Aviation Engine Types--Division in Classes--Anzani Engines--
Canton and Unne Engine--Construction of Gnome Engines--
"Monosoupape" Gnome--German "Gnome" Type--Le Rhone Engine--
Renault Air-Cooled Engine--Simplex Model "A" Hispano-Suiza--
Curtiss Aviation Motors--Thomas-Morse Model 88 Engine--
Duesenberg Engine--Aeromarine Six-Cylinder--Wisconsin Aviation
Engines--Hall-Scott Engines--Mercedes Motor--Benz Motor--
Austro-Daimler--Sunbeam-Coatalen.
AVIATION ENGINE TYPES
Inasmuch as numerous forms of airplane engines have been devised, it
would require a volume of considerable size to describe even the most
important developments of recent years. As considerable explanatory
matter has been given in preceding chapters and the principles involved
in internal combustion engine operation considered in detail, a
relatively brief review of the features of some of the most successful
airplane motors should suffice to give the reader a complete enough
understanding of the art so all types of engines can be readily
recognized and the advantages and disadvantages of each type understood,
as well as defining the constructional features enough so the methods of
locating and repairing the common engine and auxiliary system troubles
will be fully grasped.
Aviation engines can be divided into three main classes. One of the
earliest attempts to devise distinctive power plant designs for aircraft
involved the construction of engines utilizing a radial arrangement of
the cylinders or a star-wise disposition. Among the engines of this
class may be mentioned the Anzani, R. E. P. and the Salmson or Canton
and Unne forms. The two former are air-cooled, the latter design is
water-cooled. Engines of this type have been built in cylinder numbers
ranging from three to twenty. While the simple forms were popular in the
early days of aviation engine development, they have been succeeded by
the more conventional arrangements which now form the largest class. The
reason for the adoption of a star-wise arrangement of cylinders has been
previously considered. Smoothness of running can only be obtained by
using a considerable number of cylinders. The fundamental reason for the
adoption of the star-wise disposition is that a better distribution of
stress is obtained by having all of the pistons acting on the same
crank-pin so that the crank-throw and pin are continuously under maximum
stress. Some difficulty has been experienced in lubricating the lower
cylinders in some forms of six cylinder, rotary crank, radial engines
but these have been largely overcome so they are not as serious in
practice as a theoretical consideration would indicate.
Another class of engines developed to meet aviation requirements is a
complete departure from the preceding class, though when the engines are
at rest, it is difficult to differentiate between them. This class
includes engines having a star-wise disposition of the cylinders but the
cylinders themselves and the crank-case rotate and the crank-shaft
remains stationary. The important rotary engines are the Gnome, the Le
Rhone and the Clerget. By far the most important classification is that
including engines which retain the approved design of the types of power
plants that have been so widely utilized in automobiles and which have
but slight modifications to increase reliability and mechanical strength
and produce a reduction in weight. This class includes the vertical
engines such as the Duesenberg and Hall-Scott four-cylinder; the
Wisconsin, Aeromarine, Mercedes, Benz, and Hall-Scott six-cylinder
vertical engines and the numerous eight- and twelve-cylinder Vee designs
such as the Curtiss, Renault, Thomas-Morse, Sturtevant, Sunbeam, and
others.
ANZANI ENGINES
The attention of the mechanical world was first directed to the great
possibilities of mechanical flight when Bleriot crossed the English
Channel in July, 1909, in a monoplane of his own design and
construction, having the power furnished by a small three-cylinder
air-cooled engine rated at about 24 horse-power and having cylinders
4.13 inches bore and 5.12 inches stroke, stated to develop the power at
about 1600 R.P.M. and weighing 145 pounds. The arrangement of this early
Anzani engine is shown at Fig. 190, and it will be apparent that in the
main, the lines worked out in motorcycle practice were followed to a
large extent. The crank-case was of the usual vertically divided
pattern, the cylinders and heads being cast in one piece and held to the
crank-case by stud bolts passing through substantial flanges at the
cylinder base. In order to utilize but a single crank-pin for the three
cylinders it was necessary to use two forked rods and one rod of the
conventional type. The arrangement shown at Fig. 190, called for the use
of counter-balanced flywheels which were built up in connection with
shafts and a crank-pin to form what corresponds to the usual crank-shaft
assembly.
[Illustration: Fig. 190.--Views Outlining Construction of Three-Cylinder
Anzani Aviation Motor.]
The inlet valves were of the automatic type so that a very simple valve
mechanism consisting only of the exhaust valve push rods was provided.
One of the difficulties of this arrangement of cylinders was that the
impulses are not evenly spaced. For instance, in the forms where the
cylinders were placed 60 degrees apart the space between the firing of
the first cylinder and that next in order was 120 degrees crank-shaft
rotation, after which there was an interval of 300 degrees before the
last cylinder to fire delivered its power stroke. In order to increase
the power given by the simple three-cylinder air-cooled engine a
six-cylinder water-cooled type, as shown at Figs. 191 and 192, was
devised. This was practically the same in action as the three-cylinder
except that a double throw crank-shaft was used and while the
explosions were not evenly spaced the number of explosions obtained
resulted in fairly uniform application of power.
[Illustration: Fig. 190a.--Illustrations Depicting Wrong and Right
Methods of "Swinging the Stick" to Start Airplane Engine. At Top, Poor
Position to Get Full Throw and Get Out of the Way. Below, Correct
Position to Get Quick Turn Over of Crank-Shaft and Spring Away from
Propeller.]
[Illustration: Fig. 191.--The Anzani Six-Cylinder Water-Cooled Aviation
Engine.]
[Illustration: Fig. 192.--Sectional View of Anzani Six-Cylinder
Water-Cooled Aviation Engine.]
The latest design of three-cylinder Anzani engine, which is used to some
extent for school machines, is shown at Fig. 193. In this, the
three-cylinders are symmetrically arranged about the crank-case or 120
degrees apart. The balance is greatly improved by this arrangement and
the power strokes occur at equal intervals of 240 degrees of crank-shaft
rotation. This method of construction is known as the Y design. By
grouping two of these engines together, as outlined at Fig. 194, which
gives an internal view, and at Fig. 195, which shows the sectional view,
and using the ordinary form of double throw crank-shaft with crank-pins
separated by 180 degrees, a six-cylinder radial engine is produced which
runs very quietly and furnishes a steady output of power. The
peculiarity of the construction of this engine is in the method of
grouping the connecting rod about the common crank-pin without using
forked rods or the "Mother rod" system employed in the Gnome engines. In
the Anzani the method followed is to provide each connecting rod big end
with a shoe which consists of a portion of a hollow cylinder held
against the crank-pin by split clamping rings. The dimensions of these
shoes are so proportioned that the two adjacent connecting rods of a
group of three will not come into contact even when the connecting rods
are at the minimum relative angle. The three shoes of each group rest
upon a bronze sleeve which is in halves and which surrounds the
crank-pin and rotates relatively to it once in each crank-shaft
revolution. The collars, which are of tough bronze, resist the inertia
forces while the direct pressure of the explosions is transmitted
directly to the crank-pin bushing by the shoes at the big end of the
connecting rod. The same method of construction, modified to some
extent, is used in the Le Rhone rotary cylinder engine.
[Illustration: Fig. 193.--Three-Cylinder Anzani Air-Cooled Y-Form
Engine.]
[Illustration: Fig. 194.--Anzani Fixed Crank-Case Engine of the
Six-Cylinder Form Utilizes Air Cooling Successfully.]
Both cylinders and pistons of the Anzani engines are of cast iron, the
cylinders being provided with a liberal number of cooling flanges which
are cast integrally. A series of auxiliary exhaust ports is drilled near
the base of each cylinder so that a portion of the exhaust gases will
flow out of the cylinder when the piston reaches the end of its power
stroke. This reduces the temperature of the gases passing around the
exhaust valves and prevents warping of these members. Another
distinctive feature of this engine design is the method of attaching the
Zenith carburetor to an annular chamber surrounding the rear portion of
the crank-case from which the intake pipes leading to the intake valves
radiate. The magneto is the usual six-cylinder form having the armature
geared to revolve at one and one-half times crank-shaft speed.
[Illustration: Fig. 195.--Sectional View Showing Internal Parts of
Six-Cylinder Anzani Engine, with Starwise Disposition of Cylinders.]
[Illustration: Fig. 196.--The Anzani Ten-Cylinder Aviation Engine at
the Left, and the Twenty-Cylinder Fixed Type at the Right.]
The Anzani aviation engines are also made in ten- and twenty-cylinder
forms as shown at Fig. 196. It will be apparent that in the
ten-cylinder form explosions will occur every 72 degrees of crank-shaft
rotation, while in the twenty-cylinder, 200 horse-power engine at any
instant five of the cylinders are always working and explosions are
occurring every 36 degrees of crank-shaft rotation. On the
twenty-cylinder engine, two carburetors are used and two magnetos,
which are driven at two and one-half times crank-shaft speed. The
general cylinder and valve construction is practically the same, as in
the simpler engines.
[Illustration: Fig. 197.--Application of R. E. P. Five-Cylinder
Fan-Shape Air-Cooled Motor to Early Monoplane.]
CANTON AND UNNE ENGINE
This engine, which has been devised specially for aviation service, is
generally known as the "Salmson" and is manufactured in both France and
Great Britain. It is a nine-cylinder water-cooled radial engine, the
nine cylinders being symmetrically disposed around the crank-shaft while
the nine connecting rods all operate on a common crank-pin in somewhat
the same manner as the rods in the Gnome motor. The crank-shaft of the
Salmson engine is not a fixed one and inasmuch as the cylinders do not
rotate about the crank-shaft it is necessary for that member to revolve
as in the conventional engine. The stout hollow steel crank-shaft is in
two pieces and has a single throw. The crank-shaft is built up somewhat
the same as that of the Gnome engine. Ball bearings are used throughout
this engine as will be evident by inspecting the sectional view given at
Fig. 199. The nine steel connecting rods are machined all over and are
fitted at each end with bronze bushings, the distance between the
bearing centers being about 3.25 times crank length. The method of
connecting up the rods to the crank-pin is one of the characteristic
features of this design. No "mother" rod as supplied in the Gnome engine
is used in this type inasmuch as the steel cage or connecting rod
carrier is fitted with symmetrically disposed big end retaining pins.
Inasmuch as the carrier is mounted on ball bearings some means must be
provided of regulating the motion of the carrier as if no means were
provided the resulting motion of the pistons would be irregular.
[Illustration: Fig. 198.--The Canton and Unne Nine-Cylinder Water-Cooled
Radial Engine.]
The method by which the piston strokes are made to occur at precise
intervals involves a somewhat lengthy and detailed technical
explanation. It is sufficient to say that an epicyclic train of gears,
one of which is rigidly attached to the crank-case so it cannot rotate
is used, while other gears make a connection between the fixed gear and
with another gear which is exactly the same size as the fixed gear
attached to the crank-case and which is formed integrally with the
connecting rod carrier. The action of the gearing is such that the cage
carrying the big end retaining pins does not rotate independently of
the crank-shaft, though, of course, the crank-shaft or rather crank-pin
bearings must turn inside of the big end carrier cage.
[Illustration: Fig. 199.--Sectional View Showing Construction of Canton
and Unne Water-Cooled Radial Cylinder Engine.]
Cylinders of this engine are of nickel steel machined all over and carry
water-jackets of spun copper which are attached to the cylinders by
brazing. The water jackets are corrugated to permit the cylinder to
expand freely. The ignition is similar to that of the fixed crank
rotating cylinder engine. An ordinary magneto of the two spark type
driven at 1-3/4 times crank-shaft speed is sufficient to ignite the
seven-cylinder form, while in the nine-cylinder engines the ignition
magneto is of the "shield" type giving four sparks per revolution. The
magneto is driven at 1-1/9 times crank-shaft speed. Nickel steel valves
are used and are carried in castings or cages which screw into bosses in
the cylinder head. Each valve is cam operated through a tappet, push rod
and rocker arm, seven cams being used on a seven-cylinder engine and
nine cams on the nine-cylinder. One cam serves to open both valves as in
its rotation it lifts the tappets in succession and so operates the
exhaust and inlet valves respectively. This method of operation involves
the same period of intake and exhaust. In normal engine practice the
inlet valve opens 12 degrees late and closes 20 degrees late. The
exhaust opens 45 degrees early and closes 6 degrees late. This means
about 188 degrees in the case of inlet valve and 231 degrees crank-shaft
travel for exhaust valves. In the Salmson engine, the exhaust closes and
the inlet opens at the outer dead center and the exhaust opens and the
inlet closes at about the inner dead center. This engine is also made in
a fourteen-cylinder 200 B. H. P. design which is composed of two groups
of seven-cylinders, and it has been made in an eighteen-cylinder design
of 600 horse-power. The nine-cylinder 130 horse-power has a cylinder
bore of 4.73 inches and a stroke of 5.52 inches. Its normal speed of
rotation is 1250 R. P. M. Owing to the radial arrangement of the
cylinders, the weight is but 4-1/4 pounds per B. H. P.
CONSTRUCTION OF EARLY GNOME MOTOR
It cannot be denied that for a time one of the most widely used of
aeroplane motors was the seven-cylinder revolving air-cooled Gnome, made
in France. For a total weight of 167 pounds this motor developed 45 to
47 horse-power at 1,000 revolutions, being equal to 3.35 pounds per
horse-power, and has proved its reliability by securing many
long-distance and endurance records. The same engineers have produced
a nine-cylinder and by combining two single engines a fourteen-cylinder
revolving Gnome, having a nominal rating of 100 horse-power, with which
world's speed records were broken. A still more powerful engine has been
made with eighteen-cylinders. The nine-cylinder "monosoupape" delivers
100 horse-power at 1200 R. P. M., the engine of double that number of
cylinders is rated at about 180 horse-power.
[Illustration: Fig. 200.--Sectional View Outlining Construction of Early
Type Gnome Valve-in-Piston Type Motor.]
Except in the number of cylinders and a few mechanical details the
fourteen-cylinder motor is identical with the seven-cylinder one; fully
three-quarters of the parts used by the assemblers would do just as well
for one motor as for the other. Owing to the greater power demands of
the modern airplane the smaller sizes of Gnome engines are not used as
much as they were except for school machines. There is very little in
this motor that is common to the standard type of vertical motorcar
engine. The cylinders are mounted radially round a circular crank-case;
the crank-shaft is fixed, and the entire mass of cylinders and
crank-case revolves around it as outlined at Fig. 200. The explosive
mixture and the lubricating oil are admitted through the fixed hollow
crank-shaft, passed into the explosion chamber through an automatic
intake valve in the piston head in the early pattern, and the spent
gases exhausted through a mechanically operated valve in the cylinder
head. The course of the gases is practically a radial one. A peculiarity
of the construction of the motor is that nickel steel is used
throughout. Aluminum is employed for the two oil pump housings; the
single compression ring known as the "obdurator" for each piston is made
of brass; there are three or four brass bushes; gun metal is employed
for certain pins--the rest is machined out of chrome nickel steel. The
crank-case is practically a steel hoop, the depth depending on whether
it has to receive seven-or fourteen-cylinders; it has seven or fourteen
holes bored as illustrated on its circumference. When fourteen or
eighteen cylinders are used the holes are bored in two distinct planes,
and offset in relation one to the other.
