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Aircraft Design
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Preface
There are many excellent texts covering aircraft design from a variety of perspectives.1
Some of these are aimed at specific audiences ranging from practising aerospace engineers,
to engineering students, to amateur airplane builders. Others cover specialized
aspects of the subject such as undercarriage or propulsion system design. Some of
these are quite detailed in their presentation of the design process while others are very
general in scope. Some are overviews of all the basic aeronautical engineering subjects
that come together in the creation of a design.
University faculty that teach aircraft design courses often face difficult choices when
evaluating texts or references for their students’ use. Many texts that are suitable for use
in a design class are biased toward particular classes of aircraft such as military aircraft,
general aviation, or airliners. A text that gives excellent coverage of design basics may
prove slanted toward a class of aircraft different from that year’s project. Alternatively,
those that emphasize the correct type of vehicle may treat design fundamentals in
an unfamiliar manner. The situation may be further complicated in classes that have
several teams of students working on different types of designs, some of which ‘fit’ the
chosen text while others do not.
Most teachers would prefer a text that emphasizes the basic thought processes of
preliminary design. Such a text should encourage students to seek an understanding
of the approaches and constraints appropriate to their design assignment before they
venture too far into the analytical processes. On the other hand, students would like a
text which simply tells them where to input their design objectives into a ‘black-box’
computer code or generalized spreadsheet, and preferably, where to catch the final
design drawings and specifications as they are printed out. Faculty would like their
students to begin the design process with a thorough review of their previous courses
in aircraft performance, aerodynamics, structures, flight dynamics, propulsion, etc.
Students prefer to start with an Internet search, hoping to find a solution to their
problem that requires only minimal ‘tweaking’.
The aim of this book is to present a two pronged approach to the design process. It
is expected to appeal to both faculty and students. It sets out the basics of the design
thought process and the pathway one must travel in order to reach an aircraft design
goal for any category of aircraft. Then it presents a variety of design case studies.
These are intended to offer examples of the way the design process may be applied
to conceptual design problems typical of those actually used at the advanced level in
academic and other training curricula. It does not offer a step-by-step ‘how to’ design
guide, but shows how the basic aircraft preliminary design process can be successfully
applied to a wide range of unique aircraft. In so doing, it shows that each set of design
objectives presents its own peculiar collection of challenges and constraints. It also
shows how the classical design process can be applied to any problem.
xiv Preface
Case studies provide both student and instructor with a valuable teaching/learning
tool, allowing them to examine the way others have approached particular design challenges.
In the 1970s, the American Institute of Aeronautics and Astronautics (AIAA)
published an excellent series of design case studies2 taken from real aircraft project
developments. These provided valuable insights into the development of several, then
current, aircraft. Some other texts have employed case studies taken from industrial
practice. Unfortunately, these tend to include aspects of design that are beyond the
conceptual phase, and which are not covered in academic design courses. While these
are useful in teaching design, they can be confusing to the student who may have difficulty
discerning where the conceptual aspects of the design process ends and detailed
design ensues. The case studies offered in this text are set in the preliminary design
phase. They emphasize the thought processes and analyses appropriate at this stage of
vehicle development.
Many of the case studies presented in this text were drawn from student projects.
Hence, they offer an insight into the conceptual design process from a student perspective.
The case studies include design projects that won top awards in national and
international design competitions. These were sponsored by the National Aeronautics
and Space Administration (NASA), the US Federal Aviation Administration (FAA),
and the American Institute of Aeronautics and Astronautics (AIAA).
The authors bring a unique combination of perspectives and experience to this text.
It reflects both British and American academic practices in teaching aircraft design to
undergraduate students in aeronautical and aerospace engineering. Lloyd Jenkinson
has taught aircraft design at both Loughborough University and Southampton
University in theUKand JimMarchman has taught both aircraft and spacecraft design
at Virginia Tech in the US. They have worked together since 1997 in an experiment
that combines students from Loughborough University and Virginia Tech in international
aircraft design teams.3 In this venture, teams of students from both universities
have worked jointly on a variety of aircraft design projects. They have used exchange
visits, the Internet and teleconference communications to work together progressively,
throughout the academic year, on the conceptual design of a novel aircraft.
