Part 7

[Footnote 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)]

It is not possible to state the exact quantities of each engine that the Wrights produced up to the time that their factory ceased operation in 1915. Chenoweth gives an estimate, based on the recollection of their test foreman, of 100 vertical 4s and 50 6s. My estimate (see page 2) places the total of all engines at close to 200. Original Wright-built engines of all four of these basic designs are in existence, although they are rather widely scattered. The Smithsonian's National Air and Space Museum has examples of them all, including, of course, the unique first-flight engine. Their condition varies, but many are operable, or could easily be made so. Among the best are the first-flight engine and the last vertical 6, at the Smithsonian, the first vertical 6, at the United States Air Force Museum, and the vertical 4, at the Carillon Park Museum.

The Wrights were constantly experimenting and altering, and this in connection with the lack of complete records makes it almost impossible to state with any certainty specific performances of individual engines at given times. Weights sometimes included accessories and at others did not. Often they were of the complete powerplant unit, including radiator and water and fuel, with no clarification. In the table, performance is given in ranges which are thought to be the most representative of those actually utilized. Occasionally performances were attained even beyond the ranges given. For example, the 4×4-in. flat development engine eventually demonstrated 25 hp at an MEP of approximately 65 psi.

One important figure--the horsepower actually utilized during the first flight--is quite accurately known. In 1904 the 1904-1905 flight engine, after having been calibrated by their prony-brake test-fan method, was used to turn the 1903 flight propellers, and Orville Wright calculated this power to be 12.05 bhp by comparing the calibrated engine results with those obtained with the flight engine at Kitty Hawk when tested under similar conditions. However, since the tests were conducted in still air with the engine stationary, this did not exactly represent the flight condition. No doubt the rotational speed of the engine and propellers increased somewhat with the forward velocity of the airplane so that unless the power-rpm curve of the engine was flat, the actual horsepower utilized was probably a small amount greater than Orville's figures. The lowest power figure shown for this engine is that of its first operation.

No fuel consumption figures are given, primarily because no comprehensive data have been found. This is most probably because in the early flight years, when the Wrights were so meticulously measuring and recording technical information on the important factors affecting their work, the flights were of such short duration that fuel economy was of very minor importance. After success had been achieved, they ceased to keep detailed records on very much except their first interest--the flying machine itself--and when the time of longer flights arrived, the fuel consumption that resulted from their best engine design efforts was simply accepted. The range obtained became mostly a matter of aerodynamic design and weight carried. Orville Wright quotes an early figure of brake thermal efficiency for the 1903 engine that gives a specific fuel consumption of .580 lb of fuel per bhp/hr based on an estimate of the heating value of the fuel they had. This seems low, considering the compression ratio and probable leakage past their rather weak piston rings, but it is possible. In an undated entry, presumably in 1905, Orville Wright's notebook covered fuel consumption in terms of miles of flight; one of the stated assumptions in the entry is, "One horsepower consumes .60 pounds per horsepower hour"--still quite good for the existing conditions. Published figures for the 6-60 engine centered around .67 lb/hp hr for combined fuel and oil consumption.

The Wright Shop Engine

Despite the fact that the Wright shop engine was not a flight unit, it is interesting both because it was a well designed stationary powerplant with several exceedingly ingenious features, and because its complete success was doubtless a major factor in the Wrights' decision to design and build their own first flight engine. Put in service in their small shop in the fall of 1901, it was utilized in the construction of engine and airframe parts during the vital years from 1902 through 1908 and, in addition, it provided the sole means of determining the power output of all of their early flight engines. By means of a prony brake, its power output was carefully measured and from this the amount of power required for it to turn certain fans or test clubs was determined. These were then fitted to the flight engines and the power developed calculated from the speed at which the engines under test would turn the calibrated clubs. Although a somewhat complex method of using power per explosion of the shop engine was made necessary by the basic governor control of the engine, the final figures calculated by means of the propeller cube law seem to have been surprisingly accurate.[19] Restored under the personal direction of Charles Taylor, it is in the Henry Ford Museum in Dearborn, Michigan, together with the shop machinery it operated.

[Footnote 19: _The Papers of Wilbur and Orville Wright_, volume 2, Appendix.]