The cylinders of the small engine which have a bore of 4-3/10 inches and
a stroke of 4-7/10 inches, are machined out of the solid bar of steel
until the thickness of the walls is only 1.5 millimeters--.05905 inch,
or practically 1/16 inch. Each one has twenty-two fins which gradually
taper down as the region of greatest pressure is departed from. In
addition to carrying away heat, the fins assist in strengthening the
walls of the cylinder. The barrel of the cylinder is slipped into the
hole bored for it on the circumference of the crank-case and secured by
a locking member in the nature of a stout compression ring, sprung onto
a groove on the base of the cylinder within the crank chamber. On each
lateral face of the crank chamber are seven holes, drilled right through
the chamber parallel with the crank-shaft. Each one of these holes
receives a stout locking-pin of such a diameter that it presses against
the split rings of two adjacent cylinders; in addition each cylinder is
fitted with a key-way. This construction is not always followed, some of
the early Gnome engines using the same system of cylinder retention as
used on the latest "monosoupape" pattern.
The exhaust valve is mounted in the cylinder head, Fig. 201, its seating
being screwed in by means of a special box spanner. On the
fourteen-cylinder model the valve is operated directly by an overhead
rocker arm with a gun metal rocker at its extremity coming in contact
with the extremity of the valve stem. As in standard motor car practice,
the valve is opened under the lift of the vertical push rod, actuated by
the cam. The distinctive feature is the use of a four-blade leaf spring
with a forked end encircling the valve stems and pressing against a
collar on its extremity. On the seven-cylinder model the movement is
reversed, the valve being opened on the downward pull of the push rod,
this lifting the outer extremity of the main rocker arm, which tips a
secondary and smaller rocker arm in direct contact with the extremity
of the valve stem. The springs are the same in each case. The two types
are compared at A and B, Fig. 202.
[Illustration: Fig. 201.--Sectional View of Early Type Gnome Cylinder
and Piston Showing Construction and Application of Inlet and Exhaust
Valves.]
The pistons, like the cylinders, are machined out of the solid bar of
nickel steel, and have a portion of their wall cut away, so that the two
adjacent ones will not come together at the extremity of their stroke.
The head of the piston is slightly reduced in diameter and is provided
with a groove into which is fitted a very light L-section brass split
ring; back of this ring and carried within the groove is sprung a light
steel compression ring, serving to keep the brass ring in expansion. As
already mentioned, the intake valves are automatic, and are mounted in
the head of the piston as outlined at Fig. 202, C. The valve seating is
in halves, the lower portion being made to receive the wrist-pin and
connecting rod, and the upper portion, carrying the valve, being screwed
into it. The spring is composed of four flat blades, with the hollowed
stem of the automatic valve passing through their center and their two
extremities attached to small levers calculated to give balance against
centrifugal force. The springs are naturally within the piston, and are
lubricated by splash from the crank chamber. They are of a delicate
construction, for it is necessary that they shall be accurately balanced
so as to have no tendency to fly open under the action of centrifugal
force. The intake valve is withdrawn by the use of special tools through
the cylinder head, the exhaust valve being first dismounted.
[Illustration: Fig. 202.--Details of Old Style Gnome Motor Inlet and
Exhaust Valve Construction and Operation.]
The fourteen-cylinder motor shown at Fig. 203, has a two-throw
crank-shaft with the throws placed at 180 degrees, each one receiving
seven connecting rods. The parts are the same as for the seven-cylinder
motor, the larger one consisting of two groups placed side by side. For
each group of seven-cylinders there is one main connecting rod, together
with six auxiliary rods. The main connecting rod, which, like the
others, is of H section, has machined with it two L-section rings bored
with six holes--51-1/2 degrees apart to take the six other connecting
rods. The cage of the main connecting rod carries two ball races, one on
either side, fitting onto the crank-pin and receiving the thrust of the
seven connecting rods. The auxiliary connecting rods are secured in
position in each case by a hollow steel pin passing through the two
rings. It is evident that there is a slightly greater angularity for the
six shorter rods, known as auxiliary connecting rods, than for the
longer main rods; this does not appear to have any influence on the
running of the motor.
[Illustration: Fig. 203.--The Gnome Fourteen-Cylinder 100 Horse-Power
Aviation Engine.]
Coming to the manner in which the earliest design exhaust valves are
operated on the old style motor, this at first sight appears to be one
of the most complicated parts of the motor, probably because it is one
in which standard practice is most widely departed from. Within the
cylindrical casing bolted to the rear face of the crank-case are seven,
thin flat-faced steel rings, forming female cams. Across a diameter of
each ring is a pair of projecting rods fitting in brass guides and
having their extremities terminating in a knuckle eye receiving the
adjustable push rods operating the overhead rocker arms of the exhaust
valve. The guides are not all in the same plane, the difference being
equal to the thickness of the steel rings, the total thickness being
practically 2 inches. Within the female cams is a group of seven male
cams of the same total thickness as the former and rotating within them.
As the boss of the male cam comes into contact with the flattened
portion of the ring forming the female cam, the arm is pushed outward
and the exhaust valve opened through the medium of the push-rod and
overhead rocker. This construction was afterwards changed to seven male
cams and simple valve operating plunger and roller cam followers as
shown at Fig. 204.
On the face of the crank-case of the fourteen-cylinder motor opposite to
the valve mechanism is a bolted-on end plate, carrying a pinion for
driving the two magnetos and the two oil pumps, and having bolted to it
the distributor for the high-tension current. Each group of
seven-cylinders has its own magneto and lubricating pump. The two
magnetos and the two pumps are mounted on the fixed platform carrying
the stationary crank-shaft, being driven by the pinion on the revolving
crank chamber. The magnetos are geared up in the proportion of 4 to 7.
Mounted on the end plate back of the driving pinion are the two
high-tension distributor plates, each one with seven brass segments let
into it and connection made to the plugs by means of plain brass wire.
The wire passes through a hole in the plug and is then wrapped round
itself, giving a loose connection.
[Illustration: Fig. 204.--Cam and Cam-Gear Case of the Gnome
Seven-Cylinder Revolving Engine.]
[Illustration: Fig. 205.--Diagrams Showing Why An Odd Number of
Cylinders is Best for Rotary Cylinder Motors.]
A good many people doubtless wonder why rotary engines are usually
provided with an odd number of cylinders in preference to an even
number. It is a matter of even torque, as can easily be understood from
the accompanying diagram. Fig. 205, A, represents a six-cylinder rotary
engine, the radial lines indicating the cylinders. It is possible to
fire the charges in two ways, firstly, in rotation, 1, 2, 3, 4, 5, 6,
thus having six impulses in one revolution and none in the next; or
alternately, 1, 3, 5, 2, 4, 6, in which case the engine will have turned
through an equal number of degrees between impulses 1 and 3, and 3 and
5, but a greater number between 5 and 2, even again between 2 and 4, 4
and 6, and a less number between 6 and 1, as will be clearly seen on
reference to the diagram. Turning to Fig. 205, B, which represents a
seven-cylinder engine. If the cylinders fire alternately it is obvious
that the engine turns through an equal number of degrees between each
impulse, thus, 1, 3, 5, 7, 2, 4, 6, 1, 3, etc. Thus supposing the engine
to be revolving, the explosion takes place as each alternate cylinder
passes, for instance, the point 1 on the diagram, and the ignition is
actually operated in this way by a single contact.
[Illustration: Fig. 206.--Simple Carburetor Used On Early Gnome Engines
Attached to Fixed Crank-Shaft End.]
The crank-shaft of the Gnome, as already explained, is fixed and hollow.
For the seven- and nine-cylinder motors it has a single throw, and for
the fourteen- and eighteen-cylinder models has two throws at 180
degrees. It is of the built-up type, this being necessary on account of
the distinctive mounting of the connecting rods. The carburetor shown at
Fig. 206 is mounted at one end of the stationary crank-shaft, and the
mixture is drawn in through a valve in the piston as already explained.
There is neither float chamber nor jet. In many of the tests made at the
factory it is said the motor will run with the extremity of the gasoline
pipe pushed into the hollow crank-shaft, speed being regulated entirely
by increasing or decreasing the flow through the shut-off valve in the
base of the tank. Even under these conditions the motor has been
throttled down to run at 350 revolutions without misfiring. Its normal
speed is 1,000 to 1,200 revolutions a minute. Castor oil is used for
lubricating the engine, the oil being injected into the hollow
crank-shaft through slight-feed fittings by a mechanically operated pump
which is clearly shown in sectional diagrams at Fig. 207.
[Illustration: Fig. 207.--Sectional Views of the Gnome Oil Pump.]
The Gnome is a considerable consumer of lubricant, the makers' estimate
being 7 pints an hour for the 100 horse-power motor; but in practice
this is largely exceeded. The gasoline consumption is given as 300 to
350 grammes per horse-power. The total weight of the fourteen-cylinder
motor is 220 pounds without fuel or lubricating oil. Its full power is
developed at 1,200 revolutions, and at this speed about 9 horse-power is
lost in overcoming air resistance to cylinder rotation.
[Illustration: Fig. 208.--Simplified Diagram Showing Gnome Motor Magneto
Ignition System.]
While the Gnome engine has many advantages, on the other hand, the head
resistance offered by a motor of this type is considerable; there is a
large waste of lubricating oil due to the centrifugal force which tends
to throw the oil away from the cylinders; the gyroscopic effect of the
rotary motor is detrimental to the best working of the aeroplane, and
moreover it requires about seven per cent. of the total power developed
by the motor to drive the revolving cylinders around the shaft. Of
necessity, the compression of this type of motor is rather low, and an
additional disadvantage manifests itself in the fact that there is as
yet no satisfactory way of muffling the rotary type of motor.
GNOME "MONOSOUPAPE" TYPE
The latest type of Gnome engine is known as the "monosoupape" type
because but one valve is used in the cylinder head, the inlet valve in
the piston being dispensed with on account of the trouble caused by that
member on earlier engines. The construction of this latest type follows
the lines established in the earlier designs to some extent and it
differs only in the method of charging. The very rich mixture of gas and
air is forced into the crank-case through the jet inside the
crank-shaft, and enters the cylinder when the piston is at its lowest
position, through the half-round openings in the guiding flange and the
small holes or ports machined in the cylinder and clearly shown at Fig.
210. The returning piston covers the port, and the gas is compressed and
fired in the usual way. The exhaust is through a large single valve in
the cylinder head, which gives rise to the name "monosoupape," or
single-valve motor, and this valve also remains open a portion of the
intake stroke to admit air into the cylinder and dilute the rich gas
forced in from the crank-case interior. Aviators who have used the early
form of Gnome say that the inlet valve in the piston type was prone to
catch on fire if any valve defect materialized, but the "monosoupape"
pattern is said to be nearly free of this danger. The bore of the 100
horse-power nine-cylinder engine is 110 mm., the piston stroke 150 mm.
Extremely careful machine work and fitting is necessary. In many parts,
tolerances of less than .0004" (four ten thousandths of an inch) are all
that are allowed. This is about one-sixth the thickness of the average
human hair, and in other parts the size must be absolutely standard, no
appreciable variation being allowable. The manufacture of this engine
establishes new mechanical standards of engine production in this
country. Much machine work is needed in producing the finished
components from the bar and forging.
[Illustration: Fig. 209.--The G. V. Gnome "Monosoupape" Nine-Cylinder
Rotary Engine Mounted on Testing Stand.]
[Illustration: Fig. 210.--Sectional View Showing Construction of General
Vehicle Co. "Monosoupape" Gnome Engine.]
The cylinders, for example, are machined from 6 inch solid steel bars,
which are sawed into blanks 11 inches in length and weighing about 97
pounds. The first operation is to drill a 2-1/16 inch hole through the
center of the block. A heavy-duty drilling machine performs this work,
then the block goes to the lathe for further operations. Fig. 211 shows
six stages of the progress of a cylinder, a few of the intermediate
steps being omitted. These give, however, a good idea of the work done.
The turning of the gills, or cooling flanges, is a difficult
proposition, owing to the depth of the cut and the thin metal that forms
the gills. This operation requires the utmost care of tools and the use
of a good lubricant to prevent the metal from tearing as the tools
approach their full depth. These gills are only 0.6 mm., or 0.0237 in.,
thick at the top, tapering to a thickness of 1.4 mm. (0.0553 in.) at the
base, and are 16 mm. (0.632 in.) deep. When the machine work is
completed the cylinder weighs but 5-1/2 pounds.
[Illustration: Fig. 211.--How a Gnome Cylinder is Reduced from Solid
Chunk of Steel Weighing 97 Pounds to Finished Cylinder Weighing 5-1/2
Pounds.]
GNOME FUEL SYSTEM, IGNITION AND LUBRICATION
The following description of the fuel supply, ignition and oiling of the
"monosoupape," or single valve Gnome, is taken from "The Automobile."
Gasoline is fed to the engine by means of air pressure at 5 pounds per
sq. in., which is produced by the air pump on the engine clearly shown
at Fig. 210. A pressure gauge convenient to the operator indicates this
pressure, and a valve enables the operator to control it. No carburetor
is used. The gasoline flows from the tank through a shut-off valve near
the operator and through a tube leading through the hollow crank-shaft
to a spray nozzle located in the crank-case. There is no throttle valve,
and as each cylinder always receives the same amount of air as long as
the atmospheric pressure is the same, the output cannot be varied by
reducing the fuel supply, except within narrow limits. A fuel capacity
of 65 gallons is provided. The fuel consumption is at the rate of 12 U.
S. gallons per hour.
The high-tension magnetos, with double cam or two break per revolution
interrupter, is located on the thrust plate in an inverted position, and
is driven at such a speed as to produce nine sparks for every two
revolutions; that is, at 2-1/4 times engine speed. A Splitdorf magneto
is fitted. There is no distributor on the magneto. The high-tension
collector brush of the magneto is connected to a distributor brush
holder carried in the bearer plate of the engine. The brush in this
brush holder is pressed against a distributor ring of insulating
material molded in position in the web of a gear wheel keyed to the
thrust plate, which gear serves also for starting the engine by hand.
Molded in this ring of insulating material are nine brass contact
sectors, connecting with contact screws at the back side of the gear,
from which bare wires connect to the spark-plugs. The distributor
revolves at engine speed, instead of at half engine speed as on ordinary
engines, and the distributor brush is brought into electrical connection
with each spark-plug every time the piston in the cylinder in which this
spark-plug is located approaches the outer dead center. However, on the
exhaust stroke no spark is being generated in the magneto, hence none is
produced at the spark-plug.
[Illustration: Fig. 212.--The Gnome Engine Cam-Gear Case, a Fine Example
of Accurate Machine Work.]
Ordinarily the engine is started by turning on the propeller, but for
emergency purposes as in seaplanes or for a quick "get away" if landing
inadvertently in enemy territory, a hand starting crank is provided.
