A History of Aeronautics Part 21

The Lamplough six-cylinder two-stroke cycle rotary, shown at the Aero Exhibition at Olympia in 1911, had several innovations, including a charging pump of rotary blower type. With the six cylinders, six power impulses at regular intervals were given on each rotation; otherwise, the cycle of operations was carried out much as in other two-stroke cycle engines. The pump supplied the mixture under slight pressure to an inlet port in each cylinder, which was opened at the same time as the exhaust port, the period of opening being controlled by the piston. The rotary blower sucked the mixture from the carburettor and delivered it to a pa.s.sage communicating with the inlet ports in the cylinder walls.

A mechanically-operated exhaust valve was placed in the centre of each cylinder head, and towards the end of the working stroke this valve opened, allowing part of the burnt gases to escape to the atmosphere; the remainder was pushed out by the fresh mixture going in through the ports at the bottom end of the cylinder. In practice, one or other of the cylinders was always taking fresh mixture while working, therefore the delivery from the pump was continuous and the mixture had not to be stored under pressure.

The piston of this engine was long enough to keep the ports covered when it was at the top of the stroke, and a bottom ring was provided to prevent the mixture from entering the crank case. In addition to preventing leakage, this ring no doubt prevented an excess of oil working up the piston into the cylinder. As the cylinder fired with every revolution, the valve gear was of the simplest construction, a fixed cam lifting each valve as the cylinder came into position. The spring of the exhaust valve was not placed round the stem in the usual way, but at the end of a short lever, away from the heat of the exhaust gases. The cylinders were of cast steel, the crank case of aluminium, and ball-bearings were fitted to the crankshaft, crank pins, and the rotary blower pump. Ignition was by means of a high-tension magneto of the two-spark pattern, and with a total weight of 300 lbs. the maximum output was 102 brake horse-power, giving a weight of just under 3 lbs.

per horse-power.

One of the most successful of the two-stroke cycle engines was that designed by Mr G. F. Mort and constructed by the New Engine Company.

With four cylinders of 3.69 inches bore by 4.5 inches stroke, and running at 1,250 revolutions per minute, this engine developed 50 brake horse-power; the total weight of the engine was 155 lbs., thus giving a weight of 3.1 lbs. per horse-power. A scavenging pump of the rotary type was employed, driven by means of gearing from the engine crankshaft, and in order to reduce weight to a minimum the vanes were of aluminium. This engine was tried on a biplane, and gave very satisfactory results.

American design yields two apparently successful two-stroke cycle aero engines. A rotary called the Fredericson engine was said to give an output of 70 brake horse-power with five cylinders 4.5 inches diameter by 4.75 inches stroke, running at 1,000 revolutions per minute. Another, the Roberts two-stroke cycle engine, yielded 100 brake horse-power from six cylinders of the stepped piston design; two carburettors, each supplying three cylinders, were fitted to this engine. Ignition was by means of the usual high-tension magneto, gear-driven from the crankshaft, and the engine, which was water-cooled, was of compact design.

It may thus be seen that the two-stroke cycle type got as far as actual experiment in air work, and that with considerable success. So far, however, the greater reliability of the four-stroke cycle has rendered it practically the only aircraft engine, and the two-stroke has yet some way to travel before it becomes a formidable compet.i.tor, in spite of its admitted theoretical and questioned practical advantages.

VII. ENGINES OF THE WAR PERIOD

The princ.i.p.al engines of British, French, and American design used in the war period and since are briefly described under the four distinct types of aero engine; such notable examples as the Rolls-Royce, Sunbeam, and Napier engines have been given special mention, as they embodied--and still embody--all that is best in aero engine practice. So far, however, little has been said about the development of German aero engine design, apart from the early Daimler and other pioneer makes.

At the outbreak of hostilities in 1914, thanks to subsidies to contractors and prizes to aircraft pilots, the German aeroplane industry was in a comparatively flouris.h.i.+ng condition. There were about twenty-two establishments making different types of heavier-than-air machines, monoplane and biplane, engined for the most part with the four-cylinder Argus or the six-cylinder Mercedes vertical type engines, each of these being of 100 horse-power--it was not till war brought increasing demands on aircraft that the limit of power began to rise.

