1: An extensive bibliography, essentially as complete at this time as when it was compiled in the early 1950s, is given on pages 1240-1242 of volume 2 of The Papers of Wilbur and Orville Wright, 1953. 2: Max P. Baker was a technical adviser to the Wright estate and as such had complete access to all of the material it contained. 3: In the 1890s the wealthy inventor Sir Hiram Stevens Maxim conducted an experiment of considerable magnitude with a flying machine that utilized a twin-cylinder compound steam powerplant. It was developed to the flight-test stage. 4: Fred C. Kelly, Miracle at Kitty Hawk, 1951. 5: Charles E. Taylor (Charley Taylor to the many who knew him) was in effect the superintendent of and also the only employee to work in the original small machine shop. A most versatile and efficient mechanic and machine operator, he made many parts for all of the early engines, and in the manner of the experimental machinist, worked mainly from sketches. He also had charge of the bicycle shop and its business in the absence of the Wrights. 6: This is a charitable agency set up by the late Colonel and Mrs. E. A. Deeds primarily for the purpose of building and supporting the Deeds Carillon and the Carillon Park Museum in Dayton, Ohio. 7: The Science Museum expressed a desire to have these but never received them. There is a reference to them in a letter to the Museum from the executors of his estate dated 20 February 1948, but is seems rather obvious from the text that by this time the drawings mentioned by Orville Wright in his 1943 letter had become confused with those being prepared by Christman for the Smithsonian Institution. The Science Museum did have constructed from its own drawings a very fine replica which is completely operable at this time. 8: There is a third set of drawings prepared by the Ford Motor Company also marked as being of the 1903 engine and these are rather well distributed in various museums and institutions. What this set is based on has been impossible to determine but it is indicated from the existence of actual engines and parts and the probable date of their preparation (no date is given on the drawings themselves) that they were copied from drawings previously made, and therefore add nothing to them. The Orville Wright-Henry Ford friendship originated rather late, considering Ford's avid interest in history and mechanical things. This tardiness could possibly have been the result of Wright coolness—a coolness caused by a report, at the time the validity of the Wright patents was being so strongly contested, that Ford had advised some of those opposing the Wrights to persevere and to obtain the services of his patent counsel who had been successful in overturning the Selden automobile patent. If this barrier ever existed it was surmounted, and Ford spent much effort and went to considerable expense to collect the Wright home and machine shop for his Dearborn museum. The shop equipment apparently had been widely scattered and its retrieval was a major task. It is most likely that the drawings resulted from someone's effort to follow out an order to produce a set of Ford drawings of the original engine. A small scale model of the 1903 flight engine, constructed under the supervision of Charles Taylor, is contained in the Dearborn Museum. 9: Charles L. Manly was engaged in the development of the engine for the Langley Aerodrome. See also footnote to Table on page 62. 10: Fernand Forest, Les Bateaux Automobiles, 1906. 11: Grover Loening, letter of 10 April 1963, to the Smithsonian Institution. 12: Assuming a rich mixture, consumption of all the air, and an airbrake thermal efficiency of 24.50% for the original engine, the approximate volumetric efficiency of the cylinder is calculated to have been just under 40%. 13: A rather thorough stress analysis of the rod shows it to compare very favorably with modern practice. In the absence of an indicator card for the 1903 engine, if a maximum gas pressure of five times the MEP is assumed, the yield-tension factor of safety is measurably higher than that of two designs of piston engines still in wide service, and the column factor of safety only slightly less. The shear stresses in the brazed and threaded joints are so low as to be negligible. 14: Rankin Kennedy, Flying Machines—Practice and Design, 1909. 15: Considerable doubt surrounds Whitehead's actual flight accomplishments, but Pruckner's engines were certainly used, as several were sold to early pioneers, including Charles Wittemann. It is probable that the specific power output was not very great, for the air-cooled art of this time was not very advanced and Pruckner had a rather poor fin design. But the change to water cooling eliminated this trouble, and the engines were most simple, should have been relatively quite light, and with enough development could probably have been made into sufficiently satisfactory flying units for that period. 16: A drawing of the camshaft is held by The Franklin Institute. 17: Baker states that the first crankshaft was made from a slab of armor plate and if this is correct the alloy was a rather complex one of approximately .30-.35 carbon, .30-.80 manganese, .10 silicon, .04 phosphorus, .02 sulphur, 3.25-3.50 nickel, 0.00-1.90 chromium; however, all the rest of the evidence, including Orville Wright's statement to Dr. Gough, would seem to show that it was made of what was called tool steel (approximately 1.0 carbon). 18: Their intended piston ring tension is not known. Measurements of samples from the 4-and 6-cylinder vertical engines vary greatly, ranging from less than 1/2 lb per sq in. to almost 1-1/4 lb. The validity of these data is very questionable as they apply to parts with unknown length of service and amount of wear. It seems quite certain, however, that even when new the unit tension figure with their wide rings was only a small fraction of that of the modern aircraft piston engine. 19: The Papers of Wilbur and Orville Wright, volume 2, Appendix. 20: The Wrights apparently never applied for an engine patent of any kind. This no doubt grew out of their attitude of regarding the engine as an accessory and deprecating their work in this field. A reasonably complete patent search indicates that this particular cam device has never been patented, although a much more complex arrangement accomplishing the same purpose was patented in 1900, and a patent application on a cam-actuating mechanism substantially identical to that of the Wrights and intended for use in a golf practice apparatus is pending at the present time. a: Concurrently with the Wrights' first engine work, Manly was developing the engine for the Langley Aerodrome, and a comparison of the Wrights' engine development with that of Manly is immediately suggested, but no meaningful comparison of the two efforts can be drawn. Beyond the objective of producing a power unit to accomplish human flight and the fact that all three individuals were superb mechanics, the two efforts had nothing in common. The Wrights' goal was an operable and reasonably lightweight unit to be obtained quickly and cheaply. Manly's task was to obtain what was for the time an inordinately light engine and, although the originally specified power was considerably greater than that of the Wrights, it was still reasonable even though Manly himself apparently increased it on the assumption that Langley would need more power than he thought. The cost and time required were very much greater than the Wrights expended. He ended up with an engine of extraordinary performance for its time, containing many features utilized in much later important service engines. His weight per horsepower was not improved upon for many years. The Wrights' engine proved its practicability in actual service. The Manly engine never had this opportunity but its successful ground tests indicated an equal potential in this respect. A description of the Langley-Manly engine and the history of its development is contained in Smithsonian Annals of Flight number 6, "Langley's Aero Engine of 1903," by Robert B. Meyer (xi+193 pages, 44 figures; Smithsonian Institution Press, 1971)