This is supported in bearings secured to the pressed steel carriers of
the engine and is provided with a universal joint between the two
supports so as to prevent binding of the crank in the bearings due to
possible distortion of the supports. The gear on this starting crank and
the one on the thrust plate with which it meshes are cut with helical
teeth of such hand that the starting pinion is thrown out of mesh as
soon as the engine picks up its cycle. A coiled spring surrounds part of
the shaft of the starting crank and holds it out of gear when not in
use.
[Illustration: Fig. 213.--G. V. Gnome "Monosoupape," with Cam-Case Cover
Removed to Show Cams and Valve-Operating Plungers with Roller Cam
Followers.]
Lubricating oil is carried in a tank of 25 gallon capacity, and if this
tank has to be placed in a low position it is connected with the
air-pressure line, so that the suction of the oil pump is not depended
upon to get the oil to the pump. From the bottom of the oil tank a pipe
leads to the pump inlet. There are two outlets from the pump, each
entering the hollow crank-shaft, and there is a branch from each outlet
pipe to a circulation indicator convenient to the operator. One of the
oil leads feeds to the housing in the thrust plate containing the two
rear ball bearings, and the other lead feeds through the crank-pin to
the cams, as already explained.
Owing to the effect of centrifugal force and the fact that the oil is
not used over again, the oil consumption of a revolving cylinder engine
is considerably higher than that of a stationary cylinder engine. Fuel
consumption is also somewhat higher, and for this reason the revolving
cylinder engine is not so well suited for types of airplanes designed
for long trips, as the increased weight of supplies required for such
trips, as compared with stationary cylinder type motors, more than
offsets the high weight efficiency of the engine itself. But for short
trips, and especially where high speed is required, as in single seated
scout and battle planes or "avions de chasse," as the French say, the
revolving cylinder engine has the advantage. The oil consumption of the
Gnome engine is as high as 2.4 gallon per hour. Castor oil is used for
lubrication because it is not cut by the gasoline mist present in the
engine interior as an oil of mineral derivation would be.
GERMAN "GNOME" TYPE ENGINE
[Illustration: Fig. 214.--The 50 Horse-Power Rotary Bayerischen Motoren
Gesellschaft Engine, a German Adaptation of the Early Gnome Design.]
A German adaptation of the Gnome design is shown at Fig. 214. This is
known as the Bayerischen Motoren Gesellschaft engine and the type shown
is an early design rated at 50 horse-power. The bore is 110 mm., the
stroke is 120 mm., and it is designed to run at a speed of 1,200 R. P.
M. It is somewhat similar in design to the early Gnome "valve-in-piston"
design except that two valves are carried in the piston top instead of
one. The valve operating arrangement is different also, as a single four
point cam is used to operate the seven exhaust valves. It is driven by
epicyclic gearing, the cam being driven by an internal gear machined
integrally with it, the cam being turned at 7/8 times the engine speed.
Another feature is the method of holding the cylinders on the
crank-case. The cylinder is provided with a flange that registers with a
corresponding member of the same diameter on the crank-case. A U
section, split clamping ring is bolted in place as shown, this holding
both flanges firmly together and keeping the cylinder firmly seated
against the crank-case flange. The "monosoupape" type has also been
copied and has received some application in Germany, but the most
successful German airplanes are powered with six-cylinder vertical
engines such as the Benz and Mercedes.
THE LE RHONE MOTOR
The Le Rhone motor is a radial revolving cylinder engine that has many
of the principles which are incorporated in the Gnome but which are
considered to be an improvement by many foreign aviators. Instead of
having but one valve in the cylinder head, as the latest type
"monosoupape" Gnome has, the Le Rhone has two valves, one for intake and
one for exhaust in each cylinder. By an ingenious rocker arm and tappet
rod arrangement it is possible to operate both valves with a single push
rod. Inlet pipes communicate with the crank-case at one end and direct
the fresh gas to the inlet valve cage at the other. Another peculiarity
in the design is the method of holding the cylinders in place. Instead
of having a vertically divided crank-case as the Gnome engine has and
clamping both halves of the case around the cylinders, the crank-case of
the Le Rhone engine is in the form of a cylinder having nine bosses
provided with threaded openings into which the cylinders are screwed. A
thread is provided at the base of each cylinder and when the cylinder
has been screwed down the proper amount it is prevented from further
rotation about its own axis by a substantial lock nut which screws down
against the threaded boss on the crank-case. The external appearance of
the Le Rhone type motor is clearly shown at Fig. 215, while the general
features of construction are clearly outlined in the sectional views
given at Figs. 216 and 217.
[Illustration: Fig. 215--Nine-Cylinder Revolving Le Rhone Type Aviation
Engine.]
[Illustration: Fig. 216.--Part Sectional Views of Le Rhone Rotary
Cylinder Engine, Showing Method of Cylinder Retention, Valve Operation
and Novel Crank Disc Assembly.]
[Illustration: Fig. 217.--Side Sectional View of Le Rhone Aviation
Engine.]
[Illustration: Fig. 218.--View Showing Le Rhone Valve Action and
Connecting Rod Big End Arrangement.]
The two main peculiarities of this motor are the method of valve
actuation by two large cams and the distinctive crank-shaft and
connecting rod big end construction. The connecting rods are provided
with "feet" or shoes on the end which fit into grooves lined with
bearing metal which are machined into crank discs revolving on ball
bearings and which are held together so that the connecting rod big ends
are sandwiched between them by clamping screws. This construction is a
modification of that used on the Anzani six-cylinder radial engine.
There are three grooves machined in each crank disc and three connecting
rod big ends run in each pair of grooves. The details of this
construction can be readily ascertained by reference to explanatory
diagrams at Figs. 218 and 219, A. Three of the rods which work in the
groove nearest the crank-pin are provided with short shoes as shown at
Fig. 219, B. The short shoes are used on the rods employed in cylinders
number 1, 4, and 7. The set of connecting rods that work in the central
grooves are provided with medium-length shoes and actuate the pistons in
cylinders numbers 3, 6, and 9. The three rods that work in the outside
grooves have still longer shoes and are employed in cylinders numbers 2,
5, and 8. The peculiar profile of the inlet and exhaust cam plates are
shown at C, Fig. 219, while the construction of the wrist-pin, wrist-pin
bushing and piston are clearly outlined at the sectional view at E. The
method of valve actuation is clearly outlined at Fig. 220, which shows
an end section through the cam case and also a partial side elevation
showing one of the valve operating levers which is fulcrumed at a
central point and which has a roller at one end bearing on one cam while
the roller or cam follower at the other end bears on the other cam. The
valve rocker arm actuating rod is, of course, operated by this simple
lever and is attached to it in such a way that it can be pulled down to
depress the inlet valve and pushed up to open the exhaust valve.
[Illustration: Fig. 219.--Diagrams Showing Important Components of Le
Rhone Motor.]
[Illustration: Fig. 220.--How the Cams of the Le Rhone Motor Can Operate
Two Valves with a Single Push Rod.]
A carburetor of peculiar construction is employed in the Le Rhone
engine, this being a very simple type as outlined at Fig. 221. It is
attached to the threaded end of the hollow crank-shaft by a right and
left coupling. The fuel is pumped to the spray nozzle, the opening in
which is controlled by a fuel regulating needle having a long taper
which is lifted out of the jet opening when the air-regulating slide is
moved. The amount of fuel supplied the carburetor is controlled by a
special needle valve fitting which combines a filter screen and which is
shown at B. In regulating the speed of the Le Rhone engine, there are
two possible means of controlling the mixture, one by altering the
position of the air-regulating slide, which also works the metering
needle in the jet, and the other by controlling the amount of fuel
supplied to the spray nozzle through the special fitting provided for
that purpose.
[Illustration: Fig. 221.--The Le Rhone Carburetor at A and Fuel Supply
Regulating Device at B.]
In considering the action of this engine one can refer to Fig. 222. The
crank O. M. is fixed, while the cylinders can turn about the crank-shaft
center O and the piston turns around the crank-pin M, because of the
eccentricity of the centers of rotation the piston will reciprocate in
the cylinders. This distance is at its maximum when the cylinder is
above O and at a minimum when it is above M, and the difference between
these two positions is equal to the stroke, which is twice the distance
of the crank-throw O, M. The explosion pressure resolves itself into the
force F exerted along the line of the connecting rod A, M, and also into
a force N, which tends to make the cylinders rotate around point O in
the direction of the arrow. An odd number of cylinders acting on one
crank-pin is desirable to secure equally spaced explosions, as the basic
action is the same as the Gnome engine.
[Illustration: Fig. 222.--Diagrams Showing Le Rhone Motor Action and
Firing Order.]
The magneto is driven by a gear having 36 teeth attached to crank-case
which meshes with 16-tooth pinion on armature. The magneto turns at 2.25
times crank-case speed. Two cams, one for inlet, one for exhaust, are
mounted on a carrying member and act on nine rocker arms which are
capable of giving a push-and-pull motion to the valve-actuating
rocker-operating rods. A gear driven by the crank-case meshes with a
larger member having internal teeth carried by the cam carrier. Each cam
has five profiles and is mounted in staggered relation to the other.
These give the nine fulcrumed levers the proper motion to open the inlet
and exhaust valves at the proper time. The cams are driven at 45/50 or
9/10 of the motor speed. The cylinder dimensions and timing follows; the
weight can be approximated by figuring 3 pounds per horse-power.
80 H.P. 105 M/M bore 4.20" bore.
140 M/M stroke 5.60" stroke.
110 H.P. 112 M/M bore 4.48" bore.
170 M/M stroke 6.80" stroke.
Timing--Intake valve opening, lag 18 deg.} 18 deg.}
Intake valve closing, lag 35 deg.} 35 deg.}
Exhaust valve opening, lead 55 deg.} 110 H.P. 45 deg.} 80 H.P.
Exhaust valve closing, lag 5 deg.} 5 deg.}
Ignition time advance 26 deg.} 26 deg.}
[Illustration: Fig. 223.--Diagram Showing Positions of Piston in Le
Rhone Rotary Cylinder Motor.]
THE RENAULT AIR-COOLED VEE ENGINE
[Illustration: Fig. 224.--Diagrams Showing Valve Timing of Le Rhone
Aviation Engine.]
[Illustration: Fig. 225.--Diagrams Showing How Cylinder Cooling is
Effected in Renault Vee Engines.]
Air-cooled stationary engines are rarely used in airplanes, but the
Renault Freres of France have for several years manufactured a complete
series of such engines of the general design shown at Fig. 225, ranging
from a low-powered one developed eight or nine years ago and rated at
40 and 50 horse-power, to later eight-cylinder models rated at 70
horse-power and a twelve-cylinder, or twin six, rated at 90 horse-power.
The cylinders are of cast iron and are furnished with numerous cooling
ribs which are cast integrally. The cylinder heads are separate
castings and are attached to the cylinder as in early motorcycle engine
practice, and serve to hold the cylinder in place on the aluminum alloy
crank-case by a cruciform yoke and four long hold-down bolts (Fig. 226).
The pistons are of cast steel and utilize piston rings of cast iron. The
valves are situated on the inner side of the cylinder head, the
arrangement being unconventional in that the exhaust valves are placed
above the inlet. The inlet valves seat in an extension of the combustion
head and are actuated by direct push rod and cam in the usual manner
while an overhead gear in which rockers are operated by push rods is
needed to actuate the exhaust valves. The valve action is clearly shown
in Figs. 226 and 227. The air stream by which the cylinders are cooled
is produced by a centrifugal or blower type fan of relatively large
diameter which is mounted on the end of a crank-shaft and the air blast
is delivered from this blower into an enclosed space between the
cylinder from which it escapes only after passing over the cooling fins.
In spite of the fact that considerable prejudice exists against
air-cooling fixed cylinder engines, the Renault has given very good
service in both England and France.
[Illustration: Fig. 226.--End Sectional View of Renault Air-Cooled
Aviation Engine.]
[Illustration: Fig. 227.--Side Sectional View of Renault Twelve-Cylinder
Air-Cooled Aviation Engine Crank-Case, Showing Use of Plain and Ball
Bearings for Crank-Shaft Support.]
As will be seen by the sectional view at Fig. 227, the steel crank-shaft
is carried in a combination of plain bearings inside the crank-case and
by ball bearings at the ends. Owing to air cooling, special precautions
are taken with the lubrication system, though the lubrication is not
forced or under high pressure. An oil pump of the gear-wheel type
delivers oil from the sump at the bottom of the crank-case to a chamber
above, from which the oil flows by gravity along suitable channels to
the various main bearings. It flows from the bearings into hollow rings
fastened to the crank-webs, and the oil thrown from the whirling
connecting rod big ends bathes the internal parts in an oil mist. In the
eight-cylinder designs ignition is effected by a magneto giving four
sparks per revolution and is accordingly driven at engine speed. In the
twelve-cylinder machine two magnetos of the ordinary revolving armature
or two-spark type, each supplying six cylinders, are fitted as outlined
at Fig. 228. The carburetor is a float feed form. Warm air is supplied
for Winter and damp weather by air pipes surrounding the exhaust pipes.
The normal speed of the Renault engine is 1,800 R. P. M., but as the
propeller is mounted upon an extension of the cam-shaft the normal
propeller speed is but half that of the engine, which makes it possible
to use a propeller of large diameter and high efficiency. Owing to the
air cooling, but low compression may be used, this being about 60 pounds
per square inch, which, of course, lowers the mean effective pressure
and makes the engine less efficient than water-cooled forms where it is
possible to use compression pressure of 100 or more pounds per square
inch. The 70 horse-power engine has cylinders with a bore of 3.78 inches
and a stroke of 5.52 inches. Its weight is given as 396 pounds, when in
running order, which figures 5.7 pounds per horse-power. The same
cylinder size is used on the twelve-cylinder 100 horse-power and the
stroke is the same. This engine in running order weighs 638 pounds,
which figures approximately 6.4 pounds per B. H. P.
[Illustration: Fig. 228.--End View of Renault Twelve-Cylinder Engine
Crank-Case, Showing Magneto Mounting.]
[Illustration: Fig. 229.--Diagram Outlining Renault Twelve-Cylinder
Engine Ignition System.]
SIMPLEX MODEL "A" HISPANO-SUIZA
The Model A is of the water-cooled four-cycle Vee type, with eight
cylinders, 4.7245 inch bore by 5.1182 inch stroke, piston displacement
718 cubic inches. At sea-level it develops 150 horse-power at 1,450 R.
P. M. It can be run successfully at much higher speeds, depending on
propeller design and gearing, developing proportionately increased
power. The weight, including carburetor, two magnetos, propeller hub,
starting magneto and crank, but without radiator, water or oil or
exhaust pipes, is 445 pounds. Average fuel consumption is .5 pound per
horse-power hour and the oil consumption at 1,450 R. P. M. is three
quarts per hour. The external appearance is shown at Fig. 230.
Four cylinders are contained in each block, which is of built-up
construction; the water jackets and valve ports are cast aluminum and
the individual cylinders heat-treated steel forgings threaded into the
bored holes of the aluminum castings. Each block after assembly is given
a number of protective coats of enamel, both inside and out, baked on.
