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dihedral planes； or dihedral propeller blades。
Dirigible。Obedient to a rudder； something that may
be steered or directed。
Helicopter。Flying machine the lifting power of which
is furnished by vertical propellers。
Lateral Curvature。Parabolic form in a transverse direction。
Lateral Equilibrium or Stability。Maintenance of the
machine on an even keel transversely。 If the lateral
equilibrium is perfect the extreme ends of the machine
will be on a dead level。
Longitudinal Equilibrium or Stability。Maintenance of
the machine on an even keel from front to rear。
Monoplane。Flying machine with one supporting； or
surface plane。
Multiplane。Flying machine with more than three surface
planes。
Ornithopter。Flying machine with movable bird…like
wings。
Parabolic Curves。Having the form of a parabolaa
conic section。
Pitch of Propeller Blade。See 〃Twist。〃
Ribs。The pieces over which the cloth covering is
stretched。
Spread。The distance from end to end of the main surface；
the transverse dimension。
Stanchions。Upright pieces connecting the upper and
lower frames。
Struts。The pieces which hold together longitudinally
the main frame beams。
Superposed。Placed one over another。
Surface Area。The amount of cloth…covered supporting
surface which furnishes the sustaining quality。
Sustentation。Suspension in the air。 Power of sustentation；
the quality of sustaining a weight in the air。
Triplane。Flying machine with three surface planes。
Thrust of Propeller。Power with which the blades displace
the air。
Width。The distance from the front to the rear edge
of a flying machine。
Wind Pressure。The force exerted by the wind when
a body is moving against it。 There is always more
or less wind pressure； even in a calm。
Wing Tips。The extreme ends of the main surface
planes。 Sometimes these are movable parts of the
main planes； and sometimes separate auxiliary planes。
End