Level 4 PC Assessment Review – Aviation

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Theory of Flight

• Boundary Layer

  • Very thin layer of air lying over the surface of the wing
  • Includes laminar and turbulent flow, which are separated by the transition point

• Laminar flow

  • Smooth airflow over the wing
  • Initial portion until the boundary layer is tripped at the transition point
  • Laminar flow airfoils reduce the drag by maintaining the laminar flow throughout a greater percentage of the chord

• Conventional Airfoils

  • Thickest airfoils are generally thickest at 25% of the chord

• Aspect ratio

  • Dividing span by the average chord

• Wash in vs wash out

  • Wash in: increasing the angle of incidence at the wing tip relative to the wing root
  • Wash out: decreasing the angle of incidence at the wing tip

• Wing tip modifications designed to increase lift or reduce drag

  • Wing tip fuel tanks
  • Winglets
  • Drooping wing tips

• Slots and slats

  • Slots: auxiliary airfoils that remain fixed on the leading edge
  • Slats: auxiliary airfoils that move out in front of the leading edge at high angles of attack

• Camber

  • Curvature of the airfoil

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Instruments

• Pitot static system
  • Pitot static system
  • Connected to the airspeed indicator, altimeter and vertical speed indicator
  • Includes a pitot pressure source and static pressure source
    • Pitot tube measures ram air pressure, or dynamic pressure, by the air rushing in due to the forward movement of the aircraft
    • Static port measures the differences in atmospheric pressure, and are not affected by ram air pressure
  • All instruments are connected to the static pressure source, where only the airspeed indicator is attached to the pitot tube
• Airspeed Indicator errors
  • Density Error
  • Density of air depends on atmospheric pressure and temperature
  • These variables affect the air speed indicator reading as it changes the pressure differential between components within the airspeed indicator
  • Position Error
  • Depends on location of pitot tube on the aircraft
  • Farther back on the aircraft, it may receive more eddies and give a less accurate reading, where as at the front of the aircraft it is in more smooth, laminar flow
  • Lag Error
  • Mechanical error due to friction between working parts
  • Icing or Water Error
  • Blocks the pitot or static pressure sources
• Airspeeds
  • Indicated
  • What is read off the airspeed dial
  • Calibrated
  • Indicated corrected for instrument error
  • Equivalent
  • Calibrated corrected for compressibility factor
  • True
  • Equivalent corrected for the airspeed indicator error due to density and the temperature
  • Actual speed of the airplane through the air mass
  • Mnemonic to remember airspeeds: ICE Tea is a Pretty Cool Drink
  • Moves in a zig zag pattern from I to P to C, and so on to show the different airspeeds (top row) and the factor (bottom row) that changes it to the next airspeed

I C E T

P       C       D

• Density altitude

  • Pressure altitude corrected for temperature

• Precession

  • Tendency of a rotating body, when a force is applied perpendicular to its plane of rotation, to turn in the direction of its rotation 90 degrees to its axis and take up a new plane of rotation parallel to the force applied.

• Mach number

  • Mach number is calculated by dividing the airspeed by the speed of sound

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Engine

• Fuel selector valve
  • Use to select desired fuel tank to draw fuel from
  • Use to shut off the flow of fuel from the tanks
• Throttle
  • Forward movement opens the throttle valve, which increases the fuel to air mixture and increases the power being produced by the engine
• Gauges
  • Oil Pressure Gauge
  • Indicates oil pressure supplied by the oil pump to lubricate the engine
  • Oil Temperature Gauge
  • Gives a reading of the temperature of the oil
  • Cylinder Head Temperature Gauge
  • Records the temperature of one or more of the engine cylinder heads
  • Gives a reasonably good indication of the effectiveness of the engine cooling system
  • Carburetor Air Temperature Gauge
  • Indicates temperature of the mixture entering the manifold
  • Or may record temperature of the intake air entering the carburetor
  • Tachometer
  • Shows the speed at which the engine crankshaft is turning in hundreds of revolutions per minute
  • Arcs:
    • Green – good
    • Yellow – caution range
    • Red – danger range
  • Manifold Pressure Gauge
  • Settings are controlled by the throttle
  • Indicates the pressure of the fuel to air mixture in the engine intake manifold between the cylinders and the carburetor
• Pitch
  • Distance a propeller travels forward in one revolution
• Thrust is maintained throughout most of the diameter of the propeller by means of the variation in airfoil sections and the angle of attack
• Increase in Altitude
  • Air becomes less dense so power decreases without corrective action by the pilot

Meteorology

• Surface friction on winds

  • Causes lower wind speeds than would be expected from the pressure gradient
  • Slows down the wind speed due to contact resistance with the ground

• Define air mass

  • Large section of the troposphere with uniform properties of temperature, moisture within the horizontal.

• Anabatic and katabatic winds

  • Anabatic: up slope winds flowing from valleys up the slopes to higher elevations
  • Katabatic: down slope winds flowing from high elevation down to the valleys below
  • Mnemonic: Ana ran up the hill and kicked the cat down

• Gust

  • Rapid and irregular change of wind speed

• Main factors determining weather in an airmass

  • Moisture content
  • Cooling process
  • Stability of the air

• Stable air conditions

  • Stratus clouds
  • Poor visibility
  • Steady precipitation

• Unstable air conditions

  • Cumuloform clouds
  • Good visibility
  • Showering precipitation

• Cold Air Mass

  • More dense so sinks
  • Undercuts warmer air where will ascend over the colder air

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Navigation

• Great Circle
  • Shortest distance between two points on the surface of the earth
• Rhumb Line
  • Lines that cuts all meridians at the same angle
  • Allows for constant direction so that the navigator may have a constant heading
• TVMDC Headings
  • Variation is the angle between true and magnetic headings
  • Deviation is the angle between magnetic and compass headings
  • Moving from T -> M -> C add west and subtract east (east is least, west is best)
• Isogonal Line
  • Lines drawn joining places having the same variation
• Agonic Line
  • Joining places of zero variation
• Compass Lead and Lag
  • ANDS – acceleration causes turns to the north, deceleration causes turns to the south
  • Occurs on east and west headings
• Meridians of Longitude
  • Semi-great circles joining the geographical poles of the earth
  • Measured 0 to 180 degrees east and west
• Parallels of Latitude
  • Circles in the Earth’s surface that lie parallel to the equator
  • Measured 0 to 90 degrees north and south of the equator

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