Coats on the inside are applied under pressure. The pistons are aluminum
castings, ribbed. Connecting rods are tubular, of the forked type. One
rod bears directly on the crank-pin; the other rod has a bearing on the
outside of the one first mentioned.
The crank-shaft is of the five-bearing type, very short, stiff in
design, bored for lightness and for the oiling system. The crank-shaft
extension is tapered for the French standard propeller hub, which is
keyed and locked to the shaft. This makes possible instant change of
propellers. The case is in two halves divided on the center line of the
crank-shaft, the bearings being fitted between the upper and lower
sections. The lower half is deep, providing a large oil reservoir and
stiffening the engine. The upper half is simple and provides magneto
supports on extension ledges of the two main faces. The valves are of
large diameter with hollow stems, working in cast iron bushings. They
are directly operated by a single hollow cam-shaft located over the
valves. The cam-shafts are driven from the crank-shaft by vertical
shafts and bevel gears. The cam-shafts, cams and heads of the valve
stems are all enclosed in oil-tight removable housings of cast aluminum.
[Illustration: Fig. 230.--The Simplex Model A Hispano-Suiza Aviation
Engine, a Very Successful Form.]
Oiling is by a positive pressure system. The oil is taken through a
filter and steel tubes cast in the case to main bearings, through
crank-shaft to crank-pins. The fourth main bearing is also provided with
an oil lead from the system and through tubes running up the end of each
cylinder block, oil is provided for the cam-shafts, cams and bearings.
The surplus oil escapes through the end of the cam-shaft where the
driving gears are mounted, and with the oil that has gathered in the top
casing, descends through the drive shaft and gears to the sump.
Ignition is by two eight-cylinder magnetos firing two spark-plugs per
cylinder. The magnetos are driven from each of the two vertical shafts
by small bevel pinions meshing in bevel gears. The carburetor is mounted
between the two cylinder blocks and feeds the two blocks through
aluminum manifolds which are partly water-jacketed. The engine can be
equipped with a geared hand crank-starting device.
STURTEVANT MODEL 5A 140 HORSE-POWER ENGINE
These motors are of the eight-cylinder "V" type, four-stroke cycle,
water-cooled, having a bore of 4 inches and a stroke of 5-1/2 inches,
equivalent to 102 mm. x 140 mm. The normal operating speed of the
crank-shaft is 2,000 R. P. M. The propeller shaft is driven through
reducing gears which can be furnished in different gear ratios. The
standard ratio is 5:3, allowing a propeller speed of 1,200 R. P. M.
The construction of the motor is such as to permit of the application of
a direct drive. The change from the direct drive to gear drive, or vice
versa, can be accomplished in approximately one hour.
The cylinders are cast in pairs from an aluminum alloy and are provided
with steel sleeves, carefully fitted into each cylinder. A perfect
contact is secured between cylinder and sleeve; at the same time a
sleeve can be replaced without injury to the cylinder proper. No
difficulties due to expansion occur on account of the rapid transmission
of heat and the fact that the sleeve is always at higher temperature
than the cylinder. A moulded copper asbestos gasket is placed between
the cylinder and the head, permitting the cooling water to circulate
freely and at the same time insuring a tight joint. The cylinder heads
are cast in pairs from an aluminum alloy and contain ample water
passages for circulation of cooling water over the entire head. Trouble
due to hot valves is thereby eliminated, a most important consideration
in the operation of an aeroplane motor. The water jacket of the head
corresponds to the water jacket of the cylinders and large openings in
both allow the unobstructed circulation of the cooling water. The
cylinder heads and cylinders are both held to the base by six long
bolts. The valves are located in the cylinder heads and are mechanically
operated. The valves and valve springs are especially accessible and of
such size as to permit high volumetric efficiency. The valves are
constructed of hardened tungsten steel, the heads and stems being made
from one piece. The valve rocker arms located on the top of the cylinder
are provided with adjusting screws. A check nut enables the adjusting
screw to be securely locked in position, once the correct clearance has
been determined. The rocker arm bearings are adequately lubricated by a
compression grease cup. Cam-rollers are interposed between the cams and
the push rods in order to reduce the side thrust on the push rods.
A system of double springs is employed which greatly reduces the stress
on each spring and insures utmost reliability. A spring of extremely
large diameter returns the valve; a second spring located at the
cylinder base handles the push rod linkage. These springs, which operate
under low stress, are made from the best of steel and are given a
special double heat treatment. The pistons are made from a special
aluminum alloy; are deeply ribbed in the head for cooling and strength
and provided with two piston rings. These pistons are exceedingly light
weight in order to minimize vibration and prevent wear on the bearings.
The piston pin is made of chrome nickel steel, bored hollow and
hardened. It is allowed to turn, both in piston and connecting rod. The
piston rings are of special design, developed after years of
experimenting in aeronautical engines.
The connecting rods are of "H" section, machined all over from forgings
of a special air-hardening chrome nickel steel which, after being heat
treated has a tensile strength of 280,000 pounds per square inch. They
are consequently very strong and yet unusually light, and being machined
all over are of absolutely uniform section, which gives as nearly
perfect balance as can be obtained. The big ends are lined with white
metal and the small ends are bushed with phosphor bronze. The connecting
rods are all alike and take their bearings side by side on the
crank-pin, the cylinders being offset to permit of this arrangement. The
crank-shaft is machined from the highest grade chrome nickel steel, heat
treated in order to obtain the best properties of this material. It is
2-1/4 inches in diameter (57 mm.) and bored hollow throughout, insuring
maximum strength with minimum weight. It is carried in three large,
bronze-backed white metal bearings. A new method of producing these
bearings insures a perfect bond between the two metals and eliminates
breakage.
The base is cast from an aluminum alloy. Great strength and rigidity is
combined with light weight. The sides extend considerably below the
center line of the crank-shaft, providing an extremely deep section. At
all highly stressed points, deep ribs are provided to distribute the
load evenly and eliminate bending. The lower half of the base is of cast
aluminum alloy of extreme lightness. This collects the lubricating oil
and acts as a small reservoir for same. An oil-filtering screen of large
area covers the entire surface of the sump. The propeller shaft is
carried on two large annular ball bearings driven from the crank-shaft
by hardened chrome nickel steel spur gears. These gears are contained
within an oil-tight casing integral with the base on the opposite end
from the timing gears. A ball-thrust bearing is provided on the
propeller shaft to take the thrust of a propeller or tractor, as the
case may be. In case of the direct drive a stub shaft is fastened direct
to the crank-shaft and is fitted with a double thrust bearing.
The cam-shaft is contained within the upper half of the base between the
two groups of cylinders, and is supported in six bronze bearings. It is
bored hollow throughout and the cams are formed integral with the shaft
and ground to the proper shape and finish. An important development in
the shape of cams has resulted in a maintained increase of power at high
speeds. The gears operating the cam-shaft, magneto, oil and water pumps
are contained within an oil-tight casing and operate in a bath of oil.
Lubrication is of the complete forced circulating system, the oil being
supplied to every bearing under high pressure by a rotary pump of large
capacity. This is operated by gears from the crank-shaft. The oil
passages from the pump to the main bearings are cast integral with the
base, the hollow crank-shaft forming a passage through the connecting
rod bearings and the hollow cam-shaft distributing the oil to the
cam-shaft bearings. The entire surface of the lower half of the base is
covered with a fine mesh screen through which the oil passes before
reaching the pump. Approximately one gallon of oil is contained within
the base and this is continually circulated through an external tank by
a secondary pump operated by an eccentric on the cam-shaft. This also
draws fresh oil from the external tank which can be made of any desired
capacity.
SPECIFICATIONS--MODEL 5A TYPE 8
Horse-power rating, 140 at 2,000 R. P. M.
Bore, 4 inches = 102 mm.
Stroke, 5-1/2 inches = 140 mm.
Number of cylinders, 8.
Arrangement of cylinders, "V."
Cooling, water. Circulation by centrifugal pump.
Cycle, four stroke.
Ignition (double), 2 Bosch or Splitdorf magnetos.
Carburetor, Zenith duplex. Water jacket manifold.
Oiling system, complete forced. Circulating gear pump.
Normal crank-shaft speed, 2,000 R. P. M.
Propeller shaft, 3/5 crank-shaft speed at normal, 1,200 R. P. M.
Stated power at 30" barometer, 140 B. H. P.
Stated weight with all accessories but without water, gasoline or oil,
514 pounds = 234 kilos.
Weight per B. H. P., 3.7 pounds = 1.68 kilos.
Stated weight with all accessories with water, 550 pounds = 250 kilos.
Weight per B. H. P. with water, 3.95 pounds = 1.79 kilos.
THE CURTISS AVIATION MOTORS
The Curtiss OX motor has eight cylinders, 4-inch bore, 5-inch stroke,
delivers 90 horse-power at 1,400 turns, and the weight turns out at 4.17
pounds per horse-power. This motor has cast iron cylinders with monel
metal jackets, overhead inclined valves operated by means of two rocker
arms, push-and-pull rods from the central cam-shaft located in the
crank-case. The cam and push rod design is extremely ingenious and the
whole valve construction turns out very light. This motor is an
evolution from the early Curtiss type motor which was used by Glenn
Curtiss when he won the Gordon Bennett Cup at Rheims. A slightly larger
edition of this type motor is the OXX-5, as shown at Figs. 231 and 232,
which has cylinders 4-1/4 inches by 5 inches, delivers 100 horse-power
at 1,400 turns and has the same fuel and oil consumption as the OX type
motor, namely, .60 pound of fuel per brake horse-power hour and .03
pound of lubricating oil per brake horse-power hour.
[Illustration: Fig. 231.--The Curtiss OXX-5 Aviation Engine is an
Eight-Cylinder Type Largely Used on Training Machines.]
The Curtiss Company have developed in the last two years a larger-sized
motor now known as the V-2, which was originally rated at 160
horse-power and which has since been refined and improved so that the
motor gives 220 horse-power at 1,400 turns, with a fuel consumption of
52/100 of a pound per brake horse-power hour and an oil consumption of
.02 of a pound per brake horse-power hour. This larger motor has a
weight of 3.45 pounds per horse-power and is now said to be giving very
satisfactory service. The V-2 motor has drawn steel cylinders, with a
bore of 5 inches and a stroke of 7 inches, with a steel water jacket top
and a monel metal cylindrical jacket, both of which are brazed on to the
cylinder barrel itself. Both these motors use side by side connecting
rods and fully forced lubrication. The cam-shafts act as a gallery from
which the oil is distributed to the cam-shaft bearings, the main
crank-shaft bearings, and the gearing. Here again we find extremely
short rods, which, as before mentioned, enables the height and the
consequent weight of construction to be very much reduced. For ordinary
flying at altitudes of 5,000 to 6,000 feet, the motors are sent out with
an aluminum liner, bolted between the cylinder and the crank-case in
order to give a compression ratio which does not result in pre-ignition
at a low altitude. For high flying, however, these aluminum liners are
taken out and the compression volume is decreased to about 18.6 per
cent. of the total volume.
[Illustration: Fig. 232.--Top and Bottom Views of the Curtiss OXX-5 100
Horse-Power Aviation Engine.]
The Curtiss Aeroplane Company announces that it has recently built, and
is offering, a twelve-cylinder 5" x 7" motor, which was designed for
aeronautical uses primarily. This engine is rated at 250 horse-power,
but it is claimed to develop 300 at 1,400 R. P. M. Weights--Motor, 1,125
pounds; radiator, 120 pounds; cooling water, 100 pounds; propeller, 95
pounds.
Gasoline Consumption per Horse-power Hour, 6/10 pounds.
Oil Consumption per Hour at Maximum Speed--2 pints.
Installation Dimensions--Overall length, 84-5/8 inches; overall width,
34-1/8 inches; overall depth, 40 inches; width at bed, 30-1/2 inches;
height from bed, 21-1/8 inches; depth from bed, 18-1/2 inches.
THOMAS-MORSE MODEL 88 ENGINE
The Thomas-Morse Aircraft Corporation of Ithaca, N. Y., has produced a
new engine, Model 88, bearing a close resemblance to the earlier model.
The main features of that model have been retained; in fact, many parts
are interchangeable in the two engines. Supported by the great
development in the wide use of aluminum, the Thomas engineers have
adopted this material for cylinder construction, which adoption forms
the main departure from previous accepted design.
The marked tendency to-day toward a higher speed of rotation has been
conclusively justified, in the opinion of the Thomas engineers, by the
continued reliable performance of engines with crank-shafts operating at
speeds near 2,000 revolutions per minute, driving the propeller through
suitable gearing at the most efficient speed. High speed demands that
the closest attention be paid to the design of reciprocating and
rotating parts and their adjacent units. Steel of the highest
obtainable tensile strength must be used for connecting rods and piston
pins, that they may be light and yet retain a sufficient factor of
safety. Piston design is likewise subjected to the same strict scrutiny.
At the present day, aluminum alloy pistons operate so satisfactorily
that they may be said to have come to stay.
The statement often made in the past, that the gearing down of an engine
costs more in the weight of reduction gears and propeller shaft than is
warranted by the increase in horse-power, is seldom heard to-day.
The mean effective pressure remaining the same, the brake horse-power of
any engine increases as the speed. That is, an engine delivering 100
brake horse-power at 1,500 revolutions per minute will show 133 brake
horse-power at 2,000 revolutions per minute, an increase of 33 brake
horse-power. To utilize this increase in horse-power, a matter of some
fifteen pounds must be spent in gearing and another fifteen perhaps on
larger valves, bearings, etc. Two per cent. may be assumed lost in the
gears. In other words, the increase in horse-power due to increasing the
speed has been attained at the expense of about one pound per brake
horse-power.
The advantages of the eight-cylinder engine over the six and twelve,
briefly stated, are: lower weight per horse-power, shorter length,
simpler and stiffer crank-shaft, cam-shaft and crank-case, and simpler
and more direct manifold arrangement. As to torque, the eight is
superior to the six, and yet in practice not enough inferior to the
twelve to warrant the addition of four more cylinders. It must, however,
be recognized that the eight is subject to the action of inherent
unbalanced inertia couples, which set up horizontal vibrations,
impossible of total elimination. These vibrations are functions of the
reciprocating weights, which, as already mentioned, are cut down to the
minimum. Vibrations due to the elasticity of crank-case, crank-shaft,
etc., can be and are reduced in the Thomas engine to minor quantities by
ample webbing of the crank-case and judicious use of metal elsewhere.
All things considered, there is actually so little difference to be
discerned between the balance of a properly designed eight-cylinder
engine and that of a six or twelve as to make a discussion of the pros
and cons more one of theory than of practice.
The main criticisms of the L head cylinder engine are that it is less
efficient and heavier. This is granted, as it relates to cylinders
alone. More thorough investigation, however, based on the main
desideratum, weight-power ratio, leads us to other conclusions,
particularly with reference to high speed engines. The valve gear must
not be forgotten. A cylinder cannot be taken completely away from its
component parts and judged, as to its weight value, by itself alone. A
part away from the whole becomes an item unimportant in comparison with
the whole. The valve gear of a high speed engine is a too often
overlooked feature. The stamp of approval has been made by high speed
automobile practice upon the overhead cam-shaft drive, with valves in
the cylinder head operated direct from the cam-shaft or by means of
valve lifters or short rockers.
