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_THE ENGINEER SERIES_
THE GYROSCOPIC COMPASS
A NON-MATHEMATICAL TREATMENT
_THE ENGINEER SERIES_
THE
GYROSCOPIC COMPASS
A NON-MATHEMATICAL TREATMENT
BY
T. W. CHALMERS, B.SC., A.M.I.MECH.E.
(ON THE EDITORIAL STAFF OF “THE ENGINEER”)
ILLUSTRATED
LONDON
CONSTABLE & COMPANY, LTD.
10 ORANGE STREET, LEICESTER SQUARE. W.C.
1920
_Printed in Great Britain_
PREFACE
The chapters composing this book originally appeared as a series of
articles in _The Engineer_ during January, February, and March of
the current year. The articles were written in the belief that many
readers would welcome a clear and full, non-mathematical exposition
of the gyroscopic compass, its theory and practical construction. The
gyro-compass represents at once the most involved and abstruse and
the most important and valuable of all the practical applications
to which the gyroscope, so far, has been put. As a navigational
instrument it is now in practically universal use in all the chief war
navies of the world, and is to-day being adopted by several important
representatives of the mercantile marine. Remarkable figures were shown
to the author recently which demonstrated that not only was navigation
by the gyro-compass much more accurate than by the magnetic compass,
but that the increased accuracy reduced the length of the voyage of
a mercantile vessel to an extent that resulted in saving a quantity
of fuel the value of which on a single trip would go a considerable
way towards meeting the extra first cost of the gyro-compass. Bearing
these facts in mind the author from the outset endeavoured not only
to dispense with mathematics but to avoid introducing anything except
the most familiar physical principles and conceptions, for his object
was to explain the mode of action of the gyro-compass for the benefit
primarily of the navigating officer--naval and mercantile. If some
readers should find the treatment in places unduly prolix, the author
trusts they will exercise leniency and regard the fault as being
caused by the author’s unwillingness to take any risks in expounding a
subject, no part of which can be understood incompletely without grave
hurt to the understanding of the whole.
T. W. C.
LONDON, _May, 1920_.
CONTENTS
CHAP. PAGE
I. INTRODUCTION 1
II. ELEMENTARY GYROSCOPIC PHENOMENA 4
III. THE GYROSCOPE AND THE ROTATION OF THE EARTH 15
IV. DAMPING THE VIBRATIONS OF THE GYRO-COMPASS 29
V. THE DAMPING SYSTEM OF THE ANSCHÜTZ (1910) COMPASS 42
VI. THE DAMPING SYSTEM OF THE SPERRY COMPASS 52
VII. THE DAMPING SYSTEM OF THE BROWN COMPASS 59
VIII. THE LATITUDE ERROR 65
IX. THE NORTH STEAMING ERROR 71
X. THE BALLISTIC DEFLECTION 81
XI. THE QUADRANTAL ERROR 91
XII. THE ELIMINATION OF THE QUADRANTAL ERROR 107
XIII. CENTRIFUGAL FORCES DURING QUADRANTAL ROLLING 130
XIV. THE ANSCHÜTZ (1910) COMPASS 138
XV. THE SPERRY COMPASS 142
XVI. THE BROWN COMPASS 148
XVII. THE ANSCHÜTZ (1912) COMPASS 154
INDEX 165
LIST OF ILLUSTRATIONS
FIG. PAGE
1. Model gyroscope with three degrees of freedom 4
2. Model gyroscope with three degrees of freedom 7
3. Model gyroscope, frictional transmission of turning moment 9
4. Model gyroscope, one degree of freedom lost 11
5. Model gyroscope, second degree of freedom lost 12
6. Model gyroscope, lost degrees of freedom restored 13
7. Elementary gyroscope at equator 15
8. Gyroscopic clock 16
9. Elementary gyro-compass 18
10. Elementary compass at equator 20
11. Elementary compass at 55 deg. N. Lat. 24
12. Compass at equator and near North Pole 26
13. Pendulum and compass 32
14. Damped and undamped vibrations 35
15. Damped pendulum 37
16. Air-blast damping system of Anschütz (1910) compass 43
17. Free and damped motion of axle 49
18. Damping curve from Anschütz (1910) compass 50
19. Damping system of Sperry compass 53
20. Action of excentric pin in Sperry compass 55
21. Action of excentric pin in Sperry compass 57
22. Gyro-pendulum with axle tilted 60
23. Damping system of Brown compass 62
24. The north steaming error at 0 deg. and 60 deg. N. 72
25. Sperry correction mechanism for latitude and north steaming
errors 76
26. Ballistic force on compass when ship’s speed changes 83
27. Ballistic force on compass when ship’s speed changes 84
28. Ballistic deflection 86
29. Effect of rolling on due north course 93
30. Effect of rolling on due west course 94
31. External gimbal mounting 97
32. Effect of rolling on a due north course (simple
mounting) 98
33. Effect of rolling on a due north course (external gimbal
mounting) 99
34. Ship rolling on N.W. course 101
35. Sperry compass on N.W. course 108
36. Sperry ballistic gyro 111
37. Stabilised excentric pin (Sperry compass) 112
38. Diagram of Brown compass 113
39. Oil control bottles (Brown compass) 115
40. Brown compass on west course 117
41. Diagram of Anschütz (1912) compass 121
42. Plans of gyros (Anschütz compass) 122
43. Centrifugal forces on a pendulum 131
44. The Anschütz (1910) compass 139
45. The Sperry compass removed from binnacle 143
