Aircraft Maintenance Knowledge Levels

Knowledge Levels

• Basic knowledge levels for aircraft maintenance licenses A, B1, and B2 are indicated by indicators (1, 2, or 3) against each subject.
• Category C applicants must meet either B1 or B2 basic knowledge levels.

Level 1

• The applicant should be familiar with the basic elements.
• The applicant should be able to describe simply, using common words and examples.
• The applicant should be able to use typical terms.

Level 2

• A general knowledge of theoretical and practical aspects is required.

• The Objectives for Level 2 include:

  • Understanding theoretical fundamentals.
  • Providing descriptions with examples.
  • Using mathematical formulas with physical laws.
  • Reading and understanding sketches, drawings, and schematics.
  • Applying knowledge practically using procedures.

Level 3

• A detailed knowledge of theoretical and practical aspects is needed.

• This includes combining knowledge elements logically.

• The Objectives for Level 3 include:

  • Knowing the theory and relationships with other subjects.
  • Providing detailed descriptions using theoretical fundamentals and examples.
  • Understanding and using mathematical formulas.
  • Preparing sketches and schematics.
  • Applying knowledge using manufacturer's instructions.
  • Interpreting results and applying corrective actions.

Physics of the Atmosphere

• The learning objective is to interpret International Standard Atmosphere (ISA) conditions at sea level and identify changes in the atmosphere with altitude.

Fundamentals of the Atmosphere

• An atmosphere is a layer of gases surrounding a planet where weather and climatic conditions are generated.

Composition of the Atmosphere

• The atmosphere consists of 78% nitrogen, 21% oxygen, and 1% other gases like carbon dioxide.
• Physical properties can vary within the atmosphere affecting aircraft performance.
• Atmospheric characteristics impact aircraft operation, maintenance, lift, drag, and engine power due to density variations.

Atmospheric Regions

• The atmosphere includes the troposphere, tropopause, stratosphere, mesosphere, and thermosphere (ionosphere).
• Classification is based on temperature variations with altitude.
• Aircraft typically fly in the troposphere and the lower stratosphere.

Troposphere

• The troposphere is where almost all aircraft fly and contains water vapor, causing weather.
• The temperature drops approximately 2°C for every 1000 ft increase in altitude, a phenomenon known as the lapse rate.

Tropopause

• The tropopause is where temperature stabilizes, marking the top of the troposphere and the start of the stratosphere.
• The temperature at the tropopause is approximately -57 °C.
• The tropopause occurs at approximately 20,000 ft above the poles and at approximately 60,000 ft above the equator.
• The International Standard Atmosphere (ISA) assumes an average height of 36,000 ft for the tropopause.

Stratosphere

• The stratosphere is the atmospheric layer above the tropopause.
• There is no water vapor in the stratosphere, therefore no weather.

Atmospheric Conditions

Air Pressure

• Air pressure is caused by the weight of air above a surface.
• Average pressure values at sea level in standard conditions are:
  • 14.7 PSI
  • 29.92 inches of mercury (Hg)
  • 760 mm of Hg
  • 1013.25 millibars or hecto Pascal
• Mercury barometers measure air pressure by balancing the weight of the atmosphere against a column of mercury.
• At see level the height of murcury in the tube measures 29.92 in. Hg or 1013.25 mbar.

Air Density

• Density is the mass per unit volume and is a property that makes flight possible.
• Lower atmospheric density makes flight more difficult.
• Air is less dense at high altitudes due to lower pressure.
• Density increases as pressure increases and temperature decreases.

Air Temperature

• Air temperature decreases gradually as altitude increases.
• The lapse rate in the troposphere is 2°C per 1000 feet.
• The rate of temperature decrease remains constant until about 36,000 ft (the tropopause).
• At the tropopause, the temperature ceases to fall and remains practically constant.

Viscosity

• Viscosity is important in aerodynamics because air tends to "stick" to surfaces, slowing motion.

Humidity

• Humidity is moisture in the air, varying with temperature.
• Small water vapour proportion produces dry air.
• Significant water vapour proportion produces humid air.
• Higher air temperature enables the absorption of more water vapour.
• Air on a humid day weighs 5/8ths less than perfectly dry air.

Absolute Humidity

• Absolute humidity is the actual water vapor in air and water mixture.
• The higher the air temperature the more water vapor it can hold.
• A hygrometer is used to measure the amount of water vapor in the air.

