Flying The Big Jets (4th Edition) E-Book

Stanley Stewart

• Herausgeber: Crowood
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 483

Veröffentlichungsjahr: 2014

Beschreibung

Flying the Big Jets presents the facts that people want to know about the world of the big jets. How does a large aircraft fly? How long is the take-off run at maximum weight? How much fuel is carried on a transatlantic flight? How do the radios work? What aircraft maintenance is required? How often are the tyres changed? What is the life style of a pilot? The answers to these and a thousand other questions are given in sufficient detail to satisfy the most inquisitive of readers. Chapter by chapter the reader is taken gently from the basics of the big jets to the sophistication of the 'glass cockpit' in preparation for the pilot's seat on a Boeing 777 flight from London to Boston. Flying the Big Jets is a comprehensive book that reveals as never before the every-day working environment of the modern long-haul airline pilot. "Written by a pilot with over 15,000 flying hours on heavy jets during a 30-year career in commercial aviation, this title is a comprehensive text book taking the reader into the 'glass cockpit' of a Boeing 777. It is also a guide to the principles of flight, the art of navigation and meteorology, and an appreciation of the role played by Air Traffic Control in modern airline operations. An absorbing read for that next long-haul flight." WINGSPAN

Leseprobe

First published in Great Britain in 1984

Fourth edition published in 2002 by Airlife Publishing, an imprint of The Crowood Press Ltd Ramsbury, Marlborough Wiltshire SN8 2HR

www.crowood.com

This e-book first published in 2014

This impression 2006

© Stanley Stewart 2002

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

ISBN 978 1 84797 921 6

Dedication

Flying the Big Jets is dedicated to my sister Dorothy who died after a long illness and who was so much help in the preparation of the first edition.

Acknowledgements

I would like to thank again, without naming individuals, all those who so graciously gave their time and assistance in the preparation of the earlier editions. As far as the fourth edition is concerned, I would like to thank very much Captain John Edwards of the British Airways Boeing 777 training department. John’s help, knowledge, and enthusiasm have been invaluable and this fourth edition would, quite simply, not have been possible without his contribution. To John Edwards I owe a very great debt of thanks.

Contents

Introduction

Part 1: The Facts

Chapter 1

Principles of Flight

Chapter 2

The Jet Engine

Chapter 3

Radio and Radar

Chapter 4

Navigation – 1

Chapter 5

Navigation – 2

Chapter 6

Flight Instruments

Chapter 7

The Boeing 777 Flight Deck

Chapter 8

Meteorology

Chapter 9

Air Traffic Control

Chapter 10

Flight Crew

Part 2: The Flight

Chapter 11

London to Boston

Appendix 1

The Boeing 777

Appendix 2

Abbreviations

Index

Introduction

A myriad of books have been written on the subject of flying, from tales of the early attempts, right through the ages of flight, to space travel and science fiction fantasy. The two world wars inspired the pens of many a fine aviator, and instruction books abound on the principles of flight. Novels have been published on everything from airship disasters to Concorde dramas, the airline pilot’s story has been told, and much has been printed on the airline world. So why another book on flying? Quite simply, because it is needed! The demands of an inquisitive public have now outstripped the material available, and the information presented in this book is designed to fill the gap. ‘What is it really like to fly the big jets?’ is a question that almost everyone seems to ask, and the one that this book hopes to answer.

A great many people have now flown, and those who haven’t have seen enough on television or in the cinema to know a little of the airline world. They’ve a fairly good idea of what’s involved for the passengers in going from, say, Paris to New York, and it takes only a little more information to fill in the basic procedures for the crew.

The crew arrives about one hour before departure, checks the paperwork and the weather, and the captain makes a decision on the quantity of fuel required. The aircraft is then boarded and the pre-flight checks commenced. After the checks are completed, the passengers boarded, and the departure procedures studied, the engines are started. In radio contact with various controllers, and under their instructions, the aircraft taxies out, takes off and sets course for its destination.

En route, the aircraft is guided along a predetermined track, passing from one radio control centre to another as the flight progresses. Approaching the destination, the arrival procedures are studied and, once again in liaison with a series of controllers, the aircraft starts the descent, completes the approach, let-down and the landing phases of the flight, and taxies to the terminal building. The engines are then shut down, and the final checks completed. After a long flight, the crew will go off duty, but after a short journey they may well be going on to another destination, so the pre-flight checks are begun once again and the whole procedure repeated.

That, of course, is all very simplified, but it covers loosely the basic procedures in flying an aircraft from A to B, and perhaps on to C. However, what on the surface appears to be a fairly straightforward procedure is in fact a complex operation. The flight crew require a great deal of training, knowledge, and skill to perform their tasks safely in what is potentially a hostile environment, notoriously unforgiving of error. Although most flights are routine, with so many lives at stake alertness and vigilance become second nature, and Murphy’s Law probably applies more to the flying of aircraft than to any other task.

Murphy’s Law states that: (1) nothing is as easy as it looks; (2) everything always takes longer than expected; (3) if anything can go wrong, it will – and at the worst possible moment.

That so few incidents do occur is due in no small measure to the respect afforded to Rule 3 by everyone concerned in aviation.

In the last few years much interest has been generated about the world of big jets, and today the air travelling public is more than ever aware of its surroundings. The little information gained from a flight, or from watching aircraft at an airport or on film, is enough to whet the appetites of most for further knowledge. And what people want to know are the facts. They want to know the basic details of the flight. Any airline pilot knows the problems of being bombarded with questions in non-flying company once his occupation has been discovered. How often are the tyres changed? Does a pilot fly the same route all the time? Does he fly more than one aircraft type? Does he watch all the instruments at the same time? And a thousand similar questions.

To some, the airline world is filled with magic and mystery where even the laws of nature are defied, and for a few the flying environment distorts imagination and confuses even alert minds. It is not unusual for crews boarding the first stage of a long flight, say from Europe to Australia, to receive parting comments from passengers that they’ll see them again when they deplane in Sydney some twenty-four hours later! The passengers may complete the journey on the same aircraft but the crew will most certainly deplane for a rest at an intermediate stop.

