J U L Y 1914 559

BALANCING OF INTERNAL-COMBUSTION ENGINES.

BY H. F. FULLAGAR, M.A., CANTAB., OF NEWCASTLE-ON-TYFE.

Communicated by WILLIAM HANNING, illember, OF PARIS.

The problem of balancing internal-combustion engines is in

general much more difficult and complex than the corresponding
problem with steam-engines. The adoption in the former case of
the single-acting cylinder and trunk-piston generally necessitates
wider crank-angles than with steam. If, on the other hand, a
larger number of cylinders are employed, vibration arises owing to
the increased length and flexibility of crank-case or framing. A
further difficulty in comparison with steam practice arises from the
sudden and violent increase of pressure when the charge is fired by
a spark, which has nothing compurable in the gradual admiesion of
steam-pressure to the piston, whilst when the charge is fired by
high compression, the compression stroke produces a severe reversal
of torque i n the crankshaft and reversal of side-thrust between tlie
piston or crosshead and its guide. But while on the one hand the
difficulties of balance are greater in the case of the interna.1-
combustion engine, the neecl of perfection of balance is also
greater, owing to the purpose for which the internal-combustion
engine is particularly applicable.
[THE I.MEcH.E .]

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560 BALANCING OF INTERNAL-COMBUSTION ENGINES. JULY191’1.

I n marine work a very high standard of balance has been set

by the steam-turbine; for motor-car and aviation purposes an
even higher standard is required for the following reason : When
an engine with a very light framing is mounted on a light fusilage,

FIG.1.-Engine with Perfect Balance of Mass.

FIG.2.-Arrol Johnsoit. Engine. Xass and Ivzpulso Balanced,

Torque UyLbalanccd.

the inertia forces, which are relatively very large, unless well
balanced amongst themselves, will communicate vibration to the
whole machine. Long-distance 5ying is a t present largely A
matter of endurance of the pilot, and vibration, apart from its
effect upon the engine and fusilage, induces fatigue and saps the
nerves of the pilot and marksman.

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J m u 1914. BALANCING OF INTERNAL-COMBUSTION ENGINES. 56 1

Absolute freedom from vibration involves balance of two kinds,

balance of mass and balance of impulse.

Balance of Mass.-Dealing first with balance of mass, this

requires that if the engine be driven by some external source, t h e

FIG.3.-Rotative Engine, Jmviizg Perject Balance of Mass.

%'

L-.
.... 2-_/ ...
/'
inertia forces due to the acceleration of the rotating and reciprocating
parts neutralize each other and have no external resultant. Balance
of mass is so well understood by Members of this Institution
that it is necessary only to notice very briefly the degree attained

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562 BALANCING OF INTERNAL-COMBUSTION ENGINES. JULY 1914.

with ordinary constructions of the internal-combustion engine.

Balance of the rotating members, the crankshaft and cam-shaft,
presents, of course, no theoretical difficulty, provided the crank-
case i s sufficiently rigid t o resist the reactions set up.
The inertia forces of the reciprocating parts are of two kinds :
Primary forces, such as would result if the piston had simple
Imrmonic motion, that is, i f the connecting-rod was of infinite

FIG.4.
Ordinary 4-Cylinder Engine. Secondary Forces Entirely Unbalanced.

a ’

length ; and Secondary forces, due t o the additional motion

resulting from the finite length of the connecting-rod. This
secondary motion is almost exactly simple harmonic in character,
but has double the frequency. Perfect balance of both primary
and secondary forces cnn together be secured only by placing
connecting-rods on oppcsite sides of the crankshaft, Figs. 1 and 2.
If as usual the crankshaft revolves, the connecting-rods must be
attached to opposite cr;mlcs, but, if the cylinders revolve, both
connecting-rods can be attached t o a single crank, Fig. 3. All
three constructions can, however, have but limited application.

