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 4x4-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.
[Illustration: _Figure 16._--Shop engine, 1901, showing governor and
exhaust valve cam. (Photo courtesy R. V. Kerley.)]
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 6x7-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.
[Illustration: _Figure 17._--Shop engine, 1901, showing operation of
exhaust valve cam. (Pratt & Whitney drawing.)]
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, Editeurs, 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 Marre, 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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