ssary for a carriage engine, suggested an
idea that Charles believed had some merit. This idea, involving the use
of what the Duryeas later called a "free piston," was eventually to be
incorporated in their first engine.[7]

[Illustration: FIGURE 6.--J. FRANK DURYEA, about 1894, as drawn by George
Giguere from a photograph. (Smithsonian photo 48335.)]

Construction Begins

Back in Chicopee again, Charles began planning his first horseless
carriage. Frank later stated that they leaned heavily on the Benz
patents in their work;[8] but while the later engine and transmission
show evidence of this, only the Benz manner of placing the engine and
the flywheel seem to have been employed in the original Duryea plan.
Charles reversed the engine so that the flywheel was to the front,
rather than to the rear as in the Benz patent, but made use of Benz'
vertical crankshaft so that the flywheel rotated in a horizontal plane.
Previously most engines had used vertical flywheels; Benz, believing
that this practice would cause difficulty in steering a propelled
carriage, explained his reason for changing this feature in his U.S.
patent 385087, issued June 26, 1888:

In motors hitherto used the fly-wheels have been attached to a
horizontal shaft or axle, and have thus been made to revolve in a
vertical plane, since the horizontal shaft is best adapted to the
transmission of power. If, however, in this case we should use a
heavy rotating mass, corresponding to the power employed and
revolving rapidly in a vertical plane, the power to manage the
vehicle or boat would become very much lessened, as the flywheel
continues to revolve in its plane. I therefore so design the
apparatus that its crank shaft x has a vertical position and its
fly-wheel y revolves in a horizontal plane.... By this means the
vehicle is not only easily controlled, but also the greatest safety
is attained against capsizing.

To the Duryea plan, Benz may also have contributed the idea for
positioning the countershaft, though its location is sufficiently
obvious that Charles may have had no need for copying Benz. Charles
wisely differed from Benz in placing the flywheel forward, thus
eliminating the need for the long driving belt of the Benz carriage. Yet
he did reject the bevel gears used by Benz, which might well have been
retained, as Frank was later to prove by designing a workable
transmission