Aviation Engines Part 34

S. gallons per hour.

The high-tension magnetos, with double cam or two break per revolution interrupter, is located on the thrust plate in an inverted position, and is driven at such a speed as to produce nine sparks for every two revolutions; that is, at 2-1/4 times engine speed. A Splitdorf magneto is fitted. There is no distributor on the magneto. The high-tension collector brush of the magneto is connected to a distributor brush holder carried in the bearer plate of the engine. The brush in this brush holder is pressed against a distributor ring of insulating material molded in position in the web of a gear wheel keyed to the thrust plate, which gear serves also for starting the engine by hand.

Molded in this ring of insulating material are nine bra.s.s 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.

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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 cha.s.se," 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

[Ill.u.s.tration: Fig. 214.--The 50 Horse-Power Rotary Bayerischen Motoren Gesellschaft Engine, a German Adaptation of the Early Gnome Design.]

A German adaptation of the Gnome design is shown at Fig. 214. This is known as the Bayerischen Motoren Gesellschaft engine and the type shown is an early design rated at 50 horse-power. The bore is 110 mm., the stroke is 120 mm., and it is designed to run at a speed of 1,200 R. P.

M. It is somewhat similar in design to the early Gnome "valve-in-piston"

design except that two valves are carried in the piston top instead of one. The valve operating arrangement is different also, as a single four point cam is used to operate the seven exhaust valves. It is driven by epicyclic gearing, the cam being driven by an internal gear machined integrally with it, the cam being turned at 7/8 times the engine speed.

Another feature is the method of holding the cylinders on the crank-case. The cylinder is provided with a f.l.a.n.g.e 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 f.l.a.n.g.es firmly together and keeping the cylinder firmly seated against the crank-case f.l.a.n.g.e. The "monosoupape" type has also been copied and has received some application in Germany, but the most successful German airplanes are powered with six-cylinder vertical engines such as the Benz and Mercedes.

THE LE RHONE MOTOR

The Le Rhone motor is a radial revolving cylinder engine that has many of the principles which are incorporated in the Gnome but which are considered to be an improvement by many foreign aviators. Instead of having but one valve in the cylinder head, as the latest type "monosoupape" Gnome has, the Le Rhone has two valves, one for intake and one for exhaust in each cylinder. By an ingenious rocker arm and tappet rod arrangement it is possible to operate both valves with a single push rod. Inlet pipes communicate with the crank-case at one end and direct the fresh gas to the inlet valve cage at the other. Another peculiarity in the design is the method of holding the cylinders in place. Instead of having a vertically divided crank-case as the Gnome engine has and clamping both halves of the case around the cylinders, the crank-case of the Le Rhone engine is in the form of a cylinder having nine bosses provided with threaded openings into which the cylinders are screwed. A thread is provided at the base of each cylinder and when the cylinder has been screwed down the proper amount it is prevented from further rotation about its own axis by a substantial lock nut which screws down against the threaded boss on the crank-case. The external appearance of the Le Rhone type motor is clearly shown at Fig. 215, while the general features of construction are clearly outlined in the sectional views given at Figs. 216 and 217.

[Ill.u.s.tration: Fig. 215--Nine-Cylinder Revolving Le Rhone Type Aviation Engine.]

[Ill.u.s.tration: Fig. 216.--Part Sectional Views of Le Rhone Rotary Cylinder Engine, Showing Method of Cylinder Retention, Valve Operation and Novel Crank Disc a.s.sembly.]

[Ill.u.s.tration: Fig. 217.--Side Sectional View of Le Rhone Aviation Engine.]

[Ill.u.s.tration: 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.

[Ill.u.s.tration: Fig. 219.--Diagrams Showing Important Components of Le Rhone Motor.]

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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 s.p.a.ced explosions, as the basic action is the same as the Gnome engine.

[Ill.u.s.tration: Fig. 222.--Diagrams Showing Le Rhone Motor Action and Firing Order.]

The magneto is driven by a gear having 36 teeth attached to crank-case which meshes with 16-tooth pinion on armature. The magneto turns at 2.25 times crank-case speed. Two cams, one for inlet, one for exhaust, are mounted on a carrying member and act on nine rocker arms which are capable of giving a push-and-pull motion to the valve-actuating rocker-operating rods. A gear driven by the crank-case meshes with a larger member having internal teeth carried by the cam carrier. Each cam has five profiles and is mounted in staggered relation to the other.

