ppl pof ch 2
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Questions and Answers

What is the term for a heavier-than-air craft that requires relative movement between the air and its lifting surfaces?

  • Aeroplane
  • Aerostat
  • Helicopter
  • Aerodyne (correct)

    • What does the word 'plane' refer to in the context of an aeroplane?

  • The horizontal stabiliser
  • The vertical stabiliser
  • The complete aircraft
  • The main wings and tail-plane (correct)

    • What is the term for a lighter-than-air craft?

  • Aeroplane
  • Helicopter
  • Aerodyne
  • Aerostat (correct)

    • What is the term for a rotary-wing craft?

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

    What is the focus of this book on Principles of Flight?

    <p>The flight of aeroplanes</p> Signup and view all the answers

    What is the meaning of the Greek word 'heliko' in the context of helicopters?

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

    What percentage of the atmosphere is composed of Oxygen?

    <p>21%</p> Signup and view all the answers

    What is the approximate total depth of the atmosphere?

    <p>500 miles</p> Signup and view all the answers

    What is the primary function of the atmosphere in relation to aeroplanes?

    <p>To enable an aeroplane to fly</p> Signup and view all the answers

    What is the approximate percentage of the atmosphere that lies in the lower 50 000 feet?

    <p>90%</p> Signup and view all the answers

    What is the primary component of the atmosphere?

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

    What is the approximate altitude that jet airliners regularly fly at?

    <p>40 000 feet</p> Signup and view all the answers

    What is the term used to describe the amount of water vapour in an air mass?

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

    What is the maximum percentage of water vapour in atmospheric air by volume?

    <p>4%</p> Signup and view all the answers

    What happens to the air when it reaches its saturation point?

    <p>Water condenses out</p> Signup and view all the answers

    What is the term for the temperature at which water vapour condenses out to water?

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

    Why can you see your breath on a cold day?

    <p>Because water condenses out onto microscopic impurities in the air</p> Signup and view all the answers

    What happens to the dew point when there is more water vapour in the air?

    <p>It increases</p> Signup and view all the answers

    What occurs when air reaches its saturation point?

    <p>Cloud is formed</p> Signup and view all the answers

    What is the result when the air reaches its saturation point?

    <p>Mist or fog ensues</p> Signup and view all the answers

    What is the difference between fog and mist?

    <p>Fog has a visibility of less than 1000 m, mist has a visibility of 1000 m or more</p> Signup and view all the answers

    Why does breathing onto a cold glass surface cause the glass to mist up?

    <p>Because water condenses out onto the surface</p> Signup and view all the answers

    What is relative humidity an expression of?

    <p>The ratio of the amount of water vapour present to the amount the air can 'hold' at a given temperature</p> Signup and view all the answers

    What happens when the air temperature falls to the dew point?

    <p>The air becomes saturated and water vapour condenses</p> Signup and view all the answers

    What is the characteristic of a mixture of air and water vapour with high water vapour content?

    <p>It becomes less dense than dry air</p> Signup and view all the answers

    What is the relationship between water vapour and dry air at equal pressure?

    <p>Water vapour is lighter</p> Signup and view all the answers

    What is the main reason why air molecules are held in contact with the Earth's surface?

    <p>The Earth's force of gravity</p> Signup and view all the answers

    What is the relationship between air pressure and air density?

    <p>Air pressure is directly proportional to air density</p> Signup and view all the answers

    What happens to the volume of air when it is heated at constant pressure?

    <p>It increases</p> Signup and view all the answers

    What is the unit of measurement for air density?

    <p>Kilograms per cubic meter</p> Signup and view all the answers

    What is the effect of the weight of air above on the air near the surface?

    <p>It increases the air pressure</p> Signup and view all the answers

    What is the main factor that determines the air density?

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

    What is the result of the gravitational force acting between the Earth and air molecules?

    <p>Air molecules are held in contact with the Earth's surface</p> Signup and view all the answers

    What is the analogy used to describe the variation of pressure and density with altitude?

    <p>A stack of foam rubber blocks</p> Signup and view all the answers

    What happens to air density when temperature increases?

    <p>It decreases</p> Signup and view all the answers

    What is the effect of decreasing pressure on air density?

    <p>It decreases air density</p> Signup and view all the answers

    Why do pilots need to be careful when operating from airfields that are 'hot and high'?

    <p>Because air density is low</p> Signup and view all the answers

    What is the standard unit of pressure?

    <p>Newton per square meter</p> Signup and view all the answers

    What is the direction of the force exerted by atmospheric pressure?

