CAR-66 Category A: Module 8 Aerodynamics
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Questions and Answers

What is one of the properties mentioned in the Physics of the Atmosphere section?

  • Temperature (correct)
  • Weight
  • Lift
  • Thrust

    • What equation represents the conservation of mass in aerodynamics?

    The Continuity Equation

    Bernoulli's Equation is used in the generation of lift.

    True

    Stalling is a phenomenon where the airflow over the wing is disrupted, leading to loss of ____________.

    <p>lift</p> Signup and view all the answers

    Match the aerodynamic control device with its description:

    <p>Wing Fences = Control airflow over the wing Winglets = Reduce drag by decreasing wingtip vortices Vortex Generators = Aid in boundary layer control Saw Tooth Notch = Modify airflow to reduce drag</p> Signup and view all the answers

    What is the composition of the Earth's atmosphere?

    <p>78% Nitrogen, 21% Oxygen, 0.9% Argon</p> Signup and view all the answers

    What is the main layer of the atmosphere where weather forms such as clouds, rain, and snow are found?

    <p>Troposphere</p> Signup and view all the answers

    ______ is called the upper limit of the Troposphere where the temperature stops decreasing.

    <p>Tropopause</p> Signup and view all the answers

    Pressure is the ratio of force applied to the surface area.

    <p>True</p> Signup and view all the answers

    Match the pressure measurement unit with its description:

    <p>Pounds per square inch = Expresses force in pounds on each square inch of area Inches of Mercury = Column of mercury supported under Standard Sea Level conditions Millibars = Commonly used in weather forecasting Pascal = SI unit of pressure</p> Signup and view all the answers

    What is the standard atmospheric pressure at sea level in pascals?

    <p>101325</p> Signup and view all the answers

    What is the ICAO Standard Temperature at sea level?

    <ul> <li>15 ºC</li> </ul> Signup and view all the answers

    Define viscosity in the context of aerodynamics.

    <p>Viscosity is a measure of the resistance of fluid to an applied stress. In aerodynamics, it describes the air's internal resistance to flow and its internal friction.</p> Signup and view all the answers

    What are the common systems of measuring pressure used in aviation?

    <p>Inches of mercury (inHg)</p> Signup and view all the answers

    What is humidity?

    <p>The condition of moisture or dampness in the air is called Humidity.</p> Signup and view all the answers

    What is the term for a design where the aerofoil has more cross-sectional area above the chordline than below?

    <p>Cambered design</p> Signup and view all the answers

    What are the patterns of lines around the aerofoil referred to as?

    <p>Streamlines</p> Signup and view all the answers

    What is the point called where the velocity of free stream air decreases to zero?

    <p>Stagnation point</p> Signup and view all the answers

    Under what condition does laminar flow change to turbulent flow?

    <p>True</p> Signup and view all the answers

    According to the Bernoulli's equation, what is the relationship between speed and pressure?

    <p>Pressure + 1/2 density * velocity^2 = constant</p> Signup and view all the answers

    What is the maximum pressure value felt at the point where the full force of dynamic pressure is experienced?

    <p>Stagnation pressure</p> Signup and view all the answers

    What is the term used for the difference in static pressure at a particular point and the free-stream static pressure?

    <p>Pressure coefficient (Cp)</p> Signup and view all the answers

    Stalling occurs when the airflow breaks away from the bottom surface of the wing.

    <p>False</p> Signup and view all the answers

    The pressure coefficient (Cp) can be defined as (P - ρ0) / q0, where P is the static pressure, ρ0 is the free-stream static pressure, and q0 is the ______ pressure.

    <p>dynamic</p> Signup and view all the answers

    What is the term used to refer to wings designed so that the outboard sections have a smaller angle of attack than the inboard sections?

    <p>Wash Out</p> Signup and view all the answers

    What is the main factor governing where stall begins on a wing?

    <p>Shape of the wing</p> Signup and view all the answers

    Stall wedges or strips are mounted on the trailing edge of the wings.

    <p>False</p> Signup and view all the answers

    The presence of friction between the air and solid surface creates a drag force known as skin __________.

    <p>friction</p> Signup and view all the answers

    What is the total reaction force of a wing known as?

    <p>Lift</p> Signup and view all the answers

    What is the angle at which the resulting force exerted by the air on the wing is tilted backwards?

    <p>Induced angle of attack (αi)</p> Signup and view all the answers

    What is the component of the resulting force parallel to the relative wind known as?

