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fixed light- See LIGHT, FIXED.

flap- A hinged or pivoted airfoil forming the rear portion of an airfoil, used to vary the effective camber.
  split flap- A hinged plate forming the rear upper or lower portion of an airfoil. The lower portion may be deflected downward to give increased lift and drag; the upper portion may be raised over a portion of the wing for the purpose of lateral control (cf. upper-surface aileron).

flag, drip- See DRIP FLAP.

flap, pressure- See PRESSURE FLAP.

flapping angle- See ANGLE, FLAPPING.

   parachute flare- A pyrotechnic device attached to a parachute and designed to illuminate a large area when released from an aircraft at an altitude. 
  signal flare- A pyrotechnic signaling device of distinctive color and characteristics. 
  wing-tip flare- A pyrotechnic device attached to an aircraft for illuminating the ground while landing. 

flat-plate area, equivalent- See AREA, EQUIVALENT FLAT-PLATE. 

flat spin- See SPIN, FLAT.

flight path- The flight path of the center of gravity of an aircraft with reference to the earth, or with reference to a frame fixed relative to the air. (See fig. 9.)

flight-path angle- See ANGLE, FLIGHT-PATH.

float- A completely enclosed watertight structure attached to an aircraft to give it buoyancy and stability when in contact with water. 
  float, inboard stabilizing- A stabilizing float placed relatively close to the main float or hull. 
  float, outboard (or wing-tip) stabilizing- A stabilizing float placed relatively far out from the main float or hull, usually at or very near the tip of the wing. 
  float, single- A single central float fitted under a seaplane and usually requiring two stabilizing floats to give adequate stability and complete the float system. 
  float, stabilizing (or side)- A float used in addition to a single float or hull and intended to provide lateral stability while the seaplane or flying boat is at rest on the water. 

float system- The complete system of permanent floats, used to give buoyancy and stability to a seaplane or a flying boat while it is at rest on the water, and to provide hydrodynamic lift while it is taking off. 

floating aileron linkage arrangement- See AILERON LINKAGE ARRANGEMENTS.

floodlight, landing-area- A device designed to illuminate the surface of a landing area. 

floodlight system, landing-area- A complete installation of floodlighting equipment designed to illuminate a landing area. 

flotation gear- See EMERGENCY FLOTATION GEAR. 

  laminar flow- A particular type of streamline flow. The term is usually applied to the flow of a viscous liquid near solid boundaries, when the flow is not turbulent. 
  streamline flow- A fluid flow in which the streamlines, except those very near a body and in a narrow wake, do not change with time. 
  turbulent flow- Any part of a fluid flow in which the velocity at a given point varies more or less rapidly in magnitude and direction with time. 

flutter- An oscillation of definite period but unstable character set up in any part of an aircraft by a momentary disturbance, and maintained by a combination of the aerodynamic, inertial, and elastic characteristics of the member itself (cf. buffeting).

fly- (1) To operate an aircraft in flight. (2) To ride as a passenger in an aircraft. 

flying boat- A form of seaplane whose main body or hull provides flotation. 

frame, field handling- A portable frame which may be attached to an airship when it is on the ground and which is intended to provide a hold for more men than could grasp the handling rails of the cars. (See fig. 6.)

framing, stern- All framework, aft of the cruciform girder, necessary to complete the shape and contour of a rigid airship. 

free balloon- See BALLOON, FREE. 

free-balloon net- See NET, FREE-BALLOON. 

Frise aileron- See AILERON, FRISE.

fuel bypass regulator- See REGULATOR, FUEL BYPASS.

fuselage- The body, of approximately streamline form, to which the wings and tail unit of an airplane are attached. (See fig. 5.)
  monocoque fuselage- A fuselage construction which relies on the strength of the skin or shell to carry either the shear or the load due to bending moments. Monocoques may be divided into three classes (reinforced shell, semi-monocoque, and monocoque), and different portions of the same fuselage may belong to any one of these classes. The reinforced shell has the skin reinforced by a complete framework of structural members. The semimonocoque has the skin reinforced by longerons and vertical bulkheads, but has no diagonal web members. The monocoque has as its only reinforcement vertical bulkheads formed of structural members. 


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