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 UnnÉ 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. Large
image
(90 kB). Fig. 190 Fig. 190.—Views Outlining Construction of Three-Cylinder Anzani Aviation Motor. Fig. 190a 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. 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. Fig. 191 Fig. 191.—The Anzani Six-Cylinder Water-Cooled Aviation Engine. Fig. 192 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. Fig. 193 Fig. 193.—Three-Cylinder Anzani Air-Cooled Y-Form Engine. Fig. 194 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. Fig. 195 Fig. 195.—Sectional View Showing Internal Parts of Six-Cylinder Anzani Engine, with Starwise Disposition of Cylinders. Fig. 196 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. CANTON AND UNNÉ 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. Fig. 197 Fig. 197.—Application of R. E. P. Five-Cylinder Fan-Shape Air-Cooled Motor to Early Monoplane. Fig. 198 Fig. 198.—The Canton and UnnÉ 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. Fig. 199 Fig. 199.—Sectional View Showing Construction of Canton and UnnÉ 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 13/4 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 11/9 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 41/4 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 horsepower 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. Large
image
(89 kB). Fig. 200 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 43/10 inches and a stroke of 47/10 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. Fig. 201 Fig. 201.—Sectional View of Early Type Gnome Cylinder and Piston Showing Construction and Application of Inlet and Exhaust Valves. 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. Fig. 202 Fig. 202.—Details of Old Style Gnome Motor Inlet and Exhaust Valve Construction and Operation. 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. Fig. 203 Fig. 203.—The Gnome Fourteen-Cylinder 100 Horse-Power Aviation Engine. 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—511/2 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. 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. Fig. 204 Fig. 204.—Cam and Cam-Gear Case of the Gnome Seven-Cylinder Revolving Engine. 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. Fig. 205 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. Fig. 206 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. Fig. 207 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. Fig. 208 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. Fig. 209 Fig. 209.—The G. V. Gnome “Monosoupape” Nine-Cylinder Rotary Engine Mounted on Testing Stand. Fig. 210 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 21/16 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 51/2 pounds. Fig. 211 Fig. 211.—How a Gnome Cylinder is Reduced from Solid Chunk of Steel Weighing 97 Pounds to Finished Cylinder Weighing 51/2 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 21/4 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. Fig. 212 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. Fig. 213 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 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. Fig. 214.—The 50 Horse-Power Rotary Bayerischen Motoren Gesellschaft Engine, a German Adaptation of the Early Gnome Design. 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. Fig. 215 Fig. 215.—Nine-Cylinder Revolving Le Rhone Type Aviation Engine. Large
image
(96 kB). Fig. 216 Fig. 216.—Part Sectional Views of Le Rhone Rotary Cylinder Engine, Showing Method of Cylinder Retention, Valve Operation and Novel Crank Disc Assembly. Fig. 218 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. Fig. 219 Fig. 219.—Diagrams Showing Important Components of Le Rhone Motor. Large
image
(95 kB). Fig. 220 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. Fig. 221 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. Fig. 222 Fig. 222.—Diagrams Showing Le Rhone Motor Action and Firing Order. Fig. 223 Fig. 223.—Diagram Showing Positions of Piston in Le Rhone Rotary Cylinder Motor. 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° | ? | 110 H.P. | 18° | ? | 80 H.P. | | Intake valve closing, lag | 35° | ? | 35° | ? | | Exhaust valve opening, lead | 55° | ? | 45° | ? | | Exhaust valve closing, lag | 5° | ? | 5° | ? | | Ignition time advance | 26° | ? | 26° | ? | Fig. 224 Fig. 224.—Diagrams Showing Valve Timing of Le Rhone Aviation Engine. THE RENAULT AIR-COOLED VEE ENGINE Fig. 225 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 FrÈres 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. Fig. 226 Fig. 226.—End Sectional View of Renault Air-Cooled Aviation Engine. Fig. 227 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. Fig. 228 Fig. 228.—End View of Renault Twelve-Cylinder Engine Crank-Case, Showing Magneto Mounting. Fig. 229 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. Fig. 230 Fig. 230.—The Simplex Model A Hispano-Suiza Aviation Engine, a Very Successful Form. 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. 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 51/2 inches, equivalent to 102 mm. × 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 21/4 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, 51/2 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 41/4 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. Fig. 231 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. Fig. 232 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'' × 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, 845/8 inches; overall width, 341/8 inches; overall depth, 40 inches; width at bed, 301/2 inches; height from bed, 211/8 inches; depth from bed, 181/2 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. Fig. 233 Fig. 233.—End View of Thomas-Morse 150 Horse-Power Aluminum Cylinder Aviation Motor Having Detachable Cylinder Heads. 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. Fig. 234 Fig. 234.—Side View of Thomas-Morse High Speed 150 Horse-Power Aviation Motor with Geared Down Propeller Drive. The Thomas Model 88 engine is 41/8 inch bore and 51/2 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. Fig. 235 Fig. 235.—The Reduction Gear-Case of Thomas-Morse 150 Horse-Power Aviation Motor, Showing Ball Bearing and Propeller Drive Shaft Gear. SIXTEEN-VALVE DUESENBERG ENGINE This engine is a four-cylinder, 43/4'' × 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, 115/16'' 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, 21/2-inch diameter at main bearings. Connecting rod bearings, 21/4-inch diameter, 3 inches long. Front main bearing, 31/2 inches long; intermediate main bearing, 31/2 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 These motors are four-stroke cycle, six-cylinder vertical type, with cylinder 45/16'' bore by 51/8'' 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. Fig. 236 Fig. 236.—The Six-Cylinder Aeromarine Engine. 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. WISCONSIN AVIATION ENGINES 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° 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. Fig. 237.—The Wisconsin Aviation Engine, at Top, as Viewed from Carburetor Side. Below, the Exhaust Side. 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. Fig. 238 Fig. 238.—Dimensioned End Elevation of Wisconsin Six Motor. 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 51/2 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. Fig. 239 Fig. 239.—Dimensioned Side Elevation of Wisconsin Six 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. Fig. 240 Fig. 240.—Power, Torque and Efficiency Curves of Wisconsin Aviation Motor. 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. Fig. 241 Fig. 241.—Timing Diagram, Wisconsin Aviation Engine. 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 61/2 inches.
