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.
[Ill.u.s.tration: Fig. 230.--The Simplex Model A Hispano-Suiza Aviation Engine, a Very Successful Form.]
Oiling is by a positive pressure system. The oil is taken through a filter and steel tubes cast in the case to main bearings, through crank-shaft to crank-pins. The fourth main bearing is also provided with an oil lead from the system and through tubes running up the end of each cylinder block, oil is provided for the cam-shafts, cams and bearings.
The surplus oil escapes through the end of the cam-shaft where the driving gears are mounted, and with the oil that has gathered in the top casing, descends through the drive shaft and gears to the sump.
Ignition is by two eight-cylinder magnetos firing two spark-plugs per cylinder. The magnetos are driven from each of the two vertical shafts by small bevel pinions meshing in bevel gears. The carburetor is mounted between the two cylinder blocks and feeds the two blocks through aluminum manifolds which are partly water-jacketed. The engine can be equipped with a geared hand crank-starting device.
STURTEVANT MODEL 5A 140 HORSE-POWER ENGINE
These motors are of the eight-cylinder "V" type, four-stroke cycle, water-cooled, having a bore of 4 inches and a stroke of 5-1/2 inches, equivalent to 102 mm. 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 pa.s.sages 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 un.o.bstructed circulation of the cooling water. The cylinder heads and cylinders are both held to the base by six long bolts. The valves are located in the cylinder heads and are mechanically operated. The valves and valve springs are especially accessible and of such size as to permit high volumetric efficiency. The valves are constructed of hardened tungsten steel, the heads and stems being made from one piece. The valve rocker arms located on the top of the cylinder are provided with adjusting screws. A check nut enables the adjusting screw to be securely locked in position, once the correct clearance has been determined. The rocker arm bearings are adequately lubricated by a compression grease cup. Cam-rollers are interposed between the cams and the push rods in order to reduce the side thrust on the push rods.
A system of double springs is employed which greatly reduces the stress on each spring and insures utmost reliability. A spring of extremely large diameter returns the valve; a second spring located at the cylinder base handles the push rod linkage. These springs, which operate under low stress, are made from the best of steel and are given a special double heat treatment. The pistons are made from a special aluminum alloy; are deeply ribbed in the head for cooling and strength and provided with two piston rings. These pistons are exceedingly light weight in order to minimize vibration and prevent wear on the bearings.
The piston pin is made of chrome nickel steel, bored hollow and hardened. It is allowed to turn, both in piston and connecting rod. The piston rings are of special design, developed after years of experimenting in aeronautical engines.
The connecting rods are of "H" section, machined all over from forgings of a special air-hardening chrome nickel steel which, after being heat treated has a tensile strength of 280,000 pounds per square inch. They are consequently very strong and yet unusually light, and being machined all over are of absolutely uniform section, which gives as nearly perfect balance as can be obtained. The big ends are lined with white metal and the small ends are bushed with phosphor bronze. The connecting rods are all alike and take their bearings side by side on the crank-pin, the cylinders being offset to permit of this arrangement. The crank-shaft is machined from the highest grade chrome nickel steel, heat treated in order to obtain the best properties of this material. It is 2-1/4 inches in diameter (57 mm.) and bored hollow throughout, insuring maximum strength with minimum weight. It is carried in three large, bronze-backed white metal bearings. A new method of producing these bearings insures a perfect bond between the two metals and eliminates breakage.
The base is cast from an aluminum alloy. Great strength and rigidity is combined with light weight. The sides extend considerably below the center line of the crank-shaft, providing an extremely deep section. At all highly stressed points, deep ribs are provided to distribute the load evenly and eliminate bending. The lower half of the base is of cast aluminum alloy of extreme lightness. This collects the lubricating oil and acts as a small reservoir for same. An oil-filtering screen of large area covers the entire surface of the sump. The propeller shaft is carried on two large annular ball bearings driven from the crank-shaft by hardened chrome nickel steel spur gears. These gears are contained within an oil-tight casing integral with the base on the opposite end from the timing gears. A ball-thrust bearing is provided on the propeller shaft to take the thrust of a propeller or tractor, as the case may be. In case of the direct drive a stub shaft is fastened direct to the crank-shaft and is fitted with a double thrust bearing.