Relative Humidity

• Relative humidity is the amount of moisture in the air relative to saturation.
• Relative humidity significantly affects aircraft performance due to its effect on air density.
• Air is most dense when perfectly dry.
• Temperature and dew point are used more often than relative humidity in aviation for practical application.

Dew Point

• Dew point is the temperature at which water vapor condenses out of the air and becomes liquid.
• The dew point is the temperature to which air must be cooled to become saturated without changing the pressure.

Air Density

Pressure, Temperature, Altitude

• The factors affecting air density are:

  • Pressure: As atmospheric pressure decreases, air density decreases.
  • Temperature: As temperature increases, density decreases.
  • Altitude: As altitude increases, air temperature and pressure decrease.

• The decrease in air pressure has more effect on air density than temperature.

• Air becomes less dense with increasing altitude

International Standard Atmosphere (ISA)

Definition

• The International Civil Aviation Organization (ICAO) administers the International Standard Atmosphere (ISA).
• Changing atmospheric conditions cause significant changes in the performance of aircraft.
• A standard was needed to measure the performance of aircraft with changing atmospheric conditions in mind.
• Aircraft performance is measured with actual atmospheric conditions then can compared to an ideal performance by recording and correcting parameters with graphs and charts.

ISA Standard Conditions

• ISA Reference Values defines what ISA Standard Day is:
  • Lapse rate: 2 °C/1000 feet
  • Tropopause height: 36 000 feet
  • Sea level pressure: 1013.25hPa = 29.92 in Hg = 14.7 psi
  • Sea level temperature: 15 °C
  • Gravity (g): 32.174 ft/sec² = 9.81 m/s²
• When local sea level temperature is above 15 °C, an ISA+ model is used.
• In this model, the complete atmosphere is incremented by the temperature difference from current conditions and incremented by 5 °C.

Pressure and Density Altitude

• Pressure altitude is the indicated altitude when an altimeter is set to 29.92 in. Hg (1013 hPa).
• It is used for aircraft performance calculation and high altitude flight.
• High Density Altitude = Decreased Performance
• Density altitude is an indicator of aircraft performance, with published criteria in the Pilot's Operating Handbook (POH).
• The Handbook is generally based on standard atmospheric conditions at sea level.
• Aircraft will not perform according to “book numbers” unless there is use of published performance criteria.

Aerodynamics I (8.2)

• The learning objectives are:
  • To describe airflow around various shapes.
  • To explain laminar flow, turbulent flow, boundary layer, free stream flow, and stagnation.
  • To explain relative airflow, upwash, downwash, vortices, and vortex formation to give students an understanding of aerofoils.
  • To find camber, chord, fineness ratio, angle of attack, and center of pressure.
  • To explain resultant force relative to lift.

Airflow Around a Body

Free Stream Airflow

• Airflow around a body can be understood by terminology and principles.
• Airflows are made visible with smoke in the Wind Tunnel
• A parallel line that the wind flow spreads out is known as Streamlines - it makes it possible to visualize the airflow around the aerofoil.
• Smooth lines mean Laminar Flow with very little drag
• Chaotic lines mean Turbulent Flow with a lot of drag
• The Lines that show the actual direction of the flow - streamlines
• A body shaped to produce the least possible resistance is called a streamline shape.

Laminar Flow

• Laminar flow occurs when streamlines maintain a uniform, parallel separation without turbulence.
• It is show as parallel straight lines.

Turbulent Flow

• Turbulent flow is the random motion of fluids with unpredictable flucuations and vortices
• There are no streamlines present
• The Velocity at which laminar flow becomes turbulent is called the "critical velocity".

Boundary Layer

• The boundary layer is a thin layer of air over the surface of an aeroplane that begins at the stagnation area.
• The stagnation point is where air is brought to rest by the leading edge which generates the boundary layer.
• Air viscosity causes some air to adhere to the wing, with wind velocities in the boundary layer varying from zero to velocity of the freestream.
• There's a tendency for it to start by being laminar, close to the leading edge of a body, but there comes a point, called the transition point, when the layer tends to breaks away and become turbulent and thicker.
  • The direction of the rotation on the upper surface of the airfoil is clockwise while anti-clockwise on the lower surface of the airfoil.
• As the speed increases, the transition point shifts forward, causing more of the of the outer layer becomes turbulent - which increases skin friction.
• Separate points occur on the wing where the boundary layers break away from the surface.

Relative Airflow

• Relative airflow is the air's movement with respect to the aircraft, parallel to and opposite the flight path.
• It's independent of wind direction or speed, depending only depends on the direction of travel.