To be fair, however, the subject of flight holds many traps for the unwary, because much is unexpected and the obvious often quite incorrect. Take one look at the Puffin bird with its over-large beak and odd-shaped body and two facts become readily apparent – walking is achieved only with the greatest of difficulty and flying is impossible. No one, of course, told the Puffin bird! Ungainly in the air as it might be, the Puffin most certainly does fly. Aircraft, however, although extremely complicated, are pieces of mechanical and electrical equipment, just like a sewing machine or a locomotive, and need to be looked after, oiled and maintained in exactly the same way. All airlines, for example, instead of using new tyres to replace old ones, use retreads wherever possible, just like on the family car; a fact that seems to amaze everyone who hears it! The big jets also have quite recognisable windscreen wipers and washers! Crews too, in general are fairly ordinary, straightforward people, doing a job of work just like anyone else, with many of the same interests, but with, perhaps, a few specialised problems of their own. It has not been unknown for a pilot suffering from, say, a sprained ankle, to be told at a hospital casualty department that he’ll be back to work in no time, the staff little realising that the rudder, one of the basic flying surfaces, is controlled by pedals, and the brakes operated by pressure from the toes. Even a slight loss of strength or movement in a foot could prove disastrous! With misunderstanding of this nature it’s not surprising that most airlines employ their own specialised medical personnel.

Within these pages as many questions as possible have been answered, and much information has been added on the training, knowledge and skills of pilots, together with facts and figures to enlighten and amuse the reader. Flying the Big Jets doesn’t attempt to tell a story, but merely presents the information that people want to know in a plain and simple manner. Although much of the material is of a technical nature the book is not a technical manual but an elementary introduction to airline flying written specifically for the layman with an interest in the big jets. Explanations are given so as to be understood by all with a very basic understanding of the sciences, with drawings and photographs being added where required.

The book has been written ‘through the eyes of a pilot’, and in ‘The Facts’ much detail is given to prepare the reader for the ‘pilot’s seat’ on an imaginary trip in ‘The Flight’. Since the range of general aviation material is large, much has been omitted in concentrating on the big jets, but care has been taken not to treat important subjects lightly. In understanding the big jets a certain basic aviation knowledge is required, but the reader is taken from the basics to the big jets in one easy leap. In a book of this nature some subject overlap is inevitable, as flight itself is the result of so many different interrelated factors, but repetition of detail has been kept to a minimum. Where required, references have been included in brackets when cross-referring to information in other sections.

Aviation language is full of abbreviations to which it is necessary to introduce the reader; for example ND, PFD, EICAS and so on. Extensive use of unfamiliar abbreviations is tiresome, however, and has been avoided where possible. To prevent confusion and aid the reader’s memory, fully expanded terms, with abbreviations in brackets, have been repeated at regular intervals, e.g. primary flight display (PFD). A list of abbreviations is also included at the end of the book.

It is hoped that this book will meet at least some of the demands of those seeking further information, but, of course, it will not satisfy all. To begin with, airline pilots fly mostly only one aircraft type, for example the Boeing 777, since the complexities of modern aeroplanes make it difficult for crews to fly more than one type at a time. Airliners vary greatly in construction and size, and what would be normal practice on one could be potentially dangerous on another. Also, pilots tend to be divided between long haul on worldwide routes, and short haul on continental flights, and what is true for one group may not be true for the other. Airlines, too, sometimes operate quite differently from their competitors, even when flying the same type of aircraft on the same routes.

Now the Boeing 777 is flying and a new big ‘twin’ is gracing the skies of the world, a fourth edition of this book is published to present the facts. The 777 is the largest twin-engined aircraft ever built with the 777-300 being the fastest of the widebody twins. The 777-300X is also the longest airliner ever made with a wingspan the same as the Boeing 747-400. The 777 is Boeing’s first fly-by-wire airliner and the latest engines of the 300X develop a total thrust not far short of the thrust produced by the four engines of the 747-400. It is a very impressive flying machine.

The facts and figures presented in the book are derived mainly from the Boeing big jets and their operating procedures flying worldwide. Although the book has been written as comprehensively as possible, however, it is obvious from what has been said that there are bound to be a few omissions and inconsistencies; crews will not always operate as stated nor will pilots everywhere live their lives in such a manner. In spite of the disclaimers, whenever a pilot is invited by non-flying friends to a dinner party, he or she can take along several copies of Flying the Big Jets, distribute them beforehand, and thereby enjoy the meal in peace.

Part 1:

The Facts

Chapter 1

Principles of Flight

An aircraft flying straight and level is influenced by four forces, as shown in Fig. 1.1, and is in balanced flight when they are in equilibrium, i.e. when lift equals weight and thrust equals drag.

1.

Lift is the upward force created by the wings and is assumed to act through a central point known as the centre of pressure.

2.

Weight of an aircraft is expressed in either kilograms or pounds and is assumed to act through a central point known as the centre of gravity.

3.

Thrust is the force of the engines, normally expressed in kilo Newtons or pounds, which propels the aircraft forward through the air and is assumed to act in line with drag.

4.

Drag is the result of the air resisting the motion of the aircraft.

Fig. 1.1 The four forces acting on an aircraft.

Lift

If a driver extends his hand out of a moving vehicle and holds his flat hand inclined to the airflow, the flow of air passing over the surface of the hand produces a force that lifts the hand upwards and pushes it backwards (Fig. 1.2). The upward component of the force is known as lift and the backward as drag. A wing is a more refined shape than a flat hand but produces lift in exactly the same way, although a lot more efficiently. An aircraft wing is fixed to the structure at an angle relative to the airflow as it flies through the sky. Air going the long way round, up and over the curve of the wing, is forced to increase speed resulting in an area of low pressure being induced on the top surface that draws the wing upwards. Some lift derives from the airflow striking the lower surface of the wing creating an increase in pressure forcing the wing upwards, but the greater lift results from the reduction in pressure above.