The overhead cam-shaft mechanism applied to an eight-cylinder engine
calls for two separate cam-shafts carried above and supported by the
cylinders in an oil-tight housing, and driven by a series of spur gears
or bevels from the crank-shaft. It is patent that this valve gearing is
heavy and complicated in comparison with the simple moving valve units
of the L head engine, which are operated from one single cam-shaft,
housed rigidly in the crank-case. The inherently lower volumetric
efficiency of the L head engine is largely overcome by the use of a
properly designed head, large valves and ample gas passages. Again, the
customary use of a dual ignition system gives to the L head a relatively
better opportunity for the advantageous placing of spark-plugs, in order
that better flame propagation and complete combustion may be secured.
[Illustration: Fig. 233.--End View of Thomas-Morse 150 Horse-Power
Aluminum Cylinder Aviation Motor Having Detachable Cylinder Heads.]
The Thomas Model 88 engine is 4-1/8 inch bore and 5-1/2 inch stroke. The
cylinders and cylinder heads are of aluminum, and as steel liners are
used in the cylinders the pistons are also made of aluminum. This engine
is actually lighter than the earlier model of less power. It weighs but
525 pounds, with self-starter. The general features of design can be
readily ascertained by study of the illustrations: Fig. 233, which shows
an end view; Fig. 234, which is a side view, and Fig. 235, which
outlines the reduction gear-case and the propeller shaft supporting
bearings.
[Illustration: Fig. 234.--Side View of Thomas-Morse High Speed 150
Horse-Power Aviation Motor with Geared Down Propeller Drive.]
SIXTEEN-VALVE DUESENBERG ENGINE
[Illustration: Fig. 235.--The Reduction Gear-Case of Thomas-Morse 150
Horse-Power Aviation Motor, Showing Ball Bearing and Propeller Drive
Shaft Gear.]
This engine is a four-cylinder, 4-3/4" x 7", 125 horse-power at 2,100 R.
P. M. of the crank-shaft and 1,210 R. P. M. of the propeller. Motors are
sold on above rating; actual power tests prove this motor capable of
developing 140 horse-power at 2,100 R. P. M. of the motor. The exact
weight with magneto, carburetor, gear reduction and propeller hub, as
illustrated, 509 pounds; without gear reduction, 436 pounds. This motor
has been produced as a power plant weighing 3.5 pounds per horse-power,
yet nothing has been sacrificed in rigidity and strength. At its normal
speed it develops 1 horse-power for every 3.5 cubic inches piston
displacement. Cylinders are semi-steel, with aluminum plates enclosing
water jackets. Pistons specially ribbed and made of Magnalite aluminum
compound. Piston rings are special Duesenberg design, being three-piece
rings. Valves are tungsten steel, 1-15/16" inlets and 2" exhausts, two
of each to each cylinder. Arranged horizontally in the head, allowing
very thorough water-jacketing. Inlet valves in cages. Exhaust valves,
seating directly in the cylinder head, are removable through the inlet
valve holes. Valve stems lubricated by splash in the valve action
covers. Valve rocker arms forged with cap screw and nut at upper end to
adjust clearance. Entirely enclosed by aluminum housing, as is entire
valve mechanism. Connecting rods are tubular, chrome nickel steel, light
and strong. Crank-shaft is one-piece forging, hollow bored, 2-1/2-inch
diameter at main bearings. Connecting rod bearings, 2-1/4-inch diameter,
3 inches long. Front main bearing, 3-1/2 inches long; intermediate main
bearing, 3-1/2 inches long; rear main bearing, 4 inches long. Crank-case
of aluminum, barrel type, oil pan on bottom removable. Hand hole plates
on both sides. Strongly webbed.
The oiling system of this sixteen-valve Duesenberg motor is one of its
vital features. An oil pump located in the base and submerged in oil
forces oil through cored passages to the three main bearings, then
through tubes under each connecting rod into which the rod dips. The oil
is thrown off from these and lubricates every part of the motor. This
constitutes the main oiling system; it is supplemented by a splash
system, there being a trough under each connecting rod into which the
rod slips. The oil is returned to the main supply sump by gravity, where
it is strained and re-used. Either system is in itself sufficient to
operate the motor. A pressure gauge is mounted for observation on a
convenient part of the system. A pressure of approximately 25 pounds is
maintained by the pressure system, which insures efficient lubrication
at all speeds of the motor. The troughs under the connecting rods are so
constructed that no matter what the angle of flight may be, oil is
retained in each individual trough so that each connecting rod can dip
up its supply of oil at each revolution.
AEROMARINE SIX-CYLINDER VERTICAL MOTOR
[Illustration: Fig. 236.--The Six-Cylinder Aeromarine Engine.]
These motors are four-stroke cycle, six-cylinder vertical type, with
cylinder 4-5/16" bore by 5-1/8" stroke. The general appearance of this
motor is shown in illustration at Fig. 236. This engine is rated at
85-90 horse-power. All reciprocating and revolving parts of this motor
are made of the highest grades of steel obtainable as are the studs,
nuts and bolts. The upper and lower parts of crank-case are made of
composition aluminum casting. Lower crank-case is made of high grade
aluminum composition casting and is bolted directly to the upper half.
The oil reservoir in this lower half casting provides sufficient oil
capacity for five hours' continuous running at full power. Increased
capacity can be provided if needed to meet greater endurance
requirements. Oil is forced under pressure to all bearings by means of
high-pressured duplex-geared pumps. One side of this pump delivers oil
under pressure to all the bearings, while the other side draws the oil
from the splash case and delivers it to the main sump. The oil reservoir
is entirely separate from the crank-case chamber. Under no circumstances
will oil flood the cylinder, and the oiling system is not affected in
any way by any angle of flight or position of motor. An oil pressure
gauge is placed on instrument board of machine, which gives at all
times the pressure in oil system, and a sight glass at lower half of
case indicates the amount of oil contained. The oil pump is external on
magneto end of motor, and is very accessible. An external oil strainer
is provided, which is removable in a few minutes' time without the loss
of any oil. All oil from reservoir to the motor passes through this
strainer. Pressure gauge feed is also attached and can be piped to any
part of machine desired.
The cylinders are made of high-grade castings and are machined and
ground accurately to size. Cylinders are bolted to crank-case with
chrome nickel steel studs and nuts which securely lock cylinder to upper
half of crank-case. The main retaining cylinder studs go through
crank-case and support crank-shaft bearings so that crank-shaft and
cylinders are tied together as one unit. Water jackets are of copper,
1/16" thick, electrically deposited. This makes a non-corrosive metal.
Cooling is furnished by a centrifugal pump, which delivers 25 gallons
per minute at 1,400 R. P. M. Pistons are made cast iron, accurately
machined and ground to exact dimensions, which are carefully balanced.
Piston rings are semi-steel rings of Aeromarine special design.
Connecting rods are of chrome nickel steel, H-section. Crank-shaft is
made of chrome nickel steel, machined all over, and cut from solid
billet, and is accurately balanced through the medium of balance weights
being forged integral with crank. It is drilled for lightness and
plugged for force feed lubrication. There are seven main bearings to
crank-shaft. All bearings are of high-grade babbitt, die cast, and are
interchangeable and easily replaced. The main bearings of the
crank-shaft are provided with a single groove to take oil under pressure
from pressure tube which is cast integral with case. Connecting rod
bearings are of the same type. The gudgeon pin is hardened, ground and
secured in connecting rod, and is allowed to work in piston. Cam-shaft
is of steel, with cams forged integral, drilled for lightness and
forced-feed lubrication, and is case-hardened. The bearings of
cam-shaft are of bronze. Magneto, two high-tension Bosch D. U. 6. The
intake manifold for carburetors are aluminum castings and are so
designed that each carburetor feeds three cylinders, thereby insuring
easy flow of vapor at all speeds. Weight, 420 pounds.
[Illustration: Fig. 237.--The Wisconsin Aviation Engine, at Top, as
Viewed from Carburetor Side. Below, the Exhaust Side.]
WISCONSIN AVIATION ENGINES
[Illustration: Fig. 238.--Dimensioned End Elevation of Wisconsin Six
Motor.]
The new six-cylinder Wisconsin aviation engines, one of which is shown
at Fig. 237, are of the vertical type, with cylinders in pairs and
valves in the head. Dimensioned drawings of the six-cylinder vertical
type are given at Figs. 238 and 239. The cylinders are made of aluminum
alloy castings, are bored and machined and then fitted with hardened
steel sleeves about 1/16 inch in thickness. After these sleeves have
been shrunk into the cylinders, they are finished by grinding in place.
Gray iron valve seats are cast into the cylinders. The valve seats and
cylinders, as well as the valve ports, are entirely surrounded by water
jackets. The valves set in the heads at an angle of 25 deg. from the
vertical, are made of tungsten steel and are provided with double
springs, the outer or main spring and the inner or auxiliary spring,
which is used as a precautionary measure to prevent a valve falling into
the cylinder in remote case of a main spring breaking. The cam-shaft is
made of one solid forging, case-hardened. It is carried in an aluminum
housing bolted to the top of the cylinders. This housing is split
horizontally, the upper half carrying the chrome vanadium steel rocker
levers. The lower half has an oil return trough cast integral, into
which the excess oil overflows and then drains back to the crank-case.
Small inspection plates are fitted over the cams and inner ends of the
cam rocker levers. The cam-shaft runs in bronze bearings and the drive
is through vertical shaft and bevel gears.
[Illustration: Fig. 239.--Dimensioned Side Elevation of Wisconsin Six
Motor.]
The crank-case is made of aluminum, the upper half carrying the
bearings for the crank-shaft. The lower half carries the oil sump in
which all of the oil except that circulating through the system at the
time is carried. The crank-shaft is made of chrome vanadium steel of an
elastic limit of 115,000 pounds. The crank-pins and ends of the shaft
are drilled for lightness and the cheeks are also drilled for oil
circulation. The crank-shaft runs in bronze-backed, Fahrig metal-lined
bearings, four in number. A double thrust bearing is also provided, so
that the motor may be used either in a tractor or pusher type of
machine. Outside of the thrust bearing an annular ball bearing is used
to take the radial load of the propeller. The propeller is mounted on a
taper. At the opposite end of the shaft a bevel gear is fitted which
drives the cam-shaft, through a vertical shaft, and also drives the
water and oil pumps and magnetos. All gears are made of chrome vanadium
steel, heat-treated.
The connecting rods are tubular and machined from chrome vanadium steel
forgings. Oil tubes are fitted to the rods which carry the oil up to the
wrist-pins and pistons. The rods complete with bushings weigh 5-1/2
pounds each. The pistons are made of aluminum alloy and are very light
and strong, weighing only 2 pounds 2 ounces each. Two leak-proof rings
are fitted to each piston. The wrist-pins are hollow, of hardened steel,
and are free to turn either in the piston or the rod. A bronze bushing
is fitted in the upper end of the rod, but no bushing is fitted in the
pistons, the hardened steel wrist-pins making an excellent bearing in
the aluminum alloy.
[Illustration: Fig. 240.--Power, Torque and Efficiency Curves of
Wisconsin Aviation Motor.]
The water circulation is by centrifugal pump, which is mounted at the
lower end of the vertical shaft. The water is pumped through brass pipes
to the lower end of the cylinder water jackets and leaves the upper end
of the jackets just above the exhaust valves. The lubricating system is
one of the main features of the engines, being designed to work with the
motor at any angle. The oil is carried in the sump, from where it is
taken by the oil circulating pump through a strainer and forced through
a header, extending the full length of the crank-case, and distributed
to the main bearings. From the main bearings it is forced through the
hollow crank-shaft to the connecting rod big ends and then through
tubes on the rods to wrist-pins and pistons. Another lead takes oil from
the main header to the cam-shaft bearings. The oil forced out of the
ends of the cam-shaft bearings fills pockets under the cams and in the
cam rocker levers. The excess flows back through pipes and through the
train of gears to the crank-case. A strainer is fitted at each end of
the crank-case, through which the oil is drawn by separate pumps and
returned to the sump. Either one of these pumps is large enough to take
care of all of the return oil, so that the operation is perfect whether
the motor is inclined up or down. No splash is used in the crank-case,
the system being a full force feed. An oil level indicator is provided,
showing the amount of oil in the sump at all times. The oil pressure in
these motors is carried at ten pounds, a relief valve being fitted to
hold the pressure constant.
[Illustration: Fig. 241.--Timing Diagram, Wisconsin Aviation Engine.]
Ignition is by two Bosch magnetos, each on a separate set of plugs fired
simultaneously on opposite sides of the cylinders. Should one magneto
fail, the other would still run the engine at only a slight loss in
power. The Zenith double carburetor is used, three cylinders being
supplied by each carburetor. This insures a higher volumetric
efficiency, which means more power, as there is no overlapping of inlet
valves whatever by this arrangement. All parts of these motors are very
accessible. The water and oil pumps, carburetors, magnetos, oil strainer
or other parts can be removed without disturbing other parts. The lower
crank-case can be removed for inspection or adjustment of bearings, as
the crank-shaft and bearing caps are carried by the upper half. The
motor supporting lugs are also part of the upper crank-case.
The six-cylinder motor, without carburetors or magnetos, weighs 547
pounds. With carburetor and magnetos, the weight is 600 pounds. The
weight of cooling water in the motor is 38 pounds. The sump will carry 4
gallons of oil, or about 28 pounds. A radiator can be furnished suitable
for the motor, weighing 50 pounds. This radiator will hold 3 gallons of
water or about 25 pounds. The motor will drive a two-blade, 8 feet
diameter by 6.25 feet pitch Paragon propeller 1400 revolutions per
minute, developing 148 horse-power. The weight of this propeller is 42
pounds. This makes a total weight of motor, complete with propeller,
radiator filled with water, but without lubricating oil, 755 pounds, or
about 5.1 pounds per horse-power for complete power plant. The fuel
consumption is .5 pound per horse-power per hour. The lubricating oil
consumption is .0175 pound per horse-power per hour, or a total of 2.6
pounds per hour at 1400 revolutions per minute. This would make the
weight of fuel and oil, per hour's run at full power at 1400 revolutions
per minute, 76.6 pounds.
PRINCIPAL DIMENSIONS
Following are the principal dimensions of the six-cylinder motor:
Bore 5 inches.
Stroke 6-1/2 inches.
Crank-shaft diameter throughout 2 inches.
Length of crank-pin and main bearings 3-1/2 inches.
Diameter of valves 3 inches (2-3/4 inches clear).
Lift of valves 1/2 inch.
Volume of compression space 22 per cent. of total.
Diameter of wrist-pins 1-3/16 inches.
Firing order 1-4-2-6-3-5.
The horse-power developed at 1200 revolutions per minute is 130, at 1300
revolutions per minute 140, at 1400 revolutions per minute 148. 1400 is
the maximum speed at which it is recommended to run these motors.