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JULY 1914. BALANCING OF INTERNAL-COMBUSTION ENGINES. 563

The ordinary motor-car engine with four cylinders operating

upon the four-stroke cycle necessarily has its crank in one plane,
180" apart in order t80 give reasonable uniformity of impulse. I n
this case the secondary forces are wholly unbalanced. When the
plane of the cranks is horizontal, the connecting-rod has moved the
piston to below midstroke by the amount a, Fig. 4,which, if the length
cf the connecting-rod be four times the crank-radius, amounts to
one-sixteenth of the stroke. As this displacement occurs twice
per revolution and affects all four pistons, the secondary forces set

FIG. 5.--"V1' Erzgine with 8 Cylinders. All Secondary Forces Unbalanced.

up are equivalent to the inertia of a single piston moving the

whole stroke, but acting with double the frequency. With n
connecting-rod of the length of five cranks, the secondary inertia
force is four-fifths of this amount. When two such sets of four
cylinders are placed together in the " V " type engine, the secondary
forces of each set are unbalanced, and their resultant is 40 per
cent. greater than either and acts in a horizontal plane, Fig. 5 .
The secondary forces of the four-cylinder engine, Fig. 4,result
from the fact that the common centre of gravity of the four pistons,
instead of being stationary, as would be the case if the connecting-

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564 BALANCING OF INTERNAL-COMBUSTION ENUINES. JULY 1914.

rods were infinitely long, has a small harmonic motion of double

frequency. It can, therefore, be balanced by reciprocating or
rotating balance-weights, driven a t twice the frequency of the
main piston. Mr. Lanchester's ingenious method of doing this is
to gear n pair of wheels carrying balance-weights to the main
crankshaft, which drives them a t double its speed. As the wheels
rotate in opposite directions, the components of the centrifugal
forces of the weights always balance themselves in the plane
through the axes of the wheels, but have a vertical component
which balances the secondary inertia forces. Such a four-cylinder
engine, though with its cranks in one plane, will have as a whole
complete balance of mass, but the method involves calling into play
two otherwise useless forces, with some addition to the weight and
number of parts.
With four cylinders operating upon the two-stroke cycle, the
cranks can, of course, be placed at right angles instead of a t 180",
and it is then possible to secure complete balance of both primary
and secondary forces, with exception of a couple produced by the
secondary forces in the plane of the cylinders and crankshaft,
which tends to rock the engine in a fore-and-aft direction. This
couple can usually be neglected in practical application. Engines
with five and six cylinders in line, with either cycle, can, of course,
be perfectly balanced as to the primary, and almost perfectly as to
the secondary inertia forces.
To sum up, therefore, the only engine constructions in common
use in which balance of mass is completely or almost completely
secured by the neutralization amongst themselves of the primary and
secondary inertia forces, are the rotating engine, Fig. 3 (page 561),
the engine with five and with six cylinders in line, and the four-
cylinder two-stroke engine with cranks a t right angles, Of course,
also multiplications of these last three of the " V " or radial type
engine, in which the parts in each axial plane are balanced, arc
completely balanced as a whole. All these engines will be
vibrationless when driven by an external source, provided the
crank-case or framing is itself perfectly rigid. I n practice, i t is
not always possible, if the engine is very long, to obtain sufficient

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JULY1914. BALANCING OF INTERNAL-COMBUSTION ENGINES. 565

rigidity. With the light motor-car type, even if the crank-case

be sufficiently rigid, it is dificult when the crankshaft is long to

FIG.6.--" Oechelhauser " Engine.

