This chapter starts (12.2) by mentioning the drawbacks of the approach conventionally adopted in second language (L2) listening instruction—in particular, its focus on the products of listening rather than the processes that contribute to it. It then offers an overview of our present understanding of what those processes are, drawing upon research findings in psycholinguistics, phonetics, and applied linguistics. section 12.3 examines what constitutes proficient listening and how the performance of an L2 listener diverges from it; and section 12.4 considers the perceptual problems caused by the nature of spoken input. Subsequent sections then cover various areas of research in L2 listening. Section 12.5 provides a brief summary of topics that have been of interest to researchers over the years; and section 12.6 reviews the large body of research into listening strategies. Section 12.7 then covers a number of interesting issues that have come to the fore in recent studies: multimodality; levels of listening vocabulary; cross-language phoneme perception; the use of a variety of accents; the validity of playing a recording twice; text authenticity; and listening anxiety. A final section (12.8) identifies one or two recurring themes that have arisen and considers how listening instruction is likely to develop in the future.

INTRODUCTION

The author and V. C. Serghides have performed statistical analyses to produce combat aircraft reliability and maintainability prediction methods [61]. These are applicable for use at the conceptual design stage, because they only require the use of readily available parameters such as wing span, engine thrust, mass, etc. These methods predict whole-aircraft values of confirmed defects per 1000 flying hours and defect maintenance hours per 100 flying hours. Predictions are also made for individual systems and allowances may be made for technology improvements, relative to the empirical database used in the method derivation. These may be used as targets for reliability performance of individual systems during the preliminary design stage.

Earlier work by the author produced a similar method for the prediction of commercial aircraft dispatch reliability [62]. The whole-aircraft equations produced are reproduced in Section C2, below.

COMMERCIAL AIRCRAFT DISPATCH RELIABILITY PREDICTION

The work reported in reference 62 showed that some systems exhibited different traits according to the type of airline operation. For example long-haul aircraft tended to have higher delay rates because they may be away from their home base for more than a week, and defects might accumulate, whereas short-haul aircraft tended to return to their home bases more often. Other considerations were also affected by the operational type, in such things as ATA Chapter 28, fuel systems, where long-haul aircraft had more complicated systems that were more delay-prone than those of short-haul aircraft. To cater for these effects, separate models were made for the relevant systems.

All the aircraft in the sample had turbo-fan engines of some sort. Some were early types with bypass ratios of less than unity and some were of the more modern ‘big-fan’ type with bypass ratios on the order of five. These two types of engines, again, exhibited different traits, so separate curves were drawn for them. After the graphs were plotted, it was decided that, for most systems, a linear regression analysis would give the fairest result. This process was carried out by the use of a least-squares fit program.

The previous chapters have shown the complexity of aircraft, and their constituent parts. Their design is a daunting, but potentially satisfying task. Designers need all the help that they can get to achieve successful results.

The usual starting point is a sound aeronautical education. Design is learnt by a combination of theoretical education and design experience at university and/or in industry. It must be stressed that design is much more than analysis. It is a creative process involving the synthesis of knowledge from many disciplines, monitored by qualitative and quantitative checks. These should assess the value of the necessary design compromises and lead to optimum designs. Advice from, and work alongside, experienced designers is an invaluable part of the education process. People learn how to design by actually doing it! Less-experienced design organizations can be helped by specialist consultants. Such help is, however, not always available, but much design knowledge and experience has been encapsulated in the publications and programs described later in this chapter.

Many individuals and organizations publish reports, papers and memoranda, many of which contain relevant data. Modern libraries use on-line computerized data bases that sort and codify these date sources on the basis of key words. A description of such reports is beyond the scope of this book. The most exciting new development has been the advent of the internet. There is a bewildering array of data, with much of interest to aircraft designers. Patience and good net-surfing skills are required.

Any bibliography is a matter of personal choice. The books, magazines and programs listed below have been found by the author to be extremely useful and are reasonably easily available. Excluded data sources are not necessarily less valuable than those listed, but are not available to the author.

