WHILE modern progress in internal combustion engine design and construction results in record eclipsing record with confusing frequency, whether it be on land, water or in the air, there is no doubt that the performance of the Supermarine seaplanes whereby the Schneider Trophy was won for all time by this country and the world's speed record established at the astounding figure of 408 m.p.h. will remain for a long time to come as a high-water mark in the history of aviation and speed attempts. And even when Stainforth's record is attacked and beaten, the story of the great en-leavour which was put out by all those connected with the production of that wonderful aircraft, the S.6.B., will stand always as a remarkable accomplishment. Particularly is this so of the power unit of the craft, the Rolls-Royce "

Rolls-Royce, Ltd., in producing this engine started at a disadvantage. They were pressed for time ; and time, as every amateur tuner knows, is a matter of great importance in preparing a racing engine, if success is to follow. That it did follow, is proof that the worldfamous Derby firm can combine hustle with perfect craftsmanship to an extent which must surely have surprised even the Americans. In the first instance the " R " engine was developed from the Rolls-Royce "Buzzard," a twelve-cylindered waterrcooled unit of 825 h.p. The cylinders in both cases are arranged in banks of six, set at an angle of 60 degrees to each other, and each block carries a camshaft driven by bevelled shafts. The bore and stroke dimensions are 152.5 mm. by 169 mm., and it measures in length 7 feet 71 inches, in height 3 feet 4 inches, and the

over-all width is 2 feet 6 inches. The air screw is geared. It will be remembered that the " R " engine was first used in the 1929 Schneider Contest. The weight of this unit is 1,530 lbs. and with a power output of 1,900 h.p. the weight per h.p. ratio is thus but .805 lbs.

Even in the light of present day knowledge and rapid progress it would seem a well-nigh impossible task to improve on this remarkable figure, yet the Rolls-Royce people decided that for the last race still more power should be obtained from the engine, and in order to secure this they concentrated on boosting up the engine to an even greater degree. An entirely new form of supercharger was designed, therefore.

In building a power unit for the Schneider machines it was highly important to reduce the bulk and frontal area to the lowest limits ; this meant that the supercharger had to be reasonably compact, and to enable them to build this unit of small diameter and yet get it to cope with the enormous quantity of air induced, it was designed so as to take in. air at both sides of the rotor. The difficulties to be overcome were numerous ; unless a blower is efficient the fuel-air charge will reach an excessive temperature, and there will be a serious loss of power. The stresses imposed on every part of the engine (already tuned to an intense degree) are magnified; the lubrication system may be affected, and the cooling also. Higher temperatures and higher revs, may be too much for plugs, piston rings and valve springs.

One by one these" snags "were dealt with and solved, and whereas the 1929 " R " engine turned over at 2,900 r.p.m., and gave off 1,900 b.h.p., the 1931 edition revs at 3,200 r.p.m., and produces 2,350 b.h.p.

The supercharger having been designed and built, the experimental work was quickly begun on the new type " R " ; Heenan and Froude produced a special water-brake for the purpose, a special fan was rigged up to reproduce the conditions of air-flow into the air intakes when the S.6.B. would be in flight, and— after serious trouble had been experienced with the exhaust fumes inside the test house, which not only affected the staff but the engine as well—a " Kestrel " engine was installed with a pusher propeller to send a stream of air through the room to clear the atmosphere. In addition, two electric fans were used to direct a cooling stream of air over the crankcase. In order to determine the correct speed of the air flow over the engine and air in

takes, pitot heads were used, and the blast kept at 400 m.p.h. Normally, engines are run on the brake with silencers, but with the " because the actual racing conditions had to be simulated, only short stubs were fitted to the exhaust ports. One can imagine what indescribable din must have arisen in the test shop when the experimental unit and

the auxilaries were all in action !

In the test bay was also installed a single-cylinder unit built up of " R " parts ; this was intended for trials in connection with plugs, valve-springs, fuels, etc. It is rather interesting that this gave far more trouble than the complete engine, and was in fact very unreliable. So the development of the new Rolls began. At first, that is to say in April last, and only five months before the date of the Contest, the engine could not be persuaded to mil for more than 20 minutes before "something went." Valve springs failed, connecting rods broke, big-ends and other parts collapsed under the terrific strain. The aim of the design and test department was to get the engine to run at full power for one hour ; so it would seem that they had a very formidable task. But by July a non-stop run for half-an-hour was achieved. As is often the case, minor troubles were most persistent, and fractured valve springs were frequently met with even after only a few minutes of running. As with the connecting rods, crankshaft:and other components

which broke, these were re-tested and, if considered necessary, replaced with others of modified type, and gradually the troubles due to failure of materials were eliminated. On 3rd August the" R" was induced to carry on at full bore for 58 minutes, then with the scheduled test almost done there was a crash and silence —a broken crankshaft. But without more ado, a modification was carried out in the design of the part, a batch of new shafts turned out, and nine days later the racing unit completed the hour at 2,350 b.h.p. Thus, the task which had been set was accomplished —and in the space of six months. To produce an engine which weighs but 1,630 lbs. and which has an output of 2,350 h.p. is in itself a triumph of engineering ; that it was done in so short a period of time makes it an epic in the annals of aeronautical history. It was not just a matter of manufacture, assembly and trial. The resources of the research and metallurgical departments were continually called into play, and the ingenuity of the designers was required again and again to solve the theoretical problems and practical difficulties which cropped up. As an example, when trouble occurred with the original type of connecting rod, due to the increase in revs and loads, it became obvious that this component would have to be completely altered in design ; a variety of alternative types were evolved, calculations made, drawings produced and experimental

parts manufactured, tested, examined and tested again. So with the crankshaft, and in connection with this part, the fact that the inertia and centrifugal forces on the centre bearing when the engine was running at normal revs was no less than nine tons conveys to some extent the nature of the stresses which had to be combated. Mixed up with all these tasks were other matters requiring attention. The oil consumption at first, was impossibly high—at one time as much as 112 gallons an hour ! Careful study, scheming and trials gradually got this figure down to about one-eighth of the original figure. Then there were minor troubles with the auxiliaries, such as oil getting into the magnetos, tendency to flood and piling-up in the carburetters, and so forth. There could be no overlooking of even the smallest detail or possible defect in order to get the " R" to give that 2,300 h.p. for one hour.

To some, perhaps, this tremendous concentrated effort may not appear as having been worth while, but there is not the slightest doubt that the knowledge acquired in those crowded six months would only have been gained in the same number of years under normal conditions of working. And besides, it won the Schneider Trophy, gave us the speed record, and has placed Britain and particularly the firm of Rolls-Royce, Ltd., in the very forefront of the world of aero engine production, a position which will long remain unassailed.