These give the nine fulcrumed levers the proper motion to open the inlet and exhaust valves at the proper time. The cams are driven at 45/50 or 9/10 of the motor speed. The cylinder dimensions and timing follows; the weight can be approximated by figuring 3 pounds per horse-power.

80 H.P. 105 M/M bore 4.20" bore.

140 M/M stroke 5.60" stroke.

110 H.P. 112 M/M bore 4.48" bore.

170 M/M stroke 6.80" stroke.

Timing--Intake valve opening, lag 18} 18} Intake valve closing, lag 35} 35} Exhaust valve opening, lead 55} 110 H.P. 45} 80 H.P.

Exhaust valve closing, lag 5} 5} Ignition time advance 26} 26}

[Ill.u.s.tration: Fig. 223.--Diagram Showing Positions of Piston in Le Rhone Rotary Cylinder Motor.]

THE RENAULT AIR-COOLED VEE ENGINE

[Ill.u.s.tration: Fig. 224.--Diagrams Showing Valve Timing of Le Rhone Aviation Engine.]

[Ill.u.s.tration: Fig. 225.--Diagrams Showing How Cylinder Cooling is Effected in Renault Vee Engines.]

Air-cooled stationary engines are rarely used in airplanes, but the Renault Freres of France have for several years manufactured a complete series of such engines of the general design shown at Fig. 225, ranging from a low-powered one developed eight or nine years ago and rated at 40 and 50 horse-power, to later eight-cylinder models rated at 70 horse-power and a twelve-cylinder, or twin six, rated at 90 horse-power.

The cylinders are of cast iron and are furnished with numerous cooling ribs which are cast integrally. The cylinder heads are separate castings and are attached to the cylinder as in early motorcycle engine practice, and serve to hold the cylinder in place on the aluminum alloy crank-case by a cruciform yoke and four long hold-down bolts (Fig. 226).

The pistons are of cast steel and utilize piston rings of cast iron. The valves are situated on the inner side of the cylinder head, the arrangement being unconventional in that the exhaust valves are placed above the inlet. The inlet valves seat in an extension of the combustion head and are actuated by direct push rod and cam in the usual manner while an overhead gear in which rockers are operated by push rods is needed to actuate the exhaust valves. The valve action is clearly shown in Figs. 226 and 227. The air stream by which the cylinders are cooled is produced by a centrifugal or blower type fan of relatively large diameter which is mounted on the end of a crank-shaft and the air blast is delivered from this blower into an enclosed s.p.a.ce between the cylinder from which it escapes only after pa.s.sing 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.

[Ill.u.s.tration: Fig. 226.--End Sectional View of Renault Air-Cooled Aviation Engine.]

[Ill.u.s.tration: 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.

[Ill.u.s.tration: Fig. 228.--End View of Renault Twelve-Cylinder Engine Crank-Case, Showing Magneto Mounting.]

[Ill.u.s.tration: Fig. 229.--Diagram Outlining Renault Twelve-Cylinder Engine Ignition System.]

SIMPLEX MODEL "A" HISPANO-SUIZA

The Model A is of the water-cooled four-cycle Vee type, with eight cylinders, 4.7245 inch bore by 5.1182 inch stroke, piston displacement 718 cubic inches. At sea-level it develops 150 horse-power at 1,450 R.

P. M. It can be run successfully at much higher speeds, depending on propeller design and gearing, developing proportionately increased power. The weight, including carburetor, two magnetos, propeller hub, starting magneto and crank, but without radiator, water or oil or exhaust pipes, is 445 pounds. Average fuel consumption is .5 pound per horse-power hour and the oil consumption at 1,450 R. P. M. is three quarts per hour. The external appearance is shown at Fig. 230.

Four cylinders are contained in each block, which is of built-up construction; the water jackets and valve ports are cast aluminum and the individual cylinders heat-treated steel forgings threaded into the bored holes of the aluminum castings. Each block after a.s.sembly 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.