    <p>in all directions</p> Signup and view all the answers

    What is the reason for the atmosphere exerting pressure on objects?

    <p>The force of gravity acting on the mass of air</p> Signup and view all the answers

    What happens to the lift generated by the wings when air density is low?

    <p>It decreases</p> Signup and view all the answers

    What is the effect of decreasing air density on the power output of the engine?

    <p>It decreases the power output</p> Signup and view all the answers

    What is the result of low air density on take-off runs?

    <p>Longer take-off runs</p> Signup and view all the answers

    What happens to atmospheric pressure with increasing altitude?

    <p>It decreases</p> Signup and view all the answers

    What is the primary source of heat for the atmospheric air?

    <p>The Earth's surface</p> Signup and view all the answers

    What is the name of the lowest layer of the atmosphere?

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

    At what altitude does the temperature begin to rise again?

    <p>18 miles</p> Signup and view all the answers

    What percentage of the total mass of the atmosphere is in the Troposphere?

    <p>75%</p> Signup and view all the answers

    What is the term for the boundary between the Troposphere and the Stratosphere?

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

    At what altitude is the temperature around -56.5°C (-69°F) in the Troposphere?

    <p>18 miles</p> Signup and view all the answers

    What is the altitude of the Troposphere over the Equator?

    <p>50 000 feet</p> Signup and view all the answers

    Why does the temperature decrease with increasing altitude in the Troposphere?

    <p>Because the Earth's surface heats up the air</p> Signup and view all the answers

    What is a measure of air's resistance to flow?

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

    What is true about the viscosity of air?

    <p>It is very low</p> Signup and view all the answers

    What is affected by the viscosity of air in flight?

    <p>The movement of air molecules</p> Signup and view all the answers

    What is a characteristic of fluids with high viscosity?

    <p>They are thick</p> Signup and view all the answers

    What is true about air compared to treacle and tar?

    <p>It has a lower viscosity</p> Signup and view all the answers

    What is the purpose of understanding ISA deviations in flight?

    <p>To understand the effect of atmosphere on instrument readings</p> Signup and view all the answers

    What is the standard sea level pressure in ISA conditions?

    <p>1013.2 millibars</p> Signup and view all the answers

    What is the term for the altitude read from an altimeter with the subscale setting of 1013.2 millibars?

    <p>Flight Level</p> Signup and view all the answers

    Why is it important to consider ISA deviations when reading aircraft performance data?

    <p>To ensure accurate performance data</p> Signup and view all the answers

    Where can more information on ISA deviations be found?

    <p>Meteorology and Aircraft (General) volumes</p> Signup and view all the answers

    What is the primary purpose of the ICAO Standard Atmosphere (ISA)?

    <p>To provide a standard reference for aerodynamicists and engineers</p> Signup and view all the answers

    What is the air pressure at Mean Sea Level in the ICAO Standard Atmosphere (ISA)?

    <p>1013.2 millibars</p> Signup and view all the answers

    What is the temperature at Mean Sea Level in the ICAO Standard Atmosphere (ISA)?

    <p>15º Celsius</p> Signup and view all the answers

    How does the temperature change with altitude in the ICAO Standard Atmosphere (ISA)?

    <p>It decreases by 2º Celsius for every 1,000 ft</p> Signup and view all the answers

    Why is it important to remember that actual atmospheric values can differ from ISA values?

    <p>Because actual values can affect aircraft performance and instrument readings</p> Signup and view all the answers

    What is the purpose of the ICAO Standard Atmosphere (ISA) in relation to aircraft instruments?

    <p>To calibrate instruments and measure aircraft performance</p> Signup and view all the answers

    What is the significance of the ICAO Standard Atmosphere (ISA) in the field of aviation?

    <p>It provides a standard reference for measuring aircraft performance and calibrating instruments</p> Signup and view all the answers

    What does the ICAO Standard Atmosphere (ISA) illustrate?

    <p>The standard variation of pressure, temperature, density, and viscosity with altitude</p> Signup and view all the answers

    What is the standard unit of temperature measurement in the aviation world outside the United States?

    <p>Degrees Celsius</p> Signup and view all the answers

    At what temperature does water freeze in degrees Celsius?

    <p>0°C</p> Signup and view all the answers

    What is the formula to convert from Fahrenheit to Celsius?

    <p>ºC = (ºF - 32) × 5/9</p> Signup and view all the answers

    What is the ratio of a Fahrenheit degree to a Celsius degree?

    <p>5/9</p> Signup and view all the answers

    At what temperature does water boil in degrees Fahrenheit?