The aircraft industry has seen a massive growth in the power and user-friendliness of computer aids. The latter part of this chapter gives an overview of a range of computerized design aids.

MILITARY AIRCRAFT TYPES

FIGHTERS

These aircraft have had several designations over the years, including pursuit and interceptor aircraft. There are many types, and definitions become blurred between fighters and bombers and ground-attack aircraft. True fighters may be divided into two major classes. The first class is that of relatively simple short-range interceptor aircraft (class 1), whilst the second used to be called ‘all-weather’ fighters which tend to have longer range and more avionic equipment (class 2). Figure 4.1 shows a plot of combat wing loading against thrust/weight ratio, which is a good indication of the manoeuvrability of combat aircraft (see Chapter 3 for the definition of thrust/weight and wing loading). Recent requirements for high agility have moved aircraft towards the top left-hand corner where high thrust/weight and low wing loading improve climb, sustained turn and attained turn performance. Most aircraft in this region are class 1 short-range fighters and class 2 are closer to the bottom-right quadrant, where the higher wing loading leads to better long-range cruise.

The class 1 short-range, high-performance interceptor carries the minimum of equipment and maximum speed is always important. However, for such an aircraft the rate of climb and manoeuvrability may be even more important. This arises from the fact that due to the fighter's necessarily short range it cannot take off until a target is definitely located, but must then rapidly climb to interception. A very high thrust/weight ratio is implied by these requirements, particularly at altitude. Compatible with reasonable operational safety, everything must be placed second to climb and interception performance. Only one crew member can be carried and acquisition and life-cycle costs are reasonably low. Due to the relative simplicity of the equipment carried, reliability should be high. The Typhoon is in this category (see Fig. 4.2).

The high thrust/weight ratio for combat manoeuvrability leads to the thought that only a little extra thrust might give vertical take-off and landing capability (VTOL). The BAE SYSTEMS Harrier has been developed into an extremely effective strike/bomber aircraft with the very significant operational advantage of lack of reliance on runways. The invention of the ski-jump runway improved payload/range by offering an extremely short take-off distance (STO). These innovations led to the extremely potent Sea Harrier interceptor aircraft flown from small aircraft carriers.

This book acts as an introduction to the full breadth of both civil and military aircraft design. It is designed for use by senior undergraduate and post-graduate aeronautical students, aerospace professionals and technically inclined aviation enthusiasts.

The book poses and answers pertinent questions about aircraft design, and in doing so gives information and advice about the whole aircraft design environment. It asks why we should design a new aircraft and gives examples of market surveys and aircraft specifications. It then answers the question, ‘Why is it that shape?’ and gives the rationale behind the configurations of a wide range of aircraft from micro-lights and helicopters to super-jumbos and V/STOL aircraft, with many others in between. Having looked at the shape, the book then examines and describes what is under the skin in terms of structure, propulsion, systems and weapons. Later chapters answer questions about aircraft costs and conceptual design and draw lessons from past projects, and then look into the future. A major part of the book answers the question, ‘What help can I get?’, with a combination of bibliography, lists of data sheets, computer tools and 100 pages of appendices of design data vital to aircraft conceptual designers (most of it previously unpublished).

The book concentrates on fixed-wing civil and military aircraft, with some reference to light aircraft and rotorcraft, but does not address the design of sailplanes, airships, flying boats or spacecraft. While these are fascinating and important subjects it was decided that the current scope of the book is sufficiently wide and further extension would make it unwieldy, although information about references that address the design of aircraft in the excluded categories is provided.

Much of the material has been developed for use in Pre-Masters and Masters’ courses in aircraft design at Cranfield University. Many of the examples and illustrations have been produced as part of Cranfield's unique group design project programmes. With the Cranfield method, conceptual design is done by the staff, thus enabling the students to start much further down the design process. They thus have the opportunity to get to grips with preliminary and detail design problems, and become much more employable in the process. This method also allows students to use modern design tools such as CAD, finite elements, laminate analysis and aerodynamic modelling.

