Part 19 (1/2)

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

=Fairing=--Usually made of thin sheet aluminium, 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. [15]

=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 any two of its surfaces. [16]

=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 pa.s.sage 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 att.i.tude may be.

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

=Inclinometer=--A curved form of spirit-level used for indicating the att.i.tude of a body relative to the horizontal.

=Instability=--An inherent tendency of a body, which, if the body is disturbed, causes it to move into a position as far as possible away from its first position.

=Instability, Neutral=--An inherent tendency of a body to remain in the position given it by the force of a disturbance, with no tendency to move farther or to return to its first position.

=Inertia=--The inherent resistance to displacement of a body as distinct from resistance the result of an external force.

=Joy-Stick=--See ”Control Lever.”

=Keel-Surface=--Everything to be seen when viewing an aeroplane from the side of it.

=King-Post=--A bracing strut; in an aeroplane, usually pa.s.sing through a surface and attached to the main spar, and from the end or ends of which wires are taken to spar, surface, or other part of the construction in order to prevent distortion. When used in connection with a controlling surface, it usually performs the additional function of a lever, control cables connecting its ends with the pilot's control lever. [17]

=Lift=--The vertical component of the reaction produced by the action of driving through the air a surface inclined upwards and towards its direction of motion.

=Lift, Margin of=--The height an aeroplane can gain in a given time and starting from a given alt.i.tude.

=Lift-Drift Ratio=--The proportion of lift to drift.

=Loading=--The weight carried by an aerofoil. Usually expressed in pounds per square foot of superficial area.