Upwash and Downwash

• The area in from of the leading edge where air flows upward - Upwash
• The area behind the training age where air flows downwards - Downwash

Vortices

• When the airflow over the top surface of a wing meets the airflow over the lower surfaces at the trailing edge at different angels, creates an effect known as vortices or eddies.

  • they rotating clockwise from the left side of the wing when viewed from the rear
  • they are view counter-clockwise from the right wing if viewed from the rear.

• These votices form together creating one bigger vortex called Wing Tip Vortices.

Wake

• Wake turbulence is a disturbance in the atmosphere from an aircraft moving through air.

Wing-Tip Vortices

• Wing tip vortices are caused when higher-pressure air leaks form under the wing which then mixes with a low-pressure air above the wing.
• The Wake turbulence is mainly caused by these wing-tip vortices.

Bernoulli’s Principle

• A principle that helps explain how an aircraft can achieve life due to the shape of the wings.
• A venturi tube has an air inlet that narrows to a throat.
• The outlet section then increases in diameter toward the rear. _ This then creates a pressure increase, causing the air to accelerate.
• Wings also use this shape to create lift in powered aircraft.

Aerofoil

• An aerofoil is the defining shape of the cross section of an aircraft wings and is necessary to create lift.

Chord Line

• The chord is a line that joins the leading edge to the trailing edge and it is used as the arbitrary reference point to measure the angular position fo the wing in relation to the airflow.

Camber

• This is defined as the curvature of an aerofoil section from the leading edge to the trailing edge.
• The degree or amount of camber is expressed as the ratio of the curve departure from the chord to the chord length.
  • The upper camber refers to the curve on the upper surface
  • Lower camber refers to the curvature of the lower surface.

Mean Camber

• The mean camber is the curved line that forms the equal distance between the upper surface of the and the lower surface of the wing.
• Camber is positive when the departure from the straight line is upward and negative when it is downward.
• When the upper and lower cambers are the same shape, the aerofoil is said to be symmetrical.

Maximun Camber

• The maximum camber is defined as the maximum or greatest distance between the cord line an the mean camber line.

Fineness Ratio

• This is the measure of the thickness of the aerofoil by the ratio of the length to breadth of the aerofoil.

Angle of attack

• The angle of attack is the angle between the chord line of the aerofoil and the free stream flow
• For a fixed airspeed, this means the angle of attack lift increase but only until the stall speed.
• This applies to wing, propeller blades, helicopter rotor blades jet engine fan, compressor, and turbine blades.

Angle of Incidence

• This refers to the fixed acute angle which the wing chord makes with the longitudinal axis of the aircraft and does not change after it is manufactured.

Aerofoil Shapes

• The various types of aerofoil shapes
  • Symmetrical aerofoil - The is the shape on both sides of the center.
• Non-symettrical aerofoil* - Where the shape on either side of the chord is not the same.

- Center of Pressure

• This is a value derived from the pressure differences between the top and bottom surfaces of the wing airfoil and refers the point at which the Total Air Reduction is produced.
• The component of the resultant force that is perpendicular to the relative airflow if lift, the component that is parallel to relative airflow is the drag induced by the generation of lift.

Aerodynamics II (8.2) Learning Objectives

• Explain the terms like induced drag, parasite drag, aspect ratio wash in and wash out, thrust, weight; describe common wing shapes, aerodynamic stall, effects of aerofoil contamination and outline their relationship to performance.

Generation of Lift

Introduction

• Lift is generated by wings are tilted downwards then forcing air downwards (Newton’s Third Law).
• The shape of the wing (Bernoulli’s principal) generates more lift because of pressure differences.

Stalling Angle

• Caused when the angle of attack increases to much that causes the airflow from the wings upper surface to separate.

Generation of Drag

Drag

• A force that is generated by any aircraft surface that deflects the smooth surface of wind on the aircraft.

Induce Drag

• This is when the Drag increases as there is an increased angle of attack.

Parasite Drag

• A drag that is created by airflow around the aircraft's surface.

Total Drag

• When added up together into one value, parasite drag increasing with the square of the airspeed, and the induced drag increases.

Lift coefficient

• A high-pressure region underneath makes up air pressure/energy that is needed on top of the wing. Creating "Lift". With high pressure, there the 5 key values:
  • Airfoil Shape
  • Airfoil Size
  • Density
  • Speed (of Air)
  • Angle of Attack

Aerodynamic curves

• An Aerodynamic curve graph is produced with a intersecting point, with an approx. of four degree's Angle of Attack. It is the angle that produces the "Lift-to-Drag" Ratio, this where is wing is fixed to the fuselage.

