The Four-Cylinder Vertical Demonstration Engine and the First Production Engine
In 1906, while still doing general development work on the flat experimental engine, the Wrights started two new engines, and for the first time the brothers engaged in separate efforts. One was “a modification of the old ones” by Wilbur and the other, “an entirely new pattern” by Orville. There is no record of any of the features of Wilbur’s project or what was done in connection with it. Two months after the experimental operation of the two designs began, an entry in Wilbur’s diary gives some weight and performance figures for the “4” x 4” rebuilt horizontal,” and since Orville’s design was vertical the data clearly refer to Wilbur’s; but since the output is given only in test-fan rpm it does not serve to indicate what had been accomplished and there is no further mention of it.
Orville’s design became the most used of any model they produced. It saw them through the years from 1906 to 1911 or 1912, which included the crucial European and United States Army demonstrations, and more engines of this model were manufactured than any of their others including their later 6-cylinder. Although its ancestry is traceable to the original 1903 engine, the design form, particularly the external configuration, was considerably altered. Along with many individual parts it retained the basic conception of four medium-size cylinders positioned in line and driving the propellers through two sprocket wheels. From the general tenor of the record it would seem, despite there being no specific indication, that from this time on Orville served as the leader in engine design, although this occurred with no effect whatsoever on their finely balanced, exactly equal partnership which endured until Wilbur’s death in 1912.
The first major change from the 1903 design, putting the engine in an upright instead of flat position, was probably done primarily to provide for a minimum variation in the location of the center of gravity with and without a passenger. Whether or not it had any influence, the vertical cylinder arrangement was becoming predominant in automobile powerplants by this time, and the Wright engines now began to resemble this prevailing form of the internal combustion engine—a basic form that, in a wide variety of uses, was to endure for a long time.
Over the years, the Wrights seem to have made many changes in the engine: the bore was varied at different times, rod assembly methods were altered, and rod ends were changed from bronze to steel. Chenoweth states that on later engines an oil-control ring was added on the bottom of the piston, necessitating a considerable increase in the length of the cylinder barrel. This arrangement could not have been considered successful, as it apparently was applied to only a limited number of units and was not carried over to the later 6-cylinder engine model. There was much experimentation with cam shapes and most probably variations of these got into production.
With the crankcase, they did not go all the way to the modern two-piece form but instead retained the one-piece construction. Assembly was effected through the ends and a detachable plate was provided on one side for access to the interior. It is clear that they regarded this ability to get at the interior of the case without major disassembly as a valuable characteristic, and later featured it in their sales literature. They were apparently willing to accept the resultant weakening of the case and continued the construction through their last engine model. The integrally cast cylinder water jackets were abandoned and the top of the crankcase was machined flat to provide a mounting deck for individual cylinders. The use of aluminum alloy was continued, and the interior of the case was provided with strengthening webs of considerable thickness, together with supporting ribs. The cam shaft was supported directly in the case.
The individual cylinder design was of extreme simplicity, a single iron casting embodying everything except the water jacket. The valves seated directly on the cast-iron cylinder head and the guides and ports were all contained in an integral boss on top of the head. The exhaust valve location on the side of the engine opposite the pilot was a decided advantage over that of the 1903 design, where the exhaust was toward the pilot. A four-cornered flange near the bottom of the cylinder provided for fastening it to the crankcase, and a threaded hole in the top of the head received a vertical eyebolt which served as the rocker-arm support. The cylinder was machined all over; two flanges, one at the bottom and the other about two-thirds of the way down provided the surfaces against which the water jacket was shrunk. The jacket was an aluminum casting incorporating the necessary bosses and double shrunk on the barrel; that is, the jacket itself was shrunk on the cylinder-barrel flanges and then steel rings were shrunk on the ends of the jacket over the flanges. The jacket thickness was reduced by machining at the ends, making a semigroove into which the steel shrink rings fitted. These rings insured the maintenance of a tight joint despite the tendency of the aluminum jacket to expand away from the cast-iron barrel.
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.