Fig. 1.2 Lift and drag.

The area of low pressure on top of the wing is not a vacuum but simply a reduced value of pressure relative to the surrounding air, and is shown as negative pressure. The area of high pressure below the wing is, similarly, an increased value relative to the surrounding air and is shown as positive pressure. The pressure pattern distribution surrounding an aircraft (Fig. 1.3) clearly shows the greater effect of the negative pressure in the lifting process. To describe lift in more precise terms it can be said that the low and high pressure areas above and below the wing combine at the trailing edge as a downwash from which the wing experiences an upward and opposite reaction in the form of lift. Thinking of lift in simple terms, however, it is not so ridiculous as it seems to imagine the aircraft being sucked into the air by the reduced pressure above the wings.

Fig. 1.3 Pressure pattern distribution around an aircraft.

Lift is affected by a number of factors. The density of the air affects lift: the higher the density the greater the lift. The airspeed over the wing, i.e. the true airspeed (TAS) of the aircraft, affects lift: the faster the speed the greater the lift. The angle at which the wing is inclined to the airflow, known as the angle of attack (Fig. 1.4), affects lift: the larger the angle the greater the lift. Since the wings are firmly fixed to the structure, the angle of attack is varied by pitching the aircraft nose up or down and is referred to as the attitude of the aircraft. To maintain constant lift, therefore, as in level flight, variation in true airspeed requires adjustment of aircraft attitude; i.e. faster airspeeds require a lower nose attitude and slower airspeeds a higher nose attitude. Wing surface area is also a function of lift: the larger the area, the greater the lift. The bigger and heavier the aircraft, therefore, the larger the wingspan and wing surface area required to produce sufficient lift. Today’s large jets are constructed with wings of enormous size, the Boeing 777-300X having a wingspan of 64.9 metres (213 feet), the same as the Boeing 747-400 wingspan.

Fig. 1.4 Angle of attack.

On modern jets the wings are swept back at a large angle (the Boeing 777 at 32°) to allow aircraft to cruise at high speeds by delaying the onset of shock waves as the airflow over the wing approaches the speed of sound (see Chapter 6 - Flight Instruments). At slow aircraft speeds, however, the lift-producing qualities of the wing are poor. High-lift-producing devices in the form of leading and trailing edge flaps are required and, when extended, increase the wing surface area and the camber of the wing shape (Fig. 1.5). With flaps fully extended the wing area is increased by twenty per cent and lift by over eighty per cent. Flaps increase lift, allowing slower speeds, and also increase drag, which retards the aircraft. Canoe-shaped fairings below the wings shroud the tracks and drive mechanisms used in flap operation.

Leading edge flaps and slats extended.

To improve lift at take-off, flaps are set at five or fifteen degrees, depending on circumstances, any increase in drag being more than compensated by increase in lift. Take-off without flap is not possible at normal operating weights. On landing, thirty degree flap is selected in normal circumstances with twenty degree flap being reserved for abnormal system situations and contaminated runways.

Fig. 1.5 The effect of flaps on wing surface area and camber.

Clean Wing

Flap at 20°

Large jets departing fully laden on long-haul flights require long takeoff runs in the order of 50–60 seconds duration before becoming airborne. At the required speed for take-off the pilot raises the aircraft nose (called rotation) to a predetermined pitch angle, to increase the angle of attack to the airflow with a resultant increase in lift, and the aircraft climbs into the air. At maximum take-off weights the big jets require speeds in the region of 165 knots (190 mph or 305 km/hr), and major airport runway lengths are normally about three and a half kilometres (over two miles) to accommodate the take-off distances required. Not all take-offs, of course, are at maximum weight, and at lower weights less lift is required. The aircraft lifts off at lower speeds and therefore requires a shorter run along the runway.

Weight

Although aircraft weights are normally given in kilograms or pounds, the enormous weight of today’s big jets becomes meaningless to many people when expressed in hundreds of thousands of a particular unit, and an appreciation of the weights involved is often better achieved by stating them in larger terms. One tonne (or metric ton) is equal to 1000 kg, which also equals 2200 lb. One ton is equal to 2240 lb. One tonne, therefore, is almost equivalent to one ton, being only 40 lb lighter. Whether units are stated in metric or imperial, or pronounced as tonnes or tons, can be seen to make little difference, and to simplify matters all weights are expressed in tons. Take, for example, the maximum take-off weight of the Boeing 777-200 of 297,600 kg or 656,000 lb. Stating this weight as almost 300 tons brings home to most the size of the aircraft. The maximum take-off weight of the 777-300X is 340 tons and the 747-400 is 397 tons.

Fig. 1.6 Take-off weight – Boeing 777-200 Series.

United Airlines Boeing 777.

Aircraft loading

To the basic weight of an aircraft is added the weight of the equipment and the weight of the crew and their bags, the resultant figure being known simply as the operating empty weight. To this weight is added the payload, which consists of the weight of the passengers (males at 78 kg/170 lb, females at 68 kg/150 lb, children at 43 kg/95 lb and infants at 10 kg/22 lb – including hand luggage and necessities) and the weight of the cargo (including passenger baggage). The operating empty weight and the payload account for all weights excluding fuel and together are known as the zero fuel weight. To the zero fuel weight is added the weight of the fuel to obtain the final take-off weight (Fig. 1.6). The total aircraft weight at any point in the flight is known as the all-up weight (AUW).

The Boeing 777-200 series approximate operating empty weight is 144 tons. Since the maximum structural weight is 297.5 tons, the maximum weight of 153.5 tons of payload and fuel able to be carried is more than the 777-200’s own weight! The maximum fuel load depends on the specific gravity of the fuel and the maximum capacity of the fuel tanks and is about 137.5 tons. The maximum number of passengers depends on the maximum number of seats it is possible to fit. The 777-200 has a seating capacity of 300–375 and the stretched 777-300 a seating capacity of 370–450, depending on the seating configuration.