    <p>Drag or Induced Drag</p> Signup and view all the answers

    What happens to the total reaction force when there is more downwash?

    <p>The total reaction force is tilted rearwards, giving rise to greater induced drag.</p> Signup and view all the answers

    What color is the angle of attack relative to the modified local airstream directions in Figure 47?

    <p>Red</p> Signup and view all the answers

    What is the mechanism by which skin friction drag is created?

    <p>Boundary Layer</p> Signup and view all the answers

    Which type of flow exists near the leading edge of the aerofoil where the air flows in a smooth layered streamlined manner?

    <p>Laminar flow</p> Signup and view all the answers

    A low Reynolds Number results in laminar flow.

    <p>True</p> Signup and view all the answers

    In wind tunnel tests, the Reynolds Number (Re) is defined as $\frac{\rho V l}{\mu}$. Here, $\rho$ is density, $V$ is velocity, $l$ is the diameter of the pipe, and $\mu$ is the viscosity coefficient.

    <p>Re = ρ V l / μ</p> Signup and view all the answers

    What is another name for the point at which the laminar flow turns turbulent?

    <p>Transition Point</p> Signup and view all the answers

    What is the primary cause of stalling due to which pressure differences between the front and rear of an aerofoil increase?

    <p>increase in the angle of attack</p> Signup and view all the answers

    What is the resistance experienced by an object in a viscous fluid, such as air, moving relative to the object?

    <p>Form Drag</p> Signup and view all the answers

    Form drag refers to the net drag force created by the difference in air pressure between the forward-facing and rearward-facing parts of an object. Is this statement true?

    <p>True</p> Signup and view all the answers

    _______ shapes are recognized for producing considerable turbulence and others known for minimizing it.

    <p>Some</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Fineness Ratio = Ratio of overall length to maximum thickness Induced Drag = 'Lift Dependant Drag'; proportional to lift Interference Drag = Generated by the collision of airstreams causing turbulence Form Drag = Result of pressure difference between object's front and rear parts</p> Signup and view all the answers

    Study Notes

    Physics of the Atmosphere

    • Aerodynamics studies the action and reaction of bodies in a moving stream of air
    • Composition of the air:
      • 78% Nitrogen
      • 21% Oxygen
      • 0.9% Argon
      • 0.03% Carbon Dioxide
      • Traces of hydrogen, helium, and neon
    • Atmosphere divided into layers:
      • Troposphere (closest to earth)
      • Tropopause (upper limit of Troposphere, temperature stops decreasing)
    • Troposphere:
      • Contains virtually all water in the atmosphere
      • Weather patterns exist here
      • Temperature decreases with an increase in height
    • Tropopause:
      • Isothermal region
      • Ranges in height between 20,000 ft (poles) to 60,000 ft (equator)
      • Temperature remains at -56.5°C

    Properties of the Atmosphere

    • Physical properties:
      • Pressure
      • Density
      • Temperature
    • Variations in properties affect aircraft performance
    • International Standard Atmosphere (ISA):
      • Reference for aerodynamic computations
      • Standard variation of properties for mid-latitudes (45°N)
      • Assumes set of conditions for performance comparison and instrument calibration
    • ISA based on Sea Level (SL) criteria

    Important Concepts

    • Atmosphere layers: Troposphere, Tropopause
    • Properties of the atmosphere: pressure, density, temperature
    • International Standard Atmosphere (ISA) for standardization### Atmosphere and Pressure
    • The standard atmospheric pressure at sea level is 1013.2 millibars or 101.3 kN/m².
    • The International Standard Atmosphere (ISA) is a theoretical model of the atmosphere, used as a standard in aerospace engineering and aviation.
    • ISA values vary with altitude, with temperature, pressure, and density decreasing as altitude increases.
    • The lapse rate is the rate of decrease of temperature with altitude, approximately 1.98°C per 1000 feet.

    Temperature

    • The standard temperature at sea level is 15°C (288 K).
    • The lapse rate continues up to an altitude of 38,000 feet, where the temperature remains at a constant -56.5°C up to 65,000 feet.

    Density

    • Density is defined as mass per unit volume of a substance, at specified temperature and pressure.
    • The density of air is a property of great importance in aerodynamics, and it decreases with altitude.