The engine was a single cylinder, 4-stroke-cycle "hot-tube" ignition type. The cylinder, of cast iron quite finely and completely finned for its day, was air-cooled, or rather, air-radiated, as there was no forced circulation of air over it, the atmosphere surrounding the engine simply soaking up the dissipated heat. Although this was possibly a desirable adjunct in winter, inside the small shop in Dayton, the temperature there in summer must have been quite high at times. The operating fuel was city illuminating gas, which was also utilized to heat, by means of a burner, the ignition tube. This part was of copper, with one completely closed end positioned directly in the burner flame; the other end was open and connected the interior of the tube to the combustion chamber. The inlet valve was of the usual automatic type while the exhaust valve was mechanically operated. The fuel gas flow was controlled by a separate valve mechanically connected to the inlet valve so that the opening of the inlet valve also opened the gas valve, and gas and air were carried into the cylinder together.

The engine was of normal stationary powerplant design, having a heavy base and two heavy flywheels, one on each side of the crank. These were necessary to ensure reasonably uniform rotational speed, as, in addition to having only one cylinder, the governing was of the hit-and-miss type. It had a 6×7-in. bore and stroke and would develop slightly over 3 hp at what was apparently its normal operating speed of 447 rpm, which gives an MEP of 27 psi.

The engine is noteworthy not only for its very successful operation but also because it incorporated two quite ingenious features. One was the speed-governing mechanism. As in the usual hit-and-miss operation, the engine speed was maintained at a constant value, the output then being determined by the number of power strokes necessary to accomplish this. The governor proper was a cylindrical weight free to slide along its axis on a shaft fastened longitudinally to a spoke of one of the flywheels. A spring forced it toward the center of the wheel, while centrifugal force pulled it toward the rim against the spring pressure. After each opening of the valve the exhaust-valve actuating lever was automatically locked in the valve-open position by a spring-loaded pawl, or catch. The lever had attached to it a small side extension, or bar, which, when properly forced, would release the catch and free the actuating lever. This bar was so positioned as to be contacted by the governor weight when the engine speed was of the desired value or lower, thus maintaining regular valve operation; but an excessive speed would move the governor weight toward the rim and the exhaust valve would then be held in the open position during the inlet stroke, so no cylinder charge would be ingested. Since the ignition was not mechanically timed, the firing of the charge was dependent only on the compression of the inlet charge in the cylinder, so it made no difference whether the governor caused the engine to cease firing for an odd or even number of revolutions, even though the engine was operating on a 4-stroke cycle at all times.

The exhaust valve operating cam was even more ingenious. To obtain operation on a 4-stroke cycle and still avoid the addition of a half-speed camshaft, a cam traveling at crankshaft speed was made to operate the exhaust valve every other revolution (see Figure 17). It consisted of a very slim quarter-moon outline fastened to a disc on the crankshaft by a single bearing bolt through its middle which served as the pivot about which it moved. Just enough clearance was provided between the inside of the quarter-moon and the crankshaft to allow the passage of the cam-follower roller. The quarter-moon, statically balanced and free to move about its pivot, basically had two positions. In one the leading edge was touching the shaft (Figure 17b), so that when the cam came to the cam follower, the follower was forced to go over the top of the cam, thus opening the exhaust valve. When the cam pivot point had passed the roller, the pressure of the exhaust valve spring forced the following edge of the cam into contact with the shaft and this movement, which separated the leading edge of the cam from the shaft, provided sufficient space between it and the shaft for the roller to enter (Figure 17c). Thus, when the leading edge of the cam next reached the roller, the roller, being held against the crankshaft by the valve spring pressure (Figure 17d), entered the space between the cam and the shaft and there was no actuation of the valve. In exiting from the space, it raised the trailing edge of the cam, forcing the leading edge against the shaft (Figure 17a) so that at the next meeting a normal valve opening would take place. The cam was maintained by friction alone in the position in which it was set by the roller, but since the amount of this could be adjusted to any value, it could be easily maintained sufficient to offset the small centrifugal force tending to put the cam in a neutral position.[20]

[Footnote 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.]

Bibliography

ANGLE, GLENN D. Wright. Pages 521-523 in _Airplane Engine Encyclopedia, an Alphabetically Arranged Compilation of All Available Data on the World's Airplane Engines_. Dayton, Ohio: The Otterbein Press, 1921.

BAKER, MAX P. The Wright Brothers as Aeronautical Engineers. _Annual Report of ... the Smithsonian Institution ... for the Year Ended June 30, 1950_, pages 209-223, 4 figures, 9 plates.

