Aviation Engines Part 37

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.

[Ill.u.s.tration: 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 princ.i.p.al features of the design are forged steel cylinders with forged steel elbows for gas pa.s.sages, pressed steel water jackets, which when welded together forms the cylinder a.s.sembly, 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 pa.s.sages, water-cooled valve guides and a very small ma.s.s of metal, which is water-cooled, surrounding the spark-plug. Of course, it is necessary to use very high compression in aviation motors in order to secure high power and economy and owing to the fact that aviation motors are worked at nearly their maximum, the heat flow through the cylinder, piston, and valves is many times higher than that encountered in automobile motors. It has been found necessary to develop special types of pistons to carry the heat from the center of the head in order to prevent pre-ignition. In the Mercedes motor the pistons have a drop forged steel head which includes the piston boss and this head is screwed into a cast iron skirt which has been machined inside to secure uniform wall thickness.

CENSORED

[A] Piston Displacement (Cubic Inches) [B] Weight of Engine with Carburetor and Ignition [C] Gas Consumption

===========+======+======+======+=======+====+======+====+================= Maker's Number Bore Stroke Name of (In- (In- and Model Cyl. ches) ches) [A] H.P. R.P.M. [B] [C]

-----------+------+------+------+-------+----+------+----+----------------- Aeromarine 6 4-1/2 5-1/8 449 85 1400 440 ...

-----------+------+------+------+-------+----+------+----+----------------- Aeromarine 12 4-5/16 5-1/8 ... ... ... 750 ...

D-12 -----------+------+------+------+-------+----+------+----+----------------- Curtiss OX 8 4 5 502.6 90 1400 375 ...

-----------+------+------+------+-------+----+------+----+----------------- Curtiss 8 4-1/4 5 567.5 100 1400 423 ...

OXX-2 -----------+------+------+------+-------+----+------+----+----------------- Curtiss V-2 8 5 7 1100 200 1400 690 ...

-----------+------+------+------+-------+----+------+----+----------------- CENSORED -----------+------+------+------+-------+----+------+----+----------------- General Ve- 9 4.33 5.9 848 100 1200 272 12 gals/hour at hicle Gnome Mono rated H.P.

-----------+------+------+------+-------+----+------+----+----------------- Gyro K 7 4-1/2 6 ... 90 1250 215 8 gals/hour at Rotary, Le Rhone Type rated H.P.

-----------+------+------+------+-------+----+------+----+----------------- Gyro L 9 4-1/2 6 859 100 1200 285 10 gals/hour at Rotary, Le Rhone Type rated H.P.

-----------+------+------+------+-------+----+------+----+----------------- Hall-Scott 4 5 7 550 90- 1400 410 ...

A-7 100 -----------+------+------+------+-------+----+------+----+----------------- Hall-Scott 6 5 7 825 125 1300 592 ...

A-5 -----------+------+------+------+-------+----+------+----+----------------- Hispano- 8 4-5/8 5 672 154 1500 455 ...

Suiza -----------+------+------+------+-------+----+------+----+----------------- Knox Motors 12 4-3/4 7 1555 300 1800 1425 31.5 gals/hour Co. -----------+------+------+------+-------+----+------+----+----------------- Maximotor 6 4-1/2 5 477 85 1600 340 ...

A-6 -----------+------+------+------+-------+----+------+----+----------------- Maximotor 6 5 6 706.8 115 1600 385 ...

B-6 -----------+------+------+------+-------+----+------+----+----------------- Maximotor 8 4-1/2 5 636 115 1600 420 ...

A-8 -----------+------+------+------+-------+----+------+----+----------------- Packard 12 12 4 6 903 225 2100 800 ...

-----------+------+------+------+-------+----+------+----+----------------- Sturtevant 8 4 5-1/2 552.9 140 2000 580 ...

5 -----------+------+------+------+-------+----+------+----+----------------- Sturtevant 8 4 5-1/2 ... 140 2000 514 13.75 gals/hour 5-A -----------+------+------+------+-------+----+------+----+----------------- Thomas 8 8 4 5-1/2 552.9 135 2000 630 ...

lbs. with self-starter -----------+------+------+------+-------+----+------+----+----------------- Thomas 88 8 4-1/8 5-1/2 552.9 150 2100 525 ...

lbs. with self-starter -----------+------+------+------+-------+----+------+----+----------------- Wisconsin 6 5 6-1/2 765.7 140 1380 637 ...

-----------+------+------+------+-------+----+------+----+----------------- Wisconsin 12 5 6-1/2 1531.4 250 1200 ... ...

The carburetor used on this 150 horse-power Mercedes motor is precisely of the same type used on the Twin Six motor. It has two venturi throats, in the center of which is placed the gasoline spray nozzle of conventional type, fixed size orifices, immediately above which are placed two panel type throttles with side outlets. An idling or primary nozzle is arranged to discharge above the top of the venturi throat. The carburetor body is of cast aluminum and is water jacketed. It is bolted directly to air pa.s.sage pa.s.sing through the top and bottom half of the crank-case which pa.s.ses 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 a.s.sist in the vaporization.

The inlet pipes themselves are copper. All the pa.s.sages 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 pa.s.ses over the bottom dead center much more slowly than with a long rod.

[Ill.u.s.tration: Fig. 245.--Part Sectional View of 90 Horse-Power Mercedes Engine, Which is Typical of the Design of Larger Sizes.]

