Part 5

Why the one-piece crankcase and cylinder jacket combination of the 1903 engine was abandoned for the individual cylinder construction can only be surmised. The difference in weight was probably slight, as the inherent weight advantage of the original crankcase casting was largely offset by the relatively heavy valve boxes, and the difference in the total amount of machining required, because of the separate valve boxes, cages, and attaching parts, also was probably slight. Although the crankcase had shown itself to be structurally weak, this could have been cared for by proper strengthening. The 1903 design did have some fundamental disadvantages: it required a fairly complex pattern and expensive casting, plus some difficult machining, part of which had to be very accurate in order to maintain both gas and water joints tight; and the failure of any one cylinder that affected the jacket meant a complete crankcase replacement.

It seems probable that a change was initially made mandatory by their intention to utilize the ported exhaust feature, the value of which they had proved in the experimental engine. The separate one-piece water jacket construction they had arrived at in this engine was available, but once the decision to change was made, the individual cylinder with its shrunk-on jacket had much to commend it--simplicity, cost, ease of manufacture and assembly and attachment, and serviceability. The advantages of the auxiliary, or ported, exhaust were not obtained without cost, however, as the water jacket around the barrel could not very easily be extended below the ports. Thus, even though the water was carried as high as possible on the upper end, a large portion of the barrel was left uncooled, and the lack of cooling at the lower end, in conjunction with the uncooled portion of the head, meant that only approximately half the entire cylinder surface was cooled directly.

The piston was generally the same as in the 1903 engine, except that six radial ribs were added on the under side of the head, tapering from maximum thickness at the center to nothing near the wall. They were probably incorporated as an added path for heat to flow from the center of the piston toward the outside, as their shape was not the best use of material for strength. The piston pin was locked in the piston by the usual set screw, but here no provision was made for the alternate practice of clamping the rod on the pin. This piston-pin setscrew construction had become a standard arrangement in automobile practice. The piston rings were the normal wide design of that time, with what would now be considered a low unit pressure.

Quite early in the life of this engine model the practice was initiated of incorporating shallow grooves in the surface of the more highly loaded thrust face of the piston below the piston pin to provide additional lubrication. This development apparently proceeded haphazardly. Figure 10c shows three of the pistons from an engine of low serial number--the first of this model to be delivered to the U.S. Navy--and it will be noted that one has no grooves, another has one, and the other has three. The eventual standardized arrangement provided three of these grooves, approximately 1/16 in. wide, extending halfway around the piston, and, although the depth was only a few thousandths of an inch, the amount of oil carried in them was apparently sufficient to assist in the lubrication of the face, as they were used in both the 4-and 6-cylinder engines.

Each cylinder was fastened to the crankcase by four nuts on studs driven into the aluminum case. Valves and rocker arms were similar to those of the early engines, the automatic inlet valve being retained. The continued use of the two-piece valve is not notable, even though one-piece forgings were available and in use at this time; the automobile continued for many years to use this construction. The camshaft was placed at the bottom of the engine, inside the crankcase, and the rocker arms were actuated by pushrods which were operated by hinged cam followers. The pushrod was fastened in the rocker by a pin, about which it operated, through its upper end and was positioned near the bottom by a guide in the crankcase deck. The lower end of the rod bore directly on the flat upper surface of the cam follower, and valve clearance adjustment was obtained by grinding this end. The camshaft and magneto were driven by the crankshaft through a three-member train of spur gears (see Figures 9, 10 and 11).

The built-up construction of the connecting rod was carried over from the first engine, and in the beginning apparently the same materials were used, except that the big end was babbited. Later the rod ends were changed from bronze to steel. The big end incorporated a small pointed scupper on one side for lubrication, as with the original, and this was sometimes drilled to feed a groove which carried oil to the rod bearing, but where the drilling was omitted, the only function the scupper then could perform was, as in the original engine, to throw a small amount of oil on the cylinder wall.

The crankshaft and flywheel were similar in design to those on the 1903 engine, except that the sharp corners at the top and bottom of the crank cheeks were machined off to save weight (see Figure 10f). An oil pump and a fuel pump were mounted side by side in bosses cast on the valve side of the crankcase; they were driven from the camshaft by worm gears and small shafts crossing the case.