BEAUMOUNT, WILLIAM WORBY. _Motor Vehicles and Motors: Their Design, Construction, and Working by Steam, Oil, and Electricity._ 2 volumes. Philadelphia: J. B. Lippincott, 1901-1902.

CHENOWETH, OPIE. Power Plants Built by the Wright Brothers. _S.A.E. Quarterly Transactions_ (January 1951), 5:14-17.

FOREST, FERNAND. _Les Bateaux automobiles._ Paris: H. Dunod et E. Pinat, Éditeurs, 1906.

GOUGH, DR. H. J. Materials of Aircraft Construction. _Journal of the Royal Aeronautical Society_ (November 1938), 42:922-1032. Illustrated.

KELLY, FRED C. _Miracle at Kitty Hawk; the Letters of Wilbur and Orville Wright._ New York: Farrar, Straus and Young, 1951.

_The Wright Brothers, a Biography Authorized by Orville Wright._ New York: Harcourt, Brace & Co., 1943.

KENNEDY, RANKIN. _Flying Machines: Practice and Design. Their Principles, Construction and Working._ 158 pages. London: Technical Publishing Co., Ltd., 1909.

LAWRANCE, CHARLES L. _The Development of the Aeroplane Engine in the United States._ Pages 409-429 in International Civil Aeronautics Conference, Washington, D.C., 12-14 December 1928, Papers Submitted by the Delegates for Consideration by the Conference. Washington: Government Printing Office, 1928.

MCFARLAND, MARVIN W. _The Papers of Wilbur and Orville Wright._ 2 volumes. New York: McGraw Hill Book Co., 1953.

RENSTROM, ARTHUR G. Wilbur and Orville Wright: A Bibliography Commemorating the Hundredth Anniversary of the Birth of Wilbur Wright, April 16, 1867. Washington, D.C.: The Library of Congress [Government Printing Office], 1968. Contains 2055 entries.

The 6-Cylinder 60-Horsepower Wright Motor. _Aeronautics_ (November 1913), 13(5):177-179.

Wright Brothers. Pages 829-830 in _Aerosphere 1939, Including World's Aircraft Engines, with Aircraft Directory_, Glenn D. Angle, editor. New York: Aircraft Publishers, 1940.

Index

Angle, Glenn D., 51

_Baby Grand Racer_, 47

Baker, Max P. 1, 10, 26, 28

Bariquand et Marré, 43, 44-45, 57-58

Beaumount, William Worby, 9, 25

Bristol Siddeley Engines, Ltd., 44-45

Carillon Park Museum, Dayton, Ohio, ix, 5n, 7, 37

Chanute, Octave, 28

Chenoweth, Opie, ix, 22, 35, 42, 63

Christman, Louis P., ix, 7, 8, 28

Cole, Gilmoure N., ix

Clarke, J. H., 18

Daimler-Benz A. G., ix, 10, 13

Engineers Club, Dayton, Ohio, ix, 32

Ford, Henry, 8

Ford, Henry, Museum, Dearborn, Michigan, 8, 64

Forest, Fernand, 11

Franklin Institute, Philadelphia, Pennsylvania, ix, 47

Gough, Dr. H. J., 58n

Howell Cheney Technical School, Manchester, Connecticut, x, 14, 15

Kelly, Fred C, 4n

Kerley, R. V., ix, 65

_Kitty Hawk Flyer_, ii, 3

Langley [Samuel P.] Aerodrome, 9, 62

Loening, Grover C, 13n

Manly, Charles L., 9, 62

Maxim, Sir Hiram Stevens, 3

McFarland, Marvin W., 1, 33, 47, 61

Miller-Knoblock Manufacturing Co., South Bend, Indiana, 26

National Park Service, Cape Hatteras National Seashore, ii, ix

Neue Automobil-Gesellschaft, 43

Porter, L. Morgan, ix

Pratt & Whitney Aircraft Corp., v, x, 37, 40-41, 49, 52, 53, 67

Pruckner, Anton, 33

Rockwell, A. L., ix, 37

Santos-Dumont, Alberto, 11

Science Museum, London, x, 5, 6, 7, 8, 11, 21, 23, 26

Taylor, Charles E., 5, 64

United Aircraft Corp., v, x

Western Society of Engineers, 2

Whitehead, Gustave, 33

Wittemann, Charles, 33n

Wright, Bishop Milton (father), 28

Wright, Katherine (sister), 4

Zenith carburetor, 52

*U.S. GOVERNMENT PRINTING OFFICE: 1971--397-764

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