quoted of the required power and weight: "Such an engine is entirely practicable. Indeed, working motors of one-half this weight per horsepower [9 pounds per horsepower] have been constructed by several different builders." It is quite obvious that with their general knowledge and the experience they had acquired in designing and building a successful shop engine for their own use, they had no cause to doubt their ability to supply a suitable powerplant when the need arose. After the characteristics of the airframe had been settled, and the engine requirements delineated in rather detailed form, they had reached the point of decision on what they termed the motor problem. Only one major element had changed greatly since their previous consideration of the matter; they had arrived at the point where they not only needed a flight engine, they wanted it quickly.

Nothing has been found that would indicate how much consideration they had given to forms of power for propulsion other than the choice they had apparently made quite early—the internal-combustion, four-stroke-cycle piston engine. Undoubtedly, steam was dismissed without being given much, if any, thought. On the face of it, the system was quite impractical for the size and kind of machine they planned; but it had been chosen by Maxim for his experiments,[3] and some thirty-five or forty years later a serious effort to produce an aviation engine utilizing steam was initiated by Lockheed. On the other hand internal-combustion two-stroke-cycle piston engines had been built and used successfully in a limited way. And since, at that time, it was probably not recognized that the maximum quantity of heat it is possible to dissipate imposed an inherent limitation on the power output of the internal-combustion engine, the two-stroke-cycle may have appeared to offer a higher output from a given engine size than the four-stroke-cycle could produce. Certainly, it would have seemed to promise much less torque variation for the same output, something that was of great importance to the Wrights. Against this, the poor scavenging efficiency of the two-stroke operation, and most probably its concurrent poor fuel economy, were always evident; and, moreover, at that time the majority of operating engines were four-stroke-cycle. Whatever their reasoning, they selected for their first powered flight the exact form of prime mover that continued to power the airplane until the advent of the aircraft gas turbine more than forty years later.

The indicated solution to their problem of obtaining the engine—and the engine that would seem by all odds most reliable—would have been to have a unit produced to their specifications by one of the best of the experienced engine builders, and to accomplish this, the most effective method would be to use the equivalent of a bid procedure. This they attempted, and sent out a letter of inquiry to a fairly large number of manufacturers. Although no copy of the letter is available, it is rather well established that it requested the price of an engine of certain limited specifications which would satisfy their flight requirements, but beyond this there is little in the record.

A more thorough examination of the underlying fundamentals, however, discloses many weaknesses in the simple assumptions that made the choice of an experienced builder seem automatic. A maximum requirement limited to only one or two units offered little incentive to a manufacturer already successfully producing in his field, and the disadvantage of the limited quantity was only accentuated by the basic requirement for a technical performance in excess of any standard of the time. Certainly there was no promise of any future quantity business or any other substantial reward. Orville Wright many times stated that they had no desire to produce their own engine, but it is doubtful that they had any real faith in the buying procedure, for they made no attempt to follow up their first inquiries or to expand the original list.

Whatever the reasoning, their judgment of the situation is obvious; they spent no time awaiting results from the letter but almost immediately started on the task of designing and building the engine themselves. Perhaps the generalities were not as governing as the two specific factors whose immediate importance were determining: cost and time. The Wrights no doubt realized that a specially designed, relatively high performance engine in very limited hand-built quantities would not only be an expensive purchased article but would also take considerable time to build, even under the most favorable circumstances. So the lack of response to their first approach did not have too much to do with their ultimate decision to undertake this task themselves.

The question of the cost of the Wrights' powerplants is most intriguing, as is that of their entire accomplishment. No detailed figures of actual engine costs are in the record, and it is somewhat difficult to imagine just how they managed to conduct an operation requiring so much effort and such material resources, given the income available from their fairly small bicycle business. The only evidence bearing on this is a statement that the maximum income from this business averaged $3,000 a year,[4] which of course had to cover not only the airplane and engine but all personal and other expenses. Yet they always had spare engines and spare parts available; they seemingly had no trouble acquiring needed materials and supplies, both simple and complex; and they apparently never were hindered at any time by lack of cash or credit. The only mention of any concern about money is a statement by Wilbur Wright in a letter of 20 May 1908 when, about to sail for France for the first public demonstrations, he wrote: "This plan would put it to the touch quickly and also help ward off an approaching financial stringency which has worried me very much for several months." It is a remarkable record in the economical use of money, considering all they had done up to that time. The myth that they had been aided by the earnings of their sister Katherine as a school teacher was demolished long ago.

The decision to build the engine themselves added one more requirement, and possibly to some extent a restriction, to the design. They undoubtedly desired to machine as much of the engine as possible in their own shop, and the very limited equipment they had would affect the variety of features and constructions that could be utilized, although experienced machine shops with sophisticated equipment were available in Dayton and it is obvious that the Wrights intended to, and did, utilize these when necessary. The use of their own equipment, of course, guaranteed that the parts they could handle themselves would be more expeditiously produced. They commenced work on the design and construction shortly before Christmas in 1902.

The subject of drawings of the engine is interesting, not only as history but also because it presents several mysteries. Taylor[5] stated, "We didn't make any drawings. One of us would sketch out the part we were talking about on a piece of scrap paper ..." Obviously somewhere in the operation some dimensions were added, for the design in many