Average weights for a Boeing 777-200 on a seven-hour flight are: operating empty weight 144 tons; payload 30–40 tons; fuel 50–55 tons (of which about 45 tons is used, the rest in reserve), and take-off weight 220–240 tons.

Flap 30° set for landing.

Weight and balance

Weight distribution on an aircraft is very important: incorrect loading can result in the aircraft being too nose-heavy or too tail-heavy and beyond the ability of the controls to correct. Payload weights and distribution are, therefore, carefully pre-planned. Most cargo (including passenger baggage already weighed at check-in) is pre-loaded on pallets designed to fit the shape of the hold. The weight of each pallet is noted and its position carefully arranged. The pallets are raised to the level of the cargo door on special loading vehicles and slid on rollers from the raised platform into predetermined positions in the hold. The required weight of fuel is decided by the captain and this weight is converted to a volume by using the specific gravity of the fuel. It is then pumped aboard by the litre or gallon into tanks in the wings and belly of the aircraft.

Passenger weights and seat allocations are noted at check-in and fed into a computer, which also receives information on the cargo distribution and final fuel load. The computer then calculates the centre of gravity and checks that this is within limits. The aircraft is designed to cope with a range of movement of the centre of gravity to allow for take-off at different weights and with varying weight distribution. During flight the fuel weight distribution changes with fuel consumption, resulting in movement of the centre of gravity. The computer, therefore, also calculates that the centre of gravity remains within limits for the entire flight. All this information is noted on a load sheet that is presented to the captain for inspection and signature when the final loading is completed just before departure.

Thrust

Static thrust is the thrust developed by a jet engine with the aircraft stationary and maximum take-off power set, and is stated in kiloNewtons (kN) or pounds (lb). Since the performance of a jet engine is proportional to the density of the intake air, the aircraft is assumed to be at sea level in the standard atmosphere of 15°C (59°F) and pressure 1013.2 hectoPascals (29.92 inches of mercury). The General Electric GE90-94B engines on the 777-200 series each develop 416.5 kN or 93,800 lb of static thrust. On the 777-300X the General Electric GE90-115Bs each develop 466.5 kN or 114,800 lb of static thrust, giving a massive total of 933 kN or 229,600 lb of static thrust produced by the two engines in the full power take-off condition.

Drag

The two basic types of drag are profile drag, caused by the shape and skin surface of the aircraft, and induced drag, a side effect of the production of lift.

Profile drag

Drag produced by the shape of the aircraft is a result of the smooth flow of air being diverted round the form of the aircraft and is in fact known as form drag. The streamlined structure of an aircraft is designed to reduce form drag to a minimum.

Drag is also produced by friction between the aircraft skin surface and the airflow and this is known as skin friction. Air flowing over a surface results in a layer of retarded air being formed in immediate contact with the surface over which it is passing. (Water in a river, for example, always flows faster in the middle than at the banks due to the same effect.) This retarded layer is known as the boundary layer and its thickness depends on the type of surface over which the air is flowing. Aircraft surfaces are highly polished to produce a thin boundary layer that maintains skin friction at a minimum.

Profile drag, then, is a combination of form drag and skin friction and is related to the speed of the aircraft, increasing markedly as the aircraft speed increases – doubling the speed of the aircraft quadruples the profile drag produced. (Any cyclist knows the problems of pedalling against a strengthening head wind as opposed to cycling in calm conditions.)

Induced drag

Induced drag is a direct result of the production of lift and is caused by the mixing of the upper and lower airflows at the trailing edge of the wings. The airflow over the top surface of the wing tends to flow inwards towards the maximum low-pressure area produced above the wing root, and the airflow under the wing tends to flow outwards from the maximum high-pressure area produced below the wing root. The two airflows meet at an angle at the trailing edge of the wing and combine to produce a rotating airflow at each wing tip known as a wing tip vortex (Fig. 1.7). These wing tip vortices rotate in the direction of the wing root and result in a high level of turbulent airflow being produced in the wake of a large aircraft. The effect of speed on induced drag is quite different from profile drag, in that induced drag actually decreases with an increase in airspeed. Wing tip vortices, therefore, are more evident at slow speeds during both take-off and landing, but are even more pronounced on the final approach to landing with landing flap set. They can be clearly seen when watching aircraft land on a rainy day with a lot of moisture in the air.

Fig. 1.7 Wing tip vortices.

Downwash at the trailing edge of the wings and wing tip vortices can be clearly seen on this landing aircraft.

Total drag

As has been stated, profile drag increases with increase in airspeed and induced drag increases with reduction in airspeed. Total drag at any one moment, therefore, consists partly of profile drag and partly of induced drag. When total aircraft drag is plotted against speed by combining the effect of the two drag types, the graph shown in Fig. 1.8 results. The graph shape is known as the drag curve and is familiar to all pilots.

The speed for minimum drag on the total drag curve corresponds to the point where profile drag and induced drag are equal. At this point an uncanny situation arises whereby either an increase or a decrease in speed results in an increase in drag. Reduction of only a few knots from this minimum drag speed results in the aircraft entering the ‘wrong’ side of the drag curve where the drag increases rapidly with reducing airspeed, and large amounts of power are required to increase aircraft speed. Cruising speeds are normally in excess of the speed for minimum drag to maintain the aircraft on the ‘right’ side of the drag curve to ensure a safe operating margin.

Fig. 1.8 Total drag curve.