Other features of the design are a very stiff crank-case, both halves of which are bolted together by means of long through bolts, the crank-shaft main bearings are seated in the lower half of the case instead of in the usual caps and no provision is made for taking up the main bearings. The Mercedes company uses a plunger type of pump having mechanically operated piston valves and it is driven by means of worm gearing.

The overhead cam-shaft construction is extremely light. The cam-shaft is mounted in a nearly cylindrical cast bronze case and is driven by means of bevel gears from the crank-shaft. The vertical bevel gear shaft through which the drive is taken from the crank-shaft to the cam-shaft operates at one and one-half times the crank-shaft speeds and the reduction to the half-time cam-shaft is secured through a pair of bevels. On this vertical shaft there is mounted the water pump and a bevel gear for driving two magnetos. The water pump mounted on this shaft tends to steady the drive and avoid vibration in the gearing.

The cylinder sizes of six-cylinder aviation motors which have been built by Mercedes are

Bore Stroke Horse-power 105 mm. 140 mm. 100 120 mm. 140 mm. 135 140 mm. 150 mm. 150 140 mm. 160 mm. 160

The largest of these motors has recently had its horse-power increased to 176 at 1450 R. P. M. This general design of motor has been the foundation for a great many other aviation motor designs, some of which have proved very successful but none of which is equal to the original.

Among the motors which follow more or less closely the scheme of design and arrangement are the Hall-Scott, the Wisconsin motor, the Renault water-cooled, the Packard, the Christofferson and the Rolls-Royce. Each of these motors show considerable variation in detail. The Rolls-Royce and Renault are the only ones who have used the steel cylinder with the steel jacket. The Wisconsin motor uses an aluminum cylinder with a hardened steel liner and cast-iron valve seats. The Christofferson has somewhat similar design to the Wisconsin with the exception that the valve seats are threaded into the aluminum jacket and the cylinder head has a blank end which is secured to the aluminum casting by means of the valve seat pieces. The Rolls-Royce motors show small differences in details of design in cylinder head and cam-shaft housing from the Mercedes on which it has taken out patents, not only abroad but in this country.

THE BENZ MOTOR

In the Kaiser prize contest for aviation motors a four-cylinder Benz motor of 130 by 180 mm. won first prize, developing 103 B. H. P. at 1290 R. P. M. The fuel consumption was 210 grams per horse-power hour. Total weight of the motor was 153 kilograms. The oil consumption was .02 of a kilogram per horse-power hour. This motor was afterward expanded into a six-cylinder design and three different sizes were built.

The accompanying table gives some of the details of weight, horse-power, etc.

Motor type B FD FF Rated horse-power 85 100 150 Horse-power at 1250 r.p.m 88 108 150 Horse-power at 1350 r.p.m 95 115 160 Bore in millimeters 106 116 130 Stroke in millimeters 150 160 180 Offset of the cylinders in millimeters 18 20 20 Rate of gasoline consumption in grams 240 230 225 Oil consumption in grams per b.h.p. hour 10 10 10 Oil capacity in kilograms 36 4 4-1/2 Water capacity in litres 5-1/2 7-1/2 9-1/2 The weight with water and oil but with two magnetos, fuel feeder and air pump in kilograms 170 200 245 The weight of motors, including the water pump, two magnetos, double ignition, etc. 160 190 230 The weight of the exhaust pipe, complete in kilograms 4 4.8 5-1/2 The weight of the propeller hub in kilograms. 3-1/2 4 4

The Benz cylinder is a simple, straightforward design and a very reliable construction and not particularly difficult to manufacture. The cylinder is cast of iron without a water jacket but including 45 degrees angle elbows to the valve ports. The cylinders are machined wherever possible and at other points have been hand filed and sc.r.a.ped, 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 pa.s.sage 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 c.o.c.ked to insert it in the guide, which has a bronze bushing at its upper end to compensate for the smaller valve stem diameter. The valve stem is 14 mm. or 9/16" in diameter and is reduced at its upper portion to 9-1/2 mm. The valves are operated through a push rod and rocker arm construction, which is 7/16" and exceedingly light.

Rocker arm supports are steel studs with enlarged heads to take a double row ball bearing. A roller is mounted at one end of the rocker arm to impinge on the end of the valve stem, and the rocker arm has an adjustable globe stud at the other end. The push rods are light steel tubes with a wall thickness of 0.75 mm. and have a hardened steel cup at their upper end to engage the rocker arm globe stud and a hardened steel globe at their lower end to socket in the roller plunger.

The Benz cam-shaft has a diameter of 26 mm. and is bored straight through 18 mm. and there is a spiral gear made integrally with the shaft in about the center of its length for driving the oil pump gear. The cam faces are 10 mm. wide. There is also, in addition to the intake and exhaust cams, a set of half compression cams. The shaft is moved longitudinally in its bearings by means of an eccentric to put these cams into action. At the fore end of the shaft is a driving gear f.l.a.n.g.e which is very small in diameter and very thin. The f.l.a.n.g.e is 68 mm. in diameter and 4 mm. thick and is tapped to take 6 mm. bolts. The total length of cam-shaft is 1038 mm., and it becomes a regular gun boring job to drill a hole of this length.

The cam-shaft gear is 140 mm. or 5-1/2 inches outside diameter. It has fifty-four teeth and the gear face is 15 mm. or 19/32". The f.l.a.n.g.e 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 pa.s.s 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 pa.s.ses, and those on either side of the center form the carburetor intake air pa.s.sages 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 a.s.sembly 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.

[Ill.u.s.tration: 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.