TWELVE-CYLINDER ENGINE
A twelve-cylinder V-type engine illustrated, is also being built by this
company, similar in dimensions of cylinders to the six. The principal
differences being in the drive to cam-shaft, which is through spur gears
instead of bevel. A hinged type of connecting rod is used which does not
increase the length of the motor and, at the same time, this
construction provides for ample bearings. A double centrifugal water
pump is provided for this motor, so as to distribute the water uniformly
to both sets of cylinders. Four magnetos are used, two for each set of
six cylinders. The magnetos are very accessibly located on a bracket on
the spur gear cover. The carburetors are located on the outside of the
motors, where they are very accessible, while the exhaust is in the
center of the valley. The crank-shaft on the twelve is 2-1/2 inches in
diameter and the shaft is bored to reduce weight. Dimensioned drawings
of the twelve-cylinder engine are given at Figs. 242 and 243 and should
prove useful for purposes of comparison with other motors.
HALL-SCOTT AVIATION ENGINES
The following specifications of the Hall-Scott "Big Four" engines apply
just as well to the six-cylinder vertical types which are practically
the same in construction except for the structural changes necessary to
accommodate the two extra cylinders. Cylinders are cast separately from
a special mixture of semi-steel, having cylinder head with valve seats
integral. Special attention has been given to the design of the water
jacket around the valves and head, there being two inches of water space
above same. The cylinder is annealed, rough machined, then the inner
cylinder wall and valve seats ground to mirror finish. This adds to the
durability of the cylinder, and diminishes a great deal of the excess
friction.
[Illustration: Fig. 242.--Dimensioned End View of Wisconsin
Twelve-Cylinder Airplane Motor.]
Great care is taken in the casting and machining of these cylinders, to
have the bore and walls concentric with each other. Small ribs are cast
between outer and inner walls to assist cooling as well as to transfer
stresses direct from the explosion to hold-down bolts which run from
steel main bearing caps to top of cylinders. The cylinders are machined
upon the sides so that when assembled on the crank-case with grooved
hold-down washers tightened, they form a solid block, greatly assisting
the rigidity of crank-case.
[Illustration: Fig. 243.--Dimensioned Side Elevation of Wisconsin
Twelve-Cylinder Airplane Motor.]
The connecting rods are very light, being of the I beam type, milled
from a solid Chrome nickel die forging. The caps are held on by two
1/2"-20 thread Chrome nickel through bolts. The rods are first roughed
out, then annealed. Holes are drilled, after which the rods are hardened
and holes ground parallel with each other. The piston end is fitted with
a gun metal bushing, while the crank-pin end carries two bronze serrated
shells, which are tinned and babbitted hot, being broached to harden the
babbitt. Between the cap and rod proper are placed laminated shims for
adjustment. Crank-cases are cast of the best aluminum alloy, hand
scraped and sand blasted inside and out. The lower oil case can be
removed without breaking any connections, so that the connecting rods
and other working parts can readily be inspected. An extremely large
strainer and dirt trap is located in the center and lowest point of the
case, which is easily removed from the outside without disturbing the
oil pump or any working parts. A Zenith carburetor is provided.
Automatic valves and springs are absent, making the adjustment simple
and efficient. This carburetor is not affected by altitude to any
appreciable extent. A Hall-Scott device, covered by U. S. Patent No.
1,078,919, allows the oil to be taken direct from the crank-case and run
around the carburetor manifold, which assists carburetion as well as
reduces crank-case heat. Two waterproof four-cylinder Splitdorf "Dixie"
magnetos are provided. Both magneto interruptors are connected to a rock
shaft integral with the motor, making outside connections unnecessary.
It is worthy of note that with this independent double magneto system,
one complete magneto can become inoperative, and still the motor will
run and continue to give good power.
The pistons as provided in the A-7 engines are cast from a mixture of
steel and gray iron. These are extremely light, yet provided with six
deep ribs under the arch head, greatly aiding the cooling of the piston
as well as strengthening it. The piston pin bosses are located very low
in order to keep the heat from the piston head away from the upper end
of the connecting rod, as well as to arrange them at the point where the
piston fits the cylinder best. Three 1/4" rings are carried. The pistons
as provided in the A-7a engines are cast from aluminum alloy. Four 1/4"
rings are carried. In both piston types a large diameter, heat treated,
Chrome nickel steel wrist-pin is provided, assembled in such a way as to
assist the circular rib between the wrist-pin bosses to keep the piston
from being distorted from the explosions.
The oiling system is known as the high pressure type, oil being forced
to the under side of the main bearings with from 5 to 30 points
pressure. This system is not affected by extreme angles obtained in
flying, or whether the motor is used for push or pull machines. A large
gear pump is located in the lowest point of the oil sump, and being
submerged at all times with oil, does away with troublesome stuffing
boxes and check valves. The oil is first drawn from the strainer in oil
sump to the long jacket around the intake manifold, then forced to the
main distributor pipe in crank-case, which leads to all main bearings. A
bi-pass, located at one end of the distributor pipe, can be regulated to
provide any pressure required, the surplus oil being returned to the
case. A special feature of this system is the dirt, water and sediment
trap, located at the bottom of the oil sump. This can be removed without
disturbing or dismantling the oil pump or any oil pipes. A small oil
pressure gauge is provided, which can be run to the aviator's instrument
board. This registers the oil pressure, and also determines its
circulation.
The cooling of this motor is accomplished by the oil as well as the
water, this being covered by patent No. 1,078,919. This is accomplished
by circulating the oil around a long intake manifold jacket; the
carburetion of gasoline cools this regardless of weather conditions.
Crank-case heat is therefore kept at a minimum. The uniform temperature
of the cylinders is maintained by the use of ingenious internal outlet
pipes, running through the head of each of the six-cylinders, rubber
hose connections being used so that any one of the cylinders may be
removed without disturbing the others. Slots are cut in these pipes so
that cooler water is drawn directly around the exhaust valves. Extra
large water jackets are provided upon the cylinders, two inches of water
space is left above the valves and cylinder head. The water is
circulated by a large centrifugal pump insuring ample circulation at all
speeds.
The crank-shaft is of the five bearing type, being machined from a
special heat treated drop forging of the highest grade nickel steel. The
forging is first drilled, then roughed out. After this the shaft is
straightened, turned down to a grinding size, then ground accurately to
size. The bearing surfaces are of extremely large size, over-size,
considering general practice in the building of high speed engines of
similar bore and stroke. The crank-shaft bearings are 2" in diameter by
1-15/16" long, excepting the rear main bearing, which is 4-3/8" long,
and front main bearing, which is 2-3/16" long. Steel oil scuppers are
pinned and sweated onto the webs of the shaft, which allows of properly
oiling the connecting rod bearings. Two thrust bearings are installed on
the propeller end of the shaft, one for pull and the other for push. The
propeller is driven by the crank-shaft flange, which is securely held in
place upon the shaft by six keys. These drive an outside propeller
flange, the propeller being clamped between them by six through bolts.
The flange is fitted to a long taper on crank-shaft. This enables the
propeller to be removed without disturbing the bolts. Timing gears and
starting ratchets are bolted to a flange turned integral with shaft.
The cam-shaft is of the one piece type, air pump eccentric, and gear
flange being integral. It is made from a low carbon specially heat
treated nickel forging, is first roughed out and drilled entire length;
the cams are then formed, after which it is case hardened and ground to
size. The cam-shaft bearings are extra long, made from Parson's White
Brass. A small clutch is milled in gear end of shaft to drive revolution
indicator. The cam-shaft is enclosed in an aluminum housing bolted
directly on top of all six cylinders, being driven by a vertical shaft
in connection with bevel gears. This shaft, in conjunction with rocker
arms, rollers and other working parts, are oiled by forcing the oil into
end of shaft, using same as a distributor, allowing the surplus supply
to flow back into the crank-case through hollow vertical tube. This
supply oils the magneto and pump gears. Extremely large Tungsten valves,
being one-half the cylinder diameter, are seated in the cylinder heads.
Large diameter oil tempered springs held in tool steel cups, locked with
a key, are provided. The ports are very large and short, being designed
to allow the gases to enter and exhaust with the least possible
resistance. These valves are operated by overhead one piece cam-shaft in
connection with short Chrome nickel rocker arms. These arms have
hardened tool steel rollers on cam end with hardened tool steel
adjusting screws opposite. This construction allows accurate valve
timing at all speeds with least possible weight.
CENSORED
GERMAN AIRPLANE MOTORS
In a paper on "Aviation Motors," presented by E. H. Sherbondy before the
Cleveland section of the S. A. E. in June, 1917, the Mercedes and Benz
airplane motor is discussed in some detail and portions of the
description follow.
[Illustration: Fig. 244.--Side and End Sectional Views of Four-Cylinder
Argus Engine, a German 100 Horse-Power Design Having Bore and Stroke of
140 mm., or 5.60 inches, and Developing Its Power at 1,368 R.P.M.
Weight, 350 Pounds.]
MERCEDES MOTOR
The 150 horse-power six-cylinder Mercedes motor is 140 millimeters bore
and 160 millimeters stroke. The Mercedes company started with
smaller-sized cylinders, namely 100 millimeters bore and 140 millimeters
stroke, six-cylinders. The principal features of the design are forged
steel cylinders with forged steel elbows for gas passages, pressed steel
water jackets, which when welded together forms the cylinder
assembly, the use of inclined overhead valves operated by means of an
overhead cam-shaft through rocker arms which multiply with the motion of
the cam. By the use of steel cylinders, not only is the weight greatly
reduced, but certain freedom from distortion through unequal sections,
leaks and cracks are entirely avoided. The construction is necessarily
very expensive. It is certainly a sound job. In the details of this
construction there are a number of important things, such as finished
gas passages, water-cooled valve guides and a very small mass of metal,
which is water-cooled, surrounding the spark-plug. Of course, it is
necessary to use very high compression in aviation motors in order to
secure high power and economy and owing to the fact that aviation motors
are worked at nearly their maximum, the heat flow through the cylinder,
piston, and valves is many times higher than that encountered in
automobile motors. It has been found necessary to develop special types
of pistons to carry the heat from the center of the head in order to
prevent pre-ignition. In the Mercedes motor the pistons have a drop
forged steel head which includes the piston boss and this head is
screwed into a cast iron skirt which has been machined inside to secure
uniform wall thickness.
CENSORED
[A] Piston Displacement (Cubic Inches)
[B] Weight of Engine with Carburetor and Ignition
[C] Gas Consumption
===========+======+======+======+=======+====+======+====+=================
Maker's |Number|Bore |Stroke| | | | |
Name | of |(In- |(In- | | | | |
and Model | Cyl. |ches) |ches) | [A] |H.P.|R.P.M.| [B]| [C]
-----------+------+------+------+-------+----+------+----+-----------------
Aeromarine | 6 |4-1/2 |5-1/8 | 449 | 85| 1400 | 440| ...
-----------+------+------+------+-------+----+------+----+-----------------
Aeromarine | 12 |4-5/16|5-1/8 | ... | ...| ... | 750| ...
D-12 | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Curtiss OX | 8 |4 |5 | 502.6 | 90| 1400 | 375| ...
-----------+------+------+------+-------+----+------+----+-----------------
Curtiss | 8 |4-1/4 |5 | 567.5 | 100| 1400 | 423| ...
OXX-2 | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Curtiss V-2| 8 |5 |7 |1100 | 200| 1400 | 690| ...
-----------+------+------+------+-------+----+------+----+-----------------
CENSORED
-----------+------+------+------+-------+----+------+----+-----------------
General Ve-| 9 |4.33 |5.9 | 848 | 100| 1200 | 272|12 gals/hour at
hicle Gnome Mono | | | | | | |rated H.P.
-----------+------+------+------+-------+----+------+----+-----------------
Gyro K | 7 |4-1/2 |6 | ... | 90| 1250| 215|8 gals/hour at
Rotary, Le Rhone Type | | | | | |rated H.P.
-----------+------+------+------+-------+----+------+----+-----------------
Gyro L | 9 |4-1/2 |6 | 859 | 100| 1200| 285|10 gals/hour at
Rotary, Le Rhone Type | | | | | |rated H.P.
-----------+------+------+------+-------+----+------+----+-----------------
Hall-Scott | 4 |5 |7 | 550 | 90-| 1400| 410| ...
A-7 | | | | | 100| | |
-----------+------+------+------+-------+----+------+----+-----------------
Hall-Scott | 6 |5 |7 | 825 | 125| 1300| 592| ...
A-5 | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Hispano- | 8 |4-5/8 |5 | 672 | 154| 1500| 455| ...
Suiza | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Knox Motors| 12 |4-3/4 |7 |1555 | 300| 1800|1425|31.5 gals/hour
Co. | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Maximotor | 6 |4-1/2 |5 | 477 | 85| 1600| 340| ...
A-6 | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Maximotor | 6 |5 |6 | 706.8 | 115| 1600| 385| ...
B-6 | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Maximotor | 8 |4-1/2 |5 | 636 | 115| 1600| 420| ...
A-8 | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Packard 12 | 12 |4 |6 | 903 | 225| 2100| 800| ...
-----------+------+------+------+-------+----+------+----+-----------------
Sturtevant | 8 |4 |5-1/2 | 552.9 | 140| 2000| 580| ...
5 | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Sturtevant | 8 |4 |5-1/2 | ... | 140| 2000| 514|13.75 gals/hour
5-A | | | | | | | |
-----------+------+------+------+-------+----+------+----+-----------------
Thomas 8 | 8 |4 |5-1/2 | 552.9 | 135| 2000| 630| ...
| | | | | | |lbs. with self-starter
-----------+------+------+------+-------+----+------+----+-----------------
Thomas 88 | 8 |4-1/8 |5-1/2 | 552.9 | 150| 2100| 525| ...
| | | | | | |lbs. with self-starter
-----------+------+------+------+-------+----+------+----+-----------------
Wisconsin | 6 |5 |6-1/2 | 765.7 | 140| 1380| 637| ...
-----------+------+------+------+-------+----+------+----+-----------------
Wisconsin | 12 |5 |6-1/2 |1531.4 | 250| 1200| ...| ...
-----------+------+------+------+-------+----+------+----+-----------------
The carburetor used on this 150 horse-power Mercedes motor is precisely
of the same type used on the Twin Six motor. It has two venturi throats,
in the center of which is placed the gasoline spray nozzle of
conventional type, fixed size orifices, immediately above which are
placed two panel type throttles with side outlets. An idling or primary
nozzle is arranged to discharge above the top of the venturi throat. The
carburetor body is of cast aluminum and is water jacketed. It is bolted
directly to air passage passing through the top and bottom half of the
crank-case which passes down through the oil reservoir. The air before
reaching the carburetor proper to some extent has cooled the oil in the
crank chamber and has itself been heated to assist in the vaporization.
The inlet pipes themselves are copper. All the passages between the
venturi throat and the inlet valve have been carefully finished and
polished. The only abnormal thing in the design of this motor is the
short connecting rod which is considerably less than twice the stroke
and would be considered very bad practice in motor car engines. A short
connecting rod, however, possesses two very real virtues in that it cuts
down height of the motor and the piston passes over the bottom dead
center much more slowly than with a long rod.