Contemporary with the Argus and Mercedes were the Austro-Daimler, Benz, and N.A.G., in vertical design, while as far as rotary types were concerned there were two, the Oberursel and the Stahlhertz; of these the former was by far the most promising, and it came to virtual monopoly of the rotary-engined plane as soon as the war demand began. It was practically a copy of the famous Gnome rotary, and thus deserves little description.

Germany, from the outbreak of war, practically, concentrated on the development of the Mercedes engine; and it is noteworthy that, with one exception, increase of power corresponding with the increased demand for power was attained without increasing the number of cylinders. The various models ranged between 75 and 260 horse-power, the latter being the most recent production of this type. The exception to the rule was the eight-cylinder 240 horse-power, which was replaced by the 260 horse-power six-cylinder model, the latter being more reliable and but very slightly heavier. Of the other engines, the 120 horsepower Argus and the 160 and 225 horse-power Benz were the most used, the Oberursel being very largely discarded after the Fokker monoplane had had its day, and the N.A.G. and Austro-Daimler Daimler also falling to comparative disuse. It may be said that the development of the Mercedes engine contributed very largely to such success as was achieved in the war period by German aircraft, and, in developing the engine, the builders were careful to make alterations in such a way as to effect the least possible change in the design of aeroplane to which they were to be fitted. Thus the engine base of the 175 horse-power model coincided precisely with that of the 150 horse-power model, and the 200 and 240 horse-power models retained the same base dimensions. It was estimated, in 1918, that well over eighty per cent of German aircraft was engined with the Mercedes type.

In design and construction, there was nothing abnormal about the Mercedes engine, the keynote throughout being extreme reliability and such simplification of design as would permit of ma.s.s production in different factories. Even before the war, the long list of records set up by this engine formed practical application of the wisdom of this policy; Bohn's flight of 24 hours 10 minutes, accomplished on July 10th and 11th, 1914, 9is an instance of this--the flight was accomplished on an Albatross biplane with a 75 horsepower Mercedes engine. The radial type, instanced in other countries by the Salmson and Anzani makes, was not developed in Germany; two radial engines were made in that country before the war, but the Germans seemed to lose faith in the type under war conditions, or it may have been that insistence on standardisation ruled out all but the proved examples of engine.

Details of one of the middle sizes of Mercedes motor, the 176 horse-power type, apply very generally to the whole range; this size was in use up to and beyond the conclusion of hostilities, and it may still be regarded as characteristic of modern (1920) German practice. The engine is of the fixed vertical type, has six cylinders in line, not off-set, and is water-cooled. The cam shaft is carried in a special bronze casing, seated on the immediate top of the cylinders, and a vertical shaft is interposed between crankshaft and camshaft, the latter being driven by bevel gearing.

On this vertical connecting-shaft the water pump is located, serving to steady the motion of the shaft. Extending immediately below the camshaft is another vertical shaft, driven by bevel gears from the crank-shaft, and terminating in a worm which drives the multiple piston oil pumps.

The cylinders are made from steel forgings, as are the valve chamber elbows, which are machined all over and welded together. A jacket of light steel is welded over the valve elbows and attached to a f.l.a.n.g.e on the cylinders, forming a water-cooling s.p.a.ce with a section of about 7/16 of an inch. The cylinder bore is 5.5 inches, and the stroke 6.29 inches. The cylinders are attached to the crank case by means of dogs and long through bolts, which have shoulders near their lower ends and are bolted to the lower half of the crank chamber. A very light and rigid structure is thus obtained, and the method of construction won the flattery of imitation by makers of other nationality.

The cooling system for the cylinders is extremely efficient. After leaving the water pump, the water enters the top of the front cylinders and pa.s.ses successively through each of the six cylinders of the row; short tubes, welded to the tops of the cylinders, serve as connecting links in the system. The Panhard car engines for years were fitted with a similar cooling system, and the White and Poppe lorry engines were also similarly fitted; the system gives excellent cooling effect where it is most needed, round the valve chambers and the cylinder heads.