The camshaft construction was considerably altered from the 1903 design. Although the reason is not entirely clear, one indication suggests that breakage or distortion of the shaft may have been encountered: whereas in the 1903 engine there had been no relationship between the location of the cams and the camshaft bearings, in this engine the exhaust valves were carefully positioned so that all cams were located very close to the supporting bearings in the crankcase. Also, the camshaft was solid, although it would seem that the original hollow shaft construction could have provided equal stiffness with less weight. The final decision was possibly determined by the practicality that there existed no standard tubing even approximating the size and wall thickness desired.

There still was no carburetor, a gear pump metering the fuel in the same manner as on the 1904-1905 engine. Basically, the intake charge was fed to the cylinders by a round gallery manifold running alongside the engine. This was split internally by a baffle extending almost from end to end, so that the fuel mixture entering the manifold on one side of the baffle was compelled to travel to the two ends before it could return to the inside cylinder, this feature being a copy of their 1903 general intake arrangement. Apparently various shapes and positions of entrance pipes with which to spray the fuel into the manifold were used; and the injection arrangement seems also to have been varied at different times. The fuel pump was not necessarily always used, as the engine in some of the illustrations did not incorporate one, the fuel apparently being fed by gravity, as on the original engine. Chenoweth describes an arrangement in which exhaust heat was applied to the inlet manifold to assist the fuel vaporization process, but it is believed that this was one of the many changes made in the engine during its lifetime and not necessarily a standard feature.

A water circulation pump was provided, driven directly by the crankshaft through a two-arm universal joint intended to care for any misalignment between the shaft and the pump. The water was piped to a horizontal manifold running along the cylinders just below the intake manifold, and a similar manifold on the other side of the engine collected it for delivery to the radiator. It is a little difficult to understand why it was not introduced at the bottom of the water jackets.

The crankcase was a relatively strong and well proportioned structure with three heavy strengthening ribs running from side to side, its only weakness being the one open side. A sheet-iron sump was fastened to the bottom by screws and it would appear from its design, method of attachment, and location of the engine mounting pads that this was added some time after the crankcase had been designed; but if so it was apparently retrofitted, as engines with quite low serial numbers have this part.

The ignition was by high-tension magneto and spark plug and this decision to change from the make-and-break system was undoubtedly the correct one, just as adoption of the other form originally was logical under the circumstances that existed then. The high-tension system was simpler and had now collected more service experience. The magneto was driven through the camshaft gear, and a shelf, or bracket, cast as an integral part of the case, was provided for mounting it. The spark advance control was in the magneto and, since spark timing was the only means of regulating the engine power and speed, a wide range of adjustment was provided.

The engine had the controllable compression release which had been added to the _No. 2_ and _No. 3_ flat engines, although mechanically it was considerably altered from the original design. Instead of the movable stop operating directly on the rocker roller to hold the exhaust valve open, it was located underneath a collar on the pushrod. This stop was hinged to the crankcase and actuated by a small rod running along and supported by the crankcase deck. Longitudinal movement of this rod in one direction would, by spring pressure on each stop, push them underneath the collars as the exhaust valves were successively opened. A reverse movement of the rod would release them (see Figure 10f). Why they retained the method of manually operating the compression release, which was the same as had been used in the 1904-1905 engine, is not quite clear. That is, the mechanism was put into operation by pulling a wire running from the pilot to a lever actuating the cam which moved the control rod. When normal valve operation was subsequently desired, the pilot was compelled to reach with his hand and operate the lever manually, whereas a second wire or push-pull mechanism would have obviated the necessity for both the awkward manual operation of the lever and the gear guard which was added to protect the pilot's hand, the lever being located close to the camshaft gear.

The 4-cylinder vertical engine was a considerable improvement over the previous designs. They had obtained a power increase of about 40 percent, with a weight decrease of 10 percent, and now had an engine whose design was almost standard form for good internal combustion engines for years to come. In fact, had they split the crankcase at the crankshaft center line and operated the inlet valves mechanically, they would have had what could be termed a truly modern design. They needed more cylinder cooling, both barrel and head, particularly the latter, and an opened-up induction system for maximum power output, but this was not what they were yet striving for. They had directly stated that they were much more interested in reliability than light weight.