Balance of Impulse but without Secondary Balaiwe.

make it so stiff that the engine will not tend to vibrate relatively
to its fly-wheel, whose mass-centre remains almost stationary.
3 8

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566

i PI
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JULY 1914. BALANCINU OF INTERNAL-COMBUSTION ENGINES. 567

Balance of Impulse.-Balance of mass, is, however, insuficient

by itself to produce a vibrationless engine, because it takes no
account of the violently fluctuating pressures in the cylinders, and
the consequent strains in the crankshaft and engine framing. To
secure freedom from vibration, it is necessary so to arrange the
cylinders in relation to the crankshaft that h strains in the framing
are either eliminated, or so balance each other as to have no
tendency to shift the centre of gravity of the engine relatively to
its crankshaft and point of support.
If in Fig. 1 (page 560) the cylinders are arranged in line and fire
simultaneously with exactly equal charges, there will be no tendency
for the engine to move, except, of course, to rotate round the
crankshaft. The same result is obtained more simply in Fig. 2,
which ensures equal pressures on the two pistons. Junker obtains
this equality of impulse, and, a t the same time, a valveless two-
stroke engine by his well-known arrangement, Fig. 6 , but this,
unfortunately is unbalanced as to the secondary mass forces. The
three cranks of each cylinder receive simu!taneous impulses once only
per revolution. The crankshaft of the two-cylinder engine shown,
therefore, receives virtually one impulse for every half-revolution.
It will be seen, moreover, that in this, as in all single-acting engines,
the pressures on the pistons during the compression and explosion
strokes twist the crankshaft first backwards and then forwards,
producing a severe condition of stress, whilst the reaction of the
crossheads on their guides also alternate in sign with each stroke.
If, however, a second pair of cylinders, each with a pair of
pistons, be arranged tandem on the top of the first two, as
shown in Fig. 7, each tandem line is then double-acting, and the
cranks of the two sets can consequently be placed a t right angles,
when balance of impulse will be obtained with primary and
secondary mass balance, except only as regards the rocking
secondary couple in the principal plane of the engine. The torque
transmitted to the crankshaft, and the reactions of the crossheads
on their guides, will then also be in one direction only. This
arrangement, however, involves very great height and large
number of parts, together with an expensive form of crankshaft,
2 s 2

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568 BALANCING OF INTERNAL-COMBUSTION ENGINES. JULY 1914.

FIG.8.-'< Fullagar" Engine. Primary and Secondary Balance of Muss,

and Balance of Impulse, if made with four Cranks.

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JULY 1914. BALANCING OF I@TERNAL-COMBUSTION ENGINES. 569

and the same results are obtained more simply, and without these
objections, in the author’s arrangement, Fig. 8.
I n this, two open-ended cylinders, each with a pair of opposed
pistons, are placed closely together side by side, and the upper
piston of one cylinder is connected to the lower piston of the other
by a pair of external oblique tie-rods, i t s shown, the piston A to
the piston D, and the piston C to the piston B. An explosion
between A and B drives B down and A up, drawing up D by the
oblique rods, and giving two equal and opposite impulses to the
two cranks. The pistons A and B, in separating, draw together
the pistons C and D, compressing the charge between them. The
engine operates upon the two-stroke cycle ; the pistons a t the ends
of their stroke uncovering inlet and exhaust ports, as in the
original Oechelhauser arrangement.
The complete engine has two such pairs of cylinders, and a
second pair of cranks a t right angles to the first. The explosions
in the four cylinders, acting upon the eight pistons, produce eight
impulses per revolution which are transmitted to the crankshaft in
equal pairs. The vertical forces a t all times balance each other,
and as in Junker’s engine are not transmitted through the engine
frame.
On referring to Fig. 9 (page 570), it will be seen that the pistons
of each pair are rigidly joined together and form one moving part.
The centre of gravity of the pistons A and D is at the point q, and
travels up and down on the linepq, whilst the centre of gravity of
the other pair of connected pistons C and B is a t the point p and
travels down and up on the same line. Thus the primary forces
are perfectly balanced, and this is probably the only engine in which
the centres of gravity of the balancing masses have exactly the
same locus.
Secondary forces result from the fact that the common centre
of gravity of all four pistons and their connecting-rods oscillates on
the line pp with an amplitude which, with a connecting-rod of the
length of five cranks, is equal to & of the stroke of each piston,
Fig. 10. This force is, however, balanced by the corresponding force
in the other pair of cylinders which osciliates in the opposite phase,

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570 BALANCING OF INTERNAL-COMBUSTION ENGINES. JULY1914.