The pistons are built up from two pieces; a dropped forged steel piston head, from which depend the piston pin bosses, is combined with a cast-iron skirt, into which the steel head is screwed. Four rings are fitted, three at the upper and one at the lower end of the piston skirt, and two lubricating oil grooves are cut in the skirt, in addition to the ring grooves. Two small rivets retain the steel head on the piston skirt after it has been screwed into position, and it is also welded at two points. The coefficient of friction between the cast-iron and steel is considerably less than that which would exist between two steel parts, and there is less tendency for the skirt to score the cylinder walls than would be the case if all steel were used--so noticeable is this that many makers, after giving steel pistons a trial, discarded them in favour of cast-iron; the Gnome is an example of this, being originally fitted with a steel piston carrying a bra.s.s ring, discarded in favour of a cast-iron piston with a percentage of steel in the metal mixture. In the Le Rhone engine the difficulty is overcome by a cast-iron liner to the cylinders.

The piston pin of the Mercedes is of chrome nickel steel, and is retained in the piston by means of a set screw and cotter pin. The connecting rods, of I section, are very short and rigid, carrying floating bronze bushes which fit the piston pins at the small end, and carrying an oil tube on each for conveying oil from the crank pin to the piston pin.

The crankshaft is of chrome nickel steel, carried on seven bearings.

Holes are drilled through each of the crank pins and main bearings, for half the diameter of the shaft, and these are plugged with pressed bra.s.s studs. Small holes, drilled through the crank cheeks, serve to convey lubricant from the main bearings to the crank pins. The propeller thrust is taken by a simple ball thrust bearing at the propeller end of the crankshaft, this thrust bearing being seated in a steel retainer which is clamped between the two halves of the crank case. At the forward end of the crankshaft there is mounted a master bevel gear on six splines; this bevel floats on the splines against a ball thrust bearing, and, in turn, the thrust is taken by the crank case cover. A stuffing box prevents the loss of lubricant out of the front end of the crank chamber, and an oil thrower ring serves a similar purpose at the propeller end of the crank chamber.

With a motor speed of 1,450 r.p.m., the vertical shaft at the forward end of the motor turns at 2,175 r.p.m., this being the speed of the two magnetos and the water pump. The lower vertical shaft bevel gear and the magneto driving gear are made integral with the vertical driving shaft, which is carried in plain bearings in an aluminium housing. This housing is clamped to the upper half of the crank case by means of three studs.

The cam-shaft carries eighteen cams, these being the inlet and exhaust cams, and a set of half compression cams which are formed with the exhaust cams and are put into action when required by means of a lever at the forward end of the cam-shaft. The cam-shaft is hollow, and serves as a channel for the conveyance of lubricating oil to each of the camshaft bearings. At the forward end of this shaft there is also mounted an air pump for maintaining pressure on the fuel supply tank, and a bevel gear tachometer drive.

Lubrication of the engine is carried out by a full pressure system.

The oil is pumped through a single manifold, with seven branches to the crankshaft main bearings, and then in turn through the hollow crankshaft to the connecting-rod big ends and thence through small tubes, already noted, to the small end bearings. The oil pump has four pistons and two double valves driven from a single eccentric shaft on which are mounted four eccentrics. The pump is continuously submerged in oil; in order to avoid great variations in pressure in the oil lines there is a piston operated pressure regulator, cut in between the pump and the oil lines.

The two small pistons of the pump take fresh oil from a tank located in the fuselage of the machine; one of these delivers oil to the cam shaft, and one delivers to the crankshaft; this fresh oil mixes with the used oil, returns to the base, and back to the main large oil pump cylinders.

By means of these small pump pistons a constant quant.i.ty of oil is kept in the motor, and the oil is continually being freshened by means of the new oil coming in. All the oil pipes are very securely fastened to the lower half of the crank case, and some cooling of the oil is effected by air pa.s.sing through channels cast in the crank case on its way to the carburettor.

