f a surface relative to its normal
direction of motion.

Factor of Safety--Usually taken to mean the result found by dividing the
stress at which a body will collapse by the maximum stress it will be
called upon to bear.

Fineness (of stream-line)--The proportion of length to maximum width.

Flying Position--A special position in which an aeroplane must be placed
when rigging it or making adjustments. It varies with different types of
aeroplanes. Would be more correctly described as "rigging position."

Fuselage--That part of an aeroplane containing the pilot, and to which
is fixed the tail-plane.

Fin--Additional keel-surface, usually mounted at the rear of an
aeroplane.

Flange (of a rib)--That horizontal part of a rib which prevents it from
bending sideways.

Flight--The sustenance of a body heavier than air by means of its action
upon the air.

Foot-pound--A measure of work representing the weight of 1 lb. raised 1
foot.

Fairing--Usually made of thin sheet aluminum, wood, or a light
construction of wood and fabric; and bent round detrimental surface in
order to give it a "fair" or "stream-like" shape.

Gravity--Is the force of the Earth's attraction upon a body. It
decreases with increase of distance from the Earth. See "Weight."

Gravity, Specific--Density of substance Density of water.
Thus, if the density of water is 10 lb. per unit volume, the same unit
volume of petrol, if weighing 7 lb., would be said to have a specific
gravity of 7/10, i.e., 0.7.

Gap (of an aeroplane)--The distance between the upper and lower surfaces
of a biplane. In a triplane or multiplane, the distance between a
surface and the one first above it.

Gap, Propeller--The distance, measured in the direction of the thrust,
between the spiral courses of the blades.

Girder--A structure designed to resist bending, and to combine lightness
and strength.

Gyroscope--A heavy circular wheel revolving at high speed, the effect of
which is a tendency to maintain its plane of rotation against disturbing
forces.

Hangar--An aeroplane shed.

Head-Resistance--Drift. The resistance of the air to the passage of a
body.

Helicopter--An air-screw revolving about a vertical axis, the direction
of its thrust being opposed to gravity.

Horizontal Equivalent--The plan view of a body whatever its attitude may
be.

Impulse--A force causing a body to gain or lose momentum.

Inclinometer--A curved form of spirit-level