Aerodyanmic Forces

• Four of them exist such;
  • Lift: Perpendicular to the relative Airflow. -Drag: A parallel that relative airflow.
  • Weight" Is Due: Gravity.
  • Thrust: Production of a plane's power.

Wing shape

- These all refer to a few things, as shape variations:

-  "Rectangular": Cheapest to build.
- "Elipitical": Most efficient.
   -"Tapered": Best compromise of speed and efficiency.
- "SweepBack": Highest speed.

Wing Geometry

• "Chord": A Straight line that attaches to the Leading and Trailing edges of an aerofoil.
• "Wingspan": From one wing tip, to the other".
• "Wing Area": Area, or platform that is projected is bounded to the leading and trailing edge and the wing tips.
  • The Total Surface Area isn't the total area covered by the Wing. The Total Surface Area includes both bottom and up.

Aspect Ratio

The result is, in division that measures by the square of the wingspan if measured by a aspect of the wing.

Aerodynamic - lift

• These are the high and low variations of the wings:
  • "Low aspect", then "High aspect"
  • The same can go for if reverse like from "high to low".

MAC- Mean Aerodynamic Chord

• Is when a non-uniform cord tapers the length of the wingspan and can determine were is best drawn.
  • This chord can determined through through area of aerofoil and can make great note.

Aircraft wings and safety

• The wings can effect, in; Torque or Wash all while in and out of the air.
• These are design, to have one wing drop with the other to retain great balance/stability.
• These are made in great angle, such as
  • "wash out," is where the wing will rise then the other drops.

Effects of Icing

• Has a big impact on planes and aerodynamics.
• It will alter the upper and lower cambers, change all aspects the "Chord line"
  • This overall impacts the shape and effect the "Angle of Attack", by lowing it.

Theory of Flight (8.3)

Learning Objectives

• To define lift, weight, thrust, drag, the best lift/drag ratio, aircraft performance, the aircrafts stability during turning, factors to wing load, methods of lift augmentation.

Aircraft Aerodynamics

• Lift, Weight, Thrust, and Drag.

The Four Forces of Aerodynamics

• There are four primary forces on an aircraft, each with different properties:

  • Lift - opposes force of weight.
  • Weight- caused by gravity that acts on the mass of the aircraft and opposes lift.
  • Thrust- the force that propels the plane.
  • Drag- backward, retarding motion caused the airplane to act in, then oppose the speed of thrust, and all while backwards when at right angles.

Parts of an airplane

• Each have different features and have a role to play.
  • "fuselage"; the body of a plane, and attaches to the Engine, Wings" etc.
  • “the wings”: act as horizontal aerofoil, with flaps to give lift.

Air craft Acs

Is the easiest way where a plane moves, each connecting together within Center of Gravity, or CG. Meaning: - Aircraft can start all axis movements in the same cycle of one single axis

Stability About the Axes

Longitudinal Stability:

• That Is when the Ac moves to keep is constant flow with with reference all to it" the AOA, so there is no stall/dive.

Lateral Stability:

Vertical Axes

The Vertical axis is a line that passes the Center of Gravity at high angles during the "Longitudinal and Lateral" which can make for flight.

Sideslip or Yawing

 - "Yaw"; Is when the nose of an aircraft is to turn on other side.
      - So for example one aircraft that has great amount force: "It will to Yaw the nose into relating airflow when one to drop", since  the effect not to great, then  has not much torque.
         - To have that fixed wash and what wing needs to drop "for example".

Pendulum

• The Pendulum is there to stop force is a Righting action, but with high the aircraft plane rolls. -A increase (or decrease) the influence high-wing the to stay straight, than increase (or decrease).

Torres effects

The air tends to spin in reverse direction due to propeller, and it makes for a counter tendency

Grounds Effect

Where aircraft tends float and near ground effect while landing, this Is is were is trap cause the speed of the plane stall. With a few things in mind;

• "wing ,air, loading"

Spiral instability

These all have negative impact in in roll, this make the aircraft tail to reverse the flow with one wing to drop. Where it gets a bad dihedral then the aircraft tends separate.

Overview of the three knowledge levels (1, 2, and 3) required for aircraft maintenance licenses A, B1, B2, and C. Level 1 covers basic elements, Level 2 requires general knowledge, and Level 3 demands detailed theoretical and practical expertise.