Stalling

As an aircraft slows, to maintain lift the angle of attack of the wing is increased by raising the nose of the aircraft with a resultant increase in induced drag. If the aircraft speed is allowed to become too slow and the nose-up attitude is excessive, a point is reached at which the angle of attack becomes critical and the smooth airflow over the wing breaks away from the upper surface producing turbulent flow (Fig. 1.9). With a breakdown in the smooth airflow all lift is lost and maximum drag results from the turbulent wake. This condition is known as stalling. With lift lost from the wings the aircraft nose pitches down and the aircraft descends very steeply, eventually adopting a relatively flat attitude. The onset of the stall is accompanied by buffeting and shaking due to the turbulent wake produced. Recovery is achieved by forcing the aircraft into a dive by pushing the control column forward, and by applying full power until flying speed is once again achieved. The aircraft can then be pulled out of the dive and flown straight and level. Obviously, stalling on a large jet aircraft is an extremely hazardous manoeuvre, and pilot training covers thoroughly the recognition of and recovery from an early approach to the stall condition long before stalling actually occurs. Stall warning devices include a ‘stick shaker’, which physically shakes the control column at early onset of the stall condition and a ‘stick pusher’, which delivers a hefty push forward to the control column at later stall development. Stalling speeds for the Boeing 777-200 at 208.6 tons (max. landing weight) are 152 knots (175 mph/281 km/hr) indicated airspeed clean (i.e. with no flaps or landing gear extended) and 107 knots (123 mph/197 km/hr) indicated with flaps fully down and landing gear lowered. The stick shaker activates at 167 and 114 knots respectively.

Fig. 1.9 Stalling – critical angle of attack.

Winglets

A wingspan in excess of 65 m (213 ft) was known to cause airport manoeuvring difficulties so winglets were introduced on the Boeing 747-400 as a compromise between the extra lift required and maintaining sufficient parking bay and hangar clearances. The Airbus A340-500/600 also has winglets for similar reasons. The design improves cruise performance, producing extra lift with low drag, while retaining low-speed handling qualities. The wing tip extension and winglet can produce fuel burn reductions in the order of 3% in comparison to the standard wing and, as such, a number of other aircraft with smaller wingspans have adopted the design. The stretched Boeing 777-200X/300X, with a wingspan of 64.9 metres (213 ft), was designed to minimise changes from the original, and does not incorporate winglets. In fact, the 777 uses the most aerodynamically efficient wing shape ever developed for subsonic commercial aircraft. As a result, the 777 can climb quickly and can cruise at higher levels and higher speeds than comparable aircraft. The wing is also effective at hot and high airports where full passenger payloads can be carried.

In-flight balance and stability

Balance

Imagine a model aircraft in a child’s bedroom hanging from the ceiling by a thread. The aircraft is balanced when the thread is attached to the point through which the centre of gravity acts. If the thread is attached aft of the centre of gravity the nose pitches down, and if attached forward of the centre of gravity the nose pitches up. A similar effect results if the point of attachment of the thread remains fixed and the centre of gravity of the model is made to move forward or aft by placing small weights on the model on either side of this point.

Imagine now an aircraft in straight and level flight suspended by the upward lift force acting through the centre of pressure in a similar manner to the model aircraft held aloft by the thread acting through the point of attachment. In the air the centre of pressure acts like a pivot, similar to the central point of a seesaw, and to maintain the aircraft in balanced flight the weight is required to act in line with lift. Attempting to balance an aircraft in this position throughout flight, however, would be like trying to balance the model aircraft on a knife edge, and is quite impractical. Lift and weight seldom act in line, owing to movement of the centre of pressure with flap selection on take-off and landing, and to the rearward movement of the centre of gravity with fuel consumption in cruise. (Fuel is first used from the centre and inboard main wing tanks and last from wing tip tanks which are well aft owing to the swept back wings (see Fuel in chapter 2). The problem is overcome by the addition of a moveable tailplane that acts as a stabilising agent; the whole tailplane being designed to vary its angle to the airflow until positioned to redress any imbalance. (This is not to be confused with the movement of the elevator which forms part of the tailplane and which is discussed later.) The variable-angled tailplane has been aptly named the horizontal stabiliser.

When the centre of gravity is aft of the centre of pressure the aircraft is tail heavy, and a further force is required to counteract the effect and stabilise flight. This is achieved by increasing the angle of attack of the stabiliser by hydro-mechanically moving the complete tailplane. The resultant increase in lift from the tailplane counteracts the tail heavy condition. Similarly, when the centre of gravity is forward of the centre of pressure and the aircraft is nose heavy, the angle of attack of the stabiliser is decreased by hydro-mechanically moving the tailplane to produce negative lift, which acts downwards, and which once again counteracts the displacement of the forces and balances the aircraft. This process of balancing the aircraft by hydraulic movement of the stabiliser is known as trimming. When handling the aircraft, the out-of-balance forces can be felt by the pilot as pressure on the control column. Operation of electric switches on the control column activates the hydraulic mechanism that moves the stabiliser. As the aircraft is trimmed the control column is relieved of the out-of-balance pressure, and the aircraft is balanced when the control column is free of pressure forces and a stable aircraft condition is maintained with hands off the controls.

Fig.1.10 Centre of pressure.

During take-off and landing the handling pilot has continually to re-trim the aircraft as flight conditions change. When the autopilot is engaged, as is normal in the cruise, trimming is controlled automatically. Before departure a computer calculates the stabiliser setting required to ‘balance’ the aircraft in the air just after take-off for the particular weight and load distribution concerned. The relevant stabiliser setting is then set on the trim scale during ground checks just before take-off.

Stability

If an object is displaced and returns to its original position it is said to be stable and, if it does not, unstable. Aircraft are designed with a degree of natural stability, and, when disturbed from their original line of flight by a gust of wind, attempt to return to the initial stable flight condition without movement of the flying controls. In large passenger transport jets a good degree of stability is desirable, and inherent stability in the three aircraft movements of pitch, roll and yaw is a feature of basic aerodynamic and structural design.

Fig. 1.11. Natural Flight Stability.

Natural flight stability

A simple picture of each movement can be drawn by imagining the centre of pressure of the aircraft as a pivot point about which the aircraft moves in all directions (Fig. 1.10).