A light steel manifold serves to connect the exhaust ports of the cylinders to the main exhaust pipe, which is inclined about 25 degrees from vertical and is arranged to give on to the atmosphere just over the top of the upper wing of the aeroplane.

As regards carburation, an automatic air valve surrounds the throat of the carburettor, maintaining normal composition of mixture. A small jet is fitted for starting and running without load. The channels cast in the crank chamber, already alluded to in connection with oil-cooling, serve to warm the air before it reaches the carburettor, of which the body is water-jacketed.

Ignition of the engine is by means of two Bosch ZH6 magnetos, driven at a speed of 2,175 revolutions per minute when the engine is running at its normal speed of 1,450 revolutions. The maximum advance of spark is 12 mm., or 32 degrees before the top dead centre, and the firing order of the cylinders is 1,5,3,6,2,4.

The radiator fitted to this engine, together with the water-jackets, has a capacity of 25 litres of water, it is rectangular in shape, and is normally tilted at an angle of 30 degrees from vertical. Its weight is 26 kg., and it offers but slight head resistance in flight.

The radial type of engine, neglected altogether in Germany, was brought to a very high state of perfection at the end of the War period by British makers. Two makes, the Cosmos Engineering Company's 'Jupiter'

and 'Lucifer,' and the A.B.C. 'Wasp II' and 'Dragon Fly 1A' require special mention for their light weight and reliability on trials.

The Cosmos 'Jupiter' was--for it is no longer being made--a 450 horse-power nine-cylinder radial engine, air-cooled, with the cylinders set in one single row; it was made both geared to reduce the propeller revolutions relatively to the crankshaft revolutions, and ungeared; the normal power of the geared type was 450 horse-power, and the total weight of the engine, including carburettors, magnetos, etc., was only 757 lbs.; the engine speed was 1,850 revolutions per minute, and the propeller revolutions were reduced by the gearing to 1,200. Fitted to a 'Bristol Badger' aeroplane, the total weight was 2,800 lbs., including pilot, pa.s.senger, two machine-guns, and full military load; at 7,000 feet the registered speed, with corrections for density, was 137 miles per hour; in climbing, the first 2,000 feet was accomplished in 1 minute 4 seconds; 4,000 feet was reached in 2 minutes 10 seconds; 6,000 feet was reached in 3 minutes 33 seconds, and 7,000 feet in 4 minutes 15 seconds. It was intended to modify the plane design and fit a new propeller, in order to attain even better results, but, if trials were made with these modifications, the results are not obtainable.

The Cosmos 'Lucifer' was a three-cylinder radial type engine of 100 horse-power, inverted Y design, made on the simplest possible principles with a view to quant.i.ty production and extreme reliability. The rated 100 horse-power was attained at 1,600 revolutions per minute, and the cylinder dimensions were 5.75 bore by 6.25 inches stroke. The cylinders were of aluminium and steel mixture, with aluminium heads; overhead valves, operated by push rods on the front side of the cylinders, were fitted, and a simple reducing gear ran them at half engine speed. The crank case was a circular aluminium casting, the engine being attached to the fuselage of the aeroplane by a circular f.l.a.n.g.e situated at the back of the case; propeller shaft and crankshaft were integral. Dual ignition was provided, the generator and distributors being driven off the back end of the engine and the distributors being easily accessible.

Lubrication was by means of two pumps, one scavenging and one suction, oil being fed under pressure from the crankshaft. A single carburettor fed all three cylinders, the branch pipe from the carburettor to the circular ring being provided with an exhaust heater. The total weight of the engine, 'all on,' was 280 lbs.