[Illustration: Fig. 245.--Part Sectional View of 90 Horse-Power Mercedes
Engine, Which is Typical of the Design of Larger Sizes.]
Other features of the design are a very stiff crank-case, both halves of
which are bolted together by means of long through bolts, the
crank-shaft main bearings are seated in the lower half of the case
instead of in the usual caps and no provision is made for taking up the
main bearings. The Mercedes company uses a plunger type of pump having
mechanically operated piston valves and it is driven by means of worm
gearing.
The overhead cam-shaft construction is extremely light. The cam-shaft is
mounted in a nearly cylindrical cast bronze case and is driven by means
of bevel gears from the crank-shaft. The vertical bevel gear shaft
through which the drive is taken from the crank-shaft to the cam-shaft
operates at one and one-half times the crank-shaft speeds and the
reduction to the half-time cam-shaft is secured through a pair of
bevels. On this vertical shaft there is mounted the water pump and a
bevel gear for driving two magnetos. The water pump mounted on this
shaft tends to steady the drive and avoid vibration in the gearing.
The cylinder sizes of six-cylinder aviation motors which have been built
by Mercedes are
Bore Stroke Horse-power
105 mm. 140 mm. 100
120 mm. 140 mm. 135
140 mm. 150 mm. 150
140 mm. 160 mm. 160
The largest of these motors has recently had its horse-power increased
to 176 at 1450 R. P. M. This general design of motor has been the
foundation for a great many other aviation motor designs, some of which
have proved very successful but none of which is equal to the original.
Among the motors which follow more or less closely the scheme of design
and arrangement are the Hall-Scott, the Wisconsin motor, the Renault
water-cooled, the Packard, the Christofferson and the Rolls-Royce. Each
of these motors show considerable variation in detail. The Rolls-Royce
and Renault are the only ones who have used the steel cylinder with the
steel jacket. The Wisconsin motor uses an aluminum cylinder with a
hardened steel liner and cast-iron valve seats. The Christofferson has
somewhat similar design to the Wisconsin with the exception that the
valve seats are threaded into the aluminum jacket and the cylinder head
has a blank end which is secured to the aluminum casting by means of the
valve seat pieces. The Rolls-Royce motors show small differences in
details of design in cylinder head and cam-shaft housing from the
Mercedes on which it has taken out patents, not only abroad but in this
country.
THE BENZ MOTOR
In the Kaiser prize contest for aviation motors a four-cylinder Benz
motor of 130 by 180 mm. won first prize, developing 103 B. H. P. at 1290
R. P. M. The fuel consumption was 210 grams per horse-power hour. Total
weight of the motor was 153 kilograms. The oil consumption was .02 of a
kilogram per horse-power hour. This motor was afterward expanded into a
six-cylinder design and three different sizes were built.
The accompanying table gives some of the details of weight, horse-power,
etc.
Motor type B FD FF
Rated horse-power 85 100 150
Horse-power at 1250 r.p.m 88 108 150
Horse-power at 1350 r.p.m 95 115 160
Bore in millimeters 106 116 130
Stroke in millimeters 150 160 180
Offset of the cylinders in millimeters 18 20 20
Rate of gasoline consumption in grams 240 230 225
Oil consumption in grams per b.h.p. hour 10 10 10
Oil capacity in kilograms 36 4 4-1/2
Water capacity in litres 5-1/2 7-1/2 9-1/2
The weight with water and oil but with
two magnetos, fuel feeder and air pump in
kilograms 170 200 245
The weight of motors, including the water
pump, two magnetos, double ignition, etc. 160 190 230
The weight of the exhaust pipe, complete
in kilograms 4 4.8 5-1/2
The weight of the propeller hub in
kilograms. 3-1/2 4 4
The Benz cylinder is a simple, straightforward design and a very
reliable construction and not particularly difficult to manufacture. The
cylinder is cast of iron without a water jacket but including 45
degrees angle elbows to the valve ports. The cylinders are machined
wherever possible and at other points have been hand filed and scraped,
after which a jacket, which is pressed in two halves, is gas welded by
means of short pipes welded on to the jacket. The bottom and the top of
the cylinders become water galleries, and by this means separate water
pipes with their attendant weight and complication are eliminated.
Rubber rings held in aluminum clamps serve to connect the cylinders
together. The whole construction turns out very neat and light. The
cylinder walls are 4 mm. or 3/16" thick and the combustion chamber is of
cylindrical pancake form and is 140 mm. or 5.60 inch in diameter. The
valve seats are 68 mm. in diameter and the valve port is 62 mm. in
diameter.
The passage joining the port is 57 mm. in diameter. In order to insert
the valves into the cylinder the valve stem is made with two diameters
and the valve has to be cocked to insert it in the guide, which has a
bronze bushing at its upper end to compensate for the smaller valve stem
diameter. The valve stem is 14 mm. or 9/16" in diameter and is reduced
at its upper portion to 9-1/2 mm. The valves are operated through a push
rod and rocker arm construction, which is 7/16" and exceedingly light.
Rocker arm supports are steel studs with enlarged heads to take a double
row ball bearing. A roller is mounted at one end of the rocker arm to
impinge on the end of the valve stem, and the rocker arm has an
adjustable globe stud at the other end. The push rods are light steel
tubes with a wall thickness of 0.75 mm. and have a hardened steel cup at
their upper end to engage the rocker arm globe stud and a hardened steel
globe at their lower end to socket in the roller plunger.
The Benz cam-shaft has a diameter of 26 mm. and is bored straight
through 18 mm. and there is a spiral gear made integrally with the shaft
in about the center of its length for driving the oil pump gear. The cam
faces are 10 mm. wide. There is also, in addition to the intake and
exhaust cams, a set of half compression cams. The shaft is moved
longitudinally in its bearings by means of an eccentric to put these
cams into action. At the fore end of the shaft is a driving gear flange
which is very small in diameter and very thin. The flange is 68 mm. in
diameter and 4 mm. thick and is tapped to take 6 mm. bolts. The total
length of cam-shaft is 1038 mm., and it becomes a regular gun boring job
to drill a hole of this length.
The cam-shaft gear is 140 mm. or 5-1/2 inches outside diameter. It has
fifty-four teeth and the gear face is 15 mm. or 19/32". The flange and
web have an average thickness of 4 mm. or 5/32" and the web is drilled
full of holes interposed between the spur gear mounted on the cam-shaft
and the cam-shaft gear. There is a gear which serves to drive the
magnetos and tachometer, also the air pump. The shaft is made integrally
with this gear and has an eccentric portion against which the air pump
roll plunger impinges.
The seven-bearing crank-shaft is finished all over in a beautiful
manner, and the shaft out of the particular motor we have shows no signs
of wear whatever. The crank-pins are 55 mm. in diameter and 69 mm. long.
Through both the crank-pin and main bearings there is drilled a 28 mm.
hole, and the crank cheeks are plugged with solder. The crank cheeks are
also built to convey the lubricant to the crank-pins. At the fore end of
the crank cheek there is pressed on a spur driving gear. There is
screwed on to the front end of the shaft a piece which forms a bevel
water pump driving gear and the starting dog. At the rear end of the
shaft very close to the propeller hub mounting there is a double thrust
bearing to take the propeller thrust.
Long, shouldered studs are screwed into the top half of the crank-case
portion of the case and pass clean through the bottom half of the case.
The case is very stiff and well ribbed. The three center bearing
diaphragms have double walls. The center one serves as a duct through
which water pipe passes, and those on either side of the center form the
carburetor intake air passages and are enlarged in section at one side
to take the carburetor barrel throttle.
The pistons are of cast iron and carry three concentric rings 1/4 inch
wide on their upper end, which are pinned at the joint. The top of the
piston forms the frustum of the cone and the pistons are 110 mm. in
length. The lower portion of the skirt is machined inside and has a wall
thickness of 1 mm. Riveted to the piston head is a conical diaphragm
which contacts with the piston pin when in place and serves to carry the
heat off the center of the piston.
The oil pump assembly comprises a pair of plunger pumps which draw oil
from a separate outside pump, and constructed integrally with it is a
gear pump which delivers the oil under about 60 pound pressure through a
set of copper pipes in the base to the main bearings. The plunger oil
pump shows great refinement of detail. A worm wheel and two eccentrics
are machined up out of one piece and serve to operate the plungers.
[Illustration: Fig. 246.--Part Sectional Side View and Sectional End
View of Benz 160 Horse-Power Aviation Engine.]
Some interesting details of the 160 horse-power Benz motor, which is
shown at Fig. 246, are reproduced from the "Aerial Age Weekly," and show
how carefully the design has been considered.
Maximum horse-power, 167.5 B. H. P.
Speed at maximum horse-power, 1,500 R. P. M.
Piston speed at maximum horse-power, 1,770 ft. per minute.
Normal horse-power, 160 B. H. P.
Speed at normal horse-power, 1,400 R. P. M.
Piston speed at normal horse-power, 1,656 ft. per minute.
Brake mean pressure at maximum horse-power, 101.2 pound per square
inch.
Brake mean pressure at normal horse-power, 103.4 pound per square
inch.
Specific power cubic inch swept volume per B. H. P., 5.46 cubic inch;
160 B. H. P.
Weight of piston, complete with gudgeon pin, rings, etc., 5.0 pound.
Weight of connecting rod, complete with bearings, 4.99 pound; 1.8
pound reciprocating.
Weight of reciprocating parts per cylinder, 6.8 pound.
Weight of reciprocating parts per square inch of piston area, 0.33
pound.
Outside diameter of inlet valve, 68 mm.; 2.68 inches.
Diameter of inlet valve port (_d_), 61.5 mm.; 2.42 inches.
Maximum lift of inlet valve (_h_), 11 mm.; 0.443 inch.
Area of inlet valve opening ([pi] _d_ _h_), 21.25 square cm.; 3.29
square inches.
Inlet valve opens, degrees on crank, top dead center.
Inlet valve closes, degrees on crank, 60 deg. late; 35 mm. late.
Outside diameter of exhaust valve, 68 mm.; 2.68 inches.
Diameter of exhaust valve port (_d_), 61.5 mm.; 2.42 inches.
Maximum lift of exhaust valve (_h_) 11 mm.; 0.433 inch.
Area of exhaust valve opening ([pi] _d_ _h_), 21.25 square cm.; 3.29
square inches.
Exhaust valve opens, degrees on crank, 60 deg. early; 35 mm. early.
Exhaust valve closes, degrees on crank, 16-1/2 deg. late; 5 mm. late.
Length of connecting rod between centers, 314 mm.; 12.36 inches.
Ratio connecting rod to crank throw, 3.49:1.
Diameter of crank-shaft, 55 mm. outside, 2.165 inches; 28 mm. inside,
1.102 inches.
Diameter of crank-pin, 55 mm. outside, 2.165 inches; 28 mm. inside,
1.102 inches.
Diameter of gudgeon pin, 30 mm. outside, 1.181 inches; 19 mm. inside,
0.708 inch.
Diameter of cam-shaft, 26 mm. outside, 1.023 inches; 18 mm. inside,
0.708 inch.
Number of crank-shaft bearings, 7.
Projected area of crank-pin bearings, 36.85 square cm.; 5.72 square
inches.
Projected area of gudgeon pin bearings, 22.20 square cm.; 3.44 square
inches.
Firing sequence, 1, 5, 3, 6, 2, 4.
Type of magnetos, ZH6 Bosch.
Direction of rotation of magneto from driving end, one clock, one
anti-clock.
Magneto timing, full advance, 30 deg. early (16 mm. early).
Type of carburetors (2) Benz design.
Fuel consumption per hour, normal horse-power, 0.57 pint.
Normal speed of propeller, engine speed, 1,400 R. P. M.
AUSTRO-DAIMLER ENGINE
One of the first very successful European flying engines which was
developed in Europe is the Austro-Daimler, which is shown in end section
in a preceding chapter. The first of these motors had four-cylinders,
120 by 140 millimeters, bore and stroke, with cast iron cylinders,
overhead valves operated by means of a single rocker arm, controlled by
two cams and the valves were closed by a single leaf spring which
oscillates with the rocker arm. The cylinders are cast singly and have
either copper or steel jackets applied to them. The four-cylinder design
was afterwards expanded to the six-cylinder design and still later a
six-cylinder motor of 130 by 175 millimeters was developed. This motor
uses an offset crank-shaft, as does the Benz motor, and the effect of
offset has been discussed earlier on in this treatise. The Benz motor
also uses an offset cam-shaft which improves the valve operation and
changes the valve lift diagram. The lubrication also is different than
any other aviation motor, since individual high pressure metering pumps
are used to deliver fresh oil only to the bearings and cylinders, as was
the custom in automobile practice some ten years ago.
SUNBEAM AVIATION ENGINES
These very successful engines have been developed by Louis Coatalen. At
the opening of the war the largest sized Coatalen motor was 225
horse-power and was of the L-head type having a single cam-shaft for
operating valves and was an evolution from the twelve-cylinder racing
car which the Sunbeam Company had previously built. Since 1914 the
Sunbeam Company have produced engines of six-, eight-, twelve- and
eighteen-cylinders from 150 to 500 horse-power with both iron and
aluminum cylinders. For the last two years all the motors have had
overhead cam-shafts with a separate shaft for operating the intake and
exhaust valves. Cam-shafts are connected through to the crank-shaft by
means of a train of spur gears, all of which are mounted on two double
row ball bearings. In the twin six, 350 horse-power engine, operating at
2100 R. P. M., requires about 4 horse-power to operate the cam-shafts.
This motor gives 362 horse-power at 2100 revolutions and has a fuel
consumption of 51/100 of a pint per brake horse-power hour. The
cylinders are 110 by 160 millimeters. The same design has been expanded
into an eighteen-cylinder which gives 525 horse-power at 2100 turns.
There has also been developed a very successful eight-cylinder motor
rated at 2220 horse-power which has a bore and stroke of 120 by 130
millimeters, weight 450 pounds. This motor is an aluminum block
construction with steel sleeves inserted. Three valves are operated, one
for the inlet and two for the exhaust. One cam-shaft operates the three
valves.
[Illustration: Fig. 247.--At Top, the Sunbeam Overhead Valve 170
Horse-Power Six-Cylinder Engine. Below, Side View of Sunbeam 350
Horse-Power Twelve-Cylinder Vee Engine.]
The modern Sunbeam engines operate with a mean effective pressure of 135
pounds with a compression ratio of 6 to 1 sea level. The connecting rods
are of the articulated type as in the Renault motor and are very short.
The weight of these motors turns out at 2.6 pounds per brake
horse-power, and they are able to go through a 100 hour test without any
trouble of any kind. The lubricating system comprises a dry base and oil
pump for drawing the oil off from the base, whence it is delivered to
the filter and cooling system. It then is pumped by a separate high
pressure gear pump through the entire motor. In these larger European
motors, castor-oil is used largely for lubrication. It is said that
without the use of castor-oil it is impossible to hold full power for
five hours. Coatalen favors aluminum cylinders rather than cast iron.