FIG.9. FIG. 10.

Complete Primary Balance. Want of Secondary Balapzce with two
Cranks Omly.

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J L L Y 1914. BALAXCINQ OF lNTERNAL-COIBUST1ON ENGINES. 57 1

and as the two pairs of cylinders are brought closely together, the
secondaiy couple, which alone remains, is much smaller than i n
Junker’s arrangement. With a six-cylinder engine of this type
even this secondary couple is entirely obliterated.
The Fullagar engine, therefore, obtains perfect or nearly perfect
balance of mass, with complete balance of impulse. Excepting the
small secondary couple above mentioned, no vertical forces are
transmitted to the engine fr<ime. The only reactions on the frames
are the hoiizontal thrusts of the crossheads on their guides, which
are :Jwnys in one direction, and are the unavoidable equivalent of
the useful torque transmitted to the crankshaft. I n respect,
therefore, of the combination of balance of mass, balance of
impulse, and good turning effort, this engine is probably superior
t o any other of the reciprocating type hitherto built.
A 500-h.p. engine of this type has been in operation about n
year. It has four cylinders of 12 inches (305 mm.) bore, and eight
pistons with a common stroke of 18 inches (457 mm.) connected
t o a. four-crank shaft. It develops 650 b.h.p. easily and its weight,
including a fly-wheel of 30 cwt. (1,500 kg.), is under 218 tons
(21,000 kg.). The four pnirs of connected pistons, weight
:cpproximately 2 tons (3,000 kg.), and, at normal speed of 350 r.p.m.
when the pistons have a mean speed of 750 feet per minute (3.8
metres per second), there is hardly any perceptible vibration. Even
when the speed is increased to 300 r.p.m., giving a piston-speed
of 900 feet per minute (4-57 metres per second), vibration is still
very slight. A t first sight, it might be supposed t h a t the oblique
rods would involve considerable friction, but the angle of the rods
is less than the maximum angle of the connecting-rods, and this
friction is actually less than would be the case if each of the eight
pistons had its own crank and connecting-rod. I n the 500 h.p.
engine above mentioned the mechanical efficiency, excluding the
air and gas-pumps, is over 90 per cent.
The condition of balance attained with tlie cross-connected
construction of engine above mentioned is all that could be required
for almost every application of internal-combustion engine ; but
there is still one unbalanced reaction of the engine itself, namely,

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573 BALANCING OF INTERNAL-COMBUSTION ENGINES. JULY 1914.

the effort of each successive impulse to rotate the engine backwards

round its crankshaft, and there is also the gyrostatic effect of the
fly-wheel or propeller which, in the peculiar case of aeroplane
engines, it may be desirable also to eliminate.
To Mr. Lanchester belongs the credit of having produced the
only engine extensively used, in which, in addition to mass balance,

FIQ.11.--“ Lanchester” Engine.

Mass and Torque Balanced, Impulse Unbalanced.

=I-

torque balance was secured between the working parts of the engine
itself. His well-known engine, which is shown in Fig. 11, was
fitted to Lanchester cars about 1896. I n this, it is sufficient to note,
the primary forces were balanced by the balance weights on the
crankshafts ; the secondary forces of the pistons balance themselves,
whilst balance of torque was secured by the oppositely rotating
fly-wheels. Balance of impulse was not cJotained.

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JULY1914. BALANCING OF INTERNAL-COMBUSTION ENGINES. 573
i
t-
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574 BALANCING OF INTERNAL-COMBUSTION ENGINES. JULY 1914.