Stability in pitching motion is a function of the tailplane, just like the fins of a missile or flights of a dart. (Not to be confused with the movement of the stabiliser in trimming the aircraft to maintain balanced flight.) If the aircraft nose is pitched up by a gust of wind, the angle of attack of both the wings and the tailplane is increased. The extra lift produced by the tailplane, being far from the centre of pressure, is sufficient, owing to the long leverage, to raise the tail and return the aircraft to straight and level flight. The opposite results with nose pitched down (Fig. 1.11).

Stability in rolling motion is a function of the dihedral construction of the wings, i.e. each wing is positioned at a slight angle (7°) to the horizontal. If the aircraft is rolled by a gust of wind it slips down and to the side in the direction of roll. As the aircraft sideslips, owing to the dihedral effect, air resistance below the lower wing pushes the wing up, while the upper wing, positioned behind the aircraft body, also owing to the dihedral effect, is protected from the sideways airflow and is unaffected. The sideslipping is arrested and the aircraft returns to level flight.

Stability in yawing motion is a function of the tail fin. If a gust of wind yaws the aircraft to the left or right the tail fin is momentarily displaced from its position. The resultant force, once again being far from the centre of pressure, is sufficient to return the tail to its original position.

Flying control surfaces

The elevators control aircraft movement in pitch, ailerons in roll, and rudder in yaw (Fig. 1.12). All control surfaces are operated hydraulically and are powered by one or more of three separate hydraulic systems, thus minimising any loss owing to system failure. Displacement of the control surfaces from the central position results in airflow over the surface of the control applying a force that moves the aircraft in the required direction.

The elevators – climbing and descending

Upward movement of the elevator results in a negative lift force being applied that forces the tail down, and therefore, the nose up, and the aircraft climbs. Downward movement of the elevator results in descent.

The ailerons – rolling and turning

Turning to the left or right is achieved by the ailerons, which roll the aircraft, resulting in a turn. Rolling of the aircraft in a turn is similar to the banking of a motorbike in a turn. (Turning is not the function of the rudder as it is on a ship.) One aileron set moves up, reducing lift which forces the wing down, while the opposite set moves down, increasing lift which forces the wing up. When the required bank is applied (the greater the bank the faster the turn) the ailerons are placed centrally and the aircraft continues to turn. Straightening of the aircraft is achieved by opposite application of the aileron controls.

Fig. 1.12 Control surfaces.

Start of high speedright turn. Inboardaileron/flaperononly operating.

The Boeing 777 has two ailerons on each wing, a long thin outboard aileron towards the wing tip and an inboard aileron, approximately in line with the engine, which is larger and squarer in shape. This inboard aileron also acts in a similar manner to a flap and has been aptly named a flaperon. When the flaps are extended the flaperon droops down in proportion to the flap extension. To increase lift the outboard ailerons also droop down slightly for flap 5 selection and beyond, but both ailerons still continue to provide roll control. At high speeds only small aileron movements are required and operation of the outboard ailerons is inhibited. When good turning ability is required at low speeds (normally after take-off, on climb and descent and on the approach) both sets of ailerons operate. The system is programmed by airspeed with both sets of ailerons becoming active below about 275 knots.

The rudder – yawing

The rudder is used for directional guidance (i.e. like the rudder of a ship) when the aircraft is on the runway and is accelerating for take-off or decelerating after landing. The rudder can also be used to steer the nose wheel up to 7° either side, both on the runway and while taxiing. For larger turns during taxiing a tiller is used to steer the nose wheel. The rudder is used during asymmetric flight (i.e. with an engine failure) to redress the imbalance caused by greater engine power on one side than on the other (see Chapter 6 - Flight Instruments). At high speeds only small rudder movements are necessary and a rudder ratio system reduces movement with increase in airspeed.

The rudder also acts as a yaw damper and operates automatically to suppress involuntary movement of the aircraft in roll and yaw, known as Dutch roll (so named from the inability of the early Dutch sailors to walk straight on land after many months at sea and much alcohol!). Dutch roll is usually initiated by a gust of wind which results in a yawing-rolling oscillation owing to the poor damping qualities of the swept-back wing. A stabilising system senses the motion and signals the rudder to apply an opposing movement that dampens the Dutch roll.

Spoilers – speed brakes

Spoilers (Fig. 1.13) are so called because they spoil the lift of the wing by disrupting the airflow on the upper surface. On landing the spoilers automatically deploy to spoil the lift and place the full weight of the aircraft firmly on the wheels. This helps to prevent the aircraft bouncing back into the air after a heavy landing and also improves braking effectiveness. On an abandoned take-off, selection of reverse thrust automatically deploys the spoilers, which once again places the full aircraft weight on the wheels to improve braking.

Fig. 1.13 Spoilers.

In flight, the spoilers can be used as speed brakes and are deployed by manual operation of a lever to slow down the aircraft rapidly or greatly increase the rate of descent. A gentle rumbling can be detected in the cabin when speed brakes are extended. Spoilers also operate as a flying control when a higher roll response is required by automatically deploying, on one side only, to aid the aircraft during turns. The automatic raising of the spoilers on the wing moving down reduces lift, which assists the movement of the down-going wing.

Slow speed left turn (flap 10° set). Inboard aileron/flaperon, outboard aileron and spoilers all operating.

Aircraft at touch-down. Full flapset, spoilers fullyraised.

Spoilers extended as speed brakes (right wing similar).

Flying controls – control column and rudder pedals

Movement of the controls (Fig. 1.14) is instinctive. On take-off, when flying speed is achieved, the control column is pulled back to ‘rotate’ the aircraft to the required nose up attitude for lift off. On landing, the control column is pulled back to ‘flare’ the aircraft to arrest the rate of descent for a smooth touch down. In flight, pulling back on the control column raises the nose and climbs the aircraft; pushing forward results in descent. Turning the yoke to the left (like the steering wheel of a vehicle) banks the aircraft to the left, with subsequent turning, and vice versa. Left rudder yaws the aircraft to the left, and right rudder to the right. Above each of the rudder footrests is a toe brake, which operates the brakes by pressure from the toes. The toe brakes apply braking to the wheel bogies on their respective sides allowing symmetrical or differential braking (like directional control on a tank – braking the right track turns the tank to the right, etc.) to supplement rudder control if required on deceleration after landing or on an abandoned take-off.

