AEROPLANE
CONSTRUCTION
_A Handbook on the various Methods and
Details of Construction employed in
the Building of Aeroplanes_
BY
SYDNEY CAMM
ASSOCIATE FELLOW ROYAL AERONAUTICAL SOCIETY
[Illustration]
LONDON
CROSBY LOCKWOOD AND SON
7, STATIONERS’ HALL COURT, LUDGATE HILL
1919
PRINTED BY
WILLIAM CLOWES AND SONS, LIMITED,
LONDON AND BECCLES.
PREFACE
The articles embodied with other matter in this book, were intended
as a broad survey of the principles and details of modern aeroplane
construction, concerning which there is a noticeable deficit amongst
existing aeronautical literature.
They were written at a time when specific references to modern British
aircraft were forbidden, and although from a comparative point of
view this is to be regretted, the details and methods dealt with are,
in the author’s opinion, representative of those most generally used
in machines of present-day design. It is hoped that the book will
appeal not only to those engaged on the manufacture, but also to those
concerned with the uses of aircraft.
S. C.
TABLE OF CONTENTS
CHAPTER I.
PAGE
INTRODUCTION 1
CHAPTER II.
MATERIALS 6
CHAPTER III.
SPARS AND STRUTS 18
CHAPTER IV.
PLANE CONSTRUCTION 30
CHAPTER V.
DETAILS OF PLANE CONSTRUCTION 40
CHAPTER VI.
INTERPLANE STRUT CONNECTIONS 51
CHAPTER VII.
WING-TRUSSING SYSTEMS 59
CHAPTER VIII.
FUSELAGE CONSTRUCTION 67
CHAPTER IX.
FUSELAGE FITTINGS 77
CHAPTER X.
UNDERCARRIAGE TYPES 86
CHAPTER XI.
UNDERCARRIAGE DETAILS 93
CHAPTER XII.
CONTROL SYSTEMS 101
CHAPTER XIII.
WIRES AND CONNECTIONS 108
CHAPTER XIV.
ENGINE MOUNTINGS 116
CHAPTER XV.
ERECTION AND ALIGNMENT 123
INDEX 135
AEROPLANE CONSTRUCTION
CHAPTER I.
INTRODUCTION.
The purpose of this book is to give some indication of the principles
and methods of construction of modern aeroplanes, as distinct from
those considerations pertaining purely to design, although occasional
references to various elementary principles of aerodynamics have
been found necessary to illustrate the why and wherefore of certain
constructional details.
To many the aeroplane is a structure of appalling flimsiness, yet the
principle which it exemplifies, that of obtaining the maximum strength
for a minimum of weight, constitutes a problem of which the solving
is not only an unceasing labour, but one demanding the observance
of the best engineering procedure. The whole future of aviation,
commercially or otherwise, may be said to be indissolubly bound up with
the development of efficiency; and whether this is to be attained in
improvements in aerodynamical qualities, by the discovery of a material
giving a greatly enhanced strength to weight ratio, or by progress in
the arrangement of the various members of the complete structure of the
aeroplane, is a matter upon which some diversity of opinion exists.
However, it is certain that the very great developments of the last few
years are due more to refinements in design rather than construction;
and it is questionable whether the constructional work of the modern
aeroplane has developed equally with design, so that, even taking for
granted the oft-repeated, but very doubtful, statement that we are
approaching the limitations of design, there is certainly plenty of
scope for experiment and improvement in the constructional principles
of the modern aeroplane.
Standardization of Details.
Whatever may be said for the standardization of aeroplane types,
a scheme which should effect a considerable saving in labour and
material, and which offers chances of success, would consist in the
standardization of metal fittings and wood components generally, for in
this direction there is certainly great need for improvement. Taking
as a hypothesis the various makes of scouting machines, we find hardly
any two details the same. This means that if in this country there are
six firms producing machines of their own design (these figures, of
course, being purely suppositionary), there will be six sets of detail
drawings, six sets of jigs, templates, and press tools, and sundry
special machine tools. There seems no valid reason why many of the
fittings for all machines within certain dimensions should not be of
standard design, and a brief review of the various details which could
be standardized without detracting in the least from aerodynamical
efficiency will indicate the extent to which the conserving of labour
could be carried. In the construction of the fuselage, the clips
fastening the longerons and cross struts could easily be of one design,
whatever the make of the machine. At present we find some clips are
bent up from a stamping and attached to the longeron without the
drilling of the latter; some built up from various parts, such as
washer-plates, duralumin pressings, and bolted through the longeron;
while some combine advantages and others the disadvantages of both. In
some cases the longerons of spruce are spindled out for lightening;
in others no spindling occurs; while in a few instances hickory or
ash, with or without channelling, is used. There are the interplane
strut attachments, stern-post fittings, control-surface hinges, and
undercarriage attachments, all showing great variations, and in all
of which the design could be brought within reasonable limits. As
indicating how unnecessary a good deal of the variation is, one may
instance the fact that for the swaged streamline, or R.A.F. wires,
there are at least three different terminals in use. Although more
difficult of achievement, there is scope for improvement in the
different arrangements for the fixed gun mounting, while a standard
instrument board would benefit the pilot.