    Pressure Measurement

    • There are three common systems of measuring pressure in aviation:
      • Pounds per square inch (psi)
      • Inches of Mercury (inHg)
      • Millibars (mb)

    Humidity

    • Humidity is the condition of moisture or dampness in the air.
    • The maximum amount of water vapour that the air can hold depends on the temperature of the air.

    Viscosity

    • Viscosity is a measure of the resistance of fluid to an applied stress.
    • Viscosity essentially describes the air's internal resistance to flow and may be thought of as a measure of its internal friction.

    Aerodynamics

    • Aerodynamics is the study of air in motion, which includes changes in the physical characteristics, such as pressure and density.
    • The study of aerodynamics involves the study of forces being generated, such as lift and drag.

    Airflow Around a Body

    • When an object is placed in the path of a uniform airflow, the airflow is disturbed, creating forces in all directions.
    • The force produced is a result of pressure and viscous forces.

    Lift and Drag

    • Lift is the component of total reaction force acting perpendicular to the free stream airflow.
    • Drag is the component of total reaction force acting parallel to the free stream airflow.

    Aerofoils

    • An aerofoil is any surface that produces an aerodynamic force when it is passed through a stream of air.
    • The cross-sectional shape of an aerofoil is curved, with a leading edge, trailing edge, chord line, and mean camber line.
    • The angle of attack (α) is the angle formed between the chord-line and relative airflow.

    Flow Characteristics

    • Streamlines are imaginary lines that indicate the instantaneous direction of flow, and if flow is steady, they also show the path that a particle of air would follow.
    • The closeness of the streamlines gives an indication of flow speed, with closer lines indicating faster air flow.Here are the study notes in detailed bullet points:

    Laminar and Turbulent Flow

    • Laminar flow is characterized by a "layered" appearance and remains unchanged unless a change is deliberately introduced
    • Laminar flow is present at the leading edge of an aerofoil, where there is an "upwash" of air
    • At the trailing edge, there is a "downwash" of air
    • The point where the velocity of the free stream air has decreased to zero is called the "Stagnation" point
    • At this point, the full force and pressure is felt, and it is the combination of both static and dynamic pressure on the aerofoil

    Generation of Lift

    • Lift is generated in accordance with the fundamental principles of physics:
      • Conservation of Energy
      • Conservation of Mass
      • Conservation of Momentum
    • The law of conservation of energy states that energy cannot be created or destroyed, only converted from one form to another
    • The continuity equation states that mass in = mass out, and is used to relate the values of density, velocity, and area at one section of a stream tube to the same quantities at another section

    Bernoulli's Equation

    • Bernoulli's equation describes the relationship between speed and pressure
    • The equation is: P + ½ ρV² = constant
    • This equation states that as the velocity of the air increases, the pressure decreases, and vice versa
    • This principle can be applied to aerodynamics, as the flow through a venturi has similar characteristics to the flow over an aerofoil

    Venturi Tube

    • A Venturi tube is a tube that gradually narrows to a throat, and then expands at the exit
    • The Venturi tube demonstrates an approximate relationship between pressure and velocity for low flow speeds
    • As air flows into the constriction, the air is squeezed, and the streamlines move closer together, resulting in an increase in velocity
    • According to Bernoulli's equation, this increase in velocity results in a decrease in static pressure

    Newton's Laws

    • Lift can also be generated by the upper and lower surfaces of the wing when air flows around the wing and is deflected downwards
    • The force exerted on the wing is equal to the rate of change of momentum of the air
    • According to Newton's Third Law of Motion, for every action, there is an equal and opposite reaction
    • Therefore, the air that is deflected downwards will produce an upward or lifting reaction on the wing

    Aerodynamic Forces

    • The lift force results from a difference in pressure between the upper and lower surfaces of the aerofoil
    • The pressure distribution can be determined by experimentation using manometers
    • The pressure coefficient (Cp) is an important quantity that leads directly to the value of the coefficient of lift (CL)

    Centre of Pressure

    • The centre of pressure (CofP) is the point at which the resultant force of pressure acts
    • The CofP is located less than halfway back along the chord
    • The vector representing lift through the centre of pressure passes through the point of minimum pressure on the upper surface

    Aerodynamic Centre

    • The aerodynamic centre (AC) is the point about which there is no change in pitching moment as the angle of attack is changed
    • The AC is located at a fixed point along the chord, regardless of the angle of attack

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    Test your knowledge of aerodynamics with this quiz, designed for CAR-66 Category A certification, covering Module 8

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