Fig.1.14 The aircraft control surfaces.

Direct physical movement of the control surfaces on large jet aircraft is beyond human strength and flying controls are normally operated by hydraulic mechanisms known as power control units (PCU), which are powered by the aircraft’s hydraulic systems. Movement of the pilot’s controls operates control valves (either via cables or via electrical signals down wires) that determine the hydraulic input to the PCU and thus the degree of movement of the control surface. Since no direct connection exists between the control surfaces and the pilot’s controls the force exerted by the airflow on a deflected control surface cannot be felt as a pressure on the control column or rudder pedals. The pilot thus has no direct feeling of flying control pressure when moving the pilot’s controls and is at risk of over-stressing the aircraft by excessive demands. To overcome the problem artificial feel is supplied by ‘feel’ units which apply pressure to the controls proportional to control surface movement. As a result the pilot obtains the sensation of flying the aircraft as if the controls were directly connected by cables to the control surfaces as they are on light aircraft. Indeed, sometimes a degree of physical effort is required to overcome the realistic feel-unit pressures transmitted to the pilot’s controls.

Figure 1.14 shows the complete aircraft and the control surfaces.

Fly-by-wire

The fly-by-wire system on the 777 uses computers to modify the inputs from the control column to the hydraulic power control units operating the control surfaces. The fly-by-wire system permits a more efficient structural design, resulting in a smaller vertical fin and tailplane, thereby reducing weight and increasing fuel economy.

The primary flight control system (PFCS) supplies manual and automatic aircraft control in pitch, roll and yaw, plus protection against over-stressing, stalling, overspeed and over-banking. Position sensors on the control column, rudder pedals and speedbrake lever convert movement into electrical signals which are sent to each of four ‘black boxes’ called actuator control electronics (ACEs). The signals from these ACEs are sent to three primary flight computers (PFCs). The PFCs receive information from other aircraft systems regarding airspeed, outside air data, attitude, angle of attack and engine thrust, plus positions of landing gear, flap, slats and speedbrake. Modified signals are then sent back to the actuator control electronic boxes and from there are sent to the hydraulic actuators which move the flying control surfaces.

Operating the fly-by-wire 777 is exactly the same as flying a ‘conventional’ aircraft, but with a lot of advantages. When hand flying a conventional aircraft, for example, each time the thrust is changed, the landing gear or flaps are moved or the speedbrake is operated, a corresponding trim change has to be made by the pilot. On the 777, all the trim changes are managed by the primary flight computers. In addition, when the pilot is turning a conventional aircraft, there is normally a requirement to pull back slightly on the control column to maintain height. On the 777, however, with normal bank angles this is also managed by the computers. Trimming by the pilot on the 777 is only required when the airspeed changes and is accomplished exactly as on a conventional aircraft. The trim switches do not directly move the tailplane, but the effect is the same. When flying the 777, therefore, the pilot is given the impression of flying a conventional aircraft.

On the 777 there is also provision for failure of one or more of the primary flight computers. If the system is slightly degraded, the pilot, when hand flying the aircraft, may have to trim for thrust changes, flap movement etc. and, if the system degrades further and all three primary flight computers fail, the aircraft flies exactly like, and with the same levels of protection as, a conventional aircraft. In the unlikely event of a complete electrical system shutdown there is also a mechanical backup. Cables from the flight deck to the stabiliser and selected spoilers allow the pilot to maintain control until the electrical system is restored.

The fly-by-wire system on the 777 can also compensate for yaw when an engine fails. A thrust asymmetry compensation (TAC) system continuously monitors engine data to determine the thrust level from each engine. If the thrust level of one engine differs by 10% or more from the other engine, the TAC system automatically adds rudder to minimise yaw. To allow the pilot sufficient roll/yaw cues to identify the initial onset of an engine failure, however, the TAC system does not immediately apply the full rudder requirement. The TAC system can be manually over-ridden by rudder pedal inputs or manually disarmed.

Chapter 2

The Jet Engine

The earliest jet engine test-bed run was conducted by Sir Frank Whittle in April 1937, but the first jet aircraft to fly was the Heinkel He 178 in August 1939. The Comet, the first jet transport, made its maiden flight in 1949, but regular transatlantic jet services did not commence until 1958 with the Comet 4 and the Boeing 707. The Boeing 747 made its first commercial New York to London flight in 1970. Concorde made its first commercial flight in 1976, simultaneously from London to Bahrain and Paris to Rio de Janeiro. In June 1994 the Boeing 777-200 flew for the first time and entered service with United Airlines one year later in June 1995.

Principles

Although the jet engine is a complicated piece of machinery, the basic workings of the engine are, in fact, quite simple (Fig. 2.1). Air is drawn in at an intake by a compressor that highly compresses the air. The highly compressed air passes to a combustion chamber where it combines with burning fuel, expanding enormously. The fuel used is kerosene, which does not ignite instantaneously but burns continuously like heating oil or paraffin. The expanding air from the combustion chamber first channels through a turbine, which turns a connecting shaft to drive the compressor, before exhausting at great speed through the jet pipe. The flow of air through the engine, even at idle power, is such that a man can be sucked into the compressor within eight metres (twenty-five feet) of the intake, and can be blown over by jet blast within forty-five metres (150 feet) of the jet pipe.

Fig. 2.1 The jet engine.