A n engine which secures perfect balance of all forces is shown

in Fig. 12. I n this, two opposed pistons i n a single cylinder are
connected to two oppositely moving crankshafts, a t opposite ends
of the engine. The shafts need, of course, to be kept in phase by
a lay-shaft and screw-gears or by a pitch-chain and spur-gears,
though the connexion has to perform no appreciable work under
normal conditions. This arrangement has the further advantage
that for aviation purposes two propellers can be driven directly.
If of the same area as a single propeller they will, of course, have
a correspondingly less diameter, and for t h e same revolutions have
41 per cent. greater pitch ratio, a feature which will considerably
increase their eEciency. If two such cylinders are placed side by
side, and their connecting-rods coupled to opposite cranks, these
rods will then balance each other. Such a n engine will have
absolutely perfect balance of all forces, mass, impulse, torque and
gyrostatic effect.
By applying this two-shaft principle to the Fullagar cross-
connected cylinder construction shown in Fig. 8 (pAge 568) a
two-stroke and double-acting engine is produced in which each
crank will receive two impulses per revolution. The engine then
consists of two horizontal cylinders with four cross-connected pistons,
one piston at either end being connected to separate crankshafts
a t either end of the engine.
A still better arrangement for the same purpose is shown i n
Fig. 13, i n which a pair of cylinders with cross-connected pistons is
arranged in a plane at right angles to that of the shafts. Two
such pairs of cylinders can be arranged side by side with the
cranks a t right angles. Small balmce-weights will then be
needed to balance the connecting-rods, and four impulses will be
transmitted to each crankshaft per revolution. As the cylinders
in either case work on the two-stroke cycle, a n air-pump of some
kind is required, and in Fig. 13 the two crossheads of each upper
cylinder are arranged to act as blowers-a method which has been
found satisfactory.
These engines have absolutely perfect balance and consequently
exert no force whatever upon t h e fusilage on which they are

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JULY
1914. BALANCING O F INTERNAL-COMBUSTION ENGINES. 575

mounted, except that due to their weight and to the useful thrust
of the propellers when this is taken by the engine framing. All
the metal in the stationary part of the engine is, moreover, usefully
employed to support the engine and propellers, whilst its disposition
renders it readily attached to and supported by the fusilage. Such
an engine would appear to meet the requirements of aviation
more completely than any arrangement yet devised, and, quite apart
from the advantages of being " two-stroke " and double-acting, is,
so far as the writer is aware, the only arrangement hitherto
proposed which secures a t the same time balance of both primary
and secondary mass forces, balance of impulse, balance of torque,
and balance of gyrostatic action.
The Paper is illustrated by 13 Figs. in the letterpress.

Discussion.
On the motion of the CHAIRMAN (Mr. Michael Longridge, Vice-
President), a hearty vote of thanks was accorded to the author for
his interesting Paper.

Sir RICHARDA. PAGET, Bart., who WRS called on by the

Chairman, said he craved the indulgence of the members for
venturing to address them upon a subject of such great technical
interest, because he was not personally an engineer. As he
had been called upon to speak, he would venture to make a
few remarks on the subject of the practical importance of balance.
Many engineers were apt to think that the balance of an internal-
combustion engine was a desirable but not necessarily a fundamental
thing, that if they could get the engine perfectly balanced, it was
simply a great deal better than if it was not. H e thought the
author had shown, however, that the balance did connote a great
deal more than that. Perfect balance seemed to connote the
perfect use of all the forces which were developed within the
engine.

