Initial Airworthiness: Determining the Acceptability of New Airborne Systems

323 Pages·2015·13.91 MB·English

by  Guy Gratton (auth.)

Initial Airworthiness
Guy Gratton
Initial Airworthiness
Determining the Acceptability
of New Airborne Systems
1 3
Guy Gratton
College of Engineering, Design
and Physical Sciences
Brunel University
Uxbridge
United Kingdom

ISBN 978-3-319-11408-8 ISBN 978-3-319-11409-5 (eBook)
DOI 10.1007/978-3-319-11409-5
Springer Cham Heidelberg New York Dordrecht London
Library of Congress Control Number: 2014952229
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Whilst the writing of this book has largely been
a solo effort, when I sit back and try to identify
the number of people from whom I have
learned the many subjects that contributed
to this book, the list is frighteningly long. I
can only conclude that I’ve been enormously
privileged to have had so many superb teachers
and colleagues, universally generous with
their time and knowledge. There are too many
to list, but anybody I have worked with, I’ve
learned from, and I’m grateful to a great many
incredibly talented colleagues over 25 years
working in this field who have been universally
generous with their time and knowledge.
However, there are seven people I’d like to
dedicate this book to. These are:
Nick Slater
Mike Auckland
Mike Chrystal
Rick Husband
Jay Madhvani
Bob Jones
Trevor Roche
All of these are colleagues who I had worked
with, and who have died in ultimately
avoidable aircraft or spacecraft accidents.
They, and many like them in the past who I
didn’t know, and many more who I hope will
never be added to this list, are the single
biggest reason for writing this book.
Preface
For they had learned that true safety was to be found in long previous training, and
not in eloquent exhortations uttered when they were going into action.
—Thucydides, ‘The History of the Peloponnesian War,’ circa 404 BC.
The practice of airworthiness is a complex one, and I doubt that anybody anywhere
in the world can truly be said to understand the subject in its entirety. However,
there are many people who need to initially study, and then to practice various
trades within this professional umbrella.
I’ve worked in the field of airworthiness in its many forms since about 1989
when as a young engineer at the Royal Aerospace Establishment (RAE), Farnbor-
ough I was asked to look into the reasons why engine mounting bolts kept failing
on a prototype experimental aeroplane—I rapidly discovered that this was an area
in which every one of the subjects I’d studied—structures, materials, aerodynamics,
writing, drafting, maths et al came together and still left my knowledge base lack-
ing. Over the years since, I’ve been called upon to consider whether a wide variety
of aircraft—both new and existing—were safe and fit for purpose, or in other words
airworthy. Mostly this has involved in-depth consideration of individual aspects
of an aircraft design; a specific instrument or system, the landing gear, the flying
qualities or the flying controls for example. However, in 1997 I was appointed by
the British Microlight Aircraft Association as their Chief Technical Officer, a post
which I held until 2005 and required me to routinely consider not any specific as-
pect, but complete aircraft designs, often starting from little more than a rough set
of drawings—but with the ultimate objective of an approved and flying aeroplane.
This post was unusual in that the comparative simplicity of microlight aeroplanes
allowed me an oversight of the whole airworthiness process in a way that the com-
plexity of modern aircraft denies to most modern engineers.
Whilst I was employed at BMAA, I was asked by Sheffield University to teach
a basic course to their undergraduates in Aerospace Engineering in aircraft certi-
fication; this was a great honour, but also concentrated my mind on how one can
go-about breaking down the skills of the airworthiness engineer and teaching them.
About the same time I was finishing a long-term personal project—a PhD thesis
vii
viii Preface
entitled “airworthiness evaluation techniques for small light aeroplanes”, which did
much the same thing. As one might expect, I referred regularly to many textbooks,
and to a greater extent to airworthiness standards published by various civil and
military authorities in the course of this work, however mainly I found myself using
my increasing store of personal notes and experience.
Then, in 2005 I made the decision to change career and became a lecturer at
Brunel University in London, teaching aeronautical engineering. Unsurprisingly,
this brought a further request to teach the subject of airworthiness. About this point,
I finally realised that there simply was no coherent textbook describing the funda-
mentals of airworthiness practice, and in particular, initial airworthiness: the meth-
ods by which the fitness for service of a new design is established: to me this was
a problem.
In 2008 I moved yet again, and at the present whilst I continue to engage with
Brunel, Sheffield and the BMAA, I now manage FAAM: the Facility for Airborne
Atmospheric Measurements which operates the UK’s BAe-146 Atmospheric Re-
search Aircraft. My previous experience has become invaluable in understanding
the complex airworthiness processes that sit behind Europe’s most complex re-
search aeroplane, but I’ve certainly learned a lot of new things to do with managing
a jet airliner, not to mention how you go about introducing a continuous stream of
new equipment onto one. Whilst at FAAM, I finally decided with a bit of encour-
agement from Springer and several colleagues to knuckle down and finish writing
this book, which was started in 2006 at Brunel.
And so, 25+ years of my own experience and study has been brought into this
book, along with many centuries of other people’s. In writing it, I have not at-
tempted to produce something that an intelligent layman could use to launch into
airworthiness practice without any other knowledge—frankly I don’t think that that
is reasonably possible. Like any other aeronautics specialist, my knowledge of air-
worthiness is built upon a much wider technical education, and I believe that this
will always remain essential. Nor have I tried to explain about how to practice in
any single environment; since there are too many working environments, civil and
military, light and heavy, regulated and deregulated. What I have done however is
lay down what I consider to be the main subject areas of initial airworthiness in a
way that I hope will be usable by practicing engineers, students, and teachers of the
subject. There are topics which might be included, but have simply been omitted
through a need to constrain the length and complexity of the book; also many topics
are addressed in a depth below that which an experienced practitioner would hope-
fully be familiar with that specialist topic—but nonetheless I have aimed to achieve
a competent overview, and hope that the reader will find it so.
Throughout this book I have attempted to teach by example, and nothing in this
is here for the sake of it—every piece of theory has been used, by me, at some point
on real-world airworthiness problems.
This book is inevitably based upon the way in which I’ve myself taught and
practiced airworthiness, and as such is structured in a way which I hope is reason-
ably sequential. This is the first such book on initial airworthiness (at-least that I
