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2075 results in Aerospace engineering

Page 37 of 104

Nonequilibrium Gas Dynamics and Molecular Simulation
  • Iain D. Boyd, Thomas E. Schwartzentruber
  • Published online:
    13 April 2017
    Print publication:
    23 March 2017
  • This current and comprehensive book provides an updated treatment of molecular gas dynamics topics for aerospace engineers, or anyone researching high-temperature gas flows for hypersonic vehicles and propulsion systems. It demonstrates how the areas of quantum mechanics, kinetic theory, and statistical mechanics can combine in order to facilitate the study of nonequilibrium processes of internal energy relaxation and chemistry. All of these theoretical ideas are used to explain the direct simulation Monte Carlo (DSMC) method, a numerical technique based on molecular simulation. Because this text provides comprehensive coverage of the physical models available for use in the DSMC method, in addition to the equations and algorithms required to implement the DSMC numerical method, readers will learn to solve nonequilibrium flow problems and perform computer simulations, and obtain a more complete understanding of various physical modeling options for DSMC than is available in other texts.

  • Appendix C - The Prediction of Aircraft Reliability and Maintainability Targets

  • John P. Fielding, Cranfield University, UK
  • Book:
    Introduction to Aircraft Design
    Published online:
    28 May 2018
    Print publication:
    03 April 2017, pp 277-281

  • Summary

    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.

  • 9 - What Help Can I Get?: Bibliography and Computer-Aided Design

  • John P. Fielding, Cranfield University, UK
  • Book:
    Introduction to Aircraft Design
    Published online:
    28 May 2018
    Print publication:
    03 April 2017, pp 144-164

  • Summary

    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.

  • 4 - Why is it That Shape?: Other Types

  • John P. Fielding, Cranfield University, UK
  • Book:
    Introduction to Aircraft Design
    Published online:
    28 May 2018
    Print publication:
    03 April 2017, pp 40-64

  • Summary

    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.

  • Preface

  • John P. Fielding, Cranfield University, UK
  • Book:
    Introduction to Aircraft Design
    Published online:
    28 May 2018
    Print publication:
    03 April 2017, pp xiii-xiv

  • Summary

    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.

  • 5 - What's Under the Skin?: Structure and Propulsion

  • John P. Fielding, Cranfield University, UK
  • Book:
    Introduction to Aircraft Design
    Published online:
    28 May 2018
    Print publication:
    03 April 2017, pp 65-82

  • Summary

    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:

  • (i) Low weight.

  • (ii) Acceptable material and manufacturing costs.

  • (iii) Adequate strength to meet the maximum expected loads, with a suitable safety factor.

  • (iv) Adequate stiffness so that distortions are kept within acceptable limits.

  • (v) Good in-service properties, such as fatigue and corrosion resistance, together with tolerance of expected temperatures and other atmospheric conditions.

    • 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.

Page 37 of 104