Non-rigid.— Adirigible whose form is maintained by the pressure of ihe contained gas assisted by the car suspension d A dirigible whose form is maintained by a rigid structure contained within the envelope.
Semi-rigid.— A dirigible whose form is maintained by means of its attachment to an exterior girder construction containing the car.
Drag, the total resistance to motion through the air of an aircraft — 1. e., the sum of the drift and head resistance.
Drift, the component of the resultant wind pressure on an aerofoil or wing surface parallel to the air stream attack ing the surface.
Elevabor, a hinged surface for controlling the longitudinal attitude of 'an aircraft — i. e., its rotation about the athwart shi axis.
e, Right or Left Hand, the distinction between a right- nd and a left-hand engine depends on the rotation of the output shaft, whether this shaft rotates in the same direction as the crank or not. A right-hand engine is one in which, when viewed from the output shaft end, the shaft is seen to rotate anti-clockwise.
Fins, small planes on aircraft to promote stability; for example, vertical tail fins, horizontal tail fins, skid fins. etc. Flight Path, the path of the centre of gravity of an air craft with reference to the air.
Gap, the distance between the projections on the vertical axis of the entering edges of an upper and lower wing of a biplane.
Helicopter, a form of aircraft whose support in the air is derived from the vertical thrust of large propellers.
Inclinometre, an instrument for measuring the angle made by any axis of an aircraft with the horizontal.
Lift, the component of the force due to the air pressure of an aerofoil, resolved perpendicular to the flight path in a vertical plane.
Monoplane, a form of airplane whose main supporting surface is disposed as a single wing on each side of the body.
Nose Dive, a dangerously steep descent, head-on.
Ornithopter, a form of aircraft deriving its support and propelling force from flapping wings.
Pitot Tube, a tube with an end open square to the fluid stream; used as a detector of an impact pressure. More usually associated with a concentric tube surrounding it, having perforations normal to the axis for indicating static Pressure. The velocity of the fluid can be determined from the difference between the impact pressure and the static pressure. This instrument is often used to determine the velocity of an aircraft through the air.
Pylon, a marker of a course.
Race of a Propeller, the air stream delivered by the pro peller.
Rudder, a hinged or pivoted surface, usually more or leas flat or stream lined, used for the purpose ,of controlling the attitude of an aircraft about its vertical axis when in motion. Skidding, sliding sideways in flight away from the centre of the turn. It is usually caused by insufficient banking in a turn, and is the opposite of side slipping.
Skids, long wooden or metal runners designed to prevent nosing of a land machine when landing or to prevent dropping into boles or ditches in rough ground. Generally designed to function should the wheels collapse or fail to act.
Slip, this term applies to propeller action and is the dif ference between the actual velocity of advance of an air craft and the speed calculated from the known pitch of the propeller and its number of revolutions.
Spread, the maximum distance laterally from tip to tip of an airplane wing.
Stability, the quality of an aircraft in flight which causes it to return to a condition of equilibrium when meeting a dis- turbance. (This is sometimes called "Dynamical stability "). Stability with reference to the vertical Isheres1.— Stability of an aircraft due to the disposition and arrangement of its fixed parts.
Lateral.— Stability with reference to the longitudinal (or fore and aft) axis.
Lossibthea1.—StabiliLy with reference to the lateral (or athwartaliipl axis.
Stiteecope, an instrument to detect the existence of a small rate of ascent or descent, principally used in ballooning. Stay, a wire, rope or the like, used as a tie piece to hold parts together, or to contribute stiffness; for example, the stays of the wing and body trussing.
Strut, a oompresaion member of a truss frame; for in. stance, the vertical members of the wing truss of a biplane. Tail, the rear portion of an aircraft, to which are usually attached rudders, elevators and fins.
Tall Irma, the vertical and horizontal surfaces attached to the tail used for stabilizing.
Thrust Deduction, due to the influence of the propellers, there is a reduction of pressure under the stern of the vessel which appreciably reduces the total propulsive effect of the propeller. This reduction is termed " Thrust deduction." Triplane, a form of airplane whose main supporting sur faces are divided into three parts, superposed.
Truss, the framing by which the wing loads are transmitted to the body; comprises struts, stays and spars.
Warp, to change the form of the wing by twisting it, usually by changing the inclination of the rear spar relative to the front spar.
main supporting surfaces of an airplane. Loading, the weight carved per unit area of support inMce.
Wing Rib, a fore and aft member of the wing structure used to support the covering and to give the wing section its form. Wing Spar, an athwartship member of the wing structure resisting tension and compression.
Yaw, to swing off the course about the vertical axis, owing to gusts or lack of directional stability.
Angle of.— The temporary angular deviation of the fore and aft axis from the course.