Energy—Stored work. For instance, a given weight of coal or petroleum stores a given quantity of energy which may be expressed in foot-pounds.
Extension—That part of the upper surface extending beyond the span of the lower surface.
Edge, Leading—The front edge of a surface relative to its normal direction of motion.
Edge, Trailing—The rear edge of 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.