This engine model was the only one of the Wright designs to be licensed and produced abroad, being manufactured in Germany by the Neue Automobil-Gesellschaft and by Bariquand et Marré in France. The latter was much more prominent and their engines were used in several early European airplanes.

The French manufacturer, without altering the basic design, made a number of changes of detail which seem to have greatly annoyed Wilbur Wright, although some of them could probably be listed as improvements, based on several features of later standard design. One consisted of an alteration in the position of the fuel and oil pumps, the latter being lowered to the level of the sump. The crankcase was drilled to provide forced-feed lubrication to the connecting rod big end and crankshaft main bearings. Strengthening ribs were added to the pistons running from the upper side of the pin bosses to the piston wall, and the crankcase studs holding down the cylinders were replaced with bolts having their heads inside the case. The hinged cam follower was omitted and the pushrod bore directly on the cam through a roller in its end. The magneto was moved toward the rear of the engine a considerable distance and an ignition timing control device was introduced between it and its driving gear. Instead of the magneto being mounted directly on the special bracket integral with the crankcase, a wooden board running from front to rear of the engine was used and this was fastened to the two engine support pads, the magneto bracket being omitted entirely.

Despite his criticism of the French motor and the quality of its manufacture, Wilbur was compelled to install one in his own exhibition airplane during his early French demonstrations at Le Mans after rod failure had broken his spare crankcase, and much of his subsequent demonstration flying was made with the French product.

The Eight-Cylinder Racing Engine

By 1909 regular and special air meets and races were being held and various competitions for trophies conducted. Among these the Gordon Bennett Cup Race for many years was considered a major event. For the 1910 competition it was decided to enter a Wright machine and, since this was a race with speed the sole objective, the available 4-cylinder engine, even in a version pushed to its maximum output, was deemed too small. They built for it a special 8-cylinder unit in a 90°V form. They were thus resorting to one of their 1904 concepts--modifying and enlarging a version known and proved in use--as the proper method of most quickly increasing output. Unfortunately again, there are essentially no detailed drawings available, so that the design cannot be studied.[16]

[Footnote 16: A drawing of the camshaft is held by The Franklin Institute.]

Only one engine is historically recorded as having been built, although in view of the Wrights' record of foresight and preparation it is almost certain that at least one spare unit, assembled or in parts, was provided. In any case, the airplane--it was called the _Baby Grand Racer_--and engine were wrecked just before the race, and no physical parts were retained, so that the sole descriptions come from external photographs, memory, and hearsay. McFarland thinks that possibly Orville Wright, particularly, was somewhat discomfited over the accident that eliminated the machine, as he had previously flown it quite successfully at a speed substantially higher than that of the ultimate winner, and he wanted to get it out of sight and mind as quickly as possible. The Air Force Museum at Wright Field, Dayton, Ohio, has an incomplete set of drawings of a 90°V, 8-cylinder Wright engine, but it is quite obvious from the basic design and individual features, as well as from at least one date on the drawings, that this conception is of a considerably later vintage than that of the _Baby Grand Racer_.

The racing engine was in essence a combination of two of the standard 4s on a redesigned crankcase utilizing as many of the 4-cylinder engine parts as possible. The rods were reported to have been placed side by side, and the regular 4-cylinder crankshaft, with alterations to accommodate the rods, was utilized. A single cam operated all the exhaust valves. It was compact and light, its only fundamental disadvantage being the inherent unbalance of the 90°V-8. The arrangement provided a much higher powered unit in the cheapest and quickest manner, and one that could be expected to operate satisfactorily with the least development.

The Six-Cylinder Vertical Engines

Shortly after the construction of the 8-cylinder engine the Wrights were again faced with the ever-recurrent problem of providing a higher powered standard production engine for their airplanes, which were now being produced in some numbers. By this time, 1911, there had been a relatively tremendous growth in both flying and automotive use of the internal combustion engine and as a result many kinds and sizes had been produced and utilized, so that numerous choices were presented to them. But if they were both to make use of their past experience and retain the simplicity they had always striven for, the more practical possibilities narrowed down to three: they could increase the cylinder size in the 4-cylinder combination, or they could go either to 6 or 8 cylinders in the approximate size they had previously used.

