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18 REPORT NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

level landing - See LANDING, LEVEL.

level-off - To make the flight path of an airplane horizontal after a climb, glide, or dive.

lift:

aerostatic lift - The difference between the weight of a volume of air and an equal volume of a gas lighter than air under given conditions.

dynamic lift - The component of the total aerodynamic force on a body perpendicular to the relative wind (See fig. 9.)

gross lift (aerostat) - The buoyancy under standard conditions of density, purity, and fullness.

useful lift (aerostat) - The lift available for carrying passengers, fuel, oil, supplies, cargo, etc. It is the difference between the gross lift and the fixed weight of an aerostat.

lift direction (stress analysis) - The direction in the plane of symmetry perpendicular to the relative wind (cf. beam, chord, drag, and side directions).

lift/drag ratio - The ratio of the lift to the drag of any body.

lift force, or component (stress analysis) - A force, or component, in the lift direction (cf. beam, chord, drag, and side forces).

light:

anchor light - A light, or group of clear lights carried on an aircraft to indicate its position at night while at anchor.

approach light - A light, usually green, designed to indicate a favorable direction of approach for landing an aircraft.

blinker light - A flashing light giving more than 20 flashes per minute.

boundary light - Any one of the lights designed to indicate the limits of the landing area of an airport or landing field.

ceiling light - Same as CEILING PROJECTOR.

course light - A light projected along the course of an airway so as to be visible chiefly from points on or near the airway.

fixed light - A light which is constant in luminous intensity with respect to both time and direction.

flashing light - A light which is intermittent as viewed from a single direction.

identification light - A group of lights, clear and colored, carried on the rear part of an airplane for identification at night.

landing-direction light - A light designed to indicate, either by itself or in conjunction with other lights, the direction in which landings are to be made.

landing light - A light carried by an aircraft to illuminate the ground while landing.

navigation light - Same as POSITION LIGHT.

obstruction light - A red light designed to indicate the position and height of an object hazardous to the operation of aircraft.

light - continued

position light - Any one of a group of lights - red, green, and clear - used aboard an aircraft to indicate its position and direction of motion.

line:

control line - One off the lines leading from the control car or compartment to the various parts of an airship and operating (either through mechanisms or directly) the rudders, valves, etc., which control the speed, altitude, etc., of the airship.

handling line (aerostat) - A line attached to the side of an airship or balloon for use by the ground crew in handling the aerostat (See fig. 3.)

handling line (airplane) - Two lines of steel strand attached to the upper wings of a seaplane for steadying it when hauled out of the water aboard ship.

main mooring line - The line dropped from the bow of an airship to be coupled to the main mooring mast line.

main mooring mast line - A line leading from the main winch of a mooring mast through the mooring attachment at the top of the mast for the purpose of attaching the main mooring line of an airship.

mast yaw line - One of the two lines leading from the winches at the base of the mooring mast through snatch blocks and carried to the leeward of the mast 60[degree symbol] from the wind direction. The airship-s yaw lines are coupled to these lines. The snatch blocks are fixed to anchorages selected so that the joined lines tend to keep the bow of the airship into the wind and prevent its overriding the mast. These lines are sometimes called "mast yaw guys" or "mast bow-steadying lines." (The main mooring line and the yaw guys, when taut establish a fixed point in space.)

mooring line - A line attached near the bow of an aircraft for securing it to the ground, buoy, anchor, or to a mooring mast.

sandbag line - A rope extending along the line of suspension ropes or bridles of a kite balloon to which are hooked the sandbags used in mooring the balloon. The purpose is to prevent wear on the suspension cordage.

shroud line - The suspension cords of a parachute which attach the harness to the canopy.

suspension line - A line attached to the hull or envelope of an airship for supporting and appendage, such as a car or fin.

yaw line - A line dropped from the bow of an airship, when mooring to the mast, to be coupled to the mast yaw line and act as a steadying line to prevent yawing or overriding the mast.