Aerodrome.--Literally a machine that runs in the air.

Aerofoil.--The advancing transverse section of an aeroplane.

Aeroplane.--A flying machine of the glider pattern, used in contra-distinction to a dirigible balloon.

Aeronaut.--A person who travels in the air.

Aerostat.--A machine sustaining weight in the air. Aballoon is an aerostat.

Aerostatic.--Pertaining to suspension in the air; the art of aerial navigation.

Ailerons.--Small stabilizing planes attached to the main planes to assist in preserving equilibrium.

Angle of Incidence.--Angle formed by making comparison with a perpendicular line or body.

Angle of Inclination.--Angle at which a flying machine rises. This angle, like that of incidence, is obtained by comparison with an upright, or perpendicular line.

Auxiliary Planes.--Minor plane surfaces, used in conjunction with the main planes for stabilizing purposes.

Biplane.--A flying-machine of the glider type with two surface planes.

Blade Twist.--The angle of twist or curvature on a propeller blade.

Cambered.--Curve or arch in plane, or wing from port to starboard.

Chassis.--The under framework of a flying machine; the framework of the lower plane.

Control.--System by which the rudders and stabilizing planes are manipulated.

Dihedral.--Having two sides and set at an angle, like 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 parabola--a 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.