The 4-in. cylinder in combination with a 5-in. stroke would provide in four cylinders about the displacement they wanted. Strokes of 6 in. were not uncommon and cylinders of 6-in. bore had been very successfully utilized in high-output automobile racing engines many years before this, so there was seemingly no reason to doubt that the 5-in. cylinder could be made to operate satisfactorily, but it is not difficult to imagine the Wrights' thoughts concerning the roughness of an engine with cylinders of this diameter. The question of the grade of available fuel may possibly have entered into their decision to some extent, but it seems far more likely that roughness, their perennial concern, was the predominant reason for not staying with the more simple 4-cylinder form (as we have seen, roughness to them meant the effect of the cylinder explosion forces). Actually, of course, they never went larger than a 4-3/8-in. cylinder bore, and later aircraft engine experience would seem generally to confirm their judgment, for with the piston engine it has always been much more difficult to make the larger bores operate satisfactorily at any given specific output.

While the 90°V, 8-cylinder arrangement would have enabled them to utilize a great number of the 4-cylinder-engine parts, it would have given them a somewhat larger engine than was their apparent desire, unless they reduced the cylinder size. And while they had had some limited experience in building and operating this kind of engine, and twice had chosen it when seeking more power, both of these choices were greatly influenced by the desire to obtain quickly an engine of higher power. It is also possible that something in their experience with the V-8 moved them away from it; the unbalanced shaking force inherent in the arrangement may well have become evident to them. What probably also helped them to their final conclusion was the fundamental consideration that the V-8 provided two extra cylinders which were not really needed.

The eventual selection of the 6-cylinder was a slight compromise. In order to get the desired output the cylinder displacement was increased, but this was done by lengthening the stroke--the first time this had been altered since the original design. The increase (from 4 to 4-1/2 in.) was only 1/2 in., and the bore, the more important influence on fuel performance, was kept the same. Overall, the choice was quite logical. They were utilizing the in-line construction upon which almost all of their now considerable experience had been based, and the sizes of and requirements for parts also conformed to this experience. They could, in fact, use many of the same parts. The natural balance of the 6-cylinder arrangement gave them a very smooth engine, and had they stiffened the shaft and counter-weighted the cranks, they would have produced the smoothest engine that could have been built at that time.

In the literature are two references to a Wright 6-cylinder engine constructed around the cylinders of the vertical 4. One of these is in Angle's _Airplane Engine Encyclopedia_, published in 1921, and the other is in _Aerosphere 1939_, published in 1940. The wording of the latter is essentially identical with that of the former; it seems a reasonable conclusion that it is a copy. Although it is possible that such an engine was built at some time, just as the 8-cylinder racing engine was cobbled up out of parts from the 4-cylinder vertical, no other record, no engines, and no illustrations have been found. It is thus quite certain that no significant quantity was ever manufactured or utilized.

The crankcase was considerably changed from that of the vertical 4, and was now in two pieces, with the split on the crankshaft center line. However, the shaft was not supported by the lower half of the case, as eventually became standard practice, but by bearing caps bolted to the ends of the upper case and, in between, to heavy ribs running across the upper case between the cylinders. The lower half of the case thus received none of the dynamic or explosion loads, and, serving only to support the engine and to provide for its mounting, was lightly ribbed. In it were incorporated integral-boss standpipe oil drains which discharged into a bolted-on sump. The upper half of the case was again left open on one side, giving the desired access to the interior, and, additionally, the design was altered to provide a method of camshaft assembly that was much simpler than that of the vertical 4 (see p. 42).

The cylinder was also greatly altered from that of the vertical 4. It was made in three parts, a piece of seamless steel tubing being shrunk on a cast-iron barrel to form the water jacket, with a cast-iron cylinder head shrunk on the upper end of the barrel. This construction compelled the use of long studs running from the cylinder head to the case for fastening down the cylinder (see Figures 12a-c). For the first time the cylinder heads were water-cooled, cored passages being provided, and more barrel surface was jacketed than previously, although a considerable area at the bottom was still left uncooled, obviously by direct intent, as the ported exhaust arrangement was no longer employed.