In this book, the authors have attempted to build on their experience in international
student teaming. They present processes and techniques that reflect the best in British
and American design education and which have been proven to work well in both
academic systems. Dr Jenkinson also brings to this text his prior experience in the
aerospace industry of the UK, having worked on the design of several successful British
aircraft. Professor Marchman’s contribution to the text also reflects his experiences in
working with students and faculty in Thailand and France in other international design
team collaborative projects.
The authors envision this text as supplementing the popular aircraft design textbooks,
currently in use at universities around the world. Books such as those reviewed by
Mason1 could be employed to present the detailed aspects of the preliminary design
process. Working within established conceptual design methodology, this book will
provide a clearer picture of the way those detailed analyses may be adapted to a wide
range of aircraft types.
It would have been impossible to write this book without the hard work and enthusiasm
shown by many of our students over more years than we care to remember. Their
continued interest in aircraft design project work and the smoothing of the difficulties
they sometimes experienced in progressing through the work was our inspiration. We
have also benefited from the many colleagues and friends who have been generous in
sharing their encouragement and knowledge with us. Aircraft design educators seem
Preface xv
to be a special breed of engineers who selflessly give their effort and time to inspire
anyone who wants to participate in their common interest. We are fortunate to count
them as our friends.
References
1 Bill Mason’s web page: www.aoe.vt.edu/Mason/ACinfoTOC.html.
2 AIAA web page: www.aiaapublications/index.
3 Jenkinson, L. R., Page, G. J., Marchman, J. F., ‘A model for international teaming in aircraft
design education’, Journal of Aircraft Design, Vol. 3, No. 4, pp. 239–247, Elsevier,
December 2000.
Acknowledgements
To all the students and staff at Loughborough and Southampton Universities who
have, over many years, contributed directly and indirectly to my understanding of the
design of aircraft, I would like to express my thanks and appreciation. For their help
with proof reading and technical advice, I thank my friends Paul Eustace and Keith
Payne. Our gratitude to all those people in industry who have provided assistance with
the projects. Finally, to my wife and family for their support and understanding over
the time when my attention was distracted by the writing of the book.
Lloyd Jenkinson
I would like to acknowledge the work done by the teams of Virginia Tech and
Loughborough University aircraft design students in creating the designs which I
attempted to describe in Chapters 7 and 10 and the contributions of colleagues such
as Bill Mason, Nathan Kirschbaum, and Gary Page in helping guide those students in
the design process. Without these people these chapters could not have been written.
Jim Marchman
Introduction
It is tempting to title this book ‘Flights of Fancy’ as this captures the excitement and
expectations at the start of a new design project. The main objective of this book is
to try to convey this feeling to those who are starting to undertake aircraft conceptual
design work for the first time. This often takes place in an educational or industrial
training establishment. Too often, in academic studies, the curiosity and fascination of
projectwork is lost under a morass of mathematics, computer programming, analytical
methods, project management, time schedules and deadlines. This is a shame as there
are very few occasions in your professional life that you will have the chance to let your
imagination and creativity flow as freely as in these exercises. As students or young
engineers, it is advisable to make the most of such opportunities.
When university faculty or counsellors interview prospective students and ask why
they want to enter the aeronautics profession, the majority will mention that they want
to design aircraft or spacecraft. They often tell of having drawn pictures of aeroplanes
since early childhood and they imagine themselves, immediately after graduation, producing
drawings for the next generation of aircraft. During their first years in the
university, these young men and women are often less than satisfied with their basic
courses in science, mathematics, and engineering as they long to ‘design’ something.
When they finally reach the all-important aircraft design course, for which they have
yearned for so long, they are often surprised. They find that the process of design
requires far more than sketching a pretty picture of their dream aircraft and entering
the performance specifications into some all-purpose computer program which will
print out a final design report.
Design is a systematic process. It not only draws upon all of the student’s previous
engineering instruction in structures, aerodynamics, propulsion, control and other
subjects, but also, often for the first time, requires that these individual academic
subjects be applied to a problem concurrently. Students find that the best aerodynamic
solution is not equated to the best structural solution to a problem. Compromises
must be made. They must deal with conflicting constraints imposed on their design
by control requirements and propulsion needs. They may also have to deal with real
world political, environmental, ethical, and human factors. In the end, they find they
must also do practical things like making sure that their ideal wing will pass through
the hangar door!