Methods of Manufacture.
It is fairly well known that the output of some firms is considerably
better than others, although the machines are of the same design.
Although a good many factors may contribute to this result, it
seems fairly certain that in some cases the methods of manufacture
must be superior, which calls for some system of standardizing the
broad principles pertaining to manufacturing procedure. Under this
arrangement a much better estimate of probable output could be made.
It is also necessary by the fact that some firms have been developed
through the exigencies of war, and not as a result of any great
manufacturing ability, whereas in peace time the spur of competition
would force the adoption of the most rapid methods of production.
The creation of a central or universal office for the design of the
various jigs used in the manufacture of aircraft, with power to
decide the process of manufacture, although a somewhat far-reaching
reform, would certainly eliminate a number of useless experiments made
by the individual constructors, and would also greatly improve the
interchangeability of the various components. In addition, fresh firms
to the aviation industry would be at once acquainted with the general
methods of manufacture, which should be of considerable assistance in
expediting initial output. Of course, this system would tend rather to
destroy individual initiative, in that much that is now left to the
skill and experience of the workman would be predetermined, although
this would be more than compensated for by the increased benefits
accruing to the State. Jigs designed to produce the same work in
different works often differ in detail considerably, and this, of
course, often influences the rate of production. As an instance, in
some works elaborate benches are considered necessary for the erection
of fuselages, while in others a pair of trestles suffices. With this
system of unified manufacturing procedure extreme regard would have to
be paid, in the design of various jigs and fixtures, to adaptability
for modifications in design. Otherwise the various alterations which
are bound to occur would result in an unnecessary expenditure on
fresh jigs. It is somewhat unfortunate that in the general design
of an aeroplane, in numerous cases, far too little regard is paid
to considerations of ease of manufacture, and this is frequently
responsible for the many changes in design after a contract has been
started. Under an ideal system of standardization, the requirements
of manufacture would necessitate consideration in the design of the
constructional details.
Metal Construction.
The question of the aircraft materials of the future is not so much
a problem as a matter of gradual evolution. In view of the dwindling
supplies of suitable timber, it certainly seems more than probable that
some form of metal construction will one day constitute the structure
of the aeroplane. The manufacture of the various components in wood
does not necessitate an extensive plant, the labour necessary is
comparatively cheap and easily available, and moreover the transitory
nature of the whole business, and the ease with which essential changes
in type can be made without the wholesale scrapping of the expensive
jigs associated with the use of steel, all strengthen the case in
favour of wood. The conclusion of hostilities would introduce another
state of affairs, and it is conceivable that the various types will
then be standardized for different purposes, which may necessitate
the greater use of steel. Certainly the advantage of steel would be
better realized under some system of standardized design, but this
unfortunately is not possible while present conditions obtain. The
advantages of metal as a material considered briefly, are that it
permits of design to close limits without the allowance of so-called
factors of safety, which are now necessary through the great variation
in the strengths of wood, manufacturing procedure would be expedited,
while one can reasonably expect a greater degree of precision in the
finished machine, due largely to the increased facilities for accurate
manufacture of components which metal affords. It is quite possible, of
course, given a uniform grade of steel, to design to extremely close
limits without fear of collapse; but the human factor in the shape of
fitter, welder, or operator introduces the unknown element, and one
for which some allowance must always be made. One cannot assert that
any very decided indication exists of a trend in modern design towards
metal construction, and it is quite possible that this will not arrive
until it is rendered imperative by reason of the scarcity of timber.
The precise composition of the metal is rather a controversial matter,
some authorities favouring steel, and others some alloy of aluminium,
such as, for instance, “duralumin.” The production of a suitable alloy
constitutes a real problem and one upon which the Advisory Committee
for Aeronautics have already made investigations and experiments. A
disadvantage with steel is that, although it is quite possible to
produce, say, a fuselage entirely of this material to withstand easily
the greatest stress encountered in flying, such a structure, owing to
the thin nature of the various components, would suffer damage through
shocks induced by rolling over rough ground, and also by handling. In
addition the effects of crystallization would require some considerable
study. These and other reasons indicate that an alloy of aluminium,
which for a given weight would be considerably more rigid than steel,
offers possibilities as a material. It might prove advantageous to
combine both metals, using steel for the more highly stressed parts,
such as, for instance, wing spar attachments, interplane bracing lugs,
and indeed any part where the load to be carried is one induced by
tension.
The foregoing is indicative of some of the more important directions
in which improvement and development are possible, and certainly ample
scope yet exists for the attention of the student, or indeed any one
interested in the future of the aviation industry.