E
Elevator—A shorter name for the elevating planes or elevating rudder, used for directing the aeroplane upward or downward.
Ellipse—An oval figure outlined by cutting a cone through from side to side on a plane not parallel to its base. Some inventors use the curves of the ellipse in forming the wings of aeroplanes. See [Hyperbola] and [Parabola].
Entry—The penetration of the air by the forward edge of aircraft surfaces. See [Angle of Entry].
Equivalent Head Area—Such an area of flat surface as will encounter head resistance equal to the total of that of the construction members of the framework—struts, braces, spars, diagonals, etc., of the aerial craft.
F
Feathering—A form of construction in which mounting on hinges, or pivots, permits the surfaces to engage the air flatwise in one direction and to pass edgewise through it in other directions.
Fin—A fixed vertical stabilizing surface, similar in form to the fin on the back of a fish.
Fish Section—A term applied to the lengthwise section of an aircraft when the outline resembles the general shape of a fish—blunted in front and tapering toward the rear. This form is believed to encounter less resistance than any other, in passing through the air.
Fixed Wheel—A wheel in a fixed mounting, so that it does not swivel as does a caster wheel.
Flapping Flight—Flight by the up-and-down beating of wings, similar to the common flight of pigeons.
Flexible Propeller—A propeller in which the blades are frames covered more or less loosely with a fabric which is in a measure free to adjust its form to the compression of the air behind it as it revolves.
Flying Angle—The angle of incidence of the main surface of an aeroplane when in flight. See [Ground Angle].
Footpound—The amount of force required to raise one pound to a height of one foot.
Fore-and-aft—From front to rear: lengthwise: longitudinal.
Fuselage—The framework of the body of an aeroplane.
G
Glider—A structure similar to an aeroplane, but without motive power.
Gliding—Flying down a slope of air with a glider, or with an aeroplane in which the propelling power is cut off.
Gliding Angle—The flattest angle at which a given machine will make a perfect glide. This angle differs with different machines. The flatter the gliding angle the safer the machine.
Ground Angle—The angle of incidence of an aeroplane surface when the machine is standing on the ground.
Guy—A wire attached to a more or less distant part of the structure of any aircraft to prevent spreading. Also used to denote controlling wires which transmit the movements of the levers.
Gyroscopic Action—The resistance which a rotating wheel, or wheel-like construction, exhibits when a disturbing force tends to change its plane of rotation.
H
Hangar—A structure for the housing of aeroplanes.
Head Resistance—The resistance encountered by a surface moving through the air.
Heavier-than-air—A term applied to flying machines whose weight is not counterbalanced or buoyed up by the lifting power of some gas lighter than air; and which weigh more than the volume of air displaced.
Helicopater—A type of flying machine in which propellers revolving horizontally lift and sustain its weight in the air.
Horizontal Rudder—The rudder surface which is used to steer an aircraft upward or downward: so-called because it lies normally in a position parallel to the horizon; that is, level.
Horse-power—An amount of work equivalent to the lifting of 33,000 footpounds in one minute. See [Footpound].
Hyperbola—The outline formed by the cutting of a cone by a plane passing one side of its axis at such an angle that it would also intersect another cone placed apex to apex on the same axis.
K
Keel—A framework extending lengthwise under an aircraft to stiffen the construction: usually employed on airships with elongated gas-bags.