The Wrights again exhibited their engineering mastery of a novel basic situation when, starting out to make flight a practical thing, they provided engine No. 3 to be used for experimental purposes. In so doing they initiated a system which continues to be fundamental in the art of providing serviceable aircraft engines to this day—one that is expensive and time consuming, but for which no substitute has yet been found. Their two objectives were: improvement in performance and improvement in reliability, and the engine was operated rather continuously from early 1904 until well into 1906. Unfortunately, again, no complete record exists of the many changes made and the ideas tested, although occasional notes are scattered through the diaries and notebooks.
In its present form—it is on exhibition at the Engineers Club in Dayton, Ohio—the No. 3 engine embodies one feature which became standard construction on all the Wright 4-cylinder models. This was the addition of a number of holes in a line part way around the circumference of the cylinder barrel so that they were uncovered by the piston at the end of its stroke toward the shaft, thus becoming exhaust ports (see Figure [9]). This arrangement, although not entirely novel, was just beginning to come into use, and in its original form the ports exhausted into a separate chamber, which in turn was evacuated by means of a mechanically operated valve, so that two exhaust valves were needed per cylinder. Elimination of this chamber and the valve arrangement is typical of the Wrights' simplifying procedure, and it would seem that they were among the very first to use this form.[14]
The primary purpose of the scheme was to reduce, by this early release and consequent pressure and temperature drop, the temperature of the exhaust gases passing the exhaust valve, this valve being one of their main sources of mechanical trouble. It is probable that with the automatic intake valves being used there was also a slight effect in the direction of increasing the inlet charge, although with the small area of the ports and the short time of opening, the amount of this was certainly minor. With the original one-piece crankcase and cylinder jacket construction, the incorporation of this auxiliary porting was not easy, but this difficulty was overcome in the development engine by making different castings for the crankcase itself and for the cylinder jacket and separating them by several inches, so that room was provided between the two for the ports.
This engine demonstrated the most power of any of the flat 4s, eventually reaching an output of approximately 25 hp, which was even somewhat more than that developed by the slightly larger 4-1/8-in.-bore flight engine, with which 21 hp was not exceeded. Indicative of the development that had taken place, the performance of the No. 3 engine was twice the utilized output of the original engine of the same size, an increase that was accomplished in a period of less than three years.
The Wrights were only twice charged with having plagiarized others' work, a somewhat unusual record in view of their successes, and both times apparently entirely without foundation. A statement was published that the 1903 flight engine was a reworked Pope Toledo automobile unit, and it was repeated in an English lecture on the Wright brothers. This was adequately refuted by McFarland but additionally, it must be noted, there was no Pope Toledo company or car when the Wright engine was built. This company, an outgrowth of another which had previously manufactured one-and two-cylinder automobiles, was formed, or reformed, and a Pope license arrangement entered into during the year 1903.
The other incident was connected with Whitehead's activities and designs. Whitehead was an early experimenter in flying, about the time of the Wrights, whose rather extraordinary claims of successful flight were published in the 1901-1903 period but received little attention until very much later. His first engines were designed by a clever engineer, Anton Pruckner, who left at the end of 1901, after which Whitehead himself became solely responsible for them. It was stated that the Wrights visited the Whitehead plant in Bridgeport, Connecticut, and that Wilbur remained for several days, spending his time in their machine shop. This was not only categorically denied by Orville Wright when he heard of it but it is quite obvious that the 1903 or any other of the Wright engine designs bears little resemblance to Pruckner's work. In fact, its principal design features are just the opposite of Pruckner's, who utilized vertical cylinders, the 2-stroke cycle, and air-cooling, which Whitehead at some point changed to water-cooling.[15]
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.