An overview of the book
This book seeks to guide the student through the preliminary stages of the aircraft
design process. This is done by both explaining the process itself (Chapters 1 and 2)
and by providing a variety of examples of actual student design projects (Chapters 3
xviii Introduction
to 10). The projects have been used as coursework at universities in theUKand the US.
It should be noted that the project studies presented are not meant to provide a ‘fill in
the blank’ template to be used by future students working on similar design problems
but to provide insight into the process itself. Each design problem, regardless of how
similar it may appear to an earlier aircraft design, is unique and requires a thorough
and systematic investigation. The project studies presented in this book merely serve
as examples of how the design process has been followed in the past by other teams
faced with the task of solving a unique problem in aircraft design.
It is impossible to design aircraft without some knowledge of the fundamental theories
that influence and control aircraft operations. It is not possible to include such
information in this text but there are many excellent books available which are written
to explain and present these theories. A bibliography containing some of these books
and other sources of information has been added to the end of the book. To understand
the detailed calculations that are described in the examples it will be necessary to use
the data and theories in such books. Some design textbooks do contain brief examples
on how the analytical methods are applied to specific aircraft. But such studies are
mainly used to support and illustrate the theories and do not take an overall view of
the preliminary design process.
The initial part of the book explains the preliminary design process. Chapter 1 briefly
describes the overall process by which an aircraft is designed. It sets the preliminary
design stages into the context of the total transformation from the initial request for
proposal to the aircraft first flight and beyond. Although this book only deals with
the early stages of the design process, it is necessary for students to understand the
subsequent stages so that decisions are taken wisely. For example, aircraft design is
by its nature an iterative process. This means that estimates and assumptions have
sometimes to be made with inadequate data. Such ‘guesstimates’must be checkedwhen
more accurate data on the aircraft is available.Without this improvement to the fidelity
of the analytical methods, subsequent design stages may be seriously jeopardized.
Chapter 2 describes, in detail, the work done in the early (conceptual) design process.
It provides a ‘route map’ to guide a student from the initial project brief to the validated
‘baseline’ aircraft layout. The early part of the chapter includes sections that deal with
‘defining and understanding the problem’, ‘collecting useful information’ and ‘setting
the aircraft requirements’. This is followed by sections that show how the initial aircraft
configuration is produced. Finally, there are sections illustrating how the initial aircraft
layout can be refined using constraint analysis and trade-off studies. The chapter ends
with a description of the ‘aircraft type specification’. This report is commonly used to
collate all the available data about the aircraft. This is important as the full geometrical
description and data will be needed in the detailed design process that follows.
Chapter 3 introduces the seven project studies that follow (Chapters 4 to 10). It
describes each of the studies and provides a format for the sequence of work to be
followed in some of the studies. The design studies are not sequential, although the
earlier ones are shown in slightly more detail. It is possible to read any of the studies
separately, so a short description of each is presented.
Chapters 4 to 10 inclusive contain each of the project studies. The projects are selected
from different aeronautical applications (general aviation, civil transports, military
aircraft) and range from small to heavy aircraft. For conciseness of presentation the
detailed calculations done to support the final designs have not been included in these
chapters but the essential input values are given so that students can perform their
own analysis. The projects are mainly based on work done by students on aeronautical
engineering degree courses. One of the studies is from industrial work and some have
Introduction xix
been undertaken for entry to design competitions. Each study has been selected to
illustrate a different aspect of preliminary design and to illustrate the varied nature of
aircraft conceptual design.
The final chapter (11) offers guidance on student design work. It presents a set of
questions to guide students in successfully completing an aircraft design project. It
includes some observations about working in groups. Help is also given on the writing
of technical reports and making technical presentations.
Engineering units of measurement
Experience in running design projects has shown that students become confused by
the units used to define parameters in aeronautics. Some detailed definitions and conversions
are contained in Appendix A at the end of the book and a quick résumé is
given here.
Many different systems of measurement are used throughout the world but two have
become most common in aeronautical engineering. In the US the now inappropriately
named ‘British’ system (foot, pound and second) is widely used. In the UK and over
most of Europe, System International (SI) (metres, newton and second) units are standard.