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576 BALANCING OF INTERNAL-COMBUSTIONENGINES. JULY 1914.
(Sir Richard A. Paget, Bart.)
Probably most of the members were familiar with the atory
of the Magdeburg hemispheres. The Magdeburg philosophers
discovered that if they took two hemispheres and exhausted the
air between them very great force was required to separate them.
He remembered seeing a picture which depicted the Magdeburg
hemispheres being pulled by two horses, one a t each end. It had
not occurred to the philosophers of Magdeburg that the same strain
would have been put on the hemispheres if only one horse had been
used and the other end of the hemisphere had been tied to a tree.
The author had made use of the exact converse of that principle.
I n his engine the force was in the centre, and the whole of the
thrust was divided into two equally and oppositely occurring
forces which were perfectly balanced. The stresses in the cylinder
were not greater than if only one side was being used; in fact,
the stresses in the cylinder of the Fullagar engine were reduced
altogether, because the effort which usually tended to blow off the
cylinder-cover in other types of engine was usefully employed to
force the piston out. Similarly, the force which it was necessary
to use in an internal-combustion engine to compress the charge was
applied by a perfectly direct method, namely, by means of din.gona1
tie-rods, instead of using the indirect method of attaching the
connecting-rod to the crankshaft, along the crankshaft to the
neighbouring crank, up the connecting-rod and so to the
neighbouring piston which was doing the compression.
It might be said, roughly speaking, that in that principle the
force of the explosion was divided into two equal and opposite
portions, each portion being in its turn divided into two. First of
all as the pistons came apart they drew together automatically the
neighbouring pistons and so compressed the charge, this doing the
negative work, that being equally and oppositely done by the
pistons next door to the cylinder in which the explosion took place.
The balance of the work that was over was directly transmitted to
the crankshaft in the form of two equal and opposite impulses on
two neighbouring cranks. The total effect of the system of balance
was to utilize the whole of the material of the engine to the greatest
possible advantage. The crankshaft received nothing but direct

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JULY 1914. BALANCING OF INTERNAL-COMBUSTION ENGINES. 577

positive and useful impulses, which were always equal and opposite.
Therefore the crankshaft could be made very much lighter than
usual. Similarly, as the cylinders of the engines were not subjected
t o any longitudinal stresses, those cylinders had to do much less
work than was usual. As a result, an engine built on that principle
weighed per horse-power roughly half that of an engine built on
the ordinary principle.

Conimun.icationas.

Mr. H. G. ALLENwrote that it was realized from the first the

important advantages to be obtained by adopting the Fullagar
method of balancing, and it was seen that there would be a great
future before this type of engine, provided the mechanical design
could be satisfactorily arranged to give simplicity of manufacture,
operation and overhaul, and his firm had therefore gone very closely
into the design of the various parts with the inventor, Mr. Fullagar.
They found the general design so satisfactory that they had n o
comments or suggestions of importance to make, and their attention
was centred chiefly on the design of the pistons and their attachments
to the connecting-rods. Naturally, the most important part of this
was the arrangement and design of the oblique rods which coupled
together in pairs pistons in cylinders side by side. The guides to
take the side thrusts due to the oblique rods presented no special
difficulties, and the chief feature was t o arrange the oblique rods
and the guides so as to eliminate all possibility of vibration in the
oblique rods. Care was taken to see that all the reciprocating
parts, particularly the pistons and crossheads, were of equal weight,
and each pair of pistons was joined together through the oblique
rods. They were then subjected to hydraulic pressure so as to
impose strains considerably higher than those which would be met
with under working conditions. Careful measurements were ma&