GENERAL

Having looked at the reasons for designing a new aircraft, its requirements and the reasons for its external shape, it is now the time to look at the interior. One might use the analogy of a human body to see that for successful operation it requires a skeleton, muscles, digestive system, sensors and a control system. These all work together efficiently even when they have different functions. The aircraft designer must produce a similar harmony within the aircraft interior. Each system is important, but each may have conflicting requirements. A good designer must weigh up the conflicts, use relevant analyses and synthesize the aircraft into an efficient whole. It is a truism that the outside of the aircraft has to be bigger than the space required inside the aircraft. It is often necessary to modify the external shape to accommodate the interior, with consequent aerodynamic changes.

To return to the body analogy, this chapter will describe the aircraft's skeleton, muscles, sensors, etc. in terms of structure and propulsion. Fuel, flying controls, avionics, furnishing and weapon systems will be described in Chapters 6 and 7.

THE STRUCTURE

An aircraft structure should be designed to meet a number of conflicting requirements which include:

Materials

Aircraft designers have a wide range of structural materials to choose from, including those described in the following subsections.

Light Alloys

Light alloys are essentially based on aluminium and are used on the majority of aircraft. Their advantages are the high strength and stiffness-to-weight ratios, relatively low cost, general ease of handling, except in special cases, availability, choice of many fabrication processes and, above-all, familiarity. Against this is the dependence upon relatively low-temperature heat-treatment processes to obtain the desired material properties, which implies poor strength and stiffness at elevated temperatures and relatively poor fatigue properties. The higher-strength alloys are poorer in fatigue and their use is restricted to predominantly compression-sensitive areas. Tensile loads produce more fatigue problems.

GENERAL

This chapter discusses the costs of buying and operating civil and military aircraft. The former costs are termed acquisition costs for both classes of aircraft, whilst the latter are termed operating costs for civil aircraft, and life-cycle costs (LCCs) for military aircraft. The acquisition costs are included as important elements of both operating costs and LCCs. The costs associated with aircraft reliability and maintenance are significant contributors to operating and LCCs, and design to reduce these costs is outlined at the end of this chapter.

ACQUISITION COSTS (THE COSTS OF BUYING OR ACQUIRING THE AIRCRAFT)

The Reasons for High Aircraft Acquisition Costs

The main reasons are:

INTRODUCTION

The design, manufacture and operation of aircraft are very complex and potentially risky activities. There is a natural tendency towards trusting tried and tested configurations, and adopting an evolutionary approach. There are many cases, however, of revolutionary design changes, such as the advent of the jet engine, or the delta wing. Revolution involves more risk, but can be very rewarding. The history of aircraft design has had many examples of excitingly innovative, not to say weird designs. A minority of these are successful, some marginally successful, but many have been failures, some of them disastrously expensive failures! This chapter will describe a number of different projects and attempt to classify the reasons that led to their difficulties.

On a more positive note, the chapter will conclude by describing a number of innovative designs that might have a great influence on the future of aeronautics – positively or negatively!

AIRCRAFT THAT SUFFERED FROM REQUIREMENTS THAT WERE TOO RESTRICTIVE, TOO AMBITIOUS OR WERE CHANGED DURING DEVELOPMENT

Ward [34] contains many examples of such projects from the depressing record of British aircraft developments since 1945, and several examples will be repeated here, both civil and military. Other sources were used for later aircraft.

The Hawker Siddeley Trident

This aircraft (Fig. 11.1) had many years of successful service in the UK and in China, and was a pioneer in the field of automatic landing, but sales were disappointing. British European Airways (BEA) were initially offered a short-haul jet transport, (the DH121) which would have carried 110 passengers over stage lengths of up to 1800 nmiles. The manufacturers’ projections in 1958 predicted sales of 550 aircraft. According to Ward [34] BEA had been examining market trends that showed a marked slip in 1958–9 and thus considered that the DH121 was too big. They required that the aircraft only have 97 seats over an 800 nmile range. The Trident was designed round this specification, as was the Spey turbo-fan engine. The aircraft satisfied the requirement, but it and the engine had limited development potential. The Boeing 727 design team developed a competing tri-jet to almost the same requirements as for the original DH121.