    <p>212°F</p> Signup and view all the answers

    What is the formula to convert from Celsius to Fahrenheit?

    <p>ºF = (ºC × 9/5) + 32</p> Signup and view all the answers

    Study Notes

    Definition of Aircraft

    • Aircraft can only fly when immersed in air.
    • Lighter-than-air craft are called aerostats (e.g. hot-air balloons).
    • Heavier-than-air craft that require relative movement between air and their lifting surfaces are called aerodynes.

    Types of Aerodynes

    • Fixed-wing craft are called generically aeroplanes.
    • Aeroplanes include mainplanes (wings), tail-plane (horizontal stabiliser), and fin (vertical stabiliser).
    • Rotary-wing craft are collectively known as helicopters.

    Etymology of Helicopter

    • The word "helicopter" comes from the Greek "pterón" (meaning wing) and "heliko" (from "helix", meaning spiral).
    • Inspired by Leonardo da Vinci's 15th-century design for a vertical take-off flying machine with a rotating spiral wing.

    Scope of the Book

    • This book focuses on the principles of flight for aeroplanes only.
    • The terms "aeroplane" and "aircraft" will be used interchangeably throughout the book.

    The Composition of the Atmosphere

    • The atmosphere is a gaseous mixture that surrounds the Earth, similar to a giant ocean of air.
    • The lower 10,000 feet of the atmosphere is where most private-pilot licence-holders operate their light aircraft.
    • Jet airliners regularly fly at altitudes up to about 40,000 feet.
    • The total depth of the atmosphere is approximately 500 miles (800 km).
    • About 90% of the mass of air lies in the lower 50,000 feet (9 miles or 15 km) of the atmosphere.

    Principal Gases in the Atmosphere

    • Nitrogen makes up 78% of the atmosphere.
    • Oxygen makes up 21% of the atmosphere.
    • The remaining 1% consists mainly of Argon and Carbon Dioxide, with traces of:
      • Carbon Monoxide
      • Helium
      • Methane
      • Hydrogen
      • Ozone

    Water Vapour and Humidity

    • Atmospheric air contains a small amount of water vapour, which varies in quantity.
    • Humidity is the measure of the amount of water vapour in an air mass.
    • Meteorologists measure humidity in terms of mass of water vapour per unit volume of air (e.g., 5 gm/m³) or mass of water vapour per unit mass of air (e.g., 3 gm/kg).
    • Water vapour in the air is usually invisible, but its influence on weather is significant.
    • The air can hold more water vapour as temperature increases, and less as temperature decreases.

    Saturation Point and Dew Point

    • When air can no longer hold any more water vapour as gas, it reaches its saturation point.
    • The temperature of air at its saturation point is called the dew point.
    • The more water vapour in the air, the higher the dew point will be.
    • When the dew point is close to the actual air temperature, the danger of condensation and mist or fog increases.

    Cloud Formation and Condensation

    • When unsaturated air rises and cools, it eventually reaches its saturation point, forming cloud.
    • Mist and fog are low-level clouds that form when the air reaches its saturation point.
    • If visibility is less than 1000 m, it is termed fog, and if 1000 m or more, it is termed mist.

    Relative Humidity

    • Relative humidity is the ratio of actual water vapour in the air to the amount the air can hold at a given temperature.
    • When the air temperature falls to the dew point, relative humidity becomes 100%, and the air becomes saturated.

    Properties of Water Vapour

    • Water vapour is lighter than dry air at equal pressure and temperature.
    • A mixture of air and water vapour is less dense if the water vapour content is high than if it is low.

    Formation of the Atmosphere

    • The atmosphere was formed over 4 billion years ago when gases were released from the Earth during its formation.
    • The Earth's gravity prevented the gases from escaping into space, causing them to spread out and cover the entire surface.

    Air Pressure and Air Density

    • Air pressure and air density are greatest near the Earth's surface and decrease with increasing altitude.
    • The weight of the air above compresses the air near the surface, leading to higher pressure and density.
    • Air density refers to the number of air molecules contained within a given volume of air and is measured in kilograms per cubic meter.
    • Air density is directly proportional to pressure and inversely proportional to temperature.

    Effects of Air Density on Aircraft Performance

    • Air density affects lift, service ceiling, and the relationship between true and indicated airspeed.
    • Low air density reduces lift, engine power output, and requires longer take-off runs.