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578 BALANCING OF INTERNAL-COMBUSTION ENGINES. JULY1914.
(Mr. H. G. Allen.)
to see whether there was any deflection, more especially, of the
light steel crossheads, and it was found after the tests had been
carried out that this was quite negligible.
The engine was run at the Queen's Engineering Works, Bedford,
a t full speed, direct-coupled t o an electric motor, and it was observed
that its balance was perfect. For the construction of the moving
parts the same accuracy was required as for the high-speed enclosed
forced lubrication steam-engine which his firm manufactured, and
the operations and methods of working were carried out on almost
exactly similar lines. The same standard of material was used i n
the construction of the Fullagar engine as in the case of an ordinary
gas-engine or high-speed steam-engine. They found t h a t there
were no unusual operations requiring any specially trained workmen.
Naturally, with a new class of engine, some special supervision was
necessary, to advise and to give information regarding the working
limits and the accuracy required for the various parts. No difficulties
were experienced which could not be avoided in making any
subsequent engine, and no awkward operations were found, such
as might be expected from the fact of the side connecting-rods
being at an angle instead of parallel with the cylinders. No special
apparatus was required for testing these engines under full load at
the works where they were manufactured, as the enh' oines were
complete i n themselves with air scavenge and gas-pnmps. A
mpply of gas and jacket cooling water was all that was needed.
The principal features in the engine were the perfect balance,
the small space occupied and the lightness in weight of the engine
as compared with any other form of gas-engine. Another
remarkable feature was the ease with which the engine could be
overhauled on account of its design, and i n consequence of all
these t h e engine was much less costly than the ordinary type of
gas-engine.

Mr. H. F. FULLAGAR wrote that he had hoped that some of those

identified with the manufacture of gas-engines and oil-engines
would join in the discussion, and give their views upon the
commercial value of balance relative to the other essentials of a n

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JULY1914. BALANCING OF INTERNAL-CQMBUSTION ENGINES. 579

internal-combustion engine. The cost of a n engine was largely

determined by the maximum pressure that occurred in working,
whilst the power was determined by the mean-effective-pressure,
and the nearer the maximum approached the mean, the lighter and
cheaper was the engine for a given power. I n the great majority
of internal-combustion engines, the inertia forces were not
cushioned at all at one end of the stroke, and only intermittently
cushioned at the other. The crankshaft and connecting-rods had,
therefore, to sustain the wear and the stresses produced by these
uncushivned forces, and this condition could not be without its
effect upon the cost of the engine. To help to fix i n one’s mind a n
idea of the size of these inertia forces, it should first he remembered
that with any given design of engine, the inertia force per square
inch of piston was independent of the size of the engine. It varied
directly with the square of the mean piston-speed, but, at a given
piston-speed, was the same per square inch of piston whatever the
size of the engine might be. For instance, with a mean piston-
speed of 750 feet per minute, if the piston, instead of being hollow,
were a solid lump of metal and had a length equal to its stroke, t h e
maximurn inertia force would be very nearly 100 lb. per square
inch, equal to the mean-effective-pressure with the four-stroke
cycle. I n any actual engine the maximum inertia force per square
inch a t 750 feet piston-speed would be less than 100 lb. per square
inch, in proportion as the actual reciprocating parts (piston and
part of connecting-rod) were lighter than a solid piston whose
length was equal to the stroke, and it would at once be seen from
this how important these inertia stresses were in practice, and how
desirable it was to avoid their being thrown upon the bearings and
working parts.
From the pnrchaser’s point of view, there could be no doubt
that t h e forces of the engine should be self-contained. Excepting
for the one reaction, which was the unavoidable equivalent of t h e
useful torque given to the crankshaft, all the reactions should be
balanced amongst themselves, and thus be prevented from reaching
the foundations o r supporting frame. That any large forces such
as the inertia forces above considered should reach, and had t o be

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580 BALANCING OF INTERNAL COMBUSTION-ENQINES. JULY 1914 *
(Mr. €I. P. Fullagar.)
absorbed by the engine supports was a t all times highly undesirable,
and in the case of light, high-powered structures such as aeroplanes,
motor-cars, motor-boats, and even large cargo boats, introduced
very serious considerations. I n the author’s engine which had
been briefly referred to, the balance of both inertia and fluid
pressure forces went hand in hand with a large reduction in cost
and with other advantages of considerable practical value.
I n its early days, the balance of mass afforded by the steam-
turbine was the principal, in some cases the only, advantage
which led to its adoption in preference to the reciprocating steam-
engine for central station work, and ultimately led to a very
large extension of its field of application, and it appeared not
improbable that balance might have an equally potent influence in
the field of the internal-combustion engine.

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