The series of views in Figs. 247 to 250 inclusive, illustrates the
vertical, narrow type of engine; the V-form; and the broad arrow type
wherein three rows, each of six-cylinders, are set on a common
crank-case. In this water-cooled series the gasoline and oil consumption
are notably low, as is the weight per horse-power.
[Illustration: Fig. 248.--Side View of Eighteen-Cylinder Sunbeam
Coatalen Aircraft Engine Rated at 475 B.H.P.]
[Illustration: Fig. 249.--Sunbeam Eighteen-Cylinder Motor, Viewed from
Pump and Magneto End.]
In the eighteen-cylinder overhead valve Sunbeam-Coatalen aircraft engine
of 475 brake horse-power, there are no fewer than half a dozen magnetos.
Each magneto is inclosed. Two sparks are furnished to each cylinder
from independent magnetos. On this engine there are also no fewer than
six carburetors. Shortness of crank-shaft, and therefore of engine
length, and absence of vibration are achieved by the linking of the
connecting-rods. Those concerned with three-cylinders in the broad arrow
formation work on one crank-pin, the outer rods being linked to the
central master one. In consequence of this arrangement, the piston
travel in the case of the central row of cylinders is 160 mm., while the
stroke of the pistons of the cylinders set on either side is in each
case 168 mm. Inasmuch as each set of six-cylinders is completely
balanced in itself, this difference in stroke does not affect the
balance of the engine as a whole. The duplicate ignition scheme also
applies to the twelve-cylinder 350 brake horse-power Sunbeam-Coatalen
overhead valve aircraft engine type. It is distinguishable,
incidentally, by the passage formed through the center of each induction
pipe for the sparking plug in the center cylinder of each block of
three. In this, as in the eighteen-cylinder and the six-cylinder types,
there are two cam-shafts for each set of cylinders. These cam-shafts are
lubricated by low pressure and are operated through a train of inclosed
spur wheels at the magneto end of the machine. The six-cylinder, 170
brake horse-power vertical type employs the same general principles,
including the detail that each carburetor serves gas to a group of
three-cylinders only. It will be observed that this engine presents
notably little head resistance, being suitable for multi-engined
aircraft.
[Illustration: Fig. 250.--Propeller End of Sunbeam Eighteen-Cylinder 475
B.H.P. Aviation Engine.]
INDICATING METERS FOR AUXILIARY SYSTEMS
[Illustration: Fig. 251.--View of Airplane Cowl Board, Showing the
Various Navigating and Indicating Instruments to Aid the Aviator in
Flight.]
The proper functioning of the power plant and the various groups
comprising it may be readily ascertained at any time by the pilot
because various indicating meters and pressure gauges are provided which
are located on a dash or cowl board in front of the aviator, as shown at
Fig. 251. The speed indicator corresponds to the speedometer of an
automobile and gives an indication of the speed the airplane is making,
which taken in conjunction with the clock will make it possible to
determine the distance covered at a flight. The altimeter, which is an
aneroid barometer, outlines with fair accuracy the height above the
ground at which a plane is flying. These instruments are furnished to
enable the aviator to navigate the airplane when in the air, and if the
machine is to be used for cross-country flying, they may be supplemented
by a compass and a drift set. It will be evident that these are purely
navigating instruments and only indicate the motor condition in an
indirect manner. The best way of keeping track of the motor action is to
watch the tachometer or revolution counter which is driven from the
engine by a flexible shaft. This indicates directly the number of
revolutions the engine is making per minute and, of course, any slowing
up of the engine in normal flights indicates that something is not
functioning as it should. The tachometer operates on the same principle
as the speed indicating device or speedometer used in automobiles except
that the dial is calibrated to show revolutions per minute instead of
miles per hour. At the extreme right of the dash at Fig. 251 the spark
advance and throttle control levers are placed. These, of course,
regulate the motor speed just as they do in an automobile. Next to the
engine speed regulating levers is placed a push button cut-out switch to
cut out the ignition and stop the motor. Three pressure gauges are
placed in a line. The one at the extreme right indicates the pressure of
air on the fuel when a pressure feed system is used. The middle one
shows oil pressure, while that nearest the center of the dash board is
employed to show the air pressure available in the air starting system.
It will be evident that the character of the indicating instruments will
vary with the design of the airplane. If it was provided with an
electrical starter instead of an air system electrical indicating
instruments would have to be provided.
COMPRESSED AIR-STARTING SYSTEMS
Two forms of air-starting systems are in general use, one in which the
crank-shaft is turned by means of an air motor, the other class where
compressed air is admitted to the cylinders proper and the motor turned
over because of the air pressure acting on the engine pistons. A system
known as the "Never-Miss" utilizes a small double-cylinder air pump is
driven from the engine by means of suitable gearing and supplies air to
a substantial container located at some convenient point in the
fuselage. The air is piped from the container to a dash-control valve
and from this member to a peculiar form of air motor mounted near the
crank-shaft. The air motor consists of a piston to which a rack is
fastened which engages a gear mounted on the crank shaft provided with
some form of ratchet clutch to permit it to revolve only in one
direction, and then only when the gear is turning faster than the engine
crank-shaft.
The method of operation is extremely simple, the dash-control valve
admitting air from the supply tank to the top of the pump cylinder. When
in the position shown in cut the air pressure will force the piston and
rack down and set the engine in motion. A variety of air motors are used
and in some the pump and motor may be the same device, means being
provided to change the pump to an air motor when the engine is to be
turned over.
The "Christensen" air starting system is shown at Figs. 252 and 253. An
air pump is driven by the engine, and this supplies air to an air
reservoir or container attached to the fuselage. This container
communicates with the top of an air distributor when a suitable control
valve is open. An air pressure gauge is provided to enable one to
ascertain the air pressure available. The top of each cylinder is
provided with a check valve, through which air can flow only in one
direction, i.e., from the tank to the interior of the cylinder. Under
explosive pressure these check valves close. The function of the
distributor is practically the same as that of an ignition timer, its
purpose being to distribute the air to the cylinders of the engine only
in the proper firing order. All the while that the engine is running and
the car is in motion the air pump is functioning, unless thrown out of
action by an easily manipulated automatic control. When it is desired to
start the engine a starting valve is opened which permits the air to
flow to the top of the distributor, and then through a pipe to the check
valve on top of the cylinder about to explode. As the air is going
through under considerable pressure it will move the piston down just as
the explosion would, and start the engine rotating. The inside of the
distributor rotates and directs a charge of air to the cylinder next to
fire. In this way the engine is given a number of revolutions, and
finally a charge of gas will be ignited and the engine start off on its
cycle of operation. To make starting positive and easier some gasoline
is injected in with the air so an inflammable mixture is present in the
cylinders instead of air only. This ignites easily and the engine starts
off sooner than would otherwise be the case. The air pressure required
varies from 125 to 250 pounds per square inch, depending upon the size
and type of the engine to be set in motion.
[Illustration: Fig. 252.--Parts of Christensen Air Starting System Shown
at A, and Application of Piping and Check Valves to Cylinders of
Thomas-Morse Aeromotor Outlined at B.]
[Illustration: Fig. 253.--Diagrams Showing Installation of Air Starting
System on Thomas-Morse Aviation Motor.]
ELECTRIC STARTING SYSTEMS
Starters utilizing electric motors to turn over the engine have been
recently developed, and when properly made and maintained in an
efficient condition they answer all the requirements of an ideal
starting device. The capacity is very high, as the motor may draw
current from a storage battery and keep the engine turning over for
considerable time on a charge. The objection against their use is that
it requires considerable complicated and costly apparatus which is
difficult to understand and which requires the services of an expert
electrician to repair should it get out of order, though if battery
ignition is used the generator takes the place of the usual ignition
magneto.
In the Delco system the electric current is generated by a combined
motor-generator permanently geared to the engine. When the motor is
running it turns the armature and the motor generator is acting as a
dynamo, only supplying current to a storage battery. On account of the
varying speeds of the generator, which are due to the fluctuation in
engine speed, some form of automatic switch which will disconnect the
generator from the battery at such times that the motor speed is not
sufficiently high to generate a current stronger than that delivered by
the battery is needed. These automatic switches are the only delicate
part of the entire apparatus, and while they require very delicate
adjustment they seem to perform very satisfactorily in practice.
When it is desired to start the engine an electrical connection is
established between the storage battery and the motor-generator unit,
and this acts as a motor and turns the engine over by suitable gearing
which engages the gear teeth cut into a special gear or disc attached to
the engine crank-shaft. When the motor-generator furnishes current for
ignition as well as for starting the motor, the fact that the current
can be used for this work as well as starting justifies to a certain
extent the rather complicated mechanism which forms a complete starting
and ignition system, and which may also be used for lighting if
necessary in night flying.
An electric generator and motor do not complete a self-starting system,
because some reservoir or container for electric current must be
provided. The current from the generator is usually stored in a storage
battery from which it can be made to return to the motor or to the same
armature that produced it. The fundamental units of a self-starting
system, therefore, are a generator to produce the electricity, a storage
battery to serve as a reservoir, and an electric motor to rotate the
motor crank-shaft. Generators are usually driven by enclosed gearing,
though silent chains are used where the center distance between the
motor shaft and generator shaft is too great for the gears. An electric
starter may be directly connected to the gasoline engine, as is the case
where the combined motor-generator replaces the fly-wheel in an
automobile engine. The motor may also drive the engine by means of a
silent chain or by direct gear reduction.
Every electric starter must use a switch of some kind for starting
purposes and most systems include an output regulator and a reverse
current cut-out. The output regulator is a simple device that regulates
the strength of the generator current that is supplied the storage
battery. A reverse current cut-out is a form of check valve that
prevents the storage battery from discharging through the generator.
Brief mention is made of electric starting because such systems will
undoubtedly be incorporated in some future airplane designs. Battery
ignition is already being experimented with.
BATTERY IGNITION SYSTEM PARTS
A battery ignition system in its simplest form consists of a current
producer, usually a set of dry cells or a storage battery, an induction
coil to transform the low tension current to one having sufficient
strength to jump the air gap at the spark-plug, an igniter member
placed in the combustion chamber and a timer or mechanical switch
operated by the engine so that the circuit will be closed only when it
is desired to have a spark take place in the cylinders. Battery ignition
systems may be of two forms, those in which the battery current is
stepped up or intensified to enable it to jump an air gap between the
points of the spark plug, these being called "high tension" systems and
the low tension form (never used on airplane motors) in which the
battery current is not intensified to a great degree and a spark
produced in the cylinder by the action of a mechanical circuit breaker
in the combustion chamber. The low tension system is the simplest
electrically but the more complex mechanically. The high tension system
has the fewest moving parts but numerous electrical devices. At the
present time all airplane engines use high tension ignition systems, the
magneto being the most popular at the present time. The current
distribution and timing devices used with modern battery systems are
practically the same as similar parts of a magneto.
INDEX
PAGE
A
Action of Four-cycle Engine 38
Action of Le Rhone Rotary Engine 503
Action of Two-cycle Engine 41
Action of Vacuum Feed System 119
Actual Duration of Different Functions 93
Actual Heat Efficiency 62
Adiabatic Diagram 51
Adiabatic Law 50
Adjustment of Bearings 449
Adjustment of Carburetors 151
Aerial Motors, Must be Light 20
Aerial Motors, Operating Conditions of 19
Aerial Motors, Requirements of 19
Aeromarine Six-cylinder Engine 527
Aeronautics, Division in Branches 18
Aerostatics 18
Air-cooled Engine Design 229
Air-cooling Advantages 231
Air-cooling, Direct Method 228
Air-cooling Disadvantages 231
Air-cooling Systems 223
Aircraft, Heavier Than Air 17
Aircraft, Lighter Than Air 18
Aircraft Types, Brief Consideration of 17
Air Needed to Burn Gasoline 113
Airplane Engine, Power Needed 21
Airplane Engines, Overhauling 412
Airplane Engine, How to Time 269
Airplane Engine Lubrication 209
Airplane, How Supported 21
Airplane Motors, German 543
Airplane Motor Types 20
Airplane Motors, Weight of 21
Airplane Power Plant Installation 324
Airplane Types 18
Airplanes, Horse-power Used in 26
Air Pressure Diminution, With Altitude 144
Altitude, How it Affects Mixture 153
Aluminum, Use in Pistons 297
American Aviation Engines, Statistics 546
Anzani Radial Engine Installation 344
Anzani Six-cylinder Star Engine 465
Anzani Six-cylinder Water-cooled Engine 459
Anzani Ten- and Twenty-cylinder Engines 468
Anzani Three-cylinder Engine 459
Anzani Three-cylinder Y Type 462
Argus Engine Construction 545
Armature Windings 168
Atmospheric Conditions, Compensating For 143
Austro-Daimler Engine 557
Aviatics 18
Aviation Engine, Aeromarine 527
Aviation Engine, Anzani Six-cylinder Star 465
Aviation Engine, Canton and Unne 469
Aviation Engine Cooling 219
Aviation Engine, Curtiss 519
Aviation Engine Cylinders 233
Aviation Engine, Early Gnome 472
Aviation Engine, German Gnome Type 495
Aviation Engine, Gnome Monosoupape 486
Aviation Engine, How To Dismantle 415
Aviation Engine, How to Start 460
Aviation Engine, Le Rhone Rotary 495
Aviation Engine Oiling 218
Aviation Engine Parts, Functions of 82
Aviation Engine, Renault Air-cooled 507
Aviation Engine, Stand for Supporting 414
Aviation Engine, Sturtevant 515
Aviation Engine, Thomas-Morse 521
Aviation Engine Types 457
Aviation Engine, Wisconsin 531
Aviation Engines, Anzani Six-cylinder Water-cooled 459
Aviation Engines, Anzani Ten- and Twenty-cylinder 468
Aviation Engines, Anzani Three-cylinder 459
Aviation Engines, Anzani Y Type 462
Aviation Engines, Argus 545
Aviation Engines, Austro-Daimler 557
Aviation Engines, Benz 551
Aviation Engines, Four- and Six-cylinder 88
Aviation Engines, German 543
Aviation Engines, Hall-Scott 539
Aviation Engines, Hispano-Suiza 512
Aviation Engines, Mercedes 543
Aviation Engines, Overhauling 412
Aviation Engines, Principal Parts of 80
Aviation Engines, Starting Systems For 567
Aviation Engines, Sunbeam 558
B
Balanced Crank-shafts 318
Ball-bearing Crank-shafts 319
Battery Ignition Systems 571
Baverey Compound Nozzle 137
Bearings, Adjustment of 449
Bearing Alignment 453
Bearing Brasses, Fitting 450
Bearing Parallelism, Testing 453
Bearing Scrapers and Their Use 446
Benz Aviation Engines 551
Benz Engine Statistics 551
Berling Magneto 174
Berling Magneto, Adjustment of 180
Berling Magneto Care 180
Berling Magneto Circuits 176
Berling Magneto, Setting 178
Block Castings 234
Blowing Back 269
Bolts, Screwing Down 452
Bore and Stroke Ratio 240
Boyle's Law 49
Brayton Engine 48
Breaker Box, Adjustment of 180
Breast and Hand Drills 387
Burning Out Carbon Deposits 421
Bushings, Cam-shaft, Wear in 456
C