know of) and I’d never claim it’s as good as it could be; so, if any reader would like
Preface ix
to make any recommendations regarding corrections or improvements to this book,
I’d be delighted to receive your views via the publisher.
Finally, could I please caution all readers that this book is one man’s approach
to initial airworthiness, albeit from a fairly wide professional experience. Every
organization in the world will have its own approach, which may at-least in detail,
contradict what I’ve written here. Please as a practitioner or student treat this book
with healthy caution, and before using what I’ve written here to challenge any exist-
ing practice, do give the issue great thought!
Guy Gratton
CEng FRAeS
2014
Contents
1 W hat is Airworthiness? ............................................................................. 1
1.1 Introduction ......................................................................................... 1
1.2 T he Basic Principles of Certification .................................................. 2
1.3 Civil Aircraft Certification Practice .................................................... 4
1.3.1 Civil Design Codes ................................................................. 4
1.4 Military Aircraft Certification Practice ............................................... 11
1.5 Release for Flight Test ......................................................................... 13
2 The Atmosphere ......................................................................................... 15
2.1 General Principles of the Atmosphere ................................................. 15
2.2 T he International (or US) Standard Atmosphere................................. 18
2.2.1 T roposphere ............................................................................. 19
2.2.2 Lower Stratosphere ................................................................. 20
2.2.3 Middle Stratosphere ................................................................ 20
2.3 W hich Altitude Matters? ..................................................................... 21
2.4 V ariation in the Tropopause................................................................. 22
2.5 T he Effects of Atmospheric Conditions Upon Human Survivability ... 23
2.5.1 Pressure and Oxygen Supply .................................................. 24
2.5.2 T emperature Effects ................................................................ 28
2.6 Exercises ............................................................................................. 29
2.6.1 Standard Atmosphere Exercise ............................................... 29
2.6.2 Life Support ............................................................................ 29
2.7 Sample Answers to Exercises, With Commentary .............................. 30
2.7.1 Standard Atmosphere Exercise ............................................... 30
2.7.2 Life Support Exercise .............................................................. 31
3 The Pitot-Static System ............................................................................. 33
3.1 T he Measurement of Airspeed ............................................................ 33
3.2 Pitot-Static System Design .................................................................. 34
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3.3 Calculating Airspeed Values................................................................ 39
3.3.1 IAS .......................................................................................... 39
3.3.2 CAS ......................................................................................... 39
3.3.3 EAS ......................................................................................... 40
3.3.4 T AS .......................................................................................... 42
3.3.5 Groundspeed ........................................................................... 44
3.4 Methods of ASI Calibration ................................................................ 45
3.4.1 W ind Vector and Groundspeed Based Methods ...................... 46
3.4.2 Non-GPS Variant Methods ...................................................... 49
3.4.3 Comparison Methods .............................................................. 50
3.5 Machmeters ......................................................................................... 51
3.6 Display of Airspeed Limits ................................................................. 52
3.7 Pressure Altimetry ............................................................................... 54
3.8 Methods of Altimeter/Static System Calibration ................................ 57
3.9 Considerations of Minimum Accuracy ............................................... 58
3.10 A Note About Electronic Devices ..................................................... 59
3.11 Sample Problems ............................................................................... 60
3.11.1 Determination of TPEC ......................................................... 60
3.11.2 Determination of SPEC ......................................................... 60
3.11.3 General Pitot-Static System Problem .................................... 60
3.12 Sample Solutions ............................................................................... 61
3.12.1 Determination of TPEC ......................................................... 61
3.12.2 Determination of SPEC ......................................................... 63
4 T he Flight Envelope ................................................................................... 69
4.1 Introduction ......................................................................................... 69
4.2 Constructing the Manoeuvre Envelope ............................................... 70
4.2.1 Flaps in the Flight Envelope ................................................... 78
4.2.2 Other Services ......................................................................... 79
4.2.3 Converting and Displaying Limitations .................................. 79
4.3 Constructing the Gust Envelope .......................................................... 79
4.3.1 A Simple Model of Gust Response ......................................... 80
4.3.2 Response to a Sharp-Edged Gust ............................................ 81
4.4 Gust Loading Requirements in Civil Airworthiness Standards .......... 86
4.5 Flutter and Resonance ......................................................................... 88
4.6 Sample Problems ................................................................................. 91
4.6.1 Construction of a Manoeuvre Envelope #1 ............................. 91
4.6.2 Construction of a Manoeuvre Envelope #2 ............................. 92
4.7 Solutions to Sample Problems ............................................................ 93
4.7.1 Solution to #1 is not Shown and is an Exercise for
the Reader................................................................................ 93
5 First Principles of Structural Approval ................................................... 95
5.1 Introduction ......................................................................................... 95
5.2 T he Role of the Structural Airworthiness Engineer ............................ 96