The jet engine cycle

Jet engine operation is a continuous cycle. Air is first drawn by the compressor into the engine intake. One stage of a compressor consists of a ring of rotating blades (known as rotors) followed by a ring of stationary blades (known as stators). The rotating rotor blades propel the air through the stationary stator blades with a resultant increase in pressure. The pressure increase across each stage is relatively small so that a number of stages are necessary to produce the required pressure. On larger jet engines airflow through the compressor is improved by breaking the compressor down into two or three separate sections known as spools, each spool being driven independently by its own turbine and connecting shaft. Compressors are denoted by the letter ‘N’, and compressor spools as N1, N2 (and N3). N1, therefore, corresponds to the low pressure (LP) compressor spool at the intake and N2 (or N3) to the high pressure (HP) compressor spool before the combustion chamber.

Fig. 2.2 Fan jet principles.

An improvement to propulsive efficiency is also achieved on large engines by arranging for some N1 compressor air to bypass the main engine core and to exhaust straight to the atmosphere via a bypass duct. Such engines are known as bypass engines (Fig. 2.2). Today’s big jet engines have developed the bypass concept to such a degree that modern N1 compressors now consist mainly of a giant single ring of large blades, known as a fan, similar to a large many-bladed propeller with the tips cut off (see photograph below). And, indeed, the fan is more like a propeller than a compressor, delivering seventy-five per cent of the thrust of the complete engine and bypassing five parts of air (and up to nine parts on the larger Boeing 777 fan jets) for every one that flows through the main engine. Engine development has now turned full circle and returned to the principle of the propeller!

The portion of fan air that enters the main engine core progresses through the N2 (and N3) compressors and discharges as hot, highly compressed air into combustion chambers where about one third combines with burning fuel, combusting at a temperature of around 2000°C, while the remainder is used for cooling. The expanding exhaust flow from the combustion chambers channels through stationary convergent guide vanes that direct the flow onto the turbine blades. The turbine rotates under the force of the airflow impinging on the turbine blades, and in turn rotates its respective compressor via the connecting shaft. Aft of the turbine, the air continues to expand as it flows through the convergent duct of the jet pipe and exhausts from the engine as a high-speed jet.

Front view of the fan jet.

Fan exhaust shrouds the main jet core.

At take-off, the maximum static thrust produced by the fan jets on the Boeing 777-200 of around 94,000 lb (417 kiloNewtons) results in a radial force on each fan blade equivalent to six fully-laden London buses, and the power produced by an individual high pressure turbine blade (about the size of a credit card) equivalent to a Formula One racing engine.

Most jet engine noise is due to the shear effect of the high-speed jet of air cutting the atmosphere. An added advantage of the fan jet is the reduction in engine noise due to the bypassed air shrouding the main jet core and lessening the shear effect. This is most evident on the big twins like the Boeing 777, where the outer casing of the engine completely covers the engine assembly. Aircraft noise is measured in perceived noise decibels (PNdB), which is a measure of the type as well as the level of noise. The Boeing 777 scores about 107 PNdB at heavy-weight take-offs and landings. Airport noise limits are normally in the region of 110 PNdB maximum during the day and 102 PNdB maximum at night. Engine noise-abatement techniques involve reducing take-off power to climb power at a certain height, usually 1500 feet above the departure airport.

Engine start

The engine is first turned at speed by a small pneumatic starter motor to induce sufficient flow through the compressor. Fuel is then sprayed under pressure into the combustion chambers and igniters within the chambers are switched on to supply the initial source of ignition for the fuel. Once alight and burning, engine revolutions per minute (rpm) continue to rise until a point is reached at which the engine becomes self-sustaining. The starter is then disengaged and the igniters switched off. Engine acceleration continues until idle rpm is achieved. To accelerate beyond idle power the thrust lever is advanced on the flight deck (Fig. 2.3). The engine is shut down by simply cutting off the fuel supply.

In flight, restarting a shut-down engine is achieved by maintaining an airspeed sufficient to create enough airflow through the engine to turn the compressor. The pneumatic starter can also be used, if required, e.g. at high altitude.

Fig. 2.3 Thrust levers, 777-200.

Engine performance

The performance of a jet engine is normally expressed in pounds (lb) or kiloNewtons (kN) of thrust (see Chapter 1 - Principles of Flight). The propelling force of a jet is not the result of the action of the jet on the atmosphere but is an example of Newton’s Third Law, which states that ‘for every action there is an equal and opposite reaction’. The action of the jet force rearwards therefore results in a reaction within the engine that propels the aircraft forwards.

The continuous cycle of the jet engine results in an increased power production over that of the piston engine for a given engine size, and without the jet engine the large aircraft of today would not be flying. It has been estimated that the number of the highest-powered piston engines of comparable size required for take-off for a Boeing 777 would be as many as eighteen, and to maintain normal cruise at high altitude would require considerably more.

Fig. 2.4 The 777-200 engine indicating and crew alert system (EICAS).

Jet engine compressor speeds can be as high as 20,000 rpm, so for convenience are expressed as a percentage of the maximum; e.g. in cruise the normal N1 speed is approximately 90 per cent of the maximum rpm and is displayed as such on the screen. The normal maximum operating speed of 100 per cent can be exceeded for short periods, and indicated rpm in excess of 100 per cent can actually be achieved on the display (e.g. maximum takeoff N1 103 per cent). The fans on the 777, however, are very large, the diameter of the General Electric engine fan, for example, being 10 feet 3 inches (3.12 metres), and as a result rotate relatively slowly. Owing to the enormous centrifugal forces involved 100% N1 on this engine is 2263 rpm.

On today’s big jets power is indicated on displays on the flight deck in terms of percentage fan (N1) speed for some manufacturers, and for others in terms of engine pressure ratio (EPR). EPR is the ratio of the turbine discharge pressure to the compressor inlet pressure. The N1 and EPR maximum limits are marked by a red line on the gauge of the engine indicating and crew alert system (EICAS) display. On engines which are not mechanically limited, engine power must not be set beyond the maximum computed value as it is possible to overboost the engines and cause damage. On take-off and climb, engine power is normally set at something less than maximum if aircraft weight allows, thus reducing engine wear and tear. Reduced power used in such cases is known as derated power.