The main features of the Santos-Dumont machine were the box-kite
form of construction, with a dihedral angle on the main planes,
and the forward elevator which could be moved in any direction
and therefore acted in the same way as the rudder at the rear of
the Wright biplane. It had a single propeller revolving in the
centre behind the wings and was fitted with an undercarriage
incorporated in the machine.

The other chief French experimenters at this period were the
Voisin Freres, whose first two machines--identical in
form--were sold to Delagrange and H. Farman, which has sometimes
caused confusion, the two purchasers being credited with the
design they bought. The Voisins, like the Wrights, based their
designs largely on the experimental work of Lilienthal, Langley,
Chanute, and others, though they also carried out tests on the
lifting properties of aerofoils in a wind tunnel of their own.
Their first machines, like those of Santos-Dumont, showed the
effects of experimenting with box-kites, some of which they had
built for M. Ernest Archdeacon in 1904. In their case the
machine, which was again a biplane, had, like both the others
previously mentioned, an elevator in front--though in this case
of monoplane form--and, as in the Wright, a rudder was fitted in
rear of the main planes. The Voisins, however, fitted a fixed
biplane horizontal 'tail'--in an effort to obtain a measure of
automatic longitudinal stability--between the two surfaces of
which the single rudder worked. For lateral stability they
depended entirely on end curtains between the upper and lower
surfaces of both the main planes and biplane tail surfaces.
They, like Santos-Dumont, fitted a wheeled undercarriage, so
that the machine was self-contained. The Voisin machine, then,