Principles of Flight for Pilots

Peter J. Swatton, Peter Belobaba, Jonathan Cooper, Roy Langton, Allan Seabridge

• Publisher: Wiley
• Year: 2011
• ISBN:
  9781119957638
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Aeronautic & Astronautic Engineering
• Index: Technology & Engineering

Organised and written as an accessible study guide for student pilots wishing to take commercial ground examinations to obtain ATPL or CPL licenses, Principles of Flight for Pilots also provides a reliable up-to-date reference for qualified and experienced personnel wishing to further improve their understanding of the Principles of Flight and related subjects. Providing a unique aerodynamics reference tool, unlike any book previously Principles of Flight for Pilots explains in significant depth all the topics necessary to pass the Principles of Flight examination as required by the EASA syllabus.

Aviation ground instructor Peter J. Swatton, well reputed for his previous works in the field of pilot ground training, presents the subject in seven parts including basic aerodynamics; level flight aerodynamics; stability; manoeuvre aerodynamics; and other aerodynamic considerations. Each chapter includes self-assessed questions, 848 in total spread over eighteen chapters, with solutions provided at the end of the book containing full calculations and explanations.

Part 1

The Preliminaries

1

Basic Principles

1.1 The Atmosphere

The Earth’s atmosphere is the layer of air that surrounds the planet and extends five hundred miles upwards from the surface. It consists of four concentric gaseous layers, the lowest of which is the troposphere in which all normal aviation activities take place. The upper boundary of the troposphere is the tropopause, which separates it from the next gaseous layer, the stratosphere. The next layer above that is the mesosphere and above that is the thermosphere.

The height of the tropopause above the surface of the earth varies with latitude and with the season of the year. It is lowest at the poles being approximately 25 000 feet above the surface of the Earth and 54 000 feet at the Equator. These heights are modified by the season, being higher in the summer hemisphere and lower in the winter hemisphere.

Above the tropopause the stratosphere extends to a height of approximately one hundred thousand feet. Although these layers of the atmosphere are important for radio-communication purposes, because of the ionised layers present, they are of no importance to the theory of flight.

Since air is compressible the troposphere contains the major part of the mass of the atmosphere. The weight of a column of air causes the atmospheric pressure and density of the column to be greatest at the surface of the Earth. Thus, air density and air pressure decrease with increasing height above the surface. Air temperature also decreases with increased height above the surface until the tropopause is reached above which the temperature remains constant through the stratosphere.

1.2 The Composition of Air

Air is a mixture of gases the main components of which are shown in Table 1.1.

Water vapour in varying quantities is found in the atmosphere up to a height of approximately 30 000 ft. The amount in any given air mass is dependent on the air temperature and the passage of the air mass in relationship to large areas of water. The higher the air temperature the greater the amount of water vapour it can hold.

1.2.1 The Measurement of Temperature

Centigrade Scale. The Centigrade scale is normally used for measuring the air temperature and for the temperature of aero-engines and their associated equipment. On this temperature scale water freezes at 0° and boils at 100° at mean sea level.

Table 1.1 Gas Components of the Air.

Element	Volume	Weight
Nitrogen	78.09%	75.5%
Oxygen	20.95%	23.1%
Argon	0.93%	1.3%
Carbon Dioxide	0.03%	0.05%

Note: For all practical purposes the atmosphere is considered to contain 21% oxygen and 79% nitrogen.

Kelvin Scale. Often for scientific purposes temperatures relative to absolute zero are used in formulae regarding atmospheric density and pressure. Temperatures relative to absolute zero are measured in Kelvin. A body is said to have no heat at absolute zero and this occurs at a temperature of –273.15 °C.

1.2.2 Air Density

Air density is mass per unit volume. The unit of air density is either kg per m³ or gm⁻³ and the symbol used is ‘ρ’. The relationship of air density to air temperature and air pressure is given by the formula:

where ρ is the density, p is pressure in hPa and T is the absolute temperature.

The Effect of Air Pressure on Air Density. If air is compressed the amount of air that can occupy a given volume increases. Therefore, both the mass and the density are increased. For the same volume if the pressure is decreased then the reverse is true. From the formula above if the air temperature remains constant then the air density is directly proportional to the air pressure. If the air pressure is doubled so is the air density.

The Effect of Air Temperature on Air Density. When air is heated it expands so that a smaller mass will occupy a given volume and provided that the air pressure remains constant then the air density will decrease. Thus, the density of the air is inversely proportional to the absolute temperature. The rapid decrease of air pressure with increased altitude has a far greater effect on the air density than does the increase of density caused by the decrease in temperature for the same increased altitude. Thus, the overall effect is for the air density to diminish with increased altitude.

The Effect of Humidity on Air Density. Until now it has been assumed that the air is perfectly dry; such is not the case. In the atmosphere there is always some water vapour present, albeit under certain conditions a miniscule amount. However, in some conditions the amount of water vapour present is an important factor when determining the performance of an aeroplane. For a given volume the amount of air occupying that volume decreases as the amount of water vapour contained in the air increases. In other words, air density decreases with increased water-vapour content. It is most dense in perfectly dry air.

1.3 The International Standard Atmosphere

The basis for all performance calculations is the International Standard Atmosphere (ISA) which is defined as a perfect dry gas, having a mean sea level temperature of +15 °C, which decreases at the rate of 1.98 °C for every 1000 ft increase of altitude up the tropopause which is at an altitude of 36 090 ft above which the temperature is assumed to remain constant at –56.5 °C. The mean sea level (MSL) atmospheric pressure is assumed 1013.2 hPa (29.92 in. Hg). See Table 1.2.

Table 1.2 International ...

Table of contents

• Cover
• Aerospace Series List
• Title Page
• Copyright
• Series Preface
• Preface
• Acknowledgements
• List of Abbreviations
• Weight and Mass
• Part 1: THE PRELIMINARIES
• Part 2:: BASIC AERODYNAMICS
• Part 3: LEVEL-FLIGHT AERODYNAMICS
• Part 4: STABILITY
• Part 5: MANOEUVRE AERODYNAMICS
• Part 6: OTHER AERODYNAMIC CONSIDERATIONS
• Part 7: CONCLUSION
• Index