It is advised that students only work in one system. Confusion (and disaster) can
occur if they are mixed. The results of the design analysis can be quoted in both types
of unit by applying standard conversions. The conversions below are typical:
1 inch = 25.4mm
1 sq. ft = 0.0929 sq.m
1 US gal = 3.785 litres
1 US gal = 0.833 Imp. gal
1 statute mile = 1.609km
1 ft/s = 0.305 m/s
1 knot = 1.69 ft/s
1 pound force = 4.448 newtons
1 horsepower = 745.7 watts
1 foot = 0.305 metres
1 cu. ft = 28.32 litres
1 Imp. gal = 4.546 litres
1 litre = 0.001 cubic metres
1 nautical mile = 1.852km
1 knot = 0.516 m/s
1 knot = 1.151 mph
1 pound mass = 0.454 kilogram
1 horsepower = 550 ft lb/s
To avoid confusing pilots and air traffic control, some international standardization of
units has had to be accepted. These include:
Aircraft altitude – feet Aircraft forward speed – knots∗
Aircraft range – nautical miles Climb rate – feet per minute
(∗ Be extra careful with the definition of units used for aircraft speed as pilots like to use
airspeed in IAS (indicated airspeed as shown on their flight instruments) and engineers
like TAS (true airspeed, the speed relative to the ambient air)).
Fortunately throughout the world, the International Standard Atmosphere (ISA)
has been adopted as the definition of atmospheric conditions. ISA charts and data
can be found in most design textbooks. In this book, which is aimed at a worldwide
readership, where possible both SI and ‘British’ units have been quoted. Our apologies
if this confuses the text in places.
xx Introduction
English – our uncommon tongue
Part of this book grew out of the authors’ collaboration in a program of international
student design projects over several years. As we have reported our experiences from
that program, observers have often noted that one thing that makes our international
collaboration easier than some others is the common language. On the other hand,
one thing we and our students have learned from this experience is that many of the
aspects of our supposedly common tongue really do not have much in common.
Pairing an Englishman and an American to create a textbook aimed at both the
US, British and other markets is an interesting exercise in spelling and language skills.
While (or is it whilst?) the primary language spoken in the United Kingdom and the
United States grows from the same roots, it has very obviously evolved somewhat
differently. An easy but interesting way to observe some of these differences is to take
a page of text from a British book and run it through an American spelling check
program. Checking an American text with an ‘English’ spell checker will produce
similar surprises.We spell many words differently, usually in small ways. Is it ‘color’ or
‘colour’; dowe ‘organize’ ourwork or ‘organise’ it? In addition, dowe use double (“) or
single (‘) strokes to indicate a quote or give emphasis to a word or phrase?Will we hold
our next meeting at 9:00 am or at 9.00 am? (we won’t even mention the 24 hour clock!).
There are also some obvious differences between terminology employed in the US
and UK. Does our automobile have a ‘bonnet’ and a ‘boot’ or a ‘hood’ and a ‘trunk’
and does its engine run on ‘gasoline’ or ‘petrol’? American ‘airplanes’ have ‘landing
gear’ while British ‘aeroplanes/airplanes or aircraft’ have ‘undercarriages’, does it have
‘reheat’ or an ‘afterburner’. Fortunately, most of us have watched enough television
shows and movies from both countries to be comfortable with these differences.
As we have pieced together this work we have often found ourselves (and our computer
spell checkers) editing each other’s work to make it conformto the conventions in
spelling, punctuation, and phraseology, assumed to be common to each of our versions
of this common language. The reader may find this evident as he or she goes from one
section of the text to another and detects changes in wording and terminology which
reflect the differing conventions in language use in the US and UK. It is hoped that
these variations, sometimes subtle and sometimes obvious, will not prove an obstacle
to the reader’s understanding of our work but will instead make it more interesting.
Finally
All aircraft projects are unique, therefore, it is impossible to provide a ‘template’ for the
work involved in the preliminary design process. However, with knowledge of the detail
steps in the preliminary design process and with examples of similar project work, it
is hoped that students will feel freer to concentrate on the innovative and analytical
aspects of the project. In this way they will develop their technical and communication
abilities in the absorbing context of preliminary aircraft design.