In Fig. 21 the body A is shown to be equipped
with the supporting plane B and the tail a, so
they are adjustable simultaneously at the same
angle, and the weight D is placed below, similar to
the other structure.

At every moment during the forward movement
of this type of structure, the rear end of
the machine has a tendency to move upwardly,
the same as the forward end, hence, when the
weight seeks, in this case to go on, it acts on the
rear plane, or tail, and causes that end to raise,
and thus by mutual action, prevents any pendulous
swing.

LOW WEIGHT NOT NECESSARY WITH SYNCHRONOUSLY-MOVING WINGS.
--A little reflection will convince
any one that if the two wings move in harmony,
the weight does not have to be placed low,
and thus still further aid in making a compact
machine. By increasing the area of the tail, and
making that a true supporting surface, instead of
a mere idler, the weight can be moved further
back, the distance transversely across the planes
may be shortened, and in that way still further
increase the lateral stability.