The world has accepted that flying is an extremely efficient means of quickly transporting people, cargo or equipment, and performing a wide range of other activities. All operators need to increase efficiency, cost-effectiveness, environmental compatibility and safety. It is often possible to do this by modifying either the design or operation of existing aircraft. This is limited, however, by the inherent capabilities of the original design and the cost-effectiveness of modifications. Under these circumstances, it is necessary to consider the initiation of the design of a new aircraft. Aircraft manufacturers are usually in the business of making profit out of building aircraft. They may do this by means of building their own existing designs, modifying their designs or licence-building the designs of other companies. Another reason for the initiation of new designs is to retain or enhance their design capabilities.

Safety is the most important aspect of aircraft design. This is the moral and legal responsibility of designers, manufacturers and operators of both civil and military aircraft. The regulations that have emerged aim to maximize safety, and must be complied with before an aircraft may receive a Type Certificate to allow it to be sold. A brief summary of such requirements is contained in Chapter 9.

In recent years there has been a considerable increase in the importance of requirements associated with aircraft-related effects on the environment. These particularly concern noise, airport local air quality and global warming. Current environmental requirements are summarized in Chapter 9.

Operator requirements and aircraft specifications come from a number of different sources, but they must all consider the needs of the aircraft operators, whether they are airlines or air forces. A certain path to disaster is to produce an aircraft that no one will buy!

Descriptions will be given of the two main means of deriving a requirement specification, namely the results of market surveys and individual aircraft operators’ specifications.

MARKET SURVEYS

The major aircraft manufacturers employ marketing departments that produce annual reports [2]. Historical data are analyzed and extrapolated in such areas as world economic indicators. Figure 2.1 shows gross domestic product (GDP) and highlights the recent recessions, and shows the close correlation between GDP and the world air travel growth in revenue passenger miles (RPM).

AVIONIC SYSTEMS

Avionics is one of the most rapidly developing fields of aircraft design. Its importance and range has increased over recent years and as much as 40% of the cost of a new aircraft can be attributed to avionics. There is a bewildering range of avionic systems, each of which usually requires the use of many acronyms.

Figure 7.1 shows an avionics fit for a medium-range airliner of the future. This aircraft is intended for flight with a crew of one or two pilots. If this aircraft had been in operation during the early post-war years, three additional crew-members would have been required, namely navigator, wireless operator and flight engineer. Modern efficient, reliable avionics have dramatically simplified these operations and have eliminated to need for these crew members.

The growth in the capabilities of military avionics has been even more dramatic and make it possible for pilots of single-seat aircraft to navigate, communicate, detect and attack targets at heights of 100 ft and speeds approaching the speed of sound. Figure 7.2 shows a schematic of such an avionic system whilst Fig. 7.3 shows the installation of components on the instrument panel.

Having looked at typical aircraft installations, the next stage is to examine the functions of various types of avionic systems in the following major groups: communications, navigation systems, radar systems and others.

Communications

Airborne communications systems vary considerably in size, weight, range, power requirements, quality of operation and cost, depending upon the desired operation.

The most common communications system in use today is the very high frequency (VHF) system. In addition to VHF equipment, large aircraft are usually equipped with high frequency (HF) communications systems and some are fitted with ultra high frequency (UHF) systems.

VHF airborne communication sets operate in the frequency range from 100 to 150 MHz. VHF receivers are manufactured that cover only the communications frequencies, or both communications and navigation frequencies. In general, the VHF radio waves follow approximately straight lines. Theoretically, the range of contact is the distance to the horizon and this distance is determined by the heights of the transmitting and receiving antennas. However, communication is sometimes possible many hundreds of miles beyond the assumed horizon range. Typical ranges are 200 miles at 20 000 ft. UHF systems are similar to VHF but operate in the 200–400 MHz band.