving along a curved path

• Only applies to winds curving around a trough/ridge or H/LP

What is Friction Force?

Friction between wind and terrain

• As roughness ^^, FF ^^

• As wind speed ^^, FF ^^

Sea Breeze Circulation (Day)

Winds blowing from sea to land

• Warm air rises over land (LP)

• Cool air rises over water (HP)

• Peaks in afternoon

• PM Tstorm can occur from cool, moist air lifted at shore

Land Breeze Circulation (Night)

Winds blowing from land to sea

• Warm air rises over sea (LP)

• Cool air rises over land (HP)

• Weaker than sea breeze

• Offshore Tstorms

Lake Breeze Circulation

Like sea breeze circulation

• Large lakes required

• Mainly spring and summer

• PM Tstorms if humid enough

Valley Breeze Circulation (Day)

Winds traveling upslope

• HP in valley

• LP and clouds/tstorms at mountain tops

Mountain Breeze Circulation (Night)

Cool dense air sinks into valley

• HP at tops, LP in valley

• creates clear, calm conditions

What is saturation?

Balance between evaporation and condensation

• Parcel holds all the WV it can at a given T

• No clouds initially

• Added WV = clouds

• Any more = precip

What is Relative Humidity?

The ratio of actual WV in the air relative to the capacity at a given T

• as T ^^, RH __

• Only represents how close air is to saturation

What is dewpoint?

The T an air parcel has to be cooled to for saturation to occur

• Direct measure of WV content

Phases of the Water Cycle?

• Evaporation

• Condensation

• Transpiration

• Sublimation

• Precipitation

• Runoff

• Infiltration

• Ground Water

• Plant Water

What phases add heat to the atmosphere?

• Condensation

• Freezing

• Deposition

What phases remove heat from the atmosphere?

• Evaporation

• Sublimation

• Melting

What is an adiabatic process?

It is a process that produces no transfer of heat energy between the environment and parcel.

What is stability?

The tendency for a parcel to return to its original position when disturbed.

What is the DALR?

9.8C/km
unsaturated

What is the Dewpoint Lapse Rate?

1.8C/km

What is the MALR?

4-9.5C/km
saturated

What are the different ways uplift can occur?

1. Convergence

2. Convection

3. Buoyancy: warm rising air and cool sinking air. up and back down

4. Frontal Lift

5. Orographic Uplift

Absolute Stability

ELR < MALR

• Lifted parcel is always colder than environment

• Sunny w flat/layered clouds

• Common w isothermal and T inversion layers

Neutral Stability

ELR = DALR (unsaturated)
ELR = MALR (saturated)

• Common in small pockets

Absolute Instability

ELR > DALR

• Shallow layer near surface

• Any lifted parcel is warmer than environment

Conditional Instability

MALR < ELR < DALR

• Stable when unsaturated

• Unstable when saturated

CST to Z (or reversed)?

+/- 6 hours

CDT to Z (or reversed)?

+/- 5 hours

EST to Z (or reversed)?

+/- 5 hours

EDT to Z (or reversed)?

+/- 4 hours

MDT to Z (or reversed)?

+/- 6 hours

PDT to Z (or reversed)?

+/- 7 hours

AKDT to Z (or reversed)?

+/- 8 hours

HST to Z (or reversed)?

+/- 10 hours

• Hawaii does not observe Daylight Savings Time

MST to Z (or reversed)?

+/- 7 hours

PST to Z (or reversed)?

+/- 8 hours

AKST to Z (or reversed)?

+/- 9 hours

Example 1: Convert the following time to UTC (Z) 1:00 pm EDT

• Step 1: Convert 1:00 pm to military time 1:00 pm = 1300

• Step 2: Figure out UTC adjustment EDT = 4 hours

• Step 3: Add adjustment to military time 1300 + 4 hours = 1700Z

Example 2: Convert the following time to UTC (Z) 5:15 am PST

• Step 1: Convert 5:15 am to military time 5:15 am = 0515

• Step 2: Figure out UTC adjustment PST = 8 hours

• Step 3: Add adjustment to military time 0515 + 8 hours = 1315Z

Example 3: Convert the following Z Time to local time (EDT) 1700Z

• Step 1: Figure out UTC adjustment EDT = 4 hours

• Step 2: Subtract UTC adjustment from Z time 1700Z – 4 hours = 1300

• Step 3: Convert military time to local time 1300 = 1:00 pm EDT

Example 4: Convert the following Z time to local time (PST) 1315Z

• Step 1: Figure out UTC adjustment PST = 8 hours

• Step 2: Subtract UTC adjustment from Z time 1315Z – 8 hours = 0515

• Step 3: Convert military time to local time 0515 = 5:15 am PST

What is cold and warm air advection?

Warm air advection occurs when a warm airmass moves into an area previously occupied by a cold air mass.

Cold air advection occurs when a cold airmass moves into an are previously occupied by a warm air mass.

Where is vorticity found?

500 mb

Where is the jet streak found?

300 mb

Where are baroclinic zones?

850 mb

What is a baroclinic zone?

An area where isotherms cross height contours at any angle.

• Do not have T gradients

AWC issues a suite of aviation weather forecasts including:

Airman’s Meteorological Information (AIRMET)
• Significant Meteorological Information (SIGMET)
• Convective SIGMETs
• Area Forecasts (FA)
• Significant Weather Prognostic Charts (low, middle, high)
• National Convective Weather Forecast (NCWF)
• Current Icing Product (CIP)
• Ceiling and Visibility Analysis (CVA)

How do radars work?

Antenna dish sends out short pulses of electromagnetic waves, traveling at the speed of light. When they hit water particles, they reflect back to the radar. How long they take to come back to the radar determines the distance.

Two radar modes?

Clear Air
Precip

Attenuation

Any process which reduces energy within the radar beam.

Precipitation Attenuation

↓↓ of energy within radar beam due to absorption/scattering of energy from precip particles.

• Related to wavelength of radar. Shorter (aircraft) wavelengths more attenuated