46. The Sperry compass 144
47. The Brown compass removed from binnacle 148
48. The Brown compass removed from binnacle 149
49. The Brown compass 150
50. Plan of Anschütz (1912) compass 155
51. Sectional elevation of Anschütz (1912) compass 159
THE GYROSCOPIC COMPASS:
A NON-MATHEMATICAL TREATMENT
CHAPTER I
INTRODUCTION
At this date it is, or should be, unnecessary to open an account
of the gyroscopic compass with a discussion of the defects of the
ordinary magnetic compass. These defects are too well known to require
mention. Recent advances in naval architecture, particularly in warship
construction, and very especially the building of submarines, have
resulted in the magnetic compass becoming less and less useful for
accurate navigation, primarily because of the upsetting influence
exercised upon it by masses of steel or iron in its neighbourhood. It
may still serve, perhaps, for the surface navigation of submarines, but
for submerged runs the use of a gyro-compass is all but essential. In
warships the weight of the guns and turrets is now so heavy that the
magnetic compass can hardly remain unaffected by them and is materially
influenced when the guns are trained to different directions. The
shells themselves as they are discharged are also said to be a cause
of error in the reading of the magnetic compass, for they tend in
most positions of the ship to drag the needle after them by magnetic
attraction as they pass along the bore of the gun.
The value of the gyro-compass is not, however, recognised only in the
world’s war navies. It is becoming increasingly appreciated in the
mercantile marine, and there can be but little doubt that the device
will soon be extensively employed on passenger liners and merchantmen
generally. In the following pages we attempt to give an account of the
working of the gyro-compass and to describe the forms assumed by the
device in practice--sufficiently fully to illustrate the theory without
going into any great detail on the constructional side--and to do so
without depending upon the reader’s possessing mathematical knowledge.
It is to be remarked that it is much easier to treat the gyroscope and
all its practical applications mathematically than non-mathematically,
and that the avoidance of mathematics generally leads to a discussion
of this essentially mathematical device which is unscientific,
unsound, and of very little practical value. We trust that our account
will be found to avoid these defects and that it will prove useful
and enlightening to those who have so far failed to understand the
behaviour of the gyroscope and its applications by reason of the
fact that hitherto all trustworthy descriptions have been couched
in a highly mathematical form or have been mere mathematics thinly
disguised in written words. It is admittedly not easy to understand
gyroscopic phenomena either with or without the aid of mathematics, but
on the other hand many of the difficulties of the subject are largely
artificial. Thus the mathematician, when dealing with it, seems to
be much more concerned with his equations than in creating a mental
picture of what they represent; yet every one of his equations can be
or should be capable of being represented physically. Those who set
out to avoid mathematics do not usually succeed in giving a discussion
sufficiently complete to be of any practical service afterwards to
their readers. Thus in dealing with the gyro-compass the so-called
“popular” description in most cases begins and ends with an explanation
of why the device possesses directive force when it is set up at the
equator. It is quite easy to demonstrate the existence of such force
at the equator. It is not so easy to show non-mathematically how the
directive force is generated and applied when the compass is situated
north or south of the equator. The necessity for damping the horizontal
vibrations of the gyro-axle and how the required damping force is
applied in practice are still more difficult to explain, while the
errors to which the gyro-compass is open--such as the latitude and
the quadrantal errors--are even more trying to make clear. The latter
subjects are usually neglected in the “popular” account of the compass.
Yet without some means of damping the vibrations referred to or of
eliminating or allowing for the various errors, the compass, even
though it can be shown to possess directive force in all latitudes,
would be utterly useless--especially on board ship--as a direction
indicator.
Finally, it may be remarked that while the gyro-compass represents
to-day probably the most intricate and involved practical application
of the gyroscope, it is not the only one of importance. This fact is to
our advantage, for if we succeed in explaining the theory and working
of the gyro-compass we shall have succeeded in placing the reader in a
position enabling him readily to understand all other devices in which
a gyroscope is employed or in which gyroscopic phenomena are developed.