    Pressure

    • Pressure is a description of the way in which a force is spread over a contact area.
    • Pressure is defined as "force per unit area".
    • Atmospheric pressure or static pressure is the pressure exerted by the atmosphere on objects immersed in it when neither the air nor the object is in motion.
    • Standard units of pressure include Newtons per square meter, pounds per square inch, bars, millibars, Pascals, and hectopascals.

    Properties of Air

    • Air possesses mass, and the force of gravity acting on that mass gives air weight.
    • The pressure and density of air decrease with altitude due to the weight of the air.
    • Variations in atmospheric pressure and density, along with humidity, affect aircraft performance and flight instruments.

    Temperature of the Atmosphere

    • The temperature of atmospheric air decreases with increasing altitude.
    • The air is not heated directly by the sun, but rather by the Earth's surface through conduction, convection, and long-wave radiation.

    The Troposphere

    • The lowest layer of atmospheric air is the Troposphere, which is heated through its proximity to the Earth's surface.
    • The Troposphere is where temperature and pressure changes cause the mixing of air, resulting in weather.
    • Almost all of the Earth's weather occurs in the Troposphere.
    • The Troposphere rises from the Earth's surface to about 50,000 feet over the Equator, 25,000 feet over the Poles, and about 36,000 feet at mid-latitudes.
    • The Troposphere contains approximately 75% of the total mass of the atmosphere and all of the water vapour.

    The Tropopause

    • The boundary between the Troposphere and the Stratosphere is called the Tropopause.
    • At the Tropopause, the temperature is around -56.5°C (-69°F) and remains constant to an altitude of about 18 miles (35 km).

    Temperature Variation with Altitude

    • The temperature begins to rise again at altitudes greater than 18 miles (35 km).
    • The temperature variation with altitude ends at around 95,000 feet.

    Physical Properties of the Atmosphere

    • Air has mass, which is an essential fact in understanding the Principles of Flight.
    • The atmosphere's physical properties, including pressure, density, temperature, and relative humidity, change under certain circumstances.

    Viscosity of Air

    • Viscosity measures the air's resistance to flow due to internal friction between air molecules moving relative to each other.
    • Air has a low viscosity, making it a "thin" fluid, similar to water.
    • In contrast, fluids like treacle and tar have high viscosity, making them "thick" fluids.
    • Despite being low, air's measurable viscosity has significant consequences for an aircraft in flight.

    ICAO Standard Atmosphere (ISA)

    • The ICAO Standard Atmosphere (ISA) is a set of standard values for air pressure, density, temperature, and humidity defined by the International Civil Aviation Organisation (ICAO) in 1964.

    Purpose of ISA

    • The ISA serves as an international standard reference for measuring aircraft performance and calibrating instruments.
    • It provides a common set of atmospheric conditions for aerodynamicists, aircraft manufacturers, and engineers to work with.

    Characteristics of ISA

    • The ISA shows a standard variation of pressure, temperature, density, and viscosity with altitude.
    • The Mean Sea Level air pressure in the ISA is 1013.2 millibars (1013.2 hectopascals) or 29.92 inches of Mercury.
    • The ISA temperature at Mean Sea Level is 15°C.
    • Temperature decreases with altitude at approximately 2°C for every 1,000 ft.

    Importance of ISA

    • ISA values are used as a reference for calibrating flight instruments, such as the altimeter and air speed indicator, and for manufacturers' figures for aircraft performance.
    • It is essential to understand the effect of the atmosphere's deviation from ISA conditions on instrument readings and aircraft performance.

    ISA and Flight Levels

    • The ISA sea level pressure of 1013.2 millibars is also the altimeter subscale setting, which a pilot selects when reading their altitude in terms of Flight Level.
    • Flight Levels are also known as Pressure Altitudes.

    Measurement of Temperature

    • The standard unit of temperature measurement in the aviation world, outside the United States, is degrees Celsius (formerly Centigrade).
    • Until the 1960s, the Fahrenheit scale was the primary scale of temperature measurement for non-scientific purposes in most English-speaking countries.

    Fahrenheit Scale

    • In the Fahrenheit scale, water freezes at 32ºF and boils at 212ºF.
    • There are 180º between the boiling points of water in the Fahrenheit scale.

    Celsius Scale

    • In the Celsius scale, water freezes at 0ºC and boils at 100ºC.
    • There are 100º between the boiling points of water in the Celsius scale.

    Conversion between Scales

    • One Fahrenheit degree is only 5/9 the value of a Celsius degree.
    • The formulae for converting between the two scales are:
      • ºC = (ºF - 32) × 5/9 (Fahrenheit to Celsius)
      • ºF = (ºC × 9/5) + 32 (Celsius to Fahrenheit)

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