- Crank-shaft diameter throughout 2 inches.
- Length of crank-pin and main bearings 31/2 inches.
- Diameter of valves 3 inches (23/4 inches clear).
- Lift of valves 1/2 inch.
- Volume of compression space 22 per cent. of total.
- Diameter of wrist-pins 13/16 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 21/2 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. Fig. 242 Fig. 242.—Dimensioned End View of Wisconsin Twelve-Cylinder Airplane Motor. Fig. 243 Fig. 243.—Dimensioned Side Elevation of Wisconsin Twelve-Cylinder Airplane Motor. 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.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. 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 115/16'' long, excepting the rear main bearing, which is 43/8'' long, and front main bearing, which is 23/16'' 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. Fig. 244 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 Maker’s Name
and Model | Num-
ber
of
Cyl. | Bore
(In.) | Stroke
(In.) | Piston
Displace-
ment
(Cubic
In.) | H.P. | R.P.M. | Weight of
Engine with
Carburetor
and Ignition | Gas
Consump-
tion | | Aeromarine | 6 | 4 | 1/2 | 5 | 1/8 | 449 | | 85 | 1400 | 440 | ... | Aeromarine
D-12 | 12 | 4 | 5/16 | 5 | 1/8 | ... | ... | ... | 750 | ... | | Curtiss OX | 8 | 4 | | 5 | | 502 | .6 | 90 | 1400 | 375 | ... | | Curtiss OXX-2 | 8 | 4 | 1/4 | 5 | | 567 | .5 | 100 | 1400 | 423 | ... | | Curtiss V-2 | 8 | 5 | | 7 | | 1100 | | 200 | 1400 | 690 | ... | | CENSORED | General Vehicle
Gnome Mono | 9 | 4 | .33 | 5 | .9 | 848 | | 100 | 1200 | 272 | 12 gals/hour
at rated H.P. | Gyro K Rotary,
Le Rhone Type | 7 | 4 | 1/2 | 6 | | ... | 90 | 1250 | 215 | 8 gals/hour
at rated H.P. | Gyro L Rotary,
Le Rhone Type | 9 | 4 | 1/2 | 6 | | 859 | | 100 | 1200 | 285 | 10 gals/hour
at rated H.P. | | Hall-Scott A-7 | 4 | 5 | | 7 | | 550 | | 90-
100 | 1400 | 410 | ... | | Hall-Scott A-5 | 6 | 5 | | 7 | | 825 | | 125 | 1300 | 592 | ... | | Hispano-Suiza | 8 | 4 | 5/8 | 5 | | 672 | | 154 | 1500 | 455 | ... | Knox Motors
Co. | 12 | 4 | 3/4 | 7 | | 1555 | | 300 | 1800 | 1425 | 31.5 gals/hour | | Maximotor A-6 | 6 | 4 | 1/2 | 5 | | 477 | | 85 | 1600 | 340 | ... | | Maximotor B-6 | 6 | 5 | | 6 | | 706 | .8 | 115 | 1600 | 385 | ... | | Maximotor A-8 | 8 | 4 | 1/2 | 5 | | 636 | | 115 | 1600 | 420 | ... | | Packard 12 | 12 | 4 | | 6 | | 903 | | 225 | 2100 | 800 | ... | | Sturtevant 5 | 8 | 4 | | 5 | 1/2 | 552 | .9 | 140 | 2000 | 580 | ... | | Sturtevant 5-A | 8 | 4 | | 5 | 1/2 | ... | 140 | 2000 | 514 | 13.75 gals/hour | | 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. Fig. 245 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 horsepower 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 91/2 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 51/2 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. Fig. 246 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 (p 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° 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 (p d h), 21.25 square cm.; 3.29 square inches.
- Exhaust valve opens, degrees on crank, 60° early; 35 mm. early.
- Exhaust valve closes, degrees on crank, 161/2° 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° 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 horsepower 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 horsepower at 2100 turns. There has also been developed a very successful eight-cylinder motor rated at 2220 horsepower 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. 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. Fig. 248 Fig. 248.—Side View of Eighteen-Cylinder Sunbeam Coatalen Aircraft Engine Rated at 475 B.H.P. Fig. 249 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. Fig. 250 Fig. 250.—Propeller End of Sunbeam Eighteen-Cylinder 475 B.H.P. Aviation Engine. INDICATING METERS FOR AUXILIARY SYSTEMS Fig. 251 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. Fig. 252 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. Fig. 253 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.
|