The A.B.C. 'Wasp II,' made by Walton Motors, Limited, is a seven-cylinder radial, air-cooled engine, the cylinders having a bore of 4.75 inches and stroke 6.25 inches. The normal brake horse-power at 1,650 revolutions is 160, and the maximum 200 at a speed of 1,850 revolutions per minute. Lubrication is by means of two rotary pumps, one feeding through the hollow crankshaft to the crank pin, giving centrifugal feed to big end and thence splash oiling, and one feeding to the nose of the engine, dropping on to the cams and forming a permanent sump for the gears on the bottom of the engine nose. Two carburettors are fitted, and two two-spark magnetos, running at one and three-quarters engine speed. The total weight of this engine is 350 lbs., or 1.75 lbs. per horse-power. Oil consumption at 1,850 revolutions is.03 pints per horse-power per hour, and petrol consumption is.56 pints per horsepower per hour. The engine thus shows as very economical in consumption, as well as very light in weight.

The A.B.C. 'Dragon Fly 1A 'is a nine-cylinder radial engine having one overhead inlet and two overhead exhaust valves per cylinder. The cylinder dimensions are 5.5 inches bore by 6.5 inches stroke, and the normal rate of speed, 1,650 revolutions per minute, gives 340 horse-power. The oiling is by means of two pumps, the system being practically identical with that of the 'Wasp II.' Oil consumption is.021 pints per brake horse-power per hour, and petrol consumption.56 pints--the same as that of the 'Wasp II.' The weight of the complete engine, including propeller boss, is 600 lbs., or 1,765 lbs. per horse-power.

These A.B.C. radials have proved highly satisfactory on tests, and their extreme simplicity of design and reliability commend them as engineering products and at the same time demonstrate the value, for aero work, of the air-cooled radial design--when this latter is accompanied by sound workmans.h.i.+p. These and the Cosmos engines represent the minimum of weight per horse-power yet attained, together with a practicable degree of reliability, in radial and probably any aero engine design.

APPENDIX A

GENERAL MENSIER'S REPORT ON THE TRIALS OF CLEMENT ADER'S AVION.

Paris, October 21, 1897.

Report on the trials of M. Clement Ader's aviation apparatus.

M. Ader having notified the Minister of War by letter, July 21, 1897, that the Apparatus of Aviation which he had agreed to build under the conditions set forth in the convention of July 24th, 1894, was ready, and therefore requesting that trials be undertaken before a Committee appointed for this purpose as per the decision of August 4th, the Committee was appointed as follows:--

Division General Mensier, Chairman; Division General Delambre, Inspector General of the Permanent Works of Coast Defence, Member of the Technical Committee of the Engineering Corps; Colonel Laussedat, Director of the Conservatoire des Arts et Metiers; Sarrau, Member of the Inst.i.tute, Professor of Mechanical Engineering at the Polytechnic School; Leaute, Member of the Inst.i.tute, Professor of Mechanical Engineering at the Polytechnique School.

Colonel Laussedat gave notice at once that his health and work as Director of the Conservatoire des Arts et Metiers did not permit him to be a member of the Committee; the Minister therefore accepted his resignation on September 24th, and decided not to replace him.

Later on, however, on the request of the Chairman of the Committee, the Minister appointed a new member General Grillon, commanding the Engineer Corps of the Military Government of Paris.

To carry on the trials which were to take place at the camp of Satory, the Minister ordered the Governor of the Military Forces of Paris to requisition from the Engineer Corps, on the request of the Chairman of the Committee, the men necessary to prepare the grounds at Satory.

After an inspection made on the 16th an aerodrome was chosen. M. Ader's idea was to have it of circular shape with a width of 40 metres and an average diameter of 450 metres. The preliminary work, laying out the grounds, interior and exterior circ.u.mference, etc., was finished at the end of August; the work of smoothing off the grounds began September 1st with forty-five men and two rollers, and was finished on the day of the first tests, October 12th.

The first meeting of the Committee was held August 18th in M. Ader's workshop; the object being to demonstrate the machine to the Committee and give all the information possible on the tests that were to be held.

After a careful examination and after having heard all the explanations by the inventor which were deemed useful and necessary, the Committee decided that the apparatus seemed to be built with a perfect understanding of the purpose to be fulfilled as far as one could judge from a study of the apparatus at rest; they therefore authorised M. Ader to take the machine apart and carry it to the camp at Satory so as to proceed with the trials.

By letter of August 19th the Chairman made report to the Minister of the findings of the Committee.