The cam-shaft is contained within the upper half of the base between the two groups of cylinders, and is supported in six bronze bearings. It is bored hollow throughout and the cams are formed integral with the shaft and ground to the proper shape and finish. An important development in the shape of cams has resulted in a maintained increase of power at high speeds. The gears operating the cam-shaft, magneto, oil and water pumps are contained within an oil-tight casing and operate in a bath of oil.
Lubrication is of the complete forced circulating system, the oil being supplied to every bearing under high pressure by a rotary pump of large capacity. This is operated by gears from the crank-shaft. The oil pa.s.sages from the pump to the main bearings are cast integral with the base, the hollow crank-shaft forming a pa.s.sage 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 pa.s.ses before reaching the pump. Approximately one gallon of oil is contained within the base and this is continually circulated through an external tank by a secondary pump operated by an eccentric on the cam-shaft. This also draws fresh oil from the external tank which can be made of any desired capacity.
SPECIFICATIONS--MODEL 5A TYPE 8
Horse-power rating, 140 at 2,000 R. P. M.
Bore, 4 inches = 102 mm.
Stroke, 5-1/2 inches = 140 mm.
Number of cylinders, 8.
Arrangement of cylinders, "V."
Cooling, water. Circulation by centrifugal pump.
Cycle, four stroke.
Ignition (double), 2 Bosch or Splitdorf magnetos.
Carburetor, Zenith duplex. Water jacket manifold.
Oiling system, complete forced. Circulating gear pump.
Normal crank-shaft speed, 2,000 R. P. M.
Propeller shaft, 3/5 crank-shaft speed at normal, 1,200 R. P. M.
Stated power at 30" barometer, 140 B. H. P.
Stated weight with all accessories but without water, gasoline or oil, 514 pounds = 234 kilos.
Weight per B. H. P., 3.7 pounds = 1.68 kilos.
Stated weight with all accessories with water, 550 pounds = 250 kilos.
Weight per B. H. P. with water, 3.95 pounds = 1.79 kilos.
THE CURTISS AVIATION MOTORS
The Curtiss OX motor has eight cylinders, 4-inch bore, 5-inch stroke, delivers 90 horse-power at 1,400 turns, and the weight turns out at 4.17 pounds per horse-power. This motor has cast iron cylinders with monel metal jackets, overhead inclined valves operated by means of two rocker arms, push-and-pull rods from the central cam-shaft located in the crank-case. The cam and push rod design is extremely ingenious and the whole valve construction turns out very light. This motor is an evolution from the early Curtiss type motor which was used by Glenn Curtiss when he won the Gordon Bennett Cup at Rheims. A slightly larger edition of this type motor is the OXX-5, as shown at Figs. 231 and 232, which has cylinders 4-1/4 inches by 5 inches, delivers 100 horse-power at 1,400 turns and has the same fuel and oil consumption as the OX type motor, namely, .60 pound of fuel per brake horse-power hour and .03 pound of lubricating oil per brake horse-power hour.
[Ill.u.s.tration: 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 alt.i.tudes 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 alt.i.tude. 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.
[Ill.u.s.tration: 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, 84-5/8 inches; overall width, 34-1/8 inches; overall depth, 40 inches; width at bed, 30-1/2 inches; height from bed, 21-1/8 inches; depth from bed, 18-1/2 inches.
THOMAS-MORSE MODEL 88 ENGINE
The Thomas-Morse Aircraft Corporation of Ithaca, N. Y., has produced a new engine, Model 88, bearing a close resemblance to the earlier model.
The main features of that model have been retained; in fact, many parts are interchangeable in the two engines. Supported by the great development in the wide use of aluminum, the Thomas engineers have adopted this material for cylinder construction, which adoption forms the main departure from previous accepted design.
The marked tendency to-day toward a higher speed of rotation has been conclusively justified, in the opinion of the Thomas engineers, by the continued reliable performance of engines with crank-shafts operating at speeds near 2,000 revolutions per minute, driving the propeller through suitable gearing at the most efficient speed. High speed demands that the closest attention be paid to the design of reciprocating and rotating parts and their adjacent units. Steel of the highest obtainable tensile strength must be used for connecting rods and piston pins, that they may be light and yet retain a sufficient factor of safety. Piston design is likewise subjected to the same strict scrutiny.
At the present day, aluminum alloy pistons operate so satisfactorily that they may be said to have come to stay.
The statement often made in the past, that the gearing down of an engine costs more in the weight of reduction gears and propeller shaft than is warranted by the increase in horse-power, is seldom heard to-day.
The mean effective pressure remaining the same, the brake horse-power of any engine increases as the speed. That is, an engine delivering 100 brake horse-power at 1,500 revolutions per minute will show 133 brake horse-power at 2,000 revolutions per minute, an increase of 33 brake horse-power. To utilize this increase in horse-power, a matter of some fifteen pounds must be spent in gearing and another fifteen perhaps on larger valves, bearings, etc. Two per cent. may be a.s.sumed 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 quant.i.ties by ample webbing of the crank-case and judicious use of metal elsewhere.
All things considered, there is actually so little difference to be discerned between the balance of a properly designed eight-cylinder engine and that of a six or twelve as to make a discussion of the pros and cons more one of theory than of practice.
The main criticisms of the L head cylinder engine are that it is less efficient and heavier. This is granted, as it relates to cylinders alone. More thorough investigation, however, based on the main desideratum, weight-power ratio, leads us to other conclusions, particularly with reference to high speed engines. The valve gear must not be forgotten. A cylinder cannot be taken completely away from its component parts and judged, as to its weight value, by itself alone. A part away from the whole becomes an item unimportant in comparison with the whole. The valve gear of a high speed engine is a too often overlooked feature. The stamp of approval has been made by high speed automobile practice upon the overhead cam-shaft drive, with valves in the cylinder head operated direct from the cam-shaft or by means of valve lifters or short rockers.
The overhead cam-shaft mechanism applied to an eight-cylinder engine calls for two separate cam-shafts carried above and supported by the cylinders in an oil-tight housing, and driven by a series of spur gears or bevels from the crank-shaft. It is patent that this valve gearing is heavy and complicated in comparison with the simple moving valve units of the L head engine, which are operated from one single cam-shaft, housed rigidly in the crank-case. The inherently lower volumetric efficiency of the L head engine is largely overcome by the use of a properly designed head, large valves and ample gas pa.s.sages. 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.
[Ill.u.s.tration: Fig. 233.--End View of Thomas-Morse 150 Horse-Power Aluminum Cylinder Aviation Motor Having Detachable Cylinder Heads.]
The Thomas Model 88 engine is 4-1/8 inch bore and 5-1/2 inch stroke. The cylinders and cylinder heads are of aluminum, and as steel liners are used in the cylinders the pistons are also made of aluminum. This engine is actually lighter than the earlier model of less power. It weighs but 525 pounds, with self-starter. The general features of design can be readily ascertained by study of the ill.u.s.trations: 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.
[Ill.u.s.tration: Fig. 234.--Side View of Thomas-Morse High Speed 150 Horse-Power Aviation Motor with Geared Down Propeller Drive.]
SIXTEEN-VALVE DUESENBERG ENGINE
[Ill.u.s.tration: Fig. 235.--The Reduction Gear-Case of Thomas-Morse 150 Horse-Power Aviation Motor, Showing